Patent Description:
High-energy dense battery cells for use on hybrid electric or full electric aircraft, such as lithium ion (Li-Ion) cells, can potentially pose a fire hazard risk due to thermal runaway between the anode and cathode active materials. Additionally, high-energy dense batteries have numerous inherent failure modes inside the cell. When considering the use of such cells for aviation, hundreds of cells, if not more, are traditionally used to meet system voltage and energy requirements. The need for reliability and safety tends to result in high-weight systems, which can be undesirable in aerospace applications.

The conventional techniques have been considered satisfactory for their intended purpose. However, there is an ever present need for improved systems and methods for packaging and using high specific energy battery cells in a safe manner with reduced weight. This disclosure provides a solution for this need. <CIT> relates to an active battery stack system.

A battery cell system includes a plurality of battery cells abutting one another to form a battery cell stack. The battery cell system includes a stack interface operatively connected to the battery cells. The stack interface includes a housing defining a center and an outer perimeter. The stack interface includes a plurality of heat dissipating field effect transistors (FETs) arranged more proximate to the outer perimeter than the center.

In some embodiments, the first annular metallic conductor is positioned at a first end of the battery cell stack and a second annular metallic conductor positioned at a second end of the battery cell stack. The plurality of battery cells can be annular. The stack interface can include an annular housing. The stack interface defines an inner perimeter and an outer perimeter. The FETs are positioned circumferentially spaced apart more proximate to the outer perimeter than the inner perimeter. The stack interface can include a battery management system (BMS) and a mechanical switch device. The BMS can be operatively connected to a plurality of sensors within at least one of the battery cells. The mechanical switch device can be configured and adapted to selectively connect or disconnect the battery cell stack from other adjacent battery cell stacks.

A main battery management system (BMS) can be operatively connected to the stack interface. The main BMS can include an annular housing and a motor drive assembly positioned within an inner diameter hole of the annular housing configured and adapted to drive circulation of a heat transfer fluid around the plurality of stacks. A plurality of sensors can be positioned within at least one of the battery cells. The plurality of sensors can include at least one of a temperature sensor, a voltage sensor, and a pressure sensor. The battery cells can be hermetically sealed. The system can includes a system housing that surrounds the plurality of battery cells and the stack interface. The system housing can have an outer surface free of vertices. The system housing can have a pill shape or cylindrical shape.

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an embodiment of a system in accordance with the disclosure is shown in <FIG> and is designated generally by reference character <NUM>. Other embodiments of systems in accordance with the disclosure, or aspects thereof, are provided in <FIG>, as will be described. The systems and methods described herein can provide battery systems with improved communication, components having an annular shape to improve thermal control, and improved cooling to not only cool a battery cell or system, but also target and prevent and/or extinguish a battery thermal runaway in volume and weight sensitive applications.

As shown in <FIG>, a battery system <NUM> includes a plurality of annular battery cells <NUM> abutting one another to form a battery cell stack <NUM>. System <NUM> includes a plurality of battery cell stacks <NUM>, e.g. stacks of battery cells <NUM>. A housing <NUM> of each battery cell <NUM> is shaped as a shallow cylindrical annulus and abut one another to form a given stack <NUM> with an annular shape, e.g. a cylindrical annulus, to facilitate cooling. A main battery management system (BMS) <NUM> is operatively connected to at least one of the stacks <NUM> of battery cells <NUM>. The main BMS <NUM> includes an annular housing <NUM>, e.g. shaped as a shallow cylindrical annulus, and a motor drive assembly <NUM> positioned within an inner diameter hole <NUM> of the annular housing <NUM> configured and adapted to drive circulation of a heat transfer fluid around the plurality of stacks <NUM>. The motor drive assembly <NUM> includes a fan <NUM> or other fluid mover to effect the movement. The motor drive assembly <NUM> and main BMS manages thermal stability of the system <NUM>. The battery system <NUM> includes system housing <NUM> that surrounds the plurality of stacks <NUM> and the main BMS <NUM>. The main BMS <NUM> is modular and can be added to the front and/or rear of the housing <NUM> as needed to achieve proper levels of redundancy. The main BMS <NUM> is operatively connected to each stack interface <NUM>, as described in more detail below.

