Patent Description:
The present disclosure relates generally to the field of batteries and battery modules. More specifically, the present disclosure relates to lithium ion battery cells that may be used with a dual energy storage system and starter battery modules.

Prior art document <CIT> discloses a dual energy storage system comprising a lead acid battery, a LTO/LMO battery and a battery control unit.

A vehicle that uses one or more battery systems for providing all or a portion of the motive power for the vehicle can be referred to as an xEV, where the term "xEV" is defined herein to include all of the following vehicles, or any variations or combinations thereof, that use electric power for all or a portion of their vehicular motive force. For example, xEVs include electric vehicles (EVs) that utilize electric power for all motive force. As will be appreciated by those skilled in the art, hybrid electric vehicles (HEVs), also considered xEVs, combine an internal combustion engine propulsion system and a battery-powered electric propulsion system, such as <NUM> Volt (V) or 130V systems. The term HEV may include any variation of a hybrid electric vehicle. For example, full hybrid systems (FHEVs) may provide motive and other electrical power to the vehicle using one or more electric motors, using only an internal combustion engine, or using both. In contrast, mild hybrid systems (MHEVs) disable the internal combustion engine when the vehicle is idling and utilize a battery system to continue powering the air conditioning unit, radio, or other electronics, as well as to restart the engine when propulsion is desired. The mild hybrid system may also apply some level of power assist, during acceleration for example, to supplement the internal combustion engine. Mild hybrids are typically 96V to 130V and recover braking energy through a belt or crank integrated starter generator. Further, a micro-hybrid electric vehicle (mHEV) also uses a "Stop-Start" system similar to the mild hybrids, but the micro-hybrid systems of a mHEV may or may not supply power assist to the internal combustion engine and operate at a voltage below 60V. For the purposes of the present discussion, it should be noted that mHEVs typically do not technically use electric power provided directly to the crankshaft or transmission for any portion of the motive force of the vehicle, but an mHEV may still be considered as an xEV since it does use electric power to supplement a vehicle's power needs when the vehicle is idling with internal combustion engine disabled and recovers braking energy through an integrated starter generator. In addition, a plug-in electric vehicle (PEV) is any vehicle that can be charged from an external source of electricity, such as wall sockets, and the energy stored in the rechargeable battery packs drives or contributes to drive the wheels. PEVs are a subcategory of EVs that include all-electric or battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and electric vehicle conversions of hybrid electric vehicles and conventional internal combustion engine vehicles.

xEVs as described above may provide a number of advantages as compared to more traditional gas-powered vehicles using only internal combustion engines and traditional electrical systems, which are typically 12V systems powered by a lead acid battery. For example, xEVs may produce fewer undesirable emission products and may exhibit greater fuel efficiency as compared to traditional internal combustion vehicles and, in some cases, such xEVs may eliminate the use of gasoline entirely, as is the case of certain types of EVs or PEVs.

As technology continues to evolve, there is a need to provide improved power sources, particularly battery modules, for such vehicles. For example, battery modules that include battery cells with relatively high nominal voltages may reduce a size and cost of the battery module because fewer battery cells are included within the battery module. Additionally, it is also desirable for battery modules to be configured to operate within existing electrical networks of xEVs without disrupting operation of the xEV electrical network.

It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain embodiments and that these aspects are not intended to limit the scope of this disclosure.

The present disclosure relates to a dual energy storage system that includes a lithium ion battery electrically coupled in parallel with a lead acid battery, where the lithium ion battery and the lead-acid battery are electrically coupled to a vehicle bus, where the lithium ion battery open circuit voltage (OCV) partially matches the lead-acid battery OCV such that the lead-acid battery OCV at <NUM>% of the lead-acid battery state of charge (SOC) and the lithium ion battery OCV at <NUM>% of the lithium ion battery SOC are within <NUM>% of <NUM> V.

The present disclosure also relates to a system that includes a lithium ion starter battery, a lead acid battery electrically coupled in parallel with the lithium ion starter battery, and a vehicle having a vehicle bus configured to establish an electrical pathway between the lithium ion starter battery, the lead acid battery, and the vehicle, and where the lithium ion starter battery open circuit voltage (OCV) partially matches the lead-acid battery OCV such that the lead-acid starter battery OCV at <NUM>% of the lead-acid battery state of charge (SOC) is about equal to the lithium ion starter battery OCV at <NUM>% of the lithium ion starter battery SOC.

The present disclosure also relates to a method that includes measuring a voltage of a lithium ion battery cell using a voltage sensor, estimating a state of charge (SOC) of the lithium ion battery cell based on the voltage of the lithium ion battery cell and a voltage profile of the lithium ion battery cell, and determining a diagnostic parameter of the lithium ion battery cell based on the SOC of the lithium ion battery cell, the voltage of the lithium ion battery cell, or both.

