BACKGROUND

[0001] The present disclosure relates, generally, to an energy storage system and, more specifically, to providing thermal management of a modular battery energy storage system, particularly during transient heat events.

[0002] The worldwide demand for electrical energy has typically been increasing year after year. In recent years, along with some concerns regarding global climate change issues, there has been a push for battery powered energy storage systems, including rechargeable battery energy storage systems. Battery energy storage systems are being used in

increasingly demanding power density levels and applications. Excessive heat generated by the energy storage systems during use can degrade performance, as well as the reliability, of the batteries comprising the energy storage system.

[0003] Thermal management is an important consideration in the design, maintenance, and operation of a battery energy storage system. In many previous instances, the thermal management systems and devices for battery energy storage systems have been designed in size and capacity to accommodate a maximum expected or worst-case load. However, the expected maximum load might typically be a transient event, where the load, and thus thermal energy generated by the battery energy storage system, rapidly increases over a relatively short period of time before returning to a lower, steady-state or average operating load and temperature. Accordingly, the thermal management systems and devices for a number of prior battery energy storage systems have been over-designed in size and capacity, resulting in such systems having an increased size, complexity, and manufacturing and operating costs.

[0004] Therefore, a system and a method that will address the foregoing issues is desirable that can efficiently manage transient thermal events of a battery energy storage system, thereby improving a performance and reliability of the battery energy storage system. DESCRIPTION OF THE DRAWINGS

[0005] These and other features and aspects of embodiments of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings, in which like characters represent like parts throughout the drawings, wherein:

[0006] FIG. 1 is a graph illustrating some beneficial aspects of phase change materials in managing transient events by an energy storage system, in accordance with an embodiment of the present disclosure;

[0007] FIG. 2 is an illustrative graph illustrating capacity fade of a module battery due to temperature rise over a period of time;

[0008] FIG. 3 A is an illustrative schematic diagram example representing a modular battery energy storage system, in accordance with an embodiment of the present disclosure;

[0009] FIG. 3B is a detailed illustrative schematic diagram of some aspects of FIG. 1, in accordance with an embodiment of the present disclosure;

[0010] FIG. 5 is a graph illustrating operating characteristics of some aspects related to an energy storage system, in accordance with an embodiment of the present disclosure;

[0011] FIG. 4 is an illustrative graph depicting operating characteristics of a modular battery energy storage system, in accordance with an embodiment of the present disclosure;

[0012] FIGS. 6 - 12 are each illustrative depictions of aspects of a modular battery energy storage system, in accordance with embodiment of the present disclosure;

[0013] FIG. 13 is an illustrative depiction of aspects of a modular battery energy storage system including cylindrical battery modules, in accordance with an embodiment of the present disclosure; and

[0014] FIGS. 14A and 14B are an illustrative schematic diagrams, including a detailed view of some aspects, of a modular battery energy storage system, in accordance with an embodiment of the present disclosure. DETAILED DESCRIPTION

[0015] When introducing elements of various embodiments of the present invention, the articles“a,”“an,”“the,” and“said” are intended to mean that there are one or more of the elements. The terms“comprising,”“including,” and“having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0016] One challenge in a battery energy storage system may be that of thermal management or battery cooling. The battery energy storage system might generally include a plurality of battery modules and maintaining a set temperature (e.g., 25 degrees Celsius) uniformly across the plurality of battery modules may be difficult to achieve. This problem may be further compounded by fluctuating loads that result in generating varying amounts of heat.

[0017] In some battery energy storage systems, cooling of the batteries may be provided, at least in part, by a HVAC (heating, ventilation, and air conditioning) system. In the context of battery energy storage systems, the HVAC system may be designed and configured to maintain the battery energy storage system at a desired (i.e., safe) operating temperature. Given the battery energy storage system may be (predictably) subjected to a transient event during which the heat generated by the batteries of the battery energy storage system increases greatly (i.e., spikes) for a short period of time (e.g., during a rapid battery discharge), the HVAC system may be designed and configured to maintain the battery energy storage system at a desired operating temperature during the transient events, at a greater expense in terms of space requirements and operating costs.

