Battery management system with hybrid electrodes

Abstract

A battery management system with a hybrid electrode is provided. The battery system in one embodiment includes a battery cell having an anode including graphite and a secondary active material exhibiting apparent thermodynamic hysteresis. A controller is operably connected to a memory configured to execute program instructions in the memory to perform charging of the battery cell to a first potential and discharging of the battery cell from the first potential to generate a first discharge comparative capacity curve. After a second charge of the battery cell to a second potential and a second discharge of the battery cell from the second potential to generate a second discharge comparative capacity curve, the controller identifies an offset between the first discharge comparative capacity curve and the second discharge comparative capacity curve, and updates a model of the battery cell based on the identified offset. The controller then modifies at least one operating parameter of the battery cell based on the updated model.

Description

Technical Field

[0001] The present disclosure relates generally to batteries and, more particularly, to battery management systems for batteries that include a material having apparent thermodynamic hysteresis as a minor component in a negative electrode. Background Art

[0002] Many new battery chemistries are entering the market to provide the capabilities required in specialized applications. At one time, the lithium-ion battery market was driven by the use of such batteries in portable electronic devices, which require high energy but only limited life and power. More recently, other industries have focused on the use of batteries. As an example, batteries are often incorporated into power tools and certain types of hybrid electric vehicles. Each new industry requires different performance characteristics. Certain applications such as automotive applications require battery stability in terms of battery safety and long life (at least 10 to 15 years) for large battery packs.

[0003] Lithium-ion batteries have become the industry standard in both electric mobility and portable electronics applications. Lithium-ion batteries operate based on the movement of lithium ions between a negative electrode (also called the "anode") and a positive electrode (also called the "cathode"). In commercially available devices, the negative electrode is based on graphite, a carbon material that intercalates lithium and has a capacity of 372 mAh / g 石墨 Silicon has been attributed to its alloying with lithium and achieving 3579 mAh / g si The ability to achieve a gravimetric density of 1.5 Å / s has been identified as a potential negative electrode material. However, currently, the use of pure silicon as a negative electrode has proven to be challenging due to the high volume expansion rate that occurs during the lithiation process of pure silicon and the associated apparent thermodynamic hysteresis, which is demonstrated in the potential-versus-capacity curve for such devices. Nevertheless, some cells incorporate small amounts of pure silicon or silicon-containing materials (such as silicon oxide (SiO) or silicon alloys (SiB3, Si2Fe, TiSi2, etc.)) into graphite-based negative electrodes to increase the gravimetric capacity of the negative electrode above the level of pure graphite.

[0004] When the battery is incorporated into a vehicle application, a battery management system (BMS) is coupled to the battery, such as a lithium-ion battery, to control the operation of the battery. The BMS generally includes a controller that executes program instructions stored in a memory to operate the battery to control the rate at which the battery is charged and discharged. The charging and discharging set points are based on a model of the battery operating parameters, which may be provided with the vehicle or may be maintained away from the vehicle. In order to ensure that the appropriate set points are selected, it is necessary to understand various battery parameters that are not easily available, including the state of charge (SOC), state of health (SOH), and battery capacity. It is also useful to present one or more of the SOC, SOH, and battery capacity to the user in order to prevent improper depletion of the battery.

[0005] Therefore, what is needed is an improved BMS. It would be advantageous if the BMS controlled the battery based on measurable electrochemical characteristics of the battery that accurately identified the battery SOC and / or SOH and / or capacity. Summary of the invention

[0006] According to one embodiment, a battery system includes: a battery cell including a cathode and an anode, the anode including a carbon-based active material and a secondary active material, the secondary active material exhibiting an apparent thermodynamic hysteresis in a potential versus capacity curve. The system includes a controller operably connected to a memory, configured to execute program instructions in the memory to identify a charging strategy for the battery. One of the steps in the identification of the charging strategy for the battery is to perform a first charge of the battery cell to a first potential, and then perform a first discharge of the battery cell from the first potential to generate a first discharge versus capacity curve. The controller is also configured to execute program instructions to perform a second charge of the battery cell to a second potential before or after the first charge and discharge, and then perform a second discharge of the battery cell from the second potential to generate a second discharge versus capacity curve. The controller then identifies an offset between the first discharge versus capacity curve and the second discharge versus capacity curve, and updates a model of the battery cell based on the identified offset. At least one operating parameter of the battery cell is modified based on the updated model and the at least one operating parameter is stored in the memory. The battery cell is then operated by the controller based on the stored modified operating parameter.

[0007] In one or more embodiments, the controller is further configured to execute program instructions to parameterize a relationship between the offset and a voltage difference between a first potential and a second potential, wherein the first potential is about 70 mV vs. lithium / lithium+, and the second potential is less than 70 mV vs. lithium / lithium+. As used herein, the word "about" when modifying a number means at least within ten percent of the number, preferably within five percent of the number, and most preferably within two percent of the number.

[0008] In one or more embodiments, the at least one operating parameter includes a capacity of the battery cell, and the controller is further configured to execute program instructions to determine a state of charge of the battery cell based on the modified capacity.

[0009] In one or more embodiments, the system further comprises a display, and the controller is further configured to execute program instructions to display the determined charging status on the display.

[0010] In one or more embodiments, the at least one operating parameter includes a charge voltage cutoff, and the system further includes a voltage meter operably connected to the controller and the battery cell, wherein the controller is further configured to execute program instructions to terminate the third charge of the battery cell based on the charge voltage cutoff.

[0011] In one or more embodiments, the at least one operating parameter includes a charging current cutoff, and the system further includes an ammeter operably connected to the controller and the battery cell, wherein the controller is further configured to execute program instructions to terminate the third charging of the battery cell based on the charging current cutoff.

[0012] In one or more embodiments, the system includes a coulomb counter. The controller is configured to execute program instructions to identify a first coulomb quantity discharged between a first discharge start and a first discharge plateau end of a first discharge specific capacity curve, and to identify a second coulomb quantity discharged between a second discharge start and a second discharge plateau end of a second discharge specific capacity curve. The controller then compares the first coulomb quantity with the second coulomb quantity and estimates the amount of coulombs associated with the secondary active material generated by charging the battery cell to the second potential.

