Electrochemical Energy Storage Systems for High Energy and Power Requirements

Abstract

An apparatus and method are described for electrochemical energy storage for high-power and high-energy autonomous applications, including electric autonomous vehicles, with remote active drive cycle monitoring and / or management and thermal management control. For autonomous vehicles, the apparatus includes at least one high-power, low-energy density tertiary storage battery designed to be low-cost, expendable, and replaceable, at least one high-energy density core battery, at least one intermediate power and energy density secondary battery for reducing the load on the core battery, and a battery controller. The energy requirements and consumption rates of the autonomous vehicle are provided such that performance degradation over the life of the system is reduced.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 078,175, entitled "Electrochemical Energy Storage System For High-Energy And High-Power Requirements," filed September 14, 2020, the entire contents of which are hereby specifically incorporated by reference into this specification for all that it discloses and teaches. [Background technology]

[0002] Electrification is accelerating in many industries as the demand for cleaner energy sources for both stationary and mobile applications is driven by both environmental and governmental forces. However, successful electrification requires (1) improvements in the performance of current state-of-the-art electrochemical energy storage devices and (2) reductions in the cost of these devices to ensure economic viability.

[0003] In dual drivetrain electric vehicles, both the front and rear wheels are driven, which requires an energy storage device for vehicle propulsion and other vehicle functions. In its simplest form, energy storage for these applications is realized using high energy / low power batteries, which are generally nearly depleted during the operation of the electric vehicle before being recharged. It is known that batteries that meet the energy needs of the vehicle cannot be recharged using high power or high energy electrical pulses, e.g., from regenerative braking, because such pulses result in accelerated battery degradation. Rather, such batteries are recharged more slowly to reduce the electrode degradation process that occurs during charging and to meet end-of-life battery requirements.

[0004] The higher the capacity of the battery, the higher the absolute magnitude of the current pulse can be, but still, according to the definition of C-rate, it results in a low charge rate compared to the total capacity of the battery. If the magnitude of the electrical pulse for a particular application results in a low C-rate to guarantee acceptable cycle life, power, increased DC resistance, end-of-life energy, and functional safety required at the automotive level, such batteries must be margin-designed. These margin-design requirements often lead to devices that require more space and add extra cost compared to systems that are optimally designed when only early-life requirements are taken into account. Furthermore, such batteries also require significant temperature control to guarantee performance, which results in a low packing density, defined as the percentage of the battery used for energy-storing components, such as battery cells, and have inherently inefficient energy recovery. Conversely, if the battery is not margin-designed, i.e., designed for early-life requirements, there is a performance gap at the end of life of the battery system that leads to safety and other issues.

[0005] A more complex system includes two batteries, one configured to accommodate the energy requirements of the electric vehicle, and a second to accommodate the power requirements. The battery that can accommodate the power requirements is generally capable of accepting electrical pulses from a regenerative device in the vehicle, but does not have sufficient capacity to store the recovered energy. This leads to the challenge of designing a battery that can accept energy from a high rate pulse, but does not have the capacity to store the recovered energy, or the energy required for the application, or designing a battery that can store energy, but does not have the ability to accept energy at a high rate.

[0006] As faster-than-expected cycles of innovation and adoption become mainstream in the on-demand transportation sector, autonomous vehicles (AVs) such as robotic delivery vehicles, self-driving taxis and driverless long-haul trucks are inspiring an ever-increasing number of companies to incorporate autonomous technology into their business models. Summary of the Invention

[0007] From the perspective of an electrochemical energy storage device, being able to control the load on the battery with remote driving cycle and thermal management control is advantageous to increase the lifespan of the storage device. An embodiment of the present electric vehicle propulsion system for autonomous applications, such as for an autonomous automobile (AV), includes at least one core or primary battery component that can provide power / energy to at least one secondary battery component such that the core component is beneficially only fully charged and discharged once per complete driving cycle, typically per day for AV applications, at a given SOC (state of charge) range. The electrochemical energy storage device described herein is designed such that the primary or core battery component, which may comprise approximately 75% of the entire electrochemical energy storage device capacity, charges and discharges at a rate that does not generate significant internal heat. This allows the primary component to be operated with or without a passive cooling system, thereby increasing the packing density when compared to components that require active thermal management. From a total capacity standpoint, the primary battery contains the most energy, and eliminating or greatly simplifying the thermal management of this component increases the energy density and reduces the overall cost of electrochemical energy storage devices.

[0008] At least one secondary battery component is connected in series with the primary component and can accept electrical energy from the primary component once the SOC of the secondary component reaches a minimum charge in the range between about 5% and about 20% of capacity before needing to be recharged. A minimum charge between about 0% and about 75% can be used, but excessive battery depletion can be an issue. A secondary component used according to the present invention can also accept energy directed by a component controller from regenerative braking or other energy recovery processes. However, the rate of charge acceptance of the secondary component is kept below a C-rate defined by the selected battery chemistry for a useful charge rate of less than 1C, an acceptable charge rate of less than 2C, and a maximum charge rate of less than 3C to maintain the desired life of the component. Multiple secondary components can be connected in parallel while continuously accepting energy from the primary battery. The secondary components can be operated in multiple configurations to provide power required for propulsion, ancillary, and / or autonomous vehicle functions. Given two such components, useful configurations, as described in more detail below, include (1) both providing power simultaneously, (2) one providing power while the second is idle, and (3) one providing power while the second is being recharged by the core battery component. Also, as described in more detail below, these configurations allow the AV to complete a daily driving cycle of approximately 15 hours each day without having to shut down due to a lack of power in the secondary or tertiary components.

[0009] To extend the life of the secondary components and ensure effective end-of-life performance, active thermal management is provided to the secondary components to ensure that the component(s) do not degrade prematurely due to high temperatures. Active thermal management is common in current electrochemical energy storage devices for the portable market. As discussed above, the present apparatus provides an advantage over current state-of-the-art systems because the portion of the system that requires active thermal management is minimized, as opposed to actively managing the temperature of the entire electrochemical energy storage system. For example, an AV that requires about 140 kh of usable energy would only require 30 kWh, or about 20%, for an active thermal management system according to the present teachings. This is in contrast to state-of-the-art systems that require most or all of the electrochemical energy storage system to have active temperature management. This is a significant advantage in terms of reduced cost, mass, volume, and system complexity.