The battery systems described herein may be used to provide power to various types of electric vehicles (xEVs) and other high voltage energy storage/expending applications (e.g., electrical grid power storage systems). Such battery systems may include one or more battery modules, each battery module having a number of battery cells (e.g., lithium-ion (Li-ion) electrochemical cells) arranged and electrically interconnected to provide particular voltages and/or currents useful to power, for example, one or more components of an xEV. As another example, battery modules in accordance with present embodiments may be incorporated with or provide power to stationary power systems (e.g., non-automotive systems).

xEvs may include a lead acid battery module (e.g., having an open circuit voltage of 12V at <NUM>% state of charge) and a Li-ion battery module (e.g., having an open circuit voltage of between <NUM>. 5V and 16V at <NUM>% state of charge) coupled to one another in a parallel configuration. In certain instances, the lead acid battery module may be used to start and/or ignite an internal combustion engine of the xEV, whereas the Li-ion battery module may be used to capture power from a regenerative braking system and to provide electricity to vehicle components when the internal combustion engine is idle. Additionally or alternatively, the Li-ion battery module may be utilized as a starter battery and provide power to start and/or ignite an internal combustion engine of the xEV. Accordingly, Li-ion batteries in 12V vehicle architectures can apply to 12V Dual Energy Storage Systems (DESS) and 12V starter applications. Unfortunately, to supply a sufficient amount of power, Li-ion battery modules include a plurality of individual Li-ion battery cells, which may add weight to the xEV and/or decrease fuel economy.

The present disclosure addresses these and other shortcomings of traditional Li-ion battery modules. For example, embodiments of the present disclosure relate to high voltage Li-ion battery cells that may form a Li-ion battery module configured to be utilized in existing electrical networks of an xEV without disrupting the xEV electrical network (e.g., the battery module provides power within a predetermined range). The high voltage Li-ion battery cells may reduce a size (e.g., volume) of the overall battery module by reducing a number of Li-ion battery cells that are included in the battery module. Further, the high voltage Li-ion battery cells may reduce costs of the battery module because of the reduced number of the Li-ion battery cells.

In some embodiments, the Li-ion battery module is configured to have an open circuit voltage (OCV) at <NUM>% state of charge (SOC) that is substantially equal to (i.e. within <NUM>% of) the OCV of the lead acid battery module at <NUM>% SOC of the lead acid battery module. Thus, the Li-ion battery module may be configured to receive charge (e.g., via regenerative braking system) while the lead acid battery is configured to provide power (e.g., to the ignition system or other electrical components of the xEV during rapid discharge conditions). Further, each Li-ion battery cell of the Li-ion battery module may have a particular chemical configuration that enables a voltage profile of the Li-ion battery cell to have an increased slope (e.g., a voltage profile having a steeper incline). Increasing the slope of the voltage profile enables an accurate estimation of SOC of an individual Li-ion battery cell based on a measured voltage of the individual Li-ion battery cell. The estimated SOC and/or the measured voltage enables a diagnostic parameter and/or status of the individual Li-ion battery cell (or, in some cases, the overall battery module) to be determined.

To help illustrate the manner in which the present embodiments may be used in a system, <FIG> is a perspective view of an embodiment of a vehicle <NUM> (e.g., an xEV), which may utilize a regenerative braking system. Although the following discussion is presented in relation to vehicles with regenerative braking systems, the techniques described herein are adaptable to other vehicles that capture/store electrical energy with a battery, which may include electric-powered and gas-powered vehicles. Further, embodiments may be employed in stationary power systems as well.

As discussed above, it would be desirable for a battery system <NUM> to be largely compatible with traditional vehicle designs. Accordingly, the battery system <NUM> may be placed in a location in the vehicle <NUM> that would have housed a traditional battery system. For example, as illustrated, the vehicle <NUM> may include the battery system <NUM> positioned similarly to a lead-acid battery of a typical combustion-engine vehicle (e.g., under the hood of the vehicle <NUM>).

In other words, the battery system <NUM> may supply power to components of the vehicle's electrical system, which may include radiator cooling fans, climate control systems, electric power steering systems, active suspension systems, auto park systems, electric oil pumps, electric super/turbochargers, electric water pumps, heated windscreen/defrosters, window lift motors, vanity lights, tire pressure monitoring systems, sunroof motor controls, power seats, alarm systems, infotainment systems, navigation features, lane departure warning systems, electric parking brakes, external lights, or any combination thereof. Illustratively, in the depicted embodiment, the energy storage component <NUM> supplies power to the vehicle console <NUM> and the ignition system <NUM>, which may be used to start (e.g., crank) an internal combustion engine <NUM>.