[0013] In one or more embodiments, the secondary active material includes silicon and the carbon-based active material is graphite.

[0014] In one or more embodiments, a method of operating a battery system includes: performing a first charge to a first potential on a battery cell including a cathode and an anode, the anode including a carbon-based active material and a secondary active material, the secondary active material showing an apparent thermodynamic hysteresis in a potential-versus-capacity curve; and then performing a first discharge of the battery cell from the first potential to generate a first discharge-versus-capacity curve under the control of a controller executing program instructions stored in a memory. The method also includes performing a second charge to a second potential on the battery cell before or after the first charge and discharge, and then performing a second discharge of the battery cell from the second potential to generate a second discharge-versus-capacity curve. The method includes identifying an offset between the first discharge-versus-capacity curve and the second discharge-versus-capacity curve using a controller, updating a model of the battery cell stored in a memory based on the identified offset, and modifying at least one operating parameter of the battery cell based on the updated model using a controller. The at least one modified operating parameter of the battery cell is stored in the memory, and the battery cell is operated under the control of the controller based on the at least one modified operating parameter stored.

[0015] According to one or more embodiments, a method of operating a battery system further includes parameterizing a relationship between the offset and a voltage difference between a first potential and a second potential, wherein the first potential is approximately 70 mV vs. lithium / lithium+ and the second potential is less than 70 mV vs. lithium / lithium+.

[0016] According to one or more embodiments, at least one of the stored modified operating parameters includes a modified capacity of the battery cell, and operating the battery cell under the control of the controller based on the at least one stored modified operating parameter includes determining a charge state of the battery cell based on the stored modified capacity.

[0017] In accordance with one or more embodiments, a method includes displaying a determined charging status on a display.

[0018] According to one or more embodiments, at least one of the stored modified operating parameters includes a modified charging voltage cutoff, and operating the battery cell under the control of the controller based on the at least one stored modified operating parameter includes terminating the third charging of the battery cell based on the modified charging voltage cutoff.

[0019] According to one or more embodiments, at least one of the stored modified operating parameters includes a modified charging current cutoff, and operating the battery cell under the control of the controller based on the at least one stored modified operating parameter includes terminating the third charging of the battery cell based on the modified charging current cutoff.

[0020] According to one or more embodiments, a method includes identifying a first number of coulombs discharged between a first start of discharge and an end of a first discharge plateau of a first discharge specific capacity curve, and identifying a second number of coulombs discharged between a second start of discharge and an end of a second discharge plateau of a second discharge specific capacity curve. The method includes comparing the first number of coulombs to the second number of coulombs and estimating an amount of coulombs associated with a secondary active material resulting from charging the battery cell to a second potential.

[0021] According to one embodiment, a battery system includes: a battery cell, which includes a cathode and an anode, the anode includes a carbon-based active material and a secondary active material, and the secondary active material exhibits an apparent thermodynamic hysteresis in a potential-versus-capacity curve. The battery system also includes a memory and a controller, the memory including program instructions stored therein, and the controller is operably connected to the memory and configured to execute the program instructions. The execution of the program instructions is completed to perform a first charge of the battery cell to a first potential, perform a first discharge of the battery cell from the first potential to generate a first discharge-versus-capacity curve, perform a second charge of the battery cell to a second potential, perform a second discharge of the battery cell from the second potential to generate a second discharge-versus-capacity curve, and identify an offset between the first discharge-versus-capacity curve and the second discharge-versus-capacity curve. Once the offset has been identified, the controller executes the program instructions to modify at least one operating parameter based on the identified offset and store at least one modified operating parameter of the battery cell in the memory. The controller then executes the program instructions to operate the battery cell under the control of the controller based on the stored at least one modified operating parameter.

[0022] According to one or more embodiments, the at least one modified operating parameter stored is a charging limit.

[0023] According to one or more embodiments, the at least one modified operating parameter stored is a charging strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic view of a battery pack according to the present disclosure.

[0025] Figure 2 Includes control Figure 1 System schematic view of a battery management system for a battery pack.

[0026] Figure 3 yes Figure 1Schematic view of a battery cell of a battery pack having an anode having a carbon-based active material (such as graphite having a lithiation / delithiation potential below 0.2 V vs. Li / Li+) and a secondary active material that exhibits apparent thermodynamic hysteresis in the potential vs. capacity curve.

[0027] Figure 4 is a graph of comparative capacity curves for lithiation and delithiation of a silicon oxide electrode, showing a lithiation / delithiation curve in which lithiation terminates at about 70 mV vs. lithium / lithium+, and a lithiation / delithiation curve in which lithiation terminates at less than about 70 mV vs. lithium / lithium+.

[0028] Figure 5 yes Figure 4 An enlarged view of a portion of the graph.

[0029] Figure 6 is a graph of comparative capacity curves for lithiation and delithiation of a graphite electrode, showing a lithiation / delithiation curve in which lithiation terminates at about 70 mV vs. lithium / lithium+, and a lithiation / delithiation curve in which lithiation terminates at less than about 70 mV vs. lithium / lithium+.

[0030] Figure 7 yes Figure 6 An enlarged view of a portion of the graph.

[0031] Figure 8 is a graph of lithiation and delithiation comparative capacity curves for an electrode including a secondary active material in the form of graphite and silicon oxide, showing a lithiation / delithiation curve in which lithiation terminates at about 70 mV vs. lithium / lithium+, and a lithiation / delithiation curve in which lithiation terminates at less than about 70 mV vs. lithium / lithium+.

[0032] Fig. 9 yes Figure 8 Expanded view of the end of the charge curve and the beginning of the discharge curve.

[0033] Fig.10 A flow chart depicting a process for modifying a model to generate optimized operating parameters in a BMS. DETAILED DESCRIPTION

[0034] For the purpose of promoting an understanding of the principles of the embodiments described herein, reference is now made to the drawings and descriptions in the following written specification. The reference is not intended to limit the scope of the subject matter. The present disclosure also includes any changes and modifications to the illustrated embodiments, and includes additional applications of the principles of the described embodiments as would normally occur to a person skilled in the art to which this document relates.