[0018] FIG. 1 is an illustrative graph 100 depicting the instantaneous load on a HVAC system of an example battery energy storage system. As shown, the instantaneous load on the HVAC system remains below an average level 105 for a majority of the operating period of FIG. 1 when the batteries of the battery energy storage system are charging. However, during a short time period (e.g., a 1 hour transient event) 110 when the batteries of the battery energy storage system are discharging, an increased load is placed on the HVAC system and the HVAC system will need to be configured to handle the peak load 115. Traditionally, the HVAC system would be sized about to absorb the excess heat generated during the transient event to maintain the battery temperature of the batteries in the battery energy storage system within acceptable limits. [0019] In some aspects, an excessive temperature rise within batteries will cause irreversible damage to the life and storage capacity of the batteries. The loss of battery storage capacity due to excessive temperatures may also lead to additional battery energy storage system costs since the system might be initially oversized to compensate for the loss of battery life. The graphic 200 in FIG. 2 illustrates the loss of storage capacity for an example battery due to temperature excesses. As shown at 205, a new battery energy storage system might be typically designed to have excess capacity 210 to account for degradation over the life of the battery storage system and to meet the performance guarantee near the end of its expected life as shown at 215. Oversizing batteries as depicted in FIG. 2 is expensive and inefficient. For example, the extra space and weight of a battery sized with 50% extra capacity can greatly impact the design, as well as initial and operating costs of a -system (e.g., automobile, energy reservoir, etc.).

[0020] In some aspects, embodiments of the present disclosure provide systems and mechanisms to efficiently and effectively manage transient thermal events associated with battery energy storage systems such that, for example, the battery energy storage systems need not be oversized for a particular application or use. Instead, the battery thermal management systems disclosed herein may be designed and implemented such that the cooling system including HVAC could be sized for average conditions and not transient events, as the thermal management system efficiently and effectively manages and/or dissipates thermal energy generated during transient events.

FIG. 3 A is a schematic diagram of an example of a modular battery energy storage system 300, in accordance with some embodiments herein. System 300 includes two modular battery energy storage units 305 and 310, although systems herein may comprise more or fewer modular battery energy storage units. Modular battery energy storage unit 305 includes a housing enclosure 312 that contains or otherwise houses a plurality of battery modules 325, 330. The battery modules each include one or more electrical terminals 340 and 345 that may be used to connect the battery modules to each other and/or other devices and systems (not shown) in parallel and/or series. Enclosure 312 includes a number of sidewalls defining the enclosure, with at least one of sidewalls is thermally conductive.

Although the embodiment of enclosure 312 in FIG 3 A includes four sidewalls, one or more central walls(not shown) may be disposed in the enclosure between the two rows (or other groupings) of batteries therein and in thermal contact with the heat transfer structure(s) 315 and 320. Enclosure 312 includes external cooling mechanisms 315 and 320 to dissipate heat channeled from an interior of the enclosure to the thermally conductive wall(s) of the enclosure. In the example of FIG. 3 A, the enclosure wall includes heatsinks. In some embodiments, the external cooling mechanism may include other types of a passive, active, or combination cooling mechanism, system, or device. Some example cooling mechanisms include air (natural or forced) and/or liquid cooling arrangements.

[0021] In the example of FIG. 3 A, enclosure 312 is filled with a plurality of prismatic batteries that are in thermal contact with a heat transfer structure 355 disposed in a phase change material (PCM) that is also disposed in enclosure 312. The PCM is dispersed in, around, and about the heat transfer structure 355. FIG. 3B provides a further detailed view of some aspects of battery energy system 300. In particular, FIG. 3B shows adjacent batteries 360 and 365 housed within enclosure 312 and surround by PCM 380 that is also disposed and dispersed within the enclosure. Thermal structure 385 comprises a heat pipe 370 and a plurality or matrix of thermally conductive fins 375 affixed to heat pipe 370. The fins increase the surface area of the thermal structure 385 exposed to the PCM and the

combination of fins 375 and heat pipe 370 provide a thermal conduit to conduct or channel heat generated by batteries 360 and 365 away from the batteries to a thermally conductive sidewall of enclosure 312, to which thermal structure 385 is thermally coupled to. If the temperature of battery exceeds the phase change temperature of PCM 380, the PCM absorbs heat from batteries 360 and 365 over a defined period of time, in accordance with the property characteristics of the particular PCM(s) used in some embodiments herein.