Additionally, the energy storage component <NUM> may capture electrical energy generated by the alternator <NUM> and/or the electric motor <NUM>. In some embodiments, the alternator <NUM> may generate electrical energy while the internal combustion engine <NUM> is running. More specifically, the alternator <NUM> may convert the mechanical energy produced by the rotation of the internal combustion engine <NUM> into electrical energy. Additionally or alternatively, when the vehicle <NUM> includes an electric motor <NUM>, the electric motor <NUM> may generate electrical energy by converting mechanical energy produced by the movement of the vehicle <NUM> (e.g., rotation of the wheels) into electrical energy. Thus, in some embodiments, the energy storage component <NUM> may capture electrical energy generated by the alternator <NUM> and/or the electric motor <NUM> during regenerative braking. As such, the alternator <NUM> and/or the electric motor <NUM> are generally referred to herein as a regenerative braking system.

To facilitate capturing and supplying electric energy, the energy storage component <NUM> may be electrically coupled to the vehicle's electric system via a bus <NUM>. For example, the bus <NUM> may enable the energy storage component <NUM> to receive electrical energy generated by the alternator <NUM> and/or the electric motor <NUM>. Additionally, the bus <NUM> may enable the energy storage component <NUM> to output electrical energy to the ignition system <NUM> and/or the vehicle console <NUM>. Accordingly, when a <NUM> volt battery system <NUM> is used, the bus <NUM> may carry electrical power typically between <NUM>-<NUM> volts.

Additionally, as depicted, the energy storage component <NUM> may include multiple battery modules. For example, in the depicted embodiment, the energy storage component <NUM> includes a Li-ion (e.g., a first) battery module <NUM> in accordance with present embodiments, and a lead-acid (e.g., a second) battery module <NUM>, where each battery module <NUM>, <NUM> includes one or more battery cells (e.g., individually sealed battery cells). In other embodiments, the energy storage component <NUM> may include any number of battery modules. Additionally, although the Li-ion battery module <NUM> and lead-acid battery module <NUM> are depicted adjacent to one another, they may be positioned in different areas around the vehicle. For example, the lead-acid battery module <NUM> may be positioned in or about the interior of the vehicle <NUM> while the Li-ion battery module <NUM> may be positioned under the hood of the vehicle <NUM>.

In some embodiments, the energy storage component <NUM> may include multiple battery modules to utilize multiple different battery chemistries. For example, when the Li-ion battery module <NUM> is used, performance of the battery system <NUM> may be improved since the Li-ion battery chemistry generally has a higher coulombic efficiency and/or a higher power charge acceptance rate (e.g., higher maximum charge current or charge voltage) than the lead-acid battery chemistry. As such, the capture, storage, and/or distribution efficiency of the battery system <NUM> may be improved.

To facilitate controlling the capturing and storing of electrical energy, the battery system <NUM> may additionally include a control module <NUM>. More specifically, the control module <NUM> may control operations of components in the battery system <NUM>, such as relays (e.g., switches) within the energy storage component <NUM>, the alternator <NUM>, and/or the electric motor <NUM>. For example, the control module <NUM> may regulate an amount of electrical energy captured/supplied by each battery module <NUM> or <NUM> (e.g., to de-rate and re-rate the battery system <NUM>), perform load balancing between the battery modules <NUM> and <NUM>, determine a state of charge (SOC) of each battery module <NUM> or <NUM>, determine a temperature of each battery module <NUM> or <NUM>, control voltage output by the alternator <NUM> and/or the electric motor <NUM>, and the like.

Accordingly, the control module <NUM> may include one or more processor <NUM> and one or more memory <NUM>. More specifically, the one or more processor <NUM> may include one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs), one or more general purpose processors, or any combination thereof. Additionally, the one or more memory <NUM> may include volatile memory, such as random access memory (RAM), and/or non-volatile memory, such as read-only memory (ROM), optical drives, hard disc drives, or solid-state drives. In some embodiments, the control module <NUM> may include portions of a vehicle control unit (VCU) and/or a separate battery control module.

As discussed above, Li-ion batteries in 12V vehicle architectures can apply to 12V Dual Energy Storage Systems (DESS) and 12V starter applications. In a 12V DESS application, the Li-ion battery <NUM> (e.g., a module having several Li-ion battery cells) may be connected in parallel to the lead acid (PbA) battery <NUM>, and both may be connected to the vehicle's electrical bus <NUM>. For 12V DESS, it is now recognized that it may be desirable for the Li-ion battery open circuit voltage (OCV) to partially match the lead acid battery OCV, such that the OCV of the lead acid battery at <NUM>% state of charge (SOC) is about equal to the OCV of the Li-ion battery at <NUM>% SOC. An example of this OCV relationship is set forth in <FIG>.