[0035] In a manner that is most helpful for understanding the claimed subject matter, various operations may be described in turn as multiple discrete actions or operations. However, the order of description should not be interpreted as implying that these operations must be order-dependent. In particular, in some embodiments, these operations are performed in an order different from the described embodiments. In additional embodiments, various additional operations are performed and / or the described operations are omitted.

[0036] The terms "comprising," "including," "having," and the like used with respect to the embodiments of the present disclosure are synonymous. As used herein, the word "about" when modifying a number means at least within 10 percent of the number, preferably within 5 percent of the number, and most preferably within 2 percent of the number.

[0037] The embodiments of the present disclosure discussed below may be applicable to any desired battery chemistry that includes an anode that incorporates a material exhibiting apparent thermodynamic hysteresis as a minor component. For illustrative purposes, some examples relate to lithium-ion batteries. As used herein, the term "lithium-ion battery" refers to any battery that includes lithium as an active material. In particular, lithium-ion batteries include, without limitation, lithium-based liquid electrolytes, solid electrolytes, gel electrolytes, and batteries commonly referred to as lithium polymer batteries or lithium-ion polymer batteries. As used herein, the term "gel electrolyte" refers to a polymer infused with a liquid electrolyte.

[0038] Reference now Figure 1 , the battery pack 100 includes a plurality of battery cells 102 arranged in a pack housing 104. Each battery cell 102 includes a battery cell housing 106 from which a positive terminal 108 and a negative terminal 110 are exposed. In one embodiment of a parallel arrangement, a plurality of positive terminals 108 are connected to each other through current collectors 112, and a plurality of negative terminals 110 are connected to each other through different current collectors 114. In another embodiment, the positive terminal 108 is connected to an adjacent negative terminal 110 through a current collector to provide a series connection. The current collectors 112 / 114 are connected to respective positive battery pack terminals 116 and negative battery pack terminals 118, and the positive battery pack terminals 116 and negative battery pack terminals 118 are connected to an external circuit 120.

[0039] In one embodiment, the external circuit 120 includes the electrical system of the vehicle in which the battery pack is positioned. The vehicle electrical system includes typical loads such as motors, lights, navigation systems, vehicle information and entertainment systems, etc. Additionally, the external circuit provides charging of the battery pack 100. To this end, in some embodiments, the motor is configured as a regenerative braking system. The external circuit 120 also includes an external charging gas connection (not shown). In some embodiments, the external circuit 120 is a test bench circuit and / or a resistor body.

[0040] exist Figure 1 In the embodiment of the present invention, the battery pack 100 includes a battery management system (BMS) 128. The BMS 128 is operably connected to each battery cell 102 via a control line 130. Figure 2 The BMS 128 is described in further detail, Figure 2 The BMS 128 is shown incorporated into a system 132 such as an automobile. In other embodiments, the system 132 is a test bench or other experimental system. The BMS 128 includes a controller 134, a memory 136, and a communication module 138. In various embodiments, the controller 134 is implemented using a general or specialized programmable processor that executes programming instructions stored in the memory 136. In some embodiments, at least some of the functionality of the controller 134 is provided by the vehicle control system 142 and / or remotely from the system 132 (such as by a remote controller located at a charging station, service center, manufacturing center, etc.). Therefore, in some embodiments, the controller 134 is embodied as a plurality of controllers located at the battery and / or remotely from the battery 102 and / or the system 132.

[0041] The instructions and data required for performing the programming functions are stored in the memory 136 together with the model of the battery 100 and / or the battery cell 102. In some embodiments, the memory 136 is embodied as a plurality of memories, which in some embodiments include one or more memories remote from the BMS 128. The processor, memory, and communication module 138 or other interface circuit configure the controller 134 to operate the battery pack 100 to charge and discharge the battery within the desired charge and discharge rate. In various embodiments, the processor, memory, and interface circuit components are provided on a printed circuit card, or are provided as circuits in an application-specific integrated circuit (ASIC). In some embodiments, the circuit is implemented using discrete components or circuits provided in a VLSI circuit. The circuits described herein are also implemented using a combination of processors, ASICs, discrete components, or VLSI circuits. For example, additional discussion of BMS can be found in U.S. Patent No. 8,188,715, issued on May 29, 2012, the contents of which are hereby incorporated by reference in their entirety.

[0042] In addition to the battery cells 102, the controller 134 is also operably connected to a sensor suite 140. The sensor suite 140 includes various sensors for ascertaining the operating conditions of the battery cells 102, including one or more temperature sensors, voltage sensors, and current / coulomb sensors. In some embodiments, each battery cell 102 is associated with a corresponding dedicated sensor suite 140 that is operably connected to the battery cell 102. In these embodiments, the sensor suite 140 includes one or more temperature sensors, voltage sensors, and current / coulomb sensors that are configured to obtain data for each individual battery cell.

[0043] In this embodiment, the controller 134 is also operably connected to the vehicle control system 142, the display 144, and the on-board diagnostic port 146 via the communication module 138. In various embodiments, the communication module 138 is configured to communicate wirelessly with one or more of the vehicle control system 142, the display 144, and the on-board diagnostic port 146.

[0044] like Figure 3 As shown in , in one embodiment, each battery cell 102 includes a positive electrode current collector 150, a positive electrode layer 152, a separator layer 154 that is omitted in some embodiments, a negative electrode 156, and a negative electrode current collector 158. In some embodiments, multiple layers of battery cells 102 are stacked on top of each other to form an electrode stack. In other embodiments, the battery cell 102 is wound around itself in a spiral shape to form a so-called "jelly roll" or "Swiss roll" configuration. In some embodiments, additional layers such as protective layers are provided.

[0045] Positive electrode current collector 150 electrically connects positive terminal 108 of battery cell 102 with positive electrode 152 to enable electrons to flow between external circuit 120 and positive electrode 152. Likewise, negative electrode current collector 158 electrically connects negative terminal 110 with negative electrode layer 156.