[0022] Herein, the combination of the PCM and heat transfer structure is referred to as a thermal capacitor. The heat transfer structure includes a matrix of fins in thermal contact with the batteries and a heat pipe (or other high thermal conductivity material or device) that extends to the thermally conductive wall(s) of the enclosure of a battery energy module herein. Notably, the PCM is also dispersed within the fins that are in thermal contact with the heat pipes and the batteries.

[0023] In some aspects, a PCM melting point could be appropriately chosen (about 25 degrees Celsius - about 100 degrees Celsius). In this manner, the PCM will remain in a solid state and not melt under normal operating conditions. During a normal temperature operation, such as a battery charging event during the day (i.e., lower C-rate), the heat from the batteries may be transferred to the thermally conductive outer wall(s) of the battery enclosure by conduction via the thermal structure (e.g., matrix of fins and heat pipe), where an external cooling device or system can dissipate the transferred thermal energy. In some regards, the battery temperature will not typically exceed the melting point of PCM due to the low amount of heat generated by the batteries during normal operation. Accordingly, the PCM will remain a solid in normal operating conditions. In some embodiments, PCMs for a battery energy storage system application herein may include, but are not limited to, organic, inorganic, metallic, eutectic alloys hydrated salts, boric acid, etc. Some PCMs like hydrated/other salts and boric acid do not melt like an organic PCM, but in principle absorb and release energy by heat of a chemical reaction. In some embodiments, the PCMs used may be reversible, meaning they could be used for multiple cycles of melting and

solidification. In some instances, the PCMs might be used for a one-time use such as, for example, in the case of boric acid being used as a safety mechanism to absorb thermal energy in the event of a thermal runaway. In some embodiments, the PCM used could be a combination of reversible and irreversible types of PCMs. In some instances, a system herein may comprise a combination of PCMs, where each PCM might have a different melting point. In some instances, including a system having a combination of PCMs, the one or more phase change materials may have a phase transition temperature greater than about 5 degrees Celsius.

[0024] However, under transient events such as, for example, ambient cycling, loss of cooling, and fast charge/discharge events (high C-rates), the battery temperature might rise due to higher ambient temperature and/or higher heat dissipation. Under these conditions, the battery temperature might rise over the melting point of the PCM. As such, the heat from the batteries would be transferred via the matrix of fins 375 and to the PCM 380 (e.g., wax) that is dispersed between, around, or about the fins, thereby causing the PCM to melt. The PCM will remain at its melting temperature until all of the PCM has turned into a liquid, thus also saturating the temperature rise in the batteries. The excess heat generated by the transient event could be stored in the PCM using its latent heat absorption properties, in an

appropriately sized thermal energy storage system herein. The stored heat (i.e., thermal energy) may further be routed to and ejected into the air via the matrix of fins 375 and heat pipe 370 (e.g., thermal structure) as normal operating conditions return.

[0025] In order for the PCM to be able to absorb additional heat, it needs to return to its solid state. Accordingly, the heat from the PCM is transported to the exterior of the battery energy storage system (e.g., 300) via the matrix of fins and heat pipe (i.e., thermal structure), whereupon the PCM can then (re-)solidify and be ready for a next heating cycle.

[0026] In some aspects, the matrix of fins 375 and heat pipe 370 (i.e., thermal structure assembly) disclosed herein has a higher thermal conductivity than the PCM 380 used in conjunction therewith in some embodiments. In this manner, thermal energy can be efficiently transferred from the PCM to a sidewall or other surface of the enclosure of a battery storage system herein.

[0027] In some aspects and embodiments, the fins of a thermal structure herein may be configured in spacing and sizing such that heat from a battery into the PCM disposed and dispersed in an enclosure of a battery storage system herein only travels a short distance to be transported by the fins and heat pipe(s) of the thermal structure. In some embodiments, the spacing and sizing of the thermally conductive fins and the heat pipe(s) may be optimized to result in maximizing an efficiency in the transfer of heat between a battery module and the PCM.