<FIG> is an embodiment of a chart <NUM> illustrating OCV <NUM> as a function of SOC <NUM> for the lead-acid battery <NUM> (e.g., represented by line <NUM>) and the Li-ion battery <NUM> (e.g., represented by line <NUM>). As shown in the illustrated embodiment of <FIG>, the 12V Li-ion battery system <NUM> has a voltage profile where at <NUM>% SOC (shown at point <NUM>), the Li-ion battery system <NUM> has a voltage of about (e.g., within <NUM>% of, within <NUM>% of, within <NUM>% of) 13V. At <NUM>% SOC, the lead acid battery <NUM> has a voltage (as shown at point <NUM>) that is about equal to (i.e. within <NUM>% of) the voltage of the Li-ion battery system <NUM> at <NUM>% SOC (as shown at point <NUM>). To the extent that the lead acid battery <NUM> and Li-ion battery <NUM> voltages do not exactly match, it is presently recognized that the voltage of the Li-ion battery <NUM> at <NUM>% SOC may be within about <NUM> millivolts (mV) or between <NUM>% and <NUM>% of the lead acid battery <NUM> voltage at <NUM>% SOC.

This OCV/SOC relationship between the lead acid battery <NUM> and the Li-ion battery <NUM> may enable the DESS to be balanced in a way that enables top end regenerative capacity and low end discharge capacity. More specifically, this relationship encourages charge acceptance using the Li-ion battery <NUM> during times of regeneration (e.g., charging), and encourages discharging from the lead acid battery <NUM> in times where rapid discharge is experienced by the energy storage component <NUM>.

The top end regenerative capacity may generally correspond to the ability of the Li-ion battery <NUM> to accept charge from a regenerative system (e.g., a regenerative braking system) even when the lead acid battery <NUM> is at <NUM>% SOC. The low end discharge capacity may generally correspond to the ability of the lead acid battery <NUM> to provide discharge current even when the Li-ion battery <NUM> is at <NUM>% SOC. Additionally or alternatively, the low end discharge capacity may correspond to the ability of the Li-ion battery <NUM> to provide discharge current when the lead acid battery <NUM> is at its lowest desired operating SOC (e.g., <NUM>% SOC). For example, the Li-ion battery <NUM> may have an SOC greater than <NUM>% at a voltage where the lead acid battery <NUM> is at <NUM>% SOC. In the illustrated embodiment of <FIG>, the lead acid battery <NUM> has a voltage of about <NUM>. 6V at <NUM>% SOC (as shown at point <NUM>), and the Li-ion battery <NUM> has an SOC of about (e.g., within <NUM>% of, within <NUM>%, or within <NUM>% of) <NUM>% at <NUM>. 6V (as shown at point <NUM>).

As discussed above, it is also now recognized that it may be desirable for the voltage profile of the Li-ion battery <NUM> to have some degree of curvature within its expected SOC operating range. For example, certain diagnostic measurements relating to the Li-ion battery <NUM> may be performed based on voltage measurements and associated SOC estimates to determine diagnostic parameters, such as a health of the Li-ion battery <NUM> and/or a remaining operating life of the Li-ion battery <NUM>. More specifically, the voltage of the Li-ion battery <NUM> may be measured (e.g., via a voltage sensor), and the SOC of the Li-ion battery <NUM> may be estimated based on the Li-ion battery voltage measurements. If the voltage remains relatively flat across a wide SOC range (i.e., the profile has little to no curvature or a very small slope), then small changes in the voltage measurement may cause relatively large changes in SOC estimation. Thus, it may be desirable to design the Li-ion battery <NUM> to have a voltage profile with a slope that is sufficiently larger than the degree of voltage measurement uncertainty, which may enable robust SOC estimation.