[0010] The core battery may be made minimally sized because it only provides for the energy needs of the AV minus that provided via energy recovery processes such as regenerative braking for a predetermined period of time through remote active drive cycle monitoring and / or governance before needing to be recharged, and does not accept high current pulses or discharge. As described in more detail below, this allows the primary battery component to optimally meet both early and end of life requirements.

[0011] At least one tertiary component of the battery system is used to accept and discharge electrical energy at a high rate from regenerative braking and other energy recovery processes to avoid rapid degradation of the secondary components unless the secondary components are designed with a significant margin to ensure maximum energy recovery efficiency. This ensures that the maximum, if not all, available energy is captured by the energy recovery process, which by its very nature can offset 20% or more of the daily power demand of AV applications. For example, a typical driving cycle may have a daily energy requirement of 125 kWh with approximately 25 kWh hours of available energy for recovery. According to an embodiment of the present apparatus, this energy is effectively recovered without adversely affecting the performance of the entire electrochemical energy storage device, thereby reducing the effective daily energy load to 100 kWh. The benefits of this energy recovery are lower overall cost, lower mass, and smaller volume when compared to current state-of-the-art devices that incorporate higher power and higher energy into a single device. Additionally, the tertiary component has a passive or no thermal management system.

[0012] The present AV energy system thus includes at least one tertiary component with an associated electrical control system. The charge acceptance and discharge rates of the tertiary component, which is advantageously placed in parallel with the primary and secondary components, are not regulated. However, there may be applications that benefit from all components being electrically parallel or series, or any combination of the two, and applications that have thermal requirements for the tertiary components that may require periodic current regulation.

[0013] The system can be operated as a forward or rear drive device, or can be combined to provide dual drive capability.

[0014] In accordance with the purpose of the embodiments of the present invention, as embodied and broadly described herein, an embodiment of an apparatus for providing high energy and high power requirements of an electric vehicle having available regenerative electric energy includes at least one high power low energy density battery charged by the regenerative electric energy of the vehicle, at least one core battery of high energy density, connected in series with the core battery to receive electric energy from the core battery, from the at least one high power low energy density battery, and from the available regenerative electric energy of the vehicle up to a selected charge rate, supporting acceleration, autonomous functions, and the like. to at least one secondary battery of intermediate power and energy density to provide the electrical loads required to power the vehicle and, as needed, auxiliary electrical loads for said vehicle, a cooling system for maintaining said at least one secondary battery at a selected temperature, and a battery controller.

[0015] In accordance with the objectives of embodiments of the present invention, as embodied and broadly described herein, an embodiment of a method herein for charging and using an electrochemical energy battery for an electric vehicle having available regenerative electric energy includes charging at least one core battery using a charger external to the autonomous vehicle when the autonomous vehicle is in an idle state; charging at least one secondary battery of intermediate power and energy density connected in series with the at least one core battery using the at least one core battery; providing propulsion and other electrical requirements of the autonomous vehicle using the at least one secondary battery; maintaining the at least one secondary battery at a selected temperature; charging at least one high power, low energy density storage battery from the regenerative electric energy capabilities of the autonomous vehicle; providing acceleration requirements of the autonomous vehicle using the high power, low energy density storage battery; and controlling the steps of battery charging, as well as the acceleration, propulsion, and other electrical requirements of the autonomous vehicle using a battery controller. Effect of the Invention

[0016] Benefits and advantages of embodiments of the present invention include, but are not limited to, providing an electrochemical energy storage system for autonomous applications, e.g., AV electric vehicles, that can address increases in total energy consumption of the system by including at least one core or primary battery component that can provide power / energy to at least one secondary battery component with or without passive cooling, beneficially such that the core component is only fully charged and discharged once per characteristic driving cycle, which in the case of AV applications is once per day. This is a significant advantage in terms of reduced cost, mass, volume, and system complexity. Actively cooled secondary component(s) refers to the component of the system that provides the necessary power for propulsion, auxiliary, and / or autonomous vehicle functions and has the greatest energy throughput over the life of the electrochemical energy storage device. At least one tertiary component is used to accept and discharge electrical energy from regenerative braking and other energy recovery processes at a high rate to avoid rapid degradation of the secondary components. Further advantages of embodiments of the present invention include the ability of the primary battery components to optimally meet both early and end of life requirements, which further extends system life as well as reduces costs. [Brief description of the drawings]