[0046] When the battery 100 is connected to an external circuit 120 that is powered by the battery 100, lithium ions are separated from the electrons in the negative electrode 156. The lithium ions travel through the separator 154 and into the positive electrode 152. The free electrons in the battery 100 flow from the negative electrode 156 to the negative terminal 110 of the battery cell 102 through the negative electrode current collector 158. The electrons are then collected by the battery current collector 114 and transported to the battery terminal 118. The electrons flow through the external circuit 120 to provide power to the external circuit 120, and then pass through the positive battery terminal 116 and return to the battery cell 102 via the positive terminal 108. Connecting the battery 100 to an external circuit that charges the battery 100 results in the opposite flow of electrons and lithium ions.

[0047] In the illustrated embodiment, the negative electrode layer 156 includes a primary active material and a secondary active material that exhibits an apparent thermodynamic hysteresis in the potential versus capacity curve. As used herein, the term "primary active material" means an active material that provides at least 50% of the electrode's lithiation capacity. In some embodiments, the primary active material provides at least 80 percent of the electrode's lithiation capacity. In some embodiments, the primary active material provides about 94 percent of the electrode's lithiation capacity. As used herein, the term "secondary active material" means an active material that provides less than 50% of the electrode's lithiation capacity. In some embodiments, the secondary active material provides less than 20% of the electrode's lithiation capacity. In some embodiments, the secondary active material provides about 6% of the electrode's lithiation capacity.

[0048] The BMS 128 uses measurable electrochemical characteristics in determining various operating characteristics of the battery 100 that result from the incorporation of a secondary active material in the negative electrode layer 156 that exhibits apparent thermodynamic hysteresis in the potential versus capacity curve. Figure 4-9 Measurable electrochemical features are explained.

[0049] Figure 4 Line 170 in FIG. 1 depicts the flow rate at 1530 mAh / g SiO The total lithiation capacity of the SiO electrode charged from a starting half-cell potential of about 1.2 V vs. Li / Li+ to 0.07 V vs. Li / Li+ (resulting in about 1.35 Ah / g SiO 1.53 Ah / g wt. capacity). Line 172 depicts the half-cell potential (V vs. Li / Li+) of the electrode as the SiO electrode is discharged following a 0.07 V vs. Li / Li+ charge. Line 174 depicts the half-cell potential (V vs. Li / Li+) of the SiO electrode as it is charged from a starting half-cell potential of about 1.2 V vs. Li / Li+ to 0.001 V vs. Li / Li+ (resulting in about 1.53 Ah / g SiO Line 176 depicts the half-cell potential (V vs. Li / Li+) of the electrode when the SiO electrode is discharged following a 0.001 V vs. Li / Li+ charge.

[0050] Figure 5 yes Figure 4 Expanded view of the end of the charge curve and the beginning of the discharge curve. Figure 4 and 5 The additional charge to 0.001 V vs. Li / Li+ produced 190 mAh / gSiO The additional capacity of the electrode is defined as 0.070 mV, which corresponds to the Li+ of the electrochemically active Si species of SiO. 3.3 In the case of stoichiometric Si, this additional capacity is equivalent to about 12% of the total capacity of the electrode. In addition, once the capacity drops to about 0.5 Ah / g SiO Some divergence is observed between discharge line 172 and discharge line 176 ( Figure 4 ), but at 0.5 Ah / g SiO and 1.2 Ah / g SiO There is very little divergence between them.

[0051] Reference now Figure 6 , line 180 depicts the 石墨 The total lithiation capacity of the graphite electrode charged from a starting half-cell potential of about 1.25 V vs. Li / Li+ to 0.07 V vs. Li / Li+ (resulting in about 0.36 Ah / g 石墨 Line 182 depicts the half-cell potential (V vs. Li / Li+) of the electrode when the graphite electrode is discharged following a 0.07 V vs. Li / Li+ charge. Line 184 depicts the half-cell potential (V vs. Li / Li+) of the graphite electrode when the graphite electrode is charged from a starting half-cell potential of about 1.2 V vs. Li / Li+ to 0.001 V vs. Li / Li+ (resulting in about 0.38 Ah / g 石墨 Line 186 depicts the half-cell potential (V vs. Li / Li+) of the electrode when the graphite electrode is discharged following a 0.001 V vs. Li / Li+ charge.

[0052] Figure 7 yes Figure 6 Expanded view of the end of the charge curve and the beginning of the discharge curve. Figure 6 and 7 The additional charge to 0.001 V vs. Li / Li+ produced 21 mAh / g 石墨 The additional capacity of the electrode is limited to 0.070 mV, which corresponds to Li 0.95 When C6 is stoichiometric, this additional capacity is equivalent to about 5% of the total capacity of the electrode.

[0053] Additionally, Figure 6 Three "plateaus" 187, 189 and 191 during charging, and three "plateaus" 188, 190 and 192 during discharging are disclosed. Figure 7 As demonstrated, when the electrode is charged to 0.001 V vs. Li / Li+ (which exceeds the 0.95 While the graphite surface stoichiometry of C6 correlates and terminates at a charge plateau 191 at about 70 mV vs. Li / Li+, the termination of plateau 192 occurs earlier in the discharge, as shown by the 2 mAh / g to the right in discharge line 186. 石墨 This is evidenced by offset 194. With this slight exception, the charge lines 180 and 184 and the discharge lines 182 and 184 are all consistent with each other.