As shown in <FIG>, the battery system <NUM> includes a fluid-to-fluid heat exchanger matrix <NUM> inside the inner diameter hole <NUM> to either transfer heat into the heat transfer fluid within housing <NUM> for battery cell stack warming, or out of the fluid for battery cell stack cooling. As fluid is drawn through inner diameter hole <NUM> by fan <NUM> (which is downstream from heat exchanger matrix <NUM>) the fluid within housing <NUM> is heated or cooled by the fluid within the heat exchange matrix <NUM> (which is fluidically isolated from the fluid within housing <NUM>). The fluid in the heat exchanger matrix <NUM> is fluidically connected to a source of heating outside of system <NUM> such as a thermal engine or electrical heater or a source of cooling such as a radiator, to enable the BMS to maintain stack temperatures within acceptable limits.

With continued reference to <FIG>, the battery system <NUM> includes a plurality of first annular metallic conductors <NUM> each positioned at a first end <NUM> of a respective stack <NUM> of battery cells <NUM> and a plurality of second annular metallic conductors <NUM> each positioned at a second end <NUM> of a respective stack <NUM> of battery cells <NUM> of the plurality of stacks <NUM> of battery cells <NUM>. Conductors <NUM> and <NUM> serve as a contactor plate and pressure plate to provide a more evenly distributed compression for the stack <NUM>. Bolts or struts <NUM> are strutted from one conductor <NUM> to the other <NUM> to force face contact between abutting cells <NUM> ensuring maximum contact surface is achieved. The annular shaped stack-up formed by the stack of battery cells <NUM>, conductors <NUM> and <NUM>, stack interfaces <NUM> (described below), and BMS <NUM> defines a central hole <NUM> for carrying a heat transfer fluid and/or coolant that creates a protective thermal barrier around all system surfaces in a thermal loop arrangement, as indicated schematically by the flow arrows. The thermal loop goes through the center hole <NUM> of the stack-up and out one end, around an outer perimeter of the stack-up, between the stack-up and the housing <NUM>, and around to the opposite end of the stack-up back through the center hole <NUM>. This thermal loop enables rapid charge of the cells <NUM> and fire abatement.

As shown in <FIG>, battery cells <NUM> can include cooling fins, metal foams or other surface projections <NUM> extending into the center hole <NUM> or extending from the outer perimeter of cells <NUM> to improve heat transfer between the heat transfer liquid/coolant and the cells <NUM>. Projections <NUM> can similarly be included on conductors <NUM>/<NUM> or stack interfaces <NUM>. In some embodiments, the heat transfer fluid can serve as coolant and fire arresting agent if/when the main BMS <NUM> detects issues. Since the coolant and retardant are one and the same fluid, the battery system <NUM> is lighter and simpler than systems where a separate coolant supply and retardant supply are needed. The heat transfer fluid maintains even thermal gradient enabling longer life and helps to maintain state of health (SOH) for a longer life.

With reference now to <FIG>, in the event of a thermal runaway of a single cell <NUM> due to internal failure, the rate of transfer of heat from the cell <NUM> to the fluid would increase naturally without any action by the BMS <NUM> or the sBMS <NUM>, due to the increased difference in temperature between the cell and the fluid. If the rate of cooling possible with the cooling projections <NUM>, e.g. fins, metal foam, etc., and normal fluid circulation rate is insufficient and the BMS <NUM> or sBMS <NUM> detects a problem a method of controlling heat transfer in a battery system is available. A method of controlling heat transfer in a battery system, e.g. battery system <NUM>, includes monitoring at least one characteristic of a battery cell, e.g. battery cell <NUM>, within the battery system with a battery management system (BMS), e.g. main BMS <NUM> or sBMS <NUM>.