[0017] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0018] [Figure 1A]FIG. 1 is a schematic diagram of a prior art battery system having both high power and high energy battery components controlled by a component controller and a regenerative braking system used to charge both the high power and high energy battery components. [Figure 1B] Schematic diagram of state of the art electrochemical energy storage systems compared to curve (c) of the present system where the storage system is designed for early life requirements and controlled to ensure compliance at end of life as the system degrades or ages. Curve (a) the system is designed with a margin for early life to ensure compliance with end of life requirements, or curve (b) the system is designed for early life requirements while sacrificing compliance at end of life. [Diagram 2] FIG. 1 is a schematic diagram of an embodiment of a battery system of the present invention showing high energy components including a primary or core battery and a secondary battery electrically connected in series with each other and to a component controller, where electrical energy from a regenerative energy source is directed by the component controller to charge the secondary and tertiary batteries, and where the core battery is discharged only during vehicle operation. [Diagram 3] FIG. 1 is a schematic diagram of another embodiment of a battery system configured to supply and receive electric energy from both the front and rear axles of an AV and having a single core battery, thereby eliminating battery redundancy as a primary cost driver of the battery system. [Figure 4] FIG. 1 is a schematic diagram of the present battery system configured to supply and receive electrical energy from both the front and rear axles of an AV, with primary components being able to be distributed throughout the AV. [Diagram 5] 1 is a graph of the state of charge of the core and secondary batteries of an embodiment of the invention illustrating the division of electrical energy between these battery components as a function of autonomous vehicle driving time from full charge to its midpoint. [Figure 6]FIG. 6 is a graph of the state of charge of the core and secondary batteries of an embodiment of the invention showing the partitioning of electrical energy between these battery components as a function of autonomous vehicle driving time from the intermediate time in FIG. 5 to the minimum state of charge for both the core and secondary batteries. [Figure 7] 1 is a graph of charge acceptance rate or C-rate as a function of state of charge for an embodiment of a tertiary battery of the present invention, as a function of (a) SOC and (b) charge pulse duration. [Figure 8A] Schematic diagrams showing two secondary battery components operated in four useful configurations, including: (1) both charged by the core battery but not powering the vehicle when idle (FIG. 8A(a)); (2) both powering the vehicle but not themselves charged by the core battery (FIG. 8B(a)); (3) one powering the vehicle and the second recharged by the core battery (FIGS. 8A(b) and 8A(c)); and (4) one powering the vehicle and the second idle (FIGS. 8B(b) and 8B(c)). [Figure 8B] Schematic diagrams showing two secondary battery components operated in four useful configurations, including: (1) both charged by the core battery but not powering the vehicle when idle (FIG. 8A(a)); (2) both powering the vehicle but not themselves charged by the core battery (FIG. 8B(a)); (3) one powering the vehicle and the second recharged by the core battery (FIGS. 8A(b) and 8A(c)); and (4) one powering the vehicle and the second idle (FIGS. 8B(b) and 8B(c)). [Figure 9]9(a) is a graph illustrating the need for more energy beyond that of a daily driving cycle to power autonomous and auxiliary vehicle functions during vehicle shutdowns that allow the core battery component to recharge the secondary battery components, along with significantly greater degradation of a single secondary battery component having a lower capacity, as shown in FIG. 9(a), compared to a higher capacity secondary component, as shown in FIG. 9(b). [Figure 10] Graph showing characteristic voltage profiles of two secondary battery components configured in parallel with each other and in series with a core battery storage component, where curve (a) shows one of the secondary components initially powering the vehicle in coordination with the tertiary component, and curve (b) shows the other secondary component starting out in an idle state and then powering the vehicle as the depleted secondary component is recharged by the core battery component, as described above in FIGS. 8A and 8B . [Figure 11] 11A-11C are graphs of capacity retention plots of both the secondary and core battery components, respectively, documenting the degradation of these components over the four-year lifespan of an electrochemical energy storage device when operating under a characteristic autonomous vehicle driving cycle, subject to both forward and reverse drive propulsion (curves (a) and (b) in FIG. 11A, respectively). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] As stated, successful electrification of autonomous applications, and autonomous vehicles (AVs) in particular, requires improvements in the performance of current state-of-the-art electrochemical energy storage devices along with reductions in the cost of said devices to ensure economic viability. The embodiments of the invention described herein address these performance and cost issues by using hybrid battery systems that can meet the energy and power requirements for several emerging power-using markets. The embodiments of the invention may be applied to mining, stationary electrical storage for homes, and AVs in addition to electrical grid storage, as examples. Autonomous vehicles are used throughout to describe and illustrate the above embodiments.

[0020] Current state-of-the-art electrochemical energy storage devices using a single chemistry are unable to provide the energy and power density required to fully automate commercial and passenger vehicle driving over the life of the vehicle. This inability arises from the distinctive nature of energy consumption in autonomous applications compared to traditional automotive applications. That is, the amount of time that an autonomous vehicle (AV) is using power from an electrochemical storage device by powering the vehicle or recovering energy through energy recovery processes such as regenerative braking is greater compared to passenger vehicles. For example, a typical daily driving cycle may result in an automobile operating for as many as 15 hours per day, with a daily energy consumption of greater than 100 kWh. Furthermore, the magnitude of the power pulses to drive AV applications is higher compared to current passenger vehicles. Thus, the total energy consumption of autonomous vehicle driving is significantly increased, and AV applications require both high energy and high power.

[0021] Existing single-chemistry battery systems are high energy / low power to support propulsion energy requirements before recharging and cannot accept high power or high current pulses that result in accelerated device degradation. The traditional approach is to over-saturate high energy components in single chemistry and single cell designs to ensure that current pulses do not result in damage to core components and to ensure that end-of-life energy, sufficient cycle life, power, and functional safety requirements are met. Because they are over-sized to meet end-of-life requirements, such larger systems are more costly, occupy more space, and require more complex thermal control strategies. Furthermore, this results in inefficient recovery from regenerative braking, as an example, when this energy could be more efficiently utilized for vehicle propulsion or other auxiliary applications. To achieve widespread AV adoption in commercial applications, low-cost-of-ownership energy solutions are needed that include both high energy density and high power characteristics to propel vehicles and power on-board electronics and sensors.

[0022] Energy storage systems having both high energy for extended vehicle operating range and high power for vehicle acceleration or high load conditions are known. FIG. 1A is a schematic diagram of a prior art battery system 10 having high power 12 and high energy 14 battery components controlled by a component controller 16. As an example, recharging power from a regenerative braking system 18 of a vehicle 19 is shown to be used to charge both the high power 12 and high energy 14 battery components. The component controller 16 may also be used to drive an electric motor of the vehicle 19 when current flows therethrough from the multiple batteries. A suitable electrically rechargeable high energy density battery is, for example, a lithium ion battery. , sulfur oxides, polymers, oxides, or combinations thereof. Various chemical properties such asThe battery may include a solid state battery having a rechargeable battery, a nickel metal hydride battery, and a sodium nickel chloride battery.

[0023] FIG. 1B is a schematic diagram of a state-of-the-art electrochemical energy storage system where the system is either over-designed for early life to ensure compliance with end-of-life requirements (curve (a) shows simulated performance to achieve desired end-of-life performance) or designed for early life requirements while sacrificing end-of-life compliance (curve (b) shows simulated performance to achieve desired early-life performance). Curve (c) shows a simulated storage system where the system is designed for early life requirements and controlled using optimized energy and power partitions with controlled operating cycles / electrochemical loading to ensure compliance at the end-of-life of the system degradation or aging.

[0024] Table 1 presents the battery characteristics for current automotive applications compared to those predicted for AV applications.

[0025] [Table 1]

[0026] Thus, the commercial introduction of AVs will place greater demands on electrochemical storage devices, both in terms of performance and cost, by significantly increasing performance requirements over those of the current commuter vehicle industry, while maintaining current costs at the cell level. The operation of large-scale AV fleets will require multiple vehicles to be used for a significant portion of their operational life, i.e., battery packs must last approximately four years under near-constant use. It is estimated that the battery pack will be required to last 24,000 hours and 400,000 miles over a four-year period while maintaining more than 80% of its initial capacity. Current EV / PHEV (electric vehicle / plug-in hybrid electric vehicle) systems are designed to meet drivetrain requirements and last approximately 8-10 years and 100,000 miles, which is 25% of the mileage requirements of AV applications, and the more aggressive performance targets of autonomous fleet applications cannot be realized using current battery pack designs. Current automotive requirements for applications ranging from 12V lithium-ion starter batteries through plug-in hybrid and fully electric systems to 48V start / stop micro-hybrid systems do not alone meet the performance and cost demands for autonomous applications.