[0054] As reference Figure 8 and 9 As discussed, by combining SiO, a material that exhibits apparent thermodynamic hysteresis in the potential versus capacity curve, with graphite, Figure 4-7 A combination of properties revealed in Figure 8 , line 200 depicts a 440 mAh / g SiOGr The total lithiation capacity of the hybrid graphite / SiO electrode was 0.42 Ah / g when charged from a starting half-cell potential of about 1.25 V vs. Li / Li+ to about 0.07 V vs. Li / Li+ (resulting in about SiOGr Line 202 depicts the half-cell potential (V vs. Li / Li+) of the electrode when the hybrid electrode is discharged following a 0.07 V vs. Li / Li+ charge. Line 204 depicts the half-cell potential (V vs. Li / Li+) of the electrode when the hybrid electrode is charged from a starting half-cell potential of about 1.25 V vs. Li / Li+ to 0.001 V vs. Li / Li+ (resulting in about 0.44 Ah / gSiOGr Line 206 depicts the half-cell potential (V vs. Li / Li+) of the graphite electrode when it is discharged following a 0.001 V vs. Li / Li+ charge. Fig. 9 As demonstrated in , after charging to 0.07 V vs. Li / Li+, the initial discharge voltage 205 is approximately 0.077 V vs. Li / Li+, and after charging to 0.001 V vs. Li / Li+, the initial discharge voltage 207 is approximately 0.013 V vs. Li / Li+.

[0055] Fig. 9 yes Figure 8 Expanded view of the end of the charge curve and the beginning of the discharge curve. Figure 8 and 9 The additional charge to 0.001V vs. Li / Li+ produces 27 mAh / gSiOGrThe additional capacity is equivalent to about 6% of the total electrode capacity when the full SOC is defined as 0.070 mV vs. Li / Li+.

[0056] Additionally, Figure 8 Revealed Figure 6 The three "plateaus" 187, 189 and 191 of are still observable as are the plateaus 209, 211 and 213. Similarly, Figure 6 The three "plateaus" 188, 190 and 192 (of the graphite electrode) are still observable as are the plateaus 208, 210 and 212. Fig. 9 As demonstrated, when the electrode is charged to 0.001 V vs. Li / Li+, the termination of plateau 212 occurs earlier in the discharge, as evidenced by the 9 mAh / s to the right in discharge line 206 compared to discharge line 202. gSiOGr This is evidenced by offset 214. In this exceptional case, charging lines 180 and 184 and discharging lines 182 and 184 are all consistent with each other.

[0057] The shift 214 occurs as a result of apparent thermodynamic hysteresis. In particular, Figure 5 As demonstrated, SiO at 0.070V vs. Li / Li+—— Figure 7 The end of the charging plateau 191 - lithiation continues at a potential below. Figure 4 As evidenced by the inflection point 216 in the discharge line 176 of , SiO does not substantially begin to delithiate until the potential rises above about 0.2 V vs. Li / Li+. Therefore, it is possible to verify the lithiation potential (also referred to as ) drops below 70 mV vs. Li / Li+, at which the graphite surface has a Li 0.95 Stoichiometry above C6. As discussed more fully below, the characterization of the offset also allows estimation of the final lithiated half-cell surface potential of the negative electrode.

[0058] In one embodiment, Fig.10The method 220 is performed at least in part by the BMS 128 to identify an offset 214 in a battery cell incorporating a negative electrode having a material with a lithiation / delithiation potential below 0.2 V vs. Li / Li+ and a material that exhibits apparent thermodynamic hysteresis in a potential versus capacity curve, typically having a material with a lithiation / delithiation potential below 0.2 V vs. Li / Li+ (e.g., a carbon-based active material such as graphite) as the primary active material. In some embodiments, the method is performed in an operational or "online" environment (such as while controlling operation of a vehicle). In other embodiments, the method is performed in an experimental or "offline" environment (such as in generating and validating an experimental internal state prediction model).

[0059] At block 222, the battery cell is charged to the full cell potential. Once the battery cell has been charged to the selected full cell potential, battery discharge is initiated at block 224. During discharge, the cell potential for the battery cell (or cells) is obtained by obtaining the voltage between the negative electrode 156 and the positive electrode 152 using the sensor assembly 140, and the obtained voltage is stored in the memory 136 (block 226). The discharged coulombs are also obtained by the sensor assembly 140 and stored in the memory 136 (block 228).

[0060] At block 230, the BMS compares the voltage and coulomb data obtained / stored from the current discharge with the data stored from the previous discharge (if any) to see if an offset 214 is evidenced. If there is no offset, both the newly obtained data and the stored data are compared. Figure 8 9. Therefore, the process returns to block 222 and a second charge is performed. In some embodiments, a significant period of time will pass between the first charge and the second charge. For example, when the BMS is at least partially implemented at a service facility, the second charge may occur several months after the initial charge. During initial testing of the battery cell, the second charge may occur immediately after the first discharge.

[0061] In some embodiments, one or more parameters for the second charge are controlled by the controller 134 to be different from the parameters of the first charge. As an example, during the initial testing of the battery cell, the first charge in some embodiments is limited to ensure that the half-cell potential does not go below 0.070 V vs. Li / Li+. This ensures that the discharge data obtained is in the form of the discharge curve 202. The full cell potential for the subsequent charge (block 222) is then increased in amount (Ah) until the offset 214 is observed. In some embodiments, the initial discharge places the half-cell potential below 0.070 V vs. Li / Li+, and the subsequent charge is reduced until the offset is observed. In either method, the initial characteristics of the half-cell are provided.

[0062] Once an offset is observed at block 230, the process proceeds to block 232 and the BMS determines whether sufficient data has been collected to parameterize the relationship between the offset and the voltage difference. Specifically, the observed offset is related to the extent to which the electrode voltage has been driven below the third plateau of graphite, i.e., ~70 mV vs. Li / Li+ (or any other selected reference voltage). As a result of such charging, the voltage of the battery cell at the beginning of discharge is lower than Li / Li+, such as Fig. 9 This is evidenced by the offset between voltage 205 and voltage 207. This relationship is provided by the following equation:

[0063]

[0064] Where V is the voltage offset at the start of discharge. Therefore, for smaller deviations below the reference voltage during the charging event, a smaller offset will be exhibited because the start discharge voltage will be closer to voltage 205. In contrast, when the charging voltage is close to 0 mV vs. Li / Li+, the observed offset is maximized and closer to voltage 207. Therefore, if sufficient data has not been collected for the desired parameterization level at block 232, the process returns to block 222 and additional data is obtained at different potentials. After the initial parameterization, the parameterization is typically repeated at intervals throughout the life of the battery cell because the electrode assemblies typically age at different rates and therefore the percentage contribution to the total capacity will change. The specific interval selected for repeated parameterization will depend on the desired accuracy and the relative changes in component aging.