[0028] In some aspects, the thermal management aspects of a battery energy storage system disclosed herein includes latent energy absorption due to a solid-to-liquid phase change of a PCM. The thermal management features of the battery energy storage system may provide a measure of thermal runaway protection by virtue of the PCM disposed between the battery modules that can absorb the excess heat generated if a runaway situation were to start, thereby effectively controlling the temperature. In some respects, the battery energy storage system herein saturates rising component temperatures at near an isothermal temperature close to the melting point of the PCM. Accordingly, fast charging and/or discharging of batteries (i.e., a higher C-rate) is possible by systems of the present disclosure. In some aspects, battery degradation may be reduced, which results in longer lasting batteries and obviating the need to initially oversize battery modules. In some embodiments, the passive thermal management provided by the combination of a thermal structure and PCM (i.e., the disclosed thermal capacitor) may reduce the size or need for external cooling mechanisms, systems, and devices in a battery energy storage system herein.

[0029] FIG. 4 includes a graph 400 that shows the temperature (y-axis) of a heat generating device (e.g., a battery) in response to a transient event (x-axis), specifically at high charge/discharge rates. Line 405 is a baseline plot of the heat generating device without any thermal management device or system. Line 410 is the same heat generating device with a thermal energy storage system that may consist of plain phase change material or other types of typical heat transfer inserts including fins, foams, etc. As seen, the temperature continues to rise with time for plot 410. The plot of line 415 depicts the influence of a heat transfer structure and PCM as disclosed herein by transferring the excess heat to the PCM and maintaining the temperature of the heat generating component at a near constant value over the course of the transient event, where the temperature is near the melting point(420) of the PCM.

[0030] In some embodiments, a battery energy storage system herein may include the benefit of reducing the size of a HVAC (or other cooling system) associated with a battery energy storage system. Referring to FIG. 1, a battery energy storage system including a thermal capacitor as disclosed herein may have the HVAC (or other cooling system) associated therewith sized to absorb the heat generated by the average load 105 while the thermal capacitor as features herein store the excess heat generated during the transient event 110, to maintain the battery temperature within acceptable limits. When the normal operating conditions return, the heat stored in the PCM could be dissipated to air/liquid for the PCM to be restored to its initial state.

[0031] By maintaining a near constant temperature, the proposed invention also mitigates the thermal runaway problem that may be thermally triggered in battery energy storage systems. Thermal runaway once triggered in a single cell might propagate to other cells and modules leading to an explosive failure. Presence of an energy absorption medium prevents the propagation of the event, thus improving the safety of the energy storage system.

[0032] FIG. 5 is an illustrative graph 500 that demonstrates a modular energy storage system having a thermal capacitor (including PCM dispersed in and about a thermal structure as disclosed herein) may enable higher C-rate operation for a same temperature or a longer life cycle for a same C-rate. Figure 5 shows the temperature rise in a battery system with and without thermal energy storage. The solid lines (505, 515, 525, 535, and 545) represent the temperature rise without a thermal energy storage system at 0.25 to 3 C. The dashed lines (510, 520, 530, 540, and 550) show the temperature rise for the same battery system with a thermal energy storage as disclosed herein. As shown, the system with the thermal energy storage enables higher C-rate operation for the same temperature rise. Alternatively, keeping the charge/discharge rate constant, the temperature rise could be limited to prolong the battery life or reduce cooling requirements.

[0033] FIG. 6 is an illustrative depiction of some aspects of a battery storage system 600, in accordance with an embodiment herein. Battery storage system 600 includes a plurality of battery modules 610, 615, 620, 625, 630, and 635 housed in an enclosure 605. Battery storage system 600 further includes thermal capacitors 640 and 645 as disclosed hereinabove (e.g., a combination of PCM and a thermal structure) that are disposed in enclosure 605 in thermal contact with the batteries and the thermally conductive sidewalls of the enclosure. Battery storage system 600 also includes external cooling devices 650 and 655, which may be passive heatsinks in the example of FIG. 6 and are cooled by air or liquid, by forced or natural convection.