[0027] To accommodate this change in requirements, embodiments of the present invention partition energy consumption into three storage devices with different performance characteristics that can effectively handle the vehicle's propulsion, auxiliary systems, and AV operating loads over the vehicle's operating life. Briefly, embodiments of the present invention include an apparatus and method for electrochemical energy storage for autonomous vehicles with remote active drive cycle monitoring and / or management, and thermal management control. The apparatus may include (1) a high power low energy density tertiary storage battery that has low cost and is designed to be expendable and replaceable, (2) a high energy density core battery or primary component, (3) a medium power and energy density secondary battery to reduce the load on the core battery, and (4) a battery controller. As described in more detail below, AV energy requirements and consumption rates are provided such that performance degradation over the life of the system is reduced. Several battery chemistries are envisioned.

[0028] An example of how multiple energy storage devices can work together is that the core or primary component can supply power / energy to the secondary component such that the core component is only fully charged and discharged, ideally once per driving cycle, a typical driving cycle for AV applications being once per day, at a selected SOC (state of charge) range between about 10% and about 95% to avoid battery degradation. In operation, the core battery can be charged at an SOC in the range between about 0% and about 100% when degradation is not an issue. The secondary component may be placed in series with the primary component and can accept energy from the primary component once the SOC of the secondary component reaches a minimum value in the range between about 5% and about 20% before requiring recharging. A minimum charge of about 0% and about 75% before recharging can be employed, but again battery degradation can be an issue. The secondary battery may accept energy from excess energy channeled from regenerative braking via the component controller or stored in the tertiary component. The rate of charge acceptance of the secondary components is limited to a rated C-rate defined by the battery chemistry, which is selected to be less than approximately 1 C. An acceptable charge rate may be a maximum of approximately 2 C, but the maximum charge rate should be less than 3 C to ensure a reasonable life of the secondary components.

[0029] Note that charging and discharging of batteries is regulated by a C-rate which is related to their maximum capacity, and batteries are commonly rated at 1C, which means that a fully charged battery rated at 1Ah will deliver 1A for the hour that the battery is discharged. The same battery discharging at 0.5C will deliver 500mA for 2 hours, and at 2C will deliver 2A for 30 minutes.

[0030] To accommodate long daily driving cycles, multiple secondary battery components may be placed in parallel as described above while continuing to accept energy from the primary battery once the SOC per battery reaches a minimum. This configuration ensures that the vehicle can complete an entire driving cycle without stopping and cannot draw power for vehicle propulsion from the core battery component, which may cause accelerated degradation of the core battery component. The secondary components may be operated in multiple configurations to provide the necessary power for propulsion, auxiliary, and / or autonomous vehicle functions. These configurations include: (1) many secondary battery components simultaneously supplying power to the AV and simultaneously accepting regenerative energy; (2) one secondary component supplying power and accepting regenerative energy while the second is idle at an SOC somewhere between the minimum SOC defined above and its fully charged state; and (3) one secondary battery component supplying power while the second battery is recharged by the core battery component and has an SOC between the minimum and fully charged SOC as defined above.

[0031] The tertiary battery component is chosen to be able to accept energy at a high rate and provide maximum efficiency for regenerative braking. The charge acceptance and discharge rates of this component will be high and it does not need to be unregulated. As an example, the tertiary system may be Lithium Iron Phosphate (LFP) with a graphite anode and thermally stable liquid electrolyte or other cathode capable of high rates and wired in parallel with the primary and secondary batteries. However, there may be applications that benefit from all components in parallel, series, or a combination of both with other battery chemistries that achieve the high rate capability requirements.

[0032] A single drivetrain system drives either the front or rear wheels, while a dual drivetrain drives both the front and rear wheels and requires multiple energy storage devices.More demanding operating conditions for AVs, such as driving time, increasing power intensity, and energy required for propulsion, are available over the life of the energy storage devices, and multiple energy storage devices and chemistries that reduce performance degradation over the life of the system can be applied to front or rear drive vehicles, and dual drive systems.

[0033] To extend the life of the secondary components and ensure effective end-of-life performance, it is expected that the secondary component(s) will require active thermal management to ensure that the components do not degrade prematurely due to high temperatures. It is also expected that the core and tertiary components will have passive or no thermal management systems. This is made possible by charging and discharging the core battery components at a rate that does not generate significant internal heat. Active thermal management is common for current electrochemical energy storage devices in the mobile market. An embodiment of the present invention provides an advantage because active thermal management is minimized. This is in contrast to current systems that require most or all of the electrochemical energy storage system to be actively managed. This advantage provides a significant reduction in cost, mass, volume, and system complexity.

[0034] Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. In the various views, like structures are identified using the same reference numerals. It will be understood that the various views are shown for the purpose of illustrating certain embodiments of the invention and are not intended to limit the invention thereto. Turning now to FIG. 2, a schematic diagram of an embodiment 20 of a battery system of the invention is shown. The high energy component 14 includes a primary or core battery 22 and a secondary battery or component 24 electrically connected in series with each other and with a component controller 16. Electrical energy from a regenerative energy source 18, for example from regenerative braking, is directed by the component controller 16 to charge the secondary component or battery 24 and the tertiary component or battery 12. The component controller 16 drives the electric motor of the vehicle 19 as current flows thereto from the secondary battery 24 and provides its other electrical requirements. The secondary battery 24 is the component of the embodiment 20 that has the greatest energy throughput over its life and is maintained at a selected temperature by a temperature controller 25. Remote active drive cycle management commands for the AV are transmitted from transmitter / receiver 26 and received by receiver / transmitter 28 to remotely control component controller 16, among other functions of the AV, and AV monitoring information is received from the AV by transmitter / receiver 28 and transmitted to transmitter / receiver 26. Here, although Figures 3 and 4 show reference numerals 28a and 28b indicating two transmitters / receivers, one for each forward and reverse drive system, in many cases a single transmitter / receiver is used.