[0065] If sufficient offset data has been obtained at block 232, the process continues to block 234. In some settings, especially operational settings, only data associated with a single offset is required. Therefore, block 232 is essentially omitted.

[0066] At block 234, following parameterization (if any), the electrode model stored in memory 136 for execution by controller 134 is updated using the data obtained at blocks 222-232. By way of example, since function "Q" is a relationship parameterized by experiment for a given battery anode composition, once a shift 214 is observed during delithiation, the degree of lithiation of the graphite surface during the immediately preceding charge period can be accurately determined by function "Q". In addition, by comparing the coulombs required to reach one or more of the three graphite plateaus 208, 210, and 212 during battery discharge with the coulombs delivered during the previous charge period to reach the associated plateau or plateaus, it is possible to: a) verify whether the graphite surface stoichiometry has increased to the Li plateau; b) verify whether the graphite surface stoichiometry has increased to the Li plateau; c) verify whether the graphite surface stoichiometry has increased to the Li plateau; 0.95 C6 and above, and b) estimate the additional capacity obtained from the second component which shows apparent thermodynamic hysteresis in the potential versus capacity curve.

[0067] Although many models have been developed for use in battery management systems as discussed in U.S. Pat. No. 8,188,715 issued May 29, 2012, U.S. Pat. No. 7,518,339 issued April 14, 2009, and U.S. Patent Application Publication No. 2018 / 0083461 (the contents of each of which are incorporated herein by reference), in one embodiment, the anode model for the lithium-ion battery anode stored in memory 136 is based on the typical structure of a physics-based lithium-ion battery model. The model is defined by the following equation:

[0068]

[0069]

[0070]

[0071]

[0072]

[0073] In this model, J is the cost function, x and z refers to the differential and algebraic states of the model, u is the battery cell voltage, f, g and h refers to the function that forms the structure of the electrochemical model, i Refers to the experiment number, Refers to i The starting conditions for the experiment, is the result of the optimization problem, and the set PDefines upper and lower limits for parameter variation. Function f, g, h It is derived using model reduction techniques from a physics-based lithium-ion battery model consisting of coupled partial differential equations.

[0074] Starting with the model above, the anode voltage at a given time generated by the model is output as (for simplicity, the experimental subscript “i” is omitted in this section), and the anode voltage at a given time obtained experimentally is provided as y exp = [V exp ,T exp ]. The structure of the cost function is typically given by:

[0075]

[0076] in and However, by using experiments to identify the magnitude of the excursions in the delithiation plateau, the cost function can be modified to include more information about the internal state of the system.

[0077] For example, one such modification is:

[0078]

[0079] in

[0080]

[0081] In this model, the function α is defined as the minimum value of the anode overpotential state within a specific charging cycle, and therefore contains information from the model about the prediction of the minimum negative electrode surface potential during charging. An example structure for this function is:

[0082]

[0083] During charging, refers to the state in the vector z. In obtaining experimental values ​​for the above model, Δ is determined for each experiment by detecting the characteristics during the slow full battery cell discharge. shift .

[0084] Once the model is updated, the updated model is used to modify one or more operating parameters for the battery cell (block 236). As used herein, the term "operating parameter" means one or more of the following: charging and discharging set points (e.g., charging voltage, charging current rate, discharging current rate, charge termination voltage, charge termination current, etc.), maximum voltage, minimum voltage, state of charge, depth of charge, temperature, and capacity. Therefore, in order to account for capacity loss as the battery cell ages, one battery management strategy is to reduce the operating regime of the battery. In particular, the maximum steady-state battery voltage decreases over time. Therefore, in one embodiment, the boundary conditions for the operating regime of the battery are modified at block 236. Therefore, since lithium plating behavior is a well-studied aging mechanism and safety issue, by detecting when the surface SOC of graphite rises to Li 0.95 C6 and above, and based on the updated model, the maximum operating voltage of the battery can be modified by the controller 124 at a time close to the lithium plating schedule of the battery (i.e., 0 mV vs. half-cell potential of Li / Li+, and Li 1.00 The graphite surface component of C6) but does not safely operate the cell at potentials in this protocol. This minimizes cell degradation while maximizing available capacity.

[0085] According to one embodiment, at block 236, the controller 134 uses the updated model data to improve the model voltage prediction, power prediction, and SOC estimation accuracy. Specifically, with the addition of Li 0.95 Model internal states associated with graphite surface stoichiometry above C6 (see e.g. Figure 6 ) is used to indicate what fraction of the delithiation capacity is produced by graphite and what fraction is produced by the second component that exhibits apparent thermodynamic hysteresis because the relative fraction is related to the difference between the charge and discharge capacities for the region associated with the third plateau (213 / 212) associated with graphite. The updated data enables more accurate SOC and voltage predictions for the model. Therefore, the controller 134 controls the display 144 to provide more accurate SOC data to the user. In some embodiments, the SOC data is in the form of a cruising range.

[0086] In one or more embodiments, without modifying the model, the method 220 is modified to calibrate the BMS limits for charging and the charging strategy executed by the BMS 128 in the operating environment. Therefore, block 234 is omitted and the process simply continues to block 236 where the controller 134 uses the updated data to adapt the empirical fast charge algorithm stored in the memory 136 without an extensive electrochemical model. The adaptation is performed on a cycle-by-cycle basis after the offset 214 is detected during a subsequent discharge. Therefore, in the next charge cycle, the controller 134 uses the updated model data to adapt the parameters for the fast charge algorithm, resulting in an iterative learning control process. In particular, what full battery cell potential corresponds to Li 0.95 Knowledge of the graphite surface stoichiometry of C6 is used to adapt the maximum voltage and / or cutoff criteria of the battery during fast charging to achieve fast charging while minimizing aging of the battery. Thus, in various embodiments, the controller 134 uses the updated data to establish voltage values ​​for constant voltage holding, establish voltage cutoff values ​​for constant current charging, establish set points for charge capacity, establish boundaries for healthy operating procedures, etc. Of course, in some embodiments in which block 234 is performed, the above parameters are also modified.