With continued reference to <FIG>, the method includes sending information from the at least one sensor to the BMS with an optical communication link, e.g. optical communication link <NUM>. The optical communication link is connected to each of the plurality of battery cells. The method includes selectively varying a fluid circulation rate in the battery system with the BMS depending on the at least one characteristic. Selectively varying the fluid circulation rate includes increasing the fluid circulation rate with the BMS if at least one of the at least one characteristic indicates thermal runaway in the battery cell to increase. In this way, the BMS acts to increase the cooling available and minimize propagation of thermal runaway to another battery cell within the battery system. Increasing the fluid circulation rate includes sending a rate increase signal from the BMS to a motor drive assembly, e.g. motor drive assembly <NUM>, having a fluid mover, e.g. fan <NUM>, propeller, or the like, to increase a circulation rate of a heat transfer fluid within the battery system. Selectively varying the fluid circulation rate in the battery system includes decreasing the fluid circulation rate with the BMS if at least one of the characteristics indicates a low temperature in the battery cell. The characteristics of the battery cell include at least one of electrical characteristics (e.g. voltage), temperature, pressure, or the presence of characteristic gases. These characteristics can be measured with sensors, e.g. sensors <NUM>, which are described in more detail below.

As shown in <FIG>, the system housing <NUM> forms a pill-shaped pod <NUM> with an outer surface <NUM> free of vertices, except for the features that may be required for mounting and attaching the battery system. Pod <NUM> can also be a cylindrical shape, which is similar to the pill shape shown except that the pod <NUM> would have flat ends instead of the arcuate ends. The aerodynamic structure allows for maximum scalability, modularization, and thermal control. The aerodynamic shape permits placement of system <NUM> exterior to the fuselage, e.g. on a wing, or interior. Those skilled in the art will readily appreciate that a variety of aerodynamic housings can be used. Housing <NUM> includes removable end caps <NUM> to allow for stack <NUM> replacement. Stack <NUM> is removable from housing <NUM> and cells <NUM> are removable from the stack <NUM>.

With reference now to <FIG>, the battery system <NUM> includes stack interfaces <NUM> having an annular shape, e.g. shaped as a shallow cylindrical annulus. Each stack interface <NUM> has an annular housing and is operatively connected to an end <NUM> of a respective stack <NUM> and is operatively connected to the battery cells <NUM> in the stack <NUM>. The annular housing defines a center (aligned with longitudinal axis A) and an outer perimeter <NUM>. A cooling loop is defined about each battery cell stack <NUM> and its respective stack interface <NUM> and through central through holes <NUM> of the battery cell stack <NUM> and the stack interface <NUM>. Each stack interface <NUM> includes a plurality of heat dissipating field effect transistors (FETs) <NUM>. Each stack interface <NUM> includes an inner perimeter <NUM>. The heat dissipating FETs <NUM> are positioned more proximate to the outer perimeter <NUM> than the inner perimeter <NUM> and/or the center and are circumferentially spaced apart along the outer perimeter <NUM> about a stack axis A. The FETs <NUM> dissipate heat in a more efficient manner due to their placement along the outer perimeter <NUM>. Each stack interface <NUM> acts as an isolation plate and includes at least one mechanical switch device <NUM>, such as a chemically and/or thermally activated/deactivated mechanical contactor configured and adapted to selectively connect or disconnect one of the stacks <NUM> of battery cells <NUM> from other adjacent stacks <NUM> of battery cells <NUM>. The mechanical switch device <NUM> is intrinsic to the stack interface <NUM> and the position therein can vary depending on the specific design of stack interface <NUM>. The isolation plate is positioned between each stack assembly (module) and houses the switch devices <NUM>. The mechanical switch device <NUM> (as opposed to electrical switches, or the like) permits reliable and quick automatic high-voltage disconnect and lock-out.

As shown in <FIG>, each stack interface <NUM> includes a BMS, e.g. a secondary battery management system (sBMS) <NUM>. The sBMS is operatively connected to a plurality of sensors <NUM> positioned within the housing <NUM> of each battery cell <NUM> and the main BMS <NUM> either by way of a single optical communication link <NUM> or by conventional electrical connections. Sensors <NUM> are configured and adapted to send data regarding at least one characteristic of a given battery cell <NUM> to sBMS <NUM> and/or the main BMS <NUM>. Sensors <NUM> within each cell <NUM> enable cell monitoring of every cell <NUM> in the system, which permits early detection of thermal runaway or other failure modes. Optical communication link <NUM> reduces weight and increases ease of assembly as there are no high-voltage flex cables or wire harnesses required. The sensors <NUM> can include one or more of temperature, particulate/gas monitoring devices, voltage and/or pressure sensors and they are integrated within the cell itself. Additional sensors <NUM> can be positioned outside of cells <NUM>. Cells <NUM> are hermetically sealed and include glass feed-throughs for communications isolation.