[0035] According to the teachings of an embodiment of the present invention, the core battery 22 is discharged only during vehicle operation during which it recharges the secondary battery 24, while regenerative charging is also performed for the secondary battery 24 and the tertiary battery 12 during vehicle operation. The core battery 22 is typically charged by an external charger 30 during idle time of the AV at the end of a driving cycle. When energy is exchanged between the vehicle's battery system and both the front and rear axles in a dual-drive AV, there are two component controllers, two secondary batteries, and two tertiary batteries, one per axle, or one of each type per axle. There may also be two primary batteries.

[0036] 3 is a schematic diagram of another embodiment of the battery system configured to supply and receive electric energy from both the front and rear axles of an AV. Regenerative electric energy source 18a draws energy from the front axle of the AV 19 and directs it by component controller 16a into tertiary battery 12a and temperature-controlled (25a) secondary battery 24a, while regenerative energy source 18b draws energy from its rear axle and directs it by component controller 16b into tertiary battery 12b and temperature-controlled (25b) secondary battery 24b. In this embodiment, the primary or core components 22 must be of higher capacity when compared to two separate axles or dual drive embodiments of the AV, but eliminating battery redundancy is beneficial since the primary components become the main cost driver of the battery system.

[0037] A further embodiment of the invention described herein is a battery system configured to supply and receive electric energy from both the front and rear axles of an AV, as shown in FIG. 4, which is a schematic diagram of the battery system in which the primary components 22 can be distributed throughout the AV 19. This provides passive thermal management of the primary battery components 22, since the cells comprising the battery components are not limited to a central location, which ensures effective heat transfer to reduce premature battery degradation. To ensure safe and reliable operation of the distributed primary battery components, abuse-resistant cell components are used that are resistant to collisions that might otherwise crush or penetrate the cells, resulting in fire. Another benefit of using distributed primary battery components is the ability to access and replace the module or modules containing the cells in the event of premature failure. Active balancing of the modules or cells to compensate for differences in module resistance is also necessary for effective and safe operation if the module or modules are replaced. This is an advantage over current state-of-the-art systems, as these technologies require the entire electrochemical energy storage system to be replaced at great cost if components prematurely age.

[0038] In use, the partitioning of electrical energy flowing into and out of the battery system of an embodiment of the invention shown in FIG. 2 is shown in FIG. 5 and 6. Turning now to FIG. 5 and 6, charging of the core battery 22 occurs only at a selected C-rate, depending on the battery, with a range of C-rates beneficially between about C / 5 and about C / 10 during the time the vehicle is not in motion (t=0), with an acceptable range between about C / 3 and about C / 20, and an operational range between about 1C and about C / 50. The core battery 22 is used for two situations: (a) recharging the secondary components of the device 20 upon reaching a selected minimum state of charge (SOC) of the secondary battery 24, as described above, and (b) transferring energy to propulsion or auxiliary functions when the secondary battery 24 fails, a situation in which the AV is instructed to return for maintenance to ensure the operation and functional safety of the AV.

[0039] If the state of charge (SOC) of the secondary battery 24 of the device 20 is below a selected SOC value, as defined above, corresponding to a time t=x, y, or z as shown in Figures 4 and 5, the secondary battery 24 is recharged at a maximum C-rate that matches the capability of the core battery 22 of the device 20. The current associated with the C-rate of the core battery 22 is not equal to that of the secondary battery 24. Advantageously, the current calculated for the selected C-rate of the core battery 22, when used to calculate the C-rate of the secondary battery 24, results in a higher C-rate, i.e., the selected current C-rate of the core battery 22 is less than the C-rate of the secondary battery 24.

[0040] If the SOC is below a selected SOC value for the secondary battery 24, as defined above, corresponding to a time t=x, y, or z, as shown in Figures 4 and 5, current is drawn from the core battery 22 of the device 20 (which may be spaced at varying time intervals and may not be continuous, depending on the operation of the AV) until a desired SOC is achieved, preferably within a range between about 95% and about 80%, with an operable range between about 100% and about 25%, as defined at a time corresponding to t=x+Δt, y+Δt, or z+Δt, as shown in Figures 5 and 6. If the SOC is above a selected SOC value, also preferably within a range between about 95% and about 80%, with an operable range between about 100% and about 25%, corresponding to a time t=x, y, or z, as shown in Figures 5 and 6, and the defined C-rate is below that highlighted in Table 2, current is supplied for the propulsion and auxiliary functions at the defined current. A battery management system (BMS) included within the component controller 16 may be used to calculate the SOC of the primary and secondary components to ensure proper function and operational control of the SOC ranges for each component. Additionally, it may be beneficial to use active cell balancing on the secondary components to increase component life. The requirement for active balancing may be dictated by the driving cycle and the aging characteristics of the chemistry used within the secondary battery, as multiple cells age at different rates which changes their internal impedance, preventing them from balancing with each other.

[0041] If the SOC is greater than or equal to a selected value for the tertiary battery 12, which is advantageously between about 30% and about 100% of the battery's total charge based on the battery pack design, and the operating range is between about 10% and about 100%, current may be applied to the vehicle 19 for propulsion and auxiliary functions. If the SOC of the tertiary battery 12 is less than the selected value and the C-rate is greater than or equal to the maximum C-rate as defined above for the secondary battery 24 of the device 20 as defined in Table 2 below, current may be applied for propulsion and auxiliary functions until the C-rate falls below a threshold value for the secondary battery 24, at which point the secondary battery 24 may take over the load from the tertiary battery 12. If the SOC is less than the selected value and the C-rate is less than the maximum C-rate as defined above for the secondary battery 24 of the device 20 as defined in Table 2, current should not be discharged from the tertiary battery 12 of the device 20, but rather current should be supplied from the secondary battery 24 of the device 20.

[0042] A tertiary battery is used to optimize the efficiency of energy recovery from regenerative braking for the embodiment of the invention shown in Figure 2. Figure 7 is a graph of the charge acceptance rate or C-rate as a function of state of charge for a tertiary battery embodiment of the invention, which is a function of (a) SOC, and (b) charge pulse duration. It can be seen that a quantifiable C-rate and precise slope as a function of SOC and charge pulse becomes a function of the cells that comprise the tertiary battery, and as discussed above, limitations on the charge C-rate can be eliminated if necessary to ensure that regenerative energy is effectively recaptured.