Such a Li-ion battery <NUM> could be developed using <NUM>, <NUM>, or <NUM> Li-ion battery cells (see, e.g., <FIG>). However, the system costs, system footprint, system cooling requirements, and similar considerations relating to the Li-ion battery module, may be directly related to the number of battery cells in the system. To reduce total system costs, either alone or in combination with reducing system footprint and cooling requirements, it may be desirable to have the minimum number of battery cells in the system that provides the voltage matching described above. For a <NUM>-cell system, a Li-ion battery cell with a nominal voltage of about <NUM>. 25V may be appropriate. For a <NUM>-cell system, a Li-ion battery cell with a nominal voltage of about <NUM>. 6V may be appropriate. Such Li-ion battery cells could also be used to produce a 12V starter battery. The battery-level voltage could be compliant to existing vehicle voltage architectures, and would also benefit total system cost reduction by minimizing the total cell count. In accordance with present embodiments, each of the Li-ion battery cells may combine to produce a nominal battery module voltage of between 12V and 16V, between <NUM>. 5V and <NUM>. 5V, or between 13V and 15V. Further, in some embodiments, the Li-ion battery module <NUM> may have a voltage between <NUM> and <NUM>. 5V, between <NUM>. 8V and <NUM>. 4V, or between 13V and <NUM>. 2V at <NUM>% SOC. As such, the Li-ion battery module <NUM> may be configured to operate within the electrical bus <NUM> of the vehicle <NUM> without disrupting the bus <NUM> (e.g., the bus <NUM>, or components associated with the bus <NUM>, may be sensitive at voltages above <NUM>. 5V and below <NUM>. 5V) and/or the control module <NUM>. For example, in some cases a battery module that operates with a voltage that is above a high voltage threshold (e.g., <NUM>. 5V or 16V) or below a low voltage threshold (e.g., 11V or <NUM>. 5V) may interfere with the control module <NUM> and/or other electronic components associated with the bus <NUM>. Therefore, the Li-ion battery module <NUM> of the present disclosure may reduce and/or eliminate interference with the control module <NUM> and/or the bus <NUM>.

<FIG> is an embodiment of a chart <NUM> illustrating battery voltage <NUM> (e.g., OCV) as a function of SOC <NUM> for each Li-ion battery cell of a <NUM>-cell Li-ion battery module (represented by line <NUM>) and a <NUM>-cell Li-ion battery module (represented by line <NUM>). For the <NUM>-cell architecture, as shown by line <NUM>, each Li-ion battery cell has a higher nominal voltage when compared to the <NUM>-cell architecture. Further, at <NUM>% SOC, each of the Li-ion battery cells of the <NUM>-cell architecture has an OCV of about <NUM> V. For a <NUM>-cell architecture, each Li-ion battery cell has a slightly lower nominal voltage as compared to the <NUM>-cell architecture, and has an OCV of about <NUM> V at <NUM>% SOC.

As discussed above, an increased slope of the voltage profile for the Li-ion battery cells may facilitate an estimation of SOC based on a voltage measurement of the Li-ion battery cell. As shown in the illustrated embodiment of <FIG>, linear trend lines were calculated to fit the actual voltage profiles for both the Li-ion battery cells of the <NUM>-cell Li-ion battery module (as shown by line <NUM>) and the <NUM>-cell Li-ion battery module (as shown by line <NUM>). The linear trend lines each include a slope that characterizes a change in voltage of the Li-ion battery cell as a function of change in SOC of the Li-ion battery cell. The slope of the linear trend lines of <FIG> is referred to herein as an average slope of the voltage profiles of the Li-ion battery cells. The linear trend line of the Li-ion battery cell of the <NUM>-cell Li-ion battery module <NUM> includes an average slope of approximately (e.g., within <NUM>% of, within <NUM>% of, or within <NUM>% of) <NUM> Volts/SOC(%). The linear trend line of the Li-ion battery cell of the <NUM>-cell Li-ion battery module <NUM> includes an average slope of approximately <NUM> Volts/SOC(%). Accordingly, in some embodiments, the Li-ion battery cells may include a voltage profile having an average slope of between <NUM> Volts/SOC(%) and <NUM> Volts/SOC(%), between <NUM> Volts/SOC(%) and <NUM> Volts/SOC(%), or between <NUM> Volts/SOC(%) and <NUM> Volts/SOC(%). While the trend lines in the illustrated embodiment of <FIG> are linear, it should be recognized that other suitably shaped trend lines may be calculated to determine a slope of the voltage profiles (a change in voltage as a function of SOC) for the Li-ion battery cells and/or to estimate the SOC of the Li-ion battery cells.

<FIG> is a perspective schematic view of an embodiment of the Li-ion battery module <NUM> having four Li-ion battery cells <NUM> in a four by one arrangement. As shown in the illustrated embodiment of <FIG>, each of the four Li-ion battery cells <NUM> are disposed in a battery module housing <NUM>. Further, the four Li-ion battery cells <NUM> may be coupled to one another via bus bars <NUM> disposed over battery cell terminals <NUM>. In some embodiments, each of the four Li-ion battery cells <NUM> are coupled to one another in series to form the Li-ion battery module <NUM> having a voltage of 12V. As such, the bus bars <NUM> may connect a positive terminal of a Li-ion battery cell <NUM> to a negative terminal of an adjacent Li-ion battery cell <NUM> to couple the Li-ion battery cells <NUM> in series. However, in other embodiments, the Li-ion battery cells <NUM> may be coupled to one another in another suitable configuration to form the Li-ion battery module <NUM> having a voltage 12V.