[0087] Regardless, once the desired modified parameter or parameters have been stored in memory, the controller 134 operates the battery cell / battery pack using the modified parameters at block 238 .

[0088] As noted above, in some embodiments, method 220 is used for parameterization and verification of electrochemical cell models. Parameterization generally requires electrical testing across the battery operating procedures together with specialized electrochemical testing. Typically, signals that can be used to quantify battery model performance are voltage and temperature. Due to the significant large number of parameters required for electrochemical model simulation, many parameters are forced to fit model predictions using only minimal experimental data. Challenges in optimization problems include the occurrence of local minima, insufficient data quality for identifying certain model parameters, and structural challenges in the model that make certain parameters non-uniquely identifiable. As a result, different parameter groups may result in similar voltage and temperature predictions from the model.

[0089] The accuracy / model quality of the fitted parameters can be determined by parameter-specific electrochemical experiments. However, such experiments can be time-consuming, and for some parameters, available methods are not always directly applicable or well refined. An alternative method to further evaluate the quality of the model is to measure the internal state of the battery, such as the negative electrode / electrolyte potential. Access to such measurements typically requires a specialized battery cell design with multiple reference electrodes. In the case of a battery comprising a multi-component negative electrode (which consists of a material having a lithiation / delithiation potential below 0.2 V vs. Li / Li+ (such as graphite) and a second material (e.g., SiO or other Si-based materials) that exhibits apparent thermodynamic hysteresis in the potential vs. capacity curve), it is possible to partially confirm the internal state prediction of the model by detecting specific electrochemical features according to method 220. These features (e.g., offset 214) indicate whether the potential of the multi-component negative electrode is reduced to below the third plateau of graphite approximately ~70 mV vs. Li / Li+.

[0090] Thus, adding a material that exhibits apparent thermodynamic hysteresis in the potential versus capacity curve (which in this example is SiO, but can be any such material, including other Si alloys, etc.) to an electrode comprising a material having a lithiation / delithiation potential below 0.2 V vs. Li / Li+ (such as a carbon-based active material, e.g., graphite) results in an electrode that exhibits readily discernible electrochemical characteristics when the electrode is charged beyond 0.07 V vs. Li / Li+. The apparent thermodynamic hysteresis in the potential versus capacity curve is used to partially confirm an electrochemical model for lithium-ion batteries having a negative electrode comprising silicon (Si), silicon oxide (SiO), and Si alloys (such as silicides) and other materials that exhibit apparent thermodynamic hysteresis. Furthermore, the apparent thermodynamic hysteresis in the potential versus capacity curve is used to identify and update a BMS and BMS strategy based on the partially confirmed electrochemical model.

[0091] In addition to updating the BMS strategy, the apparent thermodynamic hysteresis in the potential versus capacity curve is also used in the design of the BMS strategy. As an example, in a lithium-ion battery with a multi-component negative electrode (which is composed of a material having a lithiation / delithiation potential below 0.2 V vs. Li / Li+ (such as a carbon-based active material, e.g., graphite) and a second material that exhibits an apparent thermodynamic hysteresis in the potential versus capacity curve), the electrochemical characteristics associated with the apparent thermodynamic hysteresis are used to partially confirm the internal state of the battery model, adapt the battery model parameters to better predict the internal state, enable improved voltage prediction and accuracy of SOC estimation and power prediction, adapt the battery limits over the life time to control the battery aging behavior (e.g., specify one or more boundaries of a healthy operating procedure), and specify a charging strategy based on measurable electrochemical characteristics without an electrochemical model or without resorting to running such a model.

[0092] The charging strategies implemented in various embodiments include specifying a voltage for constant voltage holding, specifying a voltage cutoff for constant current charging, specifying a set point for charging capacity, and specifying boundaries for healthy operating procedures.

[0093] In one embodiment, the disclosed systems and methods are used in an experimental design to partially confirm the internal state predictions of a model of a lithium-ion battery comprising a multi-component negative electrode composed of a material having a lithiation / delithiation potential below 0.2 V vs. Li / Li+ (such as a carbon-based active material, e.g., graphite) and a second component (such as SiO) that exhibits apparent thermodynamic hysteresis in the potential versus capacity curve. In some embodiments, the confirmation occurs by detecting and measuring the accessed capacity below the third plateau of graphite, e.g., ~70 mV. The accessed capacity is attributed to the second component that exhibits apparent thermodynamic hysteresis. In one embodiment, the disclosed systems and methods are used for the adaptation of battery model parameters to better predict the internal state using the apparent thermodynamic hysteresis behavior of the component that exhibits apparent thermodynamic hysteresis.

[0094] Although primarily described with reference to lithium-ion batteries, the present disclosure is also useful in other battery cell types (such as Na-ion, Mg-ion) as long as the negative electrode contains silicon, silicon-based materials (SiO, Si alloys, etc.) and / or other materials that exhibit apparent thermodynamic hysteresis in the potential-versus-capacity curve during lithiation / delithiation.

[0095] Therefore, it will be appreciated that variations of the above and other features and functions, or alternatives thereof, may be combined desirably into many other different systems, applications or methods. Various currently unforeseen or unanticipated alternatives, modifications, variations or improvements may be made subsequently by those skilled in the art, which are also intended to be covered by the foregoing disclosure.

Claims

1. A battery system comprising: A battery cell comprising a cathode and an anode, the anode comprising a carbon-based active material and a secondary active material, the secondary active material exhibiting apparent thermodynamic hysteresis in a potential versus capacity curve; a memory including program instructions stored therein; as well as A controller operably connected to the memory and configured to execute program instructions to performing a first charge of the battery cell to a first potential, performing a first discharge of the battery cell from a first potential to generate a first discharge specific capacity curve, performing a second charge of the battery cell to a second potential, performing a second discharge of the battery cell from a second potential to generate a second discharge specific capacity curve, identifying an offset between the first discharge specific capacity curve and the second discharge specific capacity curve, updating a model of the battery cell based on the identified offset, storing in a memory at least one modified operating parameter of the battery cell based on the updated model, and The battery cell is operated under control of the controller based on the stored at least one modified operating parameter.