[0043] 7 that (a) the charge current rate (or magnitude of the charge current) may be increased as the state of charge (SOC) of the battery (preferably at the cell level) decreases, and (b) the charge current rate increases regardless of SOC as the duration of the charge pulse decreases. It is recognized that the increase in charge current from high to low SOC is non-linear, and therefore, to maximize the efficiency of energy recovery, the increase in slope is maximized at high SOC in order to reach or near the maximum charge acceptance rate for a given pulse length at an optimized SOC.

[0044] To effectively realize this embodiment, the BMS also included in the component controller 16 may be used to calculate / predict the SOC of the tertiary components, and the cells with the tertiary components are well balanced. Furthermore, active balancing may be combined with this embodiment to facilitate more effective energy recovery and extend the life of the components.

[0045] Having described general details of embodiments of the present invention, the following examples provide further details.

[0046] (Example 1) Table 2 lists example ranges of power and energy density for the primary or core, secondary, and tertiary batteries of embodiments of the present invention, which vary widely as AV applications require both high energy and high power. It should be noted that these are advantageous ranges and are listed as examples, but are not intended to limit the scope of application of embodiments of the present invention.

[0047] [Table 2]

[0048] As stated, the conventional approach has been to generously design a high energy battery with a single chemistry and single cell design so that high current pulses (high power) do not cause damage to the core battery. Since high current is relative, the higher the capacity of the core components, the higher the absolute magnitude of the current pulses will be, which may still result in a low rate when compared to the overall capacity of the core components. However, the extra battery capacity required to keep this rate low means extra cost, extra weight, and extra volume, all of which are barriers to widespread adoption in AV applications. According to the teachings of embodiments of the present invention, the core components may be made minimally sized to simply meet the energy needs of the device (AV) for a predetermined operating time before recharging, thereby reducing costs. Under these operating conditions, the core components do not accept any high current pulses and do not discharge. Furthermore, this predetermined operating time does not traditionally exist in passenger or commercial vehicles, since remote active drive cycle monitoring and / or management is new to AVs.

[0049] The secondary battery is chosen so that it can withstand higher current pulses for long periods of time. The components may provide this current at a constant rate that is effective for propelling the vehicle at low to medium acceleration rates or at a constant speed. As described above, once this battery is drained to a predetermined state of charge value, the core battery provides energy to charge the secondary battery with which it is in series electrical communication. Furthermore, as described above, other electrical configurations are possible. This charging process may occur multiple times during continuous operation of the AV. The secondary battery may provide current to auxiliary devices, to AV functions to drive the vehicle, and, if necessary, to control the climate within the vehicle, for example. Optimally, this is provided when these components are operating at a steady state such that the magnitude of the current is low and stable.

[0050] The tertiary components are chosen so that high rates of charging and discharging can be tolerated without shortening the life of the battery, so that the battery is effective in smoothing current surges (e.g., from high-speed braking where regenerative braking provides high current for a short period of time, or when the vehicle needs to accelerate quickly, thereby requiring a high current input from the battery primarily to the electric drivetrain). In the case of charging, the larger the current pulses that can be applied, the more efficient the energy recovery, which in turn reduces wear on the core and secondary batteries (thereby increasing their life). The battery can also provide the necessary current for auxiliary devices, both during surges and in steady state, to ensure proper operation, and provide excess energy to the secondary battery.

[0051] (Example 2) Table 3 compares the battery capacity (Ah), cost, and volume (L) of a battery system of an embodiment of the present invention, including a core, secondary, and tertiary battery, and potentially having different battery chemistries and cell designs, with a conventional battery system having one cell chemistry and one cell design. It can be seen from Table 3 that the battery system of the present invention can be constructed with lower capacity, lower cost, and smaller volume than a conventional, marginally designed core battery.

[0052] [Table 3]

[0053] The information used in the calculations to quantify the benefits of the present invention over current state-of-the-art or conventional batteries is as follows: (a) Conventional batteries are based on a 100 kWh design (a typical pack capacity for current commuter electric vehicles (EVs)). (b) Conventional battery and core battery voltage was considered to be 350V (again, a characteristic of typical EV battery packs, which have a voltage range between 350V and 400V). (c) Conventional and core battery costs and volumetric energy densities were $160 / kWh and 650Wh / L, respectively. (d) While conventional and core batteries perform different functions, the materials used, cell designs, and cost per Wh are similar. (e) The secondary battery of the present invention has a higher power density, but a lower energy density, and therefore is less cost effective per Wh. (f) The values ​​used to calculate cost and volume are $180 / kWh and 500Wh / L, respectively. (g) Tertiary batteries have the highest power density and lowest energy density, and are the least effective in terms of cost and space, when normalized by Wh. (h) The values ​​used to calculate cost and volume are $250 / kWh and 250Wh / L, respectively, which happen to be the same values; and (i) Due to the effective energy recovery of the present invention embodiments during operation, the controlled and effective partitioning of the electrical load, and the controlled driving cycle conditions provided by AV applications, the total capacity of the battery of the present invention can be reduced as the vehicle utilizes energy more efficiently, i.e., the battery pack energy of the present invention is sufficient to ensure that the vehicle can operate continuously for a day, and is not over-designed with power because the tertiary and secondary batteries are more effective at supplying and receiving such energy without causing cell-level damage.

[0054] (Example 3) A characteristic autonomous vehicle driving cycle, assuming both forward and reverse propulsion, was utilized to determine the regenerative energy recovery efficiency and degradation of the secondary battery components. The attributes of the driving cycle are listed in Table 4. Additionally, the simulation tracked (1) the percentage of the driving cycle completed, where less than 100% completion was not allowed, (2) the percentage of regenerative energy recaptured, with a goal of 100% recapture and utilization for propulsion, autonomous, and auxiliary vehicle functions, and (3) the energy of the secondary battery component, with a goal of minimizing the size of the secondary component since active thermal management is required, while primary and tertiary battery components are not required. Additionally, two electrochemical energy storage device configurations were modeled, where one configuration included a single secondary battery component and the second configuration included two secondary battery components arranged in parallel with each other and in series with the core battery component, as shown in FIG. 8.