[0034] FIGS. 7 - 11 illustrate various forms of thermal capacitor 640, shown in Fig 6. FIG. 7 is an illustrative depiction of some aspects of a thermal capacitor device to be used in a battery storage system 700, in accordance with an embodiment herein. Battery storage system 700 shows a section of a plurality of battery modules 705 and 710, where the thermal capacitor may include a fin geometry without any heat pipes. The fins types might be folded fins or other fin types such as zipper fins, skived fins, extruded plate fins, etc. Additionally, the battery walls may be further configured to have a heat pipe embedded therein, to facilitate heat removal from the PCM to the battery enclosure walls. The battery storage system 700 also has a PCM dispersed between the fins, in accordance with the further disclosure herein.

[0035] FIG. 8 is an illustrative depiction of some aspects of a thermal capacitor device to be used in a battery energy storage system 800, in accordance with an embodiment herein. Battery storage system 800 shows a section of a plurality of battery modules 805 and 810, where the battery modules’ walls serve as the heat conducting medium between the thin PCM layer 815 and the enclosure of the battery energy storage system. In some embodiments, the battery walls in FIG. 8 can be thermally enhanced by embedding heat pipes, graphite, etc. into them. In some aspects, the battery walls might be constructed of high thermal conductivity materials such as, for example, copper, graphite, etc., where the thickness of such materials may be altered for optimal benefit. The conductive walls may be integral to a battery or sleeves inserted over the battery. The sleeves may cover small portions or the entire periphery of the battery. [0036] FIG. 9 is an illustrative depiction of some aspects of a thermal capacitor device to be used in a battery energy storage system 900, in accordance with an embodiment herein. In the example of battery storage system 900, the walls of the batteries 905 and 910 are enhanced with an integrated fin structure (920, 925, 930, 935). The fin structure may be configured in a number of different styles, including but not limited to a zipper fin, a folded fin, etc. to improve an efficiency in the transfer of heat from the batteries 905 and 910 to PCM 915 and an enclosure(not shown in FIG. 9) of the battery energy storage system. In some aspects, the fin structure in the battery walls might be constructed of thermally conductivity materials such as, for example, copper, graphite, etc., where the thickness of such materials may be altered for optimal benefit. The fin structure may be integral to a battery or sleeves inserted over the battery. The sleeves may cover small portions or the entire periphery of the battery.

[0037] FIG. 10 is an illustrative depiction of some aspects of a thermal capacitor device to be used in a battery energy storage system 1000, in accordance with an embodiment herein. Battery storage system 1000 includes a plurality of battery modules 1005 and 1010 and a thermal capacitor. The thermal capacitor, disposed between the batteries, includes thermally conductive plate 1015 integrated with a fin structure that is thermally coupled to the batteries and the enclosure wall. The thermally conductive plate 1015 may comprise a heat pipe embedded metallic plate, a graphite embedded plate, or a plain metallic plate. Additionally, a PCM is dispersed between the fins 1020 and 1025 integrated into thermally conductive plate 1015. The fin structures, 1020 and 1025, could be, but are not limited to, folded fins, skived fins, extruded fins made of a thermally conductive material.

[0038] FIG. 11 is an illustrative depiction of some aspects of a thermal capacitor device to be used in a battery energy storage system 1100, in accordance with an embodiment herein. Battery storage system 1100 includes a plurality of battery modules 1105 and 1110 and a flexible foam embedded with PCM layer 1115. In this example embodiment, the flexibility of the foam material 1115 is significant in its ability to accommodate expansion and maintain thermal connectivity with batteries 1105 and 1110. The flexible foam might be made of a thermally conductive material in thermal connection between the battery and the enclosure walls.