2. The system of claim 1 , wherein the controller is further configured to execute program instructions to: The relationship between the offset and the voltage difference between a first potential and a second potential is parameterized, wherein the first potential is 70 mV relative to lithium / lithium+ and the second potential is lower than 70 mV relative to lithium / lithium+.

3. The system of claim 2, wherein the at least one operating parameter comprises a capacity of the battery cell, wherein the controller is further configured to execute program instructions to: A state of charge of the battery cell is determined based on the modified capacity.

4. The system of claim 3, wherein: The system also includes a display; and The controller is also configured to execute the program instructions to display the determined charging status on the display.

5. The system of claim 4, further comprising a coulomb counter, wherein the controller is further configured to execute program instructions to: Identify a first coulomb quantity discharged between a first discharge start and an end of a first discharge plateau of a first discharge specific capacity curve; Identify a second coulomb quantity discharged between a second discharge start and an end of a second discharge plateau of a second discharge specific capacity curve; comparing the first coulomb number to the second coulomb number; and The amount of coulombs associated with the secondary active material resulting from charging the cell to a second potential is estimated, wherein the first potential is 70 mV relative to lithium / lithium+ and the second potential is less than 70 mV relative to lithium / lithium+.

6. The system of claim 2, wherein the at least one operating parameter includes a charge voltage cutoff, the system further comprising: a voltage meter operably connected to the controller and the battery cell, wherein the controller is further configured to execute program instructions to: The third charging of the battery cell is terminated based on the charging voltage cutoff.

7. The system of claim 2, wherein the at least one operating parameter includes a charge current cutoff, the system further comprising: an ammeter operably connected to the controller and the battery cell, wherein the controller is further configured to execute program instructions to: The third charging of the battery cell is terminated based on the charging current cutoff.

8. The system of claim 2, wherein the carbon-based active material comprises graphite and the secondary active material comprises silicon.

9. The system of claim 1 , further comprising a coulomb counter, wherein the controller is further configured to execute program instructions to: Identify a first coulomb quantity discharged between a first discharge start and an end of a first discharge plateau of a first discharge specific capacity curve; Identify a second coulomb quantity discharged between a second discharge start and an end of a second discharge plateau of a second discharge specific capacity curve; comparing the first coulomb number to the second coulomb number; and The amount of coulombs associated with the secondary active material resulting from charging the cell to a second potential is estimated, wherein the first potential is 70 mV relative to lithium / lithium+ and the second potential is less than 70 mV relative to lithium / lithium+.

10. A method of operating a battery system, comprising: performing a first charge to a first potential on a battery cell including a cathode and an anode, the anode including a carbon-based active material and a secondary active material that exhibits apparent thermodynamic hysteresis in a potential versus capacity curve; performing a first discharge of the battery cell from a first potential to generate a first discharge specific capacity curve under control of the controller executing program instructions stored in the memory; performing a second charge of the battery cell to a second potential; performing a second discharge of the battery cell from a second potential to generate a second discharge specific capacity curve; identifying, using a controller, an offset between a first discharge specific capacity curve and a second discharge specific capacity curve; updating a model of the battery cell stored in a memory based on the identified offset; modifying, with the controller, at least one operating parameter of the battery cell based on the updated model; storing at least one modified operating parameter of the battery cell in a memory; as well as The battery cell is operated under control of the controller based on the stored at least one modified operating parameter.

11. The method according to claim 10, further comprising: The relationship between the offset and the voltage difference between a first potential and a second potential is parameterized, wherein the first potential is 70 mV relative to lithium / lithium+ and the second potential is lower than 70 mV relative to lithium / lithium+.

12. The method according to claim 11, wherein: The at least one modified operating parameter stored includes a modified capacity of the battery cell; and Operating the battery cell under control of the controller based on the stored at least one modified operating parameter includes determining a state of charge of the battery cell based on the stored modified capacity.

13. The method according to claim 12, further comprising: The determined charging status is shown on the display.

14. The method according to claim 11, wherein: the stored at least one modified operating parameter includes a modified charge voltage cutoff; and Operating the battery cell under control of the controller based on the stored at least one modified operating parameter includes terminating a third charge of the battery cell based on the modified charge voltage cutoff.

15. The method of claim 11, wherein: The stored at least one modified operating parameter includes a modified charge current cutoff; and Operating the battery cell under control of the controller based on the stored at least one modified operating parameter includes terminating a third charge of the battery cell based on the modified charge current cutoff.

16. The method according to claim 10, further comprising: Identify a first coulomb quantity discharged between a first discharge start and an end of a first discharge plateau of a first discharge specific capacity curve; Identify a second coulomb quantity discharged between a second discharge start and an end of a second discharge plateau of a second discharge specific capacity curve; comparing the first coulomb number to the second coulomb number; as well as The amount of coulombs associated with the secondary active material resulting from charging the cell to a second potential is estimated, wherein the second potential is less than 70 mV relative to Li / Li+.

17. A battery system comprising: A battery cell comprising a cathode and an anode, the anode comprising a carbon-based active material and a secondary active material, the secondary active material exhibiting apparent thermodynamic hysteresis in a potential versus capacity curve; a memory including program instructions stored therein; as well as A controller operably connected to the memory and configured to execute program instructions to performing a first charge of the battery cell to a first potential, performing a first discharge of the battery cell from a first potential to generate a first discharge specific capacity curve, performing a second charge of the battery cell to a second potential, performing a second discharge of the battery cell from a second potential to generate a second discharge specific capacity curve, identifying an offset between the first discharge specific capacity curve and the second discharge specific capacity curve, modifying at least one operating parameter based on the identified offset, storing at least one modified operating parameter of the battery cell in a memory, and The battery cell is operated under control of the controller based on the stored at least one modified operating parameter.

18. The battery system of claim 17, wherein the at least one modified operating parameter stored is a charging limit.

19. The battery system of claim 17, wherein the at least one modified operating parameter stored is a charging strategy.

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