Further, a lid <NUM> having module terminals <NUM> may be disposed over an opening <NUM> of the housing <NUM>. The module terminals <NUM> may be coupled to battery cell terminals <NUM> at respective ends <NUM> and <NUM> of the battery module housing <NUM> in order to establish an electrical connection between the Li-ion battery cells <NUM> and the module terminals <NUM>. Accordingly, the module terminals <NUM> may be coupled to the electrical bus <NUM> and/or another suitable device to provide power from the Li-ion battery cells <NUM> to a load.

<FIG> is a perspective schematic view of an embodiment of the Li-ion battery module <NUM> having four of the Li-ion battery cells <NUM> in a two by two arrangement. As shown in the illustrated embodiment of <FIG>, the Li-ion battery cells <NUM> are still coupled to one another in series, such that the bus bars <NUM> couple a positive terminal of a Li-ion battery cell <NUM> to a negative terminal of an adjacent Li-ion battery cell <NUM> (e.g., either directly adjacent or diagonally adjacent). While the bus bars <NUM> are shown in a diagonal configuration between the battery cell terminals <NUM>, it should be recognized that other battery cell terminal <NUM> and bus bar <NUM> configurations may be utilized.

<FIG> and <FIG> are perspective schematic views of embodiments of the Li-ion battery module <NUM> having five of the Li-ion battery cells <NUM> and six of the Li-ion battery cells <NUM>, respectively. Again, the Li-ion battery cells <NUM> may be coupled to one another in a series configuration and/or another suitable configuration to form the Li-ion battery module <NUM> having a voltage of 12V.

The amount of the Li-ion battery cells <NUM> included in the battery module <NUM> (e.g., <NUM>, <NUM>, <NUM>, or another suitable amount) may be dependent on a chemical configuration of the Li-ion battery cells <NUM>, which produces a predetermined nominal voltage (e.g., <NUM>. 6V or <NUM>. Generally, Li-ion battery cells will include a cathode (a positive electrode), an anode (a negative electrode), and an electrolyte. The cathode and anode each include an electrode active material that enables the electrodes to store and transfer ions (e.g., Li-ions) during charging and discharging cycles. Whether the electrode active material is suitable for the cathode or the anode is generally determined by the reference voltage of the electrode active material versus Li+/Li<NUM>. The negative electrode active materials of the Li-ion battery cells may be considered to include electrode active materials having a voltage that is lower versus Li+/Li<NUM> compared to the positive electrode active materials. The nominal voltages set forth above may be achieved primarily through appropriate selection and combination of active material chemistries for the cathode as well as the use of a suitable anode active material, although electrolyte chemistry may also have an effect on cell operation. For instance, the nominal voltage of the Li-ion battery cells may be the voltage of the positive electrode active material versus Li+/Li<NUM>, less the voltage of the negative electrode active material versus Li+/Li<NUM>.

The electrode active materials may generally be of any type, configuration, or chemistry, as long as the combination of cathode active materials and anode active materials provide the nominal voltages and voltage profiles set forth above. As an example, the anode active material may include graphite or may include a titanate-based material (e.g., lithium titanate, LTO). The cathode active material may include any one or a combination of different lithiated metal oxides, mixed metal oxide components, or lithium metal phosphates.

As used herein, lithiated metal oxides and mixed metal oxide components for the cathode active material may refer to any class of materials whose formula includes lithium and oxygen as well as one or more additional metal species (e.g., nickel, cobalt, manganese, aluminum, iron, or another suitable metal). A non-limiting list of example lithiated metal oxides may include: mixed metal compositions including lithium, nickel, manganese, and cobalt ions such as lithium nickel cobalt manganese oxide (NMC, LiNixMnyCozO<NUM>, where x+y+z=<NUM>), lithium nickel cobalt aluminum oxide (NCA) (e.g., LiNixCoyAlzO<NUM>, where x+y+z = <NUM>), lithium cobalt oxide (LCO) (e.g., LiCoO<NUM>), and lithium manganese oxide spinel (LMO-spinel) (e.g., LiMn<NUM>O<NUM>).