With continued reference to <FIG>, optical communication link <NUM> is operatively connected to each battery cell <NUM> in a stack <NUM> to communicate signals (information or power) from sensors <NUM> within each cell <NUM> via optical cable to the sBMS <NUM>, and/or from the sBMS <NUM> to sensors <NUM>. The sBMS <NUM> can provide processing and/or signal conditioning to the signals from sensors <NUM>. The sBMS <NUM> is then connected to the main BMS via optical, wireless or other form of communication link. That way, the main BMS <NUM> is operatively connected to at least one sensor <NUM> within at least one of the battery cells <NUM> via the sBMS for a given stack <NUM> and can monitor multiple stacks <NUM>. The optical communication link <NUM> is connected to the sBMS <NUM> and then to the main BMS <NUM> in <FIG> and <FIG>, but it is also contemplated that optical communication link <NUM> can connect sensors <NUM> directly to the main BMS <NUM>. The main BMS <NUM> identifies a failure mode and the appropriate corrective action that can be taken, e.g., increased cooling, repair, mechanical disconnect, or the like.

A method for detecting an mitigating failure modes in a battery cell, e.g. battery cell <NUM>, includes reading a battery cell characteristic with a sensor, e.g. sensor <NUM>, positioned within an outer housing, e.g. outer housing <NUM>, of the battery cell. The method includes sending the battery cell characteristic to a battery management system (BMS), e.g. BMS <NUM> and/or sBMS <NUM>. The method includes determining whether the battery cell characteristic meets a criteria with the BMS. The method includes signaling a failure mode if the battery cell characteristic does not meet the criteria. The method can include initiating a disconnect between the subject stack of battery cells, e.g. stack <NUM>, and a remaining portion of the stacks of battery cells, or other maintenance action, if the failure mode is signaled.

As shown in <FIG>, the battery system <NUM> includes a second system housing <NUM> that surrounds a second set of the plurality of stacks <NUM> and a second main BMS <NUM> to form a second battery pod <NUM>. The second set of the plurality of stacks <NUM> is the same as the first, and the second main BMS <NUM> is also the same as the first main BMS. The second battery pod <NUM> is connected to the first battery pod <NUM> in series.

As shown in <FIG>, in accordance with high voltage applications, another embodiment of system <NUM> includes five stacks <NUM> of battery cells <NUM> in a given pod. Each stack <NUM> uses sufficient number of cells <NUM> connected in series to meet the system voltage requirement, and other strings or stacks of cells are electrically connected in parallel to respect the cell power limits and energy requirements of the application. For example, in one embodiment, a <NUM> volt stack can include <NUM> cells (for sake of clarity not all cells are shown stacked). With this modular set up, a single pod weighs about <NUM> pounds (~<NUM>) and provides about <NUM> kWh. With two pods connected in series with a similar stack and cell quantity, 1040V and <NUM> kWh can be provided to a given load. Each cell stack <NUM> is modular in nature and the cell count within each stack can be adjusted to meet system voltage and capacity requirements. Cells <NUM> in a given stack can be replaced as-needed with new cells <NUM> and the electrodes (metallic conductors <NUM>, <NUM>) can be reused. In <FIG> the main BMS <NUM>, housing <NUM>, stack interface <NUM> and flow of the thermal loop is not depicted for sake of clarity, but it would be similar to that of <FIG>.

Claim 1:
A battery cell system (<NUM>) comprising:
a plurality of battery cells (<NUM>) abutting one another to form a battery cell stack (<NUM>); and
a stack interface (<NUM>) operatively connected to the battery cells wherein the stack interface includes a housing (<NUM>) defining a center and an outer perimeter (<NUM>), wherein the stack interface includes a plurality of heat dissipating field effect transistors, FETs (<NUM>) arranged more proximate to the outer perimeter than the center;
wherein the stack interface (<NUM>) defines an inner perimeter (<NUM>) and the outer perimeter (<NUM>), wherein the FETs are positioned circumferentially spaced apart more proximate to the outer perimeter than the inner perimeter.