[0055] 8A and 8B are schematic diagrams of two secondary battery components operated in four useful configurations to provide power needed for the AV's propulsion, auxiliary, and / or autonomous vehicle functions while ensuring uninterrupted power from the secondary components to the vehicle during one complete driving cycle, including (1) both charged by the core battery but not powering the vehicle in an idle state (FIG. 8A(a)), (2) both powering the vehicle but not themselves being charged by the core battery (FIG. 8B(a)), (3) one powering the vehicle and the second being recharged by the core battery (FIGS. 8A(b) and 8A(c)), and (4) one powering the vehicle and the second being idle (FIGS. 8B(b) and 8B(c)). The use of additional secondary batteries is envisioned, as described below.

[0056] Results from the simulations are that a single secondary battery component configuration requires a higher percentage of the total electrochemical energy storage capacity to complete the entire daily driving cycle and recover all of the regenerated energy. A summary of the results is included in Table 5. Additionally, approximately 12% more energy is required beyond the energy of the daily driving cycle to power the autonomous and auxiliary vehicle functions during vehicle shutdowns that allow the core battery components to recharge the secondary battery components. This additional energy requirement compared to a higher capacity secondary component as shown in FIG. 9(b) along with the significantly greater degradation of a single secondary battery component with a lower capacity is illustrated in FIG. 9(a) and represents a potential advantage of the multiple secondary battery component configuration.

[0057] [Table 4]

[0058] [Table 5]

[0059] 10 is a graph showing the characteristic voltage profiles of the secondary battery components when two batteries of approximately 10% of the total electrochemical energy storage capacity (total 20%) are configured in parallel with each other and in series with the core battery storage component. Curve (a) shows one of the secondary components initially providing propulsion, autonomous driving, and auxiliary function energy in coordination with the tertiary component as defined by the distribution logic described above, while curve (b) shows the other secondary component starting at idle and powering the vehicle while the depleted secondary component is being charged by the core battery component as described above in FIGS. 8A and 8B.

[0060] Advantages of using this particular autonomous vehicle include: (1) all additional energy requirements associated with autonomous and auxiliary functions while the vehicle is stopped to recharge the secondary battery components are eliminated, thereby minimizing the total energy required to complete a daily driving cycle; (2) all regenerative energy may be recovered while completing a daily driving cycle, as compared to a single secondary battery component comparison, requiring 30% of the total energy capacity, as highlighted in Table 5; (3) degradation of the secondary battery components is reduced to between 65% and 70% of the original component capacity, as compared to approximately 30% in a single secondary component configuration at the end of a four-year life of an electrochemical energy storage device; and (4) the relative capacity of the core battery components is predicted to be approximately 84% of its original capacity at the end of life (four years), thereby exceeding the end-of-life requirements. These predictions are superior to the current state-of-the-art, as the total energy of the device is calculated to be approximately equivalent, but the capacity retention at the end of four years is predicted to be approximately 77% of the initial capacity. This highlights a distinct advantage of the teachings of the present invention in addition to the fact that while the current state of the art requires thermal management of the entire electrochemical energy storage device, the present invention described herein requires thermal management of approximately 20% of the total energy contained within the electrochemical energy storage device.

[0061] 11A and 11B are graphs of capacity retention plots of both secondary and core battery components, respectively, documenting the degradation of these components over the four-year life of an electrochemical energy storage device when operated under a characteristic autonomous vehicle driving cycle, assuming both forward and reverse drive thrust (curves (a) and (b) of FIG. 11A, respectively). Curves (a) and (b) of FIG. 11A show that the electrochemical energy storage device has two secondary components whose forward and reverse component capacity retention curves differ slightly as a result of the simulated loads imposed on these components from the characteristic driving cycle varying according to the demands of autonomous driving. The core battery component capacity retention curves when subjected to the characteristic autonomous vehicle driving cycle and operated using an embodiment of the present invention show that a key end-of-life performance indicator of greater than 80% capacity retention can be achieved, with life simulation predicting greater than 84% retention at four years.

[0062] The foregoing description of the invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or to limit the invention to the precise form disclosed; obviously, many modifications and variations are possible in light of the above teachings. The embodiments have been chosen and described to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suitable for the particular uses contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.

Claims

1. 1. An apparatus for electrochemical energy storage for an electric autonomous vehicle having a regenerative electric energy source, comprising: at least one tertiary battery capable of providing acceleration for the electric autonomous vehicle and for receiving charging from the source of regenerative electric energy of the electric autonomous vehicle; at least one core battery having a higher energy density than the at least one tertiary battery and a lower power density than the at least one tertiary battery; at least one secondary battery connected in series with the at least one core battery for receiving electric energy from the at least one core battery, the secondary battery having a power density intermediate between the at least one core battery and the at least one tertiary battery and an energy density intermediate between the at least one core battery and the at least one tertiary battery for providing propulsion for the electric autonomous vehicle; a thermal management system for maintaining the at least one secondary battery at a selected temperature; and Battery Controller An apparatus comprising:

2. 10. The apparatus of claim 1, further comprising a transceiver for transmitting remote drive cycle management commands to the electric autonomous vehicle, and a transceiver for receiving the drive cycle management commands and for implementing the drive cycle management commands within the electric autonomous vehicle.

3. 10. The apparatus of claim 1, further comprising a transceiver for receiving monitoring information from the electric autonomous vehicle and a remote transceiver, the transceiver transmitting the monitoring information to the remote transceiver.

4. 2. The apparatus of claim 1, wherein the at least one secondary battery receives charge from the source of regenerative electric energy of the electric autonomous vehicle in addition to receiving electric energy from the at least one core battery.

5. 2. The apparatus of claim 1, wherein the battery controller controllably distributes an electrical load of the electric autonomous vehicle to the at least one core battery, to the at least one secondary battery, and to the at least one tertiary battery.

6. 6. The apparatus of claim 5, wherein electrical load sharing to the at least one core battery is achieved for a state of charge range between approximately 10% and approximately 95%, and electrical load sharing to the at least one secondary battery is achieved at a minimum state of charge range between approximately 5% and approximately 20%, such that the at least one core battery supplies electrical energy to the at least one secondary battery.

7. 7. The apparatus of claim 6, wherein the at least one secondary battery receives electrical energy from the at least one core battery at a charge rate of less than about 3C.

8. 6. The apparatus of claim 5, wherein electrical load sharing to the at least one tertiary battery is achieved over a state of charge range between approximately 30% and approximately 100%.