Layered-layered material and/or layered-layered spinel material may also be utilized as a cathode active material. Layered-layered materials may have the formula: xLi<NUM>M<NUM>O<NUM> • (<NUM>-x)LiM<NUM>O<NUM>, wherein: M<NUM> is Mn, Ti, Zr, and combinations thereof; M<NUM> is Mn, Ni, Co, Cr, and combinations thereof, and x is greater than <NUM> and smaller than <NUM>. As a further example, layered-layered materials may include xLi<NUM>MnO<NUM>•(<NUM>-x)LiMO<NUM> (M = Mn, Ni), and may have relatively high reference voltages (><NUM> V vs. Li+/Li<NUM>). Layered-layered spinel materials have a similar structure, and also include an embedded spinel component. A spinel structure may refer to a chemical substance that has a cubic, close-packed lattice configuration. Such layered-layered spinel materials may be produced by reducing the overall lithium content of a parent layered-layered material, while maintaining the Mn:M ratio at a constant value. One example of a layered-layered spinel may be represented by the formula LixMn<NUM>Ni<NUM>Oy, for which the end members are <NUM>. 3Li<NUM>MnO<NUM>•<NUM>. 7LiMn<NUM>Ni<NUM>O<NUM> (x = <NUM>; y = <NUM>), in which the average manganese and nickel oxidation states are <NUM>+ and <NUM>+, respectively, and LiMn<NUM>Ni<NUM>O<NUM> (x=<NUM>; y=<NUM>) in which the corresponding average oxidation states are expected to lie between <NUM>+ and <NUM>+ for Mn, and <NUM>+ and <NUM>+ for Ni, respectively. Certain layered-layered spinel cathode materials may have voltages higher than <NUM> V vs. Li+/Li<NUM>, such as up to about <NUM> V vs. Li+/Li<NUM>.

Such materials may be considered high voltage spinel (HVS) active materials, and may be referenced using spinel notation. HVS materials may have a chemical formula of LiMxMn<NUM>-xO<NUM> (using conventional spinel notation), where x may be between <NUM> and <NUM> and M represents a metal, such as a transition metal. As an example, the metal (M) may be nickel, chromium, iron, or another transition metal. In certain embodiments, HVS may have the chemical formula LiMn<NUM> Ni<NUM>O<NUM>, or LiNi<NUM>Mn<NUM>O<NUM>, or LiNiMnO<NUM>, for example. Further, such embodiments of HVS may be metal doped on the nickel side (e.g., to replace a portion of the Ni with another metal) or metal doped on the manganese side (e.g., to replace a portion of the Mn with another metal). In certain embodiments, HVS has a nominal voltage of about <NUM> V versus Li+/Li<NUM>, although higher voltages may be achieved through appropriate selection of constituent layers (e.g., in a layered-layered material).

Lithium metal phosphates for the cathode active material may refer to materials whose formula includes lithium and phosphate as well as one or more additional metal species (e.g., nickel, cobalt, manganese, iron, or another suitable metal). For example, such lithium metal phosphates may be represented as LiMPO<NUM>, wherein M is Mn, Co, Ni, Fe, Zn, Cu, Ti, Sn, Zr, V, Al, and mixtures thereof. A non-limiting list of example lithium metal phosphates may include: lithium nickel phosphate (LiNiPO<NUM>), lithium cobalt phosphate (LiCoPO<NUM>), lithium nickel manganese phosphate (LiNiMnPO<NUM>), lithium iron phosphate (LiFePO<NUM>), and lithium manganese iron phosphate (LiMnFePO<NUM>).

Again, the cathode active materials may be used alone or in an appropriate combination to achieve a suitable nominal voltage and voltage profile. Each combination may provide a particular nominal voltage and a particular voltage profile. As an example, a first cathode active material may be combined (e.g., physically blended) with one or more second cathode active materials, and the blended combination may be coated onto an appropriate collector to produce a cathode. Accordingly, each Li-ion battery cell may include a cathode having one, two, three or more active materials. Thus, the Li-ion battery cells described herein may each have a cathode formed using any one or a combination of active materials selected from a group including or, alternatively, consisting of: LiNixMnyCozO<NUM>, where x+y+z=<NUM>; LiNixCoyAlzO<NUM>, where x+y+z = <NUM>; LiCoO<NUM>; LiMn<NUM>O<NUM>; LiMxMn<NUM>-xO<NUM>; where x may be between <NUM> and <NUM> and M is nickel, chromium, or iron; LiMPO<NUM>, wherein M is Mn, Co, Ni, Fe, Zn, Cu, Ti, Sn, Zr, V, Al, and mixtures thereof such as LiNiPO<NUM>; LiCoPO<NUM>; LiNiMnPO<NUM>; LiFePO<NUM>; and LiMnFePO<NUM>.