[0039] FIG. 12 is an illustrative depiction of some aspects of a battery energy storage system 1200, in accordance with an embodiment herein. In the example of battery storage system 1200, battery modules 1210, 1215, 1220, 1225, 1230, and 1235 are housed in enclosure 1205. System 1200 further includes internal thermal capacitors 1240 and 1245, which may have an embodiment as described in FIGS. 7 - 11 or combinations thereof, to channel heat from the batteries to additional thermal capacitors 1250 and 1255, integrated into the enclosure walls, lid, and/or base. Suitable example high conductivity substrates include but are not limited to high conductivity materials like graphite, diamonds, copper, aluminum, etc. The thermal capacitors are shown located at the walls of enclosure 1205 and are also in thermal connection with the internal thermal capacitors 1240 and 1245. In some embodiments, thermal capacitors 1250 and 1255 may have fins extending to an exterior surface of the enclosure for heat dissipation by a liquid and/or air cooled mechanism. The internal thermal capacitors may or may not have a PCM dispersed in its volume. The PCMs used in the internal thermal capacitors 1240 and 1245, and external thermal capacitor 1250 and 1255 may be of different phase change temperatures to cap the temperature rise/fall at a different temperature. The PCMs between the two sets of thermal capacitors could also be of different types, for example, organic PCM internally, and high temperature hydrated salts, boric acid, etc. in the external volume.

[0040] FIG. 13 is an illustrative depiction of some aspects of a battery energy storage system 1300 including cylindrical-shaped battery cells (e.g., 1305, 1310), in accordance with an embodiment herein. In the example of battery storage system 1300, the cylindrical -shaped -cells are in thermal contact with high conductivity (e.g., aluminum, copper, etc.) fins 1315 that are themselves in thermal contact with a plurality of heat pipes 1320 (i.e., the vertically depicted lines in FIG. 13). Heat pipes 1320 are further cooled by air or liquid cooling lines 1325 and 1330 (although other cooling mechanisms in addition to or instead of the cooling lines may be used in some embodiments). The heat pipes may be thermally interfaced with fins at external walls of an enclosure where the coolant comes in to contact with heat pipes to increase surface area (not shown in FIG. 13, similar to previous embodiments). In accordance with other aspects herein, a PCM is dispersed between fins 1315, heat pipes 1320, and the cylindrical batteries (e.g., 13015, 1310). As discussed previously, heat generated by the batteries is transferred to the PCM and dispersed therefrom to fins 1315 and channeled via heat pipes 1320 from an interior area or cavity of an enclosure (not shown in FIG. 13) housing the battery storage energy system 1300 to an exterior of the enclosure that is further cooled by cooling lines 1325 and 1330. The fins 1315 may have a curvature to increase the surface contact area with the batteries. The number of fins and heat pipes and the spacing could be altered to an optimal number depending on the operating conditions as demanded by a particular application.

[0041] Battery energy storage system 1300, like other battery energy storage system embodiments disclosed herein, operates to provide temperature uniformity (isothermal) across the batteries, to remove transient thermal energy via the PCM without a need to oversize the battery energy storage system, and to further reduce battery degradation due to excessive temperatures.

[0042] FIGS. 14A and 14B include illustrative depictions of some aspects of a battery storage system 1400, in accordance with an embodiment herein. Battery storage system 1400 includes a plurality of battery modules 1405, 1410, 1415, 1420, 1425, and 1430 housed in an enclosure 1402. Battery storage system 1400 further includes thermal capacitors 1445 and 1450 as disclosed hereinabove (e.g., a combination of a PCM and a thermal structure including a combination of fins and a high thermal conductivity conductor such as, for example, a heat pipe). The system includes heat pipe embedded conductors, or internal thermal capacitors, 1435 and 1440, thermally coupled to the battery modules and the thermal capacitors to efficiently transfer heat generated by the battery modules to the thermal capacitors. The thermal capacitors are further cooled in the example of FIGS. 14A and 14B by the air convection. In the specific embodiment of FIGS. 14A and 14B, dual - cool- jets (DCJ) 1455 and 1460 are used to move air over and through fins 1470 thermally coupled to an exterior of the enclosure 1402. In some embodiments, the -DCJs benefit from have no moving parts, low operating power and costs, high reliability (e.g., rated greater than about 70,000 hours), and a thin form factor (e.g., about 1 mm thick). In other embodiments, other types of fans and/or blowers might be used to move air over and through fins 1470.

[0043] This written description uses examples to explain the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims appended hereto, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.