9. 10. The apparatus of claim 1, wherein the at least one core battery is selected from a lithium ion battery, a lithium metal battery, a nickel metal hydride battery, a sodium nickel chloride battery, and combinations thereof.

10. 10. The apparatus of claim 9, wherein the lithium ion battery and the lithium metal battery comprise solid-state batteries having sulfide, polymer, oxide, or combinations thereof chemistries.

11. 10. The apparatus of claim 1, wherein the at least one tertiary battery comprises a lithium iron phosphate cathode, a graphite anode, and a thermally stable liquid electrolyte.

12. 10. The apparatus of claim 1, wherein the at least one secondary battery comprises a nickel manganese cobalt oxide cathode with a low nickel concentration.

13. The apparatus of claim 1 , wherein the at least one tertiary battery is electrically connected in parallel with the at least one core battery and the at least one secondary battery.

14. 2. The apparatus of claim 1, wherein the at least one secondary battery comprises two secondary batteries electrically connected in parallel with each other and in series with the at least one core battery.

15. The apparatus of claim 1 , wherein the at least one core battery includes a plurality of core batteries, the plurality of core batteries being distributed within the electric autonomous vehicle.

16. 1. A method for charging and using a battery for an electric autonomous vehicle having a regenerative electric energy source, comprising: charging at least one core battery having a higher energy density than at least one tertiary battery and a lower power density than the at least one tertiary battery using a charger external to the electric autonomous vehicle when the electric autonomous vehicle is in an idle state; Charging at least one secondary battery, which is connected in series with the at least one core battery and has a power density intermediate between the at least one core battery and the at least one tertiary battery and an energy density intermediate between the at least one core battery and the at least one tertiary battery, using electrical energy from the at least one core battery; providing propulsion for the electric autonomous vehicle using the at least one secondary battery; maintaining the at least one secondary battery at a selected temperature; charging the at least one tertiary battery from the source of regenerative electric energy of the electric autonomous vehicle; providing acceleration requirements of the electric autonomous vehicle using the at least one tertiary battery; controlling the steps of battery charging, and accelerating and propelling the electric autonomous vehicle using a battery controller; The method includes:

17. 20. The method of claim 16, further comprising controlling the electric autonomous vehicle using remote drive cycle management instructions.

18. 17. The method of claim 16, further comprising charging the at least one secondary battery from the source of regenerative electric energy of the electric autonomous vehicle in addition to the step of charging the at least one secondary battery using electric energy from the at least one core battery.

19. 17. The method of claim 16, further comprising controllably distributing an electrical load of the electric autonomous vehicle to the at least one core battery, to the at least one secondary battery, and to the at least one tertiary battery using the battery controller.

20. 17. The method of claim 16, wherein the at least one core battery is selected from a lithium ion battery, a lithium metal battery, a nickel metal hydride battery, a sodium nickel chloride battery, and combinations thereof.

21. 21. The method of claim 20, wherein the lithium ion battery and the lithium metal battery comprise solid state batteries having sulfide, polymer, oxide, or combinations thereof chemistries.

22. 17. The method of claim 16, wherein the at least one tertiary battery comprises a lithium iron phosphate cathode, a graphite anode, and a thermally stable liquid electrolyte.

23. 17. The method of claim 16, wherein the at least one secondary battery comprises a nickel manganese cobalt oxide cathode with a low nickel concentration.

24. 17. The method of claim 16, wherein the at least one tertiary battery is electrically connected in parallel with the at least one core battery and the at least one secondary battery.

25. 17. The method of claim 16, wherein the at least one secondary battery comprises two secondary batteries electrically connected in parallel with each other and in series with the at least one core battery.

26. 26. The method of claim 25, wherein the two secondary batteries supply power to the electric autonomous vehicle and store electrical energy for the electric autonomous vehicle in a sequence selected from: (a) both secondary batteries supply power and store electrical energy simultaneously; (b) one secondary battery supplies power and stores electrical energy while a second secondary battery is in an idle state; and (c) one secondary battery supplies power and the second secondary battery is recharged by the at least one core battery.

27. The method of claim 16 , wherein the at least one core battery includes a plurality of core batteries, the plurality of core batteries being distributed within the electric autonomous vehicle.

28. 1. An apparatus for electrical energy storage having a regenerative electrical energy source, comprising: at least one tertiary battery for receiving charge from said source of regenerative electric energy; at least one core battery having a higher energy density than the at least one tertiary battery and a lower power density than the at least one tertiary battery; at least one secondary battery, connected in series with the at least one core battery for receiving electrical energy from the at least one core battery, the secondary battery having a power density intermediate between the at least one core battery and the at least one tertiary battery and an energy density intermediate between the at least one core battery and the at least one tertiary battery; a thermal management system for maintaining the at least one secondary battery at a selected temperature; and Battery Controller An apparatus comprising:

29. 30. The apparatus of claim 28, wherein the apparatus powers an electric autonomous vehicle.

30. 30. The apparatus of claim 29, wherein the electric autonomous vehicle further comprises a remote driving cycle governor.

31. 30. The apparatus of claim 28, wherein the at least one secondary battery receives charge from the regenerative electric energy source in addition to receiving electric energy from the at least one core battery.

32. The apparatus described in claim 28, wherein electrical loads are controllably distributed by the battery controller to the at least one core battery, to the at least one secondary battery, and to the at least one tertiary battery.

33. 30. The apparatus of claim 28, wherein the at least one core battery is selected from a lithium ion battery, a lithium metal battery, a nickel metal hydride battery, a sodium nickel chloride battery, and combinations thereof.

34. 34. The apparatus of claim 33, wherein the lithium ion and lithium metal batteries comprise solid-state batteries having sulfide, polymer, oxide, or combinations thereof chemistries.

35. 30. The apparatus of claim 28, wherein the at least one tertiary battery comprises a lithium iron phosphate cathode, a graphite anode, and a thermally stable liquid electrolyte.

36. 30. The apparatus of claim 28, wherein the at least one secondary battery comprises a nickel manganese cobalt negative electrode with a low nickel concentration.

37. 30. The apparatus of claim 28, wherein the at least one tertiary battery is electrically connected in parallel with the at least one core battery and the at least one secondary battery.

38. 30. The apparatus of claim 28, wherein the at least one secondary battery comprises two secondary batteries electrically connected in parallel with each other and in series with the at least one core battery.

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