In accordance with certain embodiments of the present disclosure, the negative electrode active materials may include certain titanate species (e.g., LTO), graphite, or a combination of the two. In still further embodiments, the negative electrode active material may include other electrode active materials either alone or in combination with LTO and/or graphite. Additionally, in certain embodiments LTO may have a spinel structure. As a non-limiting example, LTO may have a chemical formula of Li<NUM>Ti<NUM>O<NUM>. LTO may be cation doped and/or anion doped via metal doping or electronegative atom doping, respectively. One example is metal fluorine doping. Doping may change the chemical formula of LTO to M-Li<NUM>Ti<NUM>O<NUM>, where M represents a metal, such as a transition metal. As an example, the metal (M) may be barium, strontium, molybdenum, neodymium, nickel, manganese, chromium, tungsten, lanthanum, or another transition metal. Additionally, or alternatively, LTO may be carbon coated such that the LTO used to produce the negative electrode may include between <NUM>% and <NUM>% by weight carbon nanotubes or carbon nanofibers. The carbon coating may enhance conductivity of the LTO, and may passivate the LTO (e.g., via a passive layer) to suppress gas generation from a reaction with electrolyte. To form carbon coated LTO, a mechanical mixing process, such as milling, may be used. In certain embodiments, LTO may have a voltage of about <NUM>. 55V versus Li+/Li<NUM>.

In view of the foregoing, it should be appreciated that a number of different chemistries may be utilized in accordance with the nominal voltage and voltage profile considerations described herein. It is presently contemplated that battery cells having the nominal voltage and voltage profiles described herein may be produced using appropriate selection of one or a combination of the lithium metal oxide, lithium metal phosphate, high voltage spinel, or layered-layered cathode materials described above.

For a <NUM>-cell system having the desired voltage profile, and in which each cell has a nominal voltage of about <NUM> V, it is presently contemplated that such battery cells may be produced using specific cathode and anode active materials. For instance and by way of non-limiting example, higher voltage cathode materials such as HVS, either alone or in combination with one or more lithium metal oxides (e.g., NMC, NCA) may be utilized. In such embodiments, LTO may be used as the anode active material. When graphite is used as the anode active material, such high voltage cathode active materials may not necessarily be required, but may be used where deemed beneficial. For a <NUM>-cell system in which each cell has a nominal voltage of about <NUM> V, a wide variety of cathode and anode active materials may be chosen.

<FIG> is a flow chart of an embodiment of a process <NUM> that is utilized to determine a diagnostic parameter and/or status of a Li-ion battery cell <NUM> (e.g., a health of the Li-ion battery cell <NUM>, an operating life of the Li-ion battery cell <NUM>, a remaining charge of the Li-ion battery cell <NUM>, among others). For example, at block <NUM>, a voltage of the Li-ion battery cell <NUM> is measured using a voltage sensor disposed in the housing <NUM> of the Li-ion battery module <NUM>. In some embodiments, the voltage measurement of the Li-ion battery cell <NUM> may be directed to the control module <NUM> as feedback. The control module <NUM> may store the voltage profile of the Li-ion battery cell <NUM> in the memory <NUM> and estimate the SOC of the Li-ion battery cell <NUM> based on the measured voltage, as shown at block <NUM>.

Further, the control module <NUM> may utilize the SOC and/or the voltage measurement of the Li-ion battery cell <NUM> to determine a diagnostic parameter and/or status of the Li-ion battery cell <NUM>, as shown at block <NUM>. For example, the control module <NUM> may utilize the SOC and/or the voltage of the Li-ion battery cell <NUM> to calculate and/or estimate a health of the Li-ion battery cell <NUM>, an operating life of the Li-ion battery cell <NUM>, a remaining charge of the Li-ion battery cell <NUM>, a capacity of the Li-ion battery cell <NUM>, a resistance of the Li-ion battery cell <NUM>, a current of the Li-ion battery cell <NUM>, a temperature of the Li-ion battery cell <NUM>, degradation of the anode and/or the cathode of the Li-ion battery cell <NUM>, or a combination thereof.

Claim 1:
A dual energy storage system (<NUM>), comprising:
- a lithium ion battery (<NUM>) electrically coupled in parallel with a lead-acid battery (<NUM>), wherein the lithium ion battery (<NUM>) and the lead-acid battery (<NUM>) are electrically coupleable to a vehicle bus (<NUM>),
wherein the lithium ion battery open circuit voltage (OCV) partially matches the lead-acid battery OCV such that the lead-acid battery OCV at <NUM>% of the lead-acid battery state of charge (SOC) and the lithium ion battery OCV at <NUM>% of the lithium ion battery SOC are within <NUM>% of <NUM> V.