Method and system for thermal management control of lithium-ion battery systems

Abstract

Methods and systems for thermal management control of a lithium-ion battery system. The battery system can provide backup power for information technology (IT) equipment. In response to the lithium-ion battery being in an inactive state (not charging or discharging), a primary cooling system can be used to maintain the temperature of the battery at or below an optimal storage temperature for the battery. If the primary cooling system is insufficient, a secondary cooling system operating in addition to the primary system can be used to maintain the temperature at or below the optimal storage temperature. The optimal storage temperature for the battery is determined based on the effort to cool the battery and the degradation of the battery.

Description

Technical Field

[0001] Embodiments of this disclosure generally relate to the thermal management of battery systems used in data center or information technology (IT) equipment setups. Thermal management of battery systems can be optimized to reduce battery system degradation and the effort required to cool the battery under active and inactive conditions. Background Technology

[0002] Information technology (IT) includes technologies such as computers accessible via the Internet or local networks, which provide storage or access to data, websites, computer programs, etc.

[0003] IT equipment such as servers can perform critical operations that need to continue even when mains power is unavailable (e.g., during power outages or maintenance). Lithium-ion batteries provide the necessary backup power, allowing IT equipment to remain operational for critical operations when the mains power source (such as the grid) fails. Therefore, the availability and functionality of such lithium-ion backup batteries are extremely important and must be maintained.

[0004] In some scenarios, a "battery room" can house all such lithium-ion backup batteries for centralized battery management. When the main power supply fails, the batteries in the room can provide backup power for IT equipment. However, it is well known that lithium-ion batteries degrade over time (e.g., their energy storage capacity decreases).

[0005] Battery degradation rates typically depend on storage temperature. Higher storage temperatures generally lead to faster degradation, but require less cooling effort to maintain. Therefore, data center development needs to manage batteries in a way that considers both degradation and cooling effort. Summary of the Invention

[0006] In a first aspect, a method is provided for managing a battery system for an information technology (IT) device, comprising:

[0007] It has been determined that the lithium-ion battery is currently inactive; and

[0008] In response to the lithium-ion battery being in an inactive state,

[0009] a) Use the main cooling system to maintain the battery temperature at or below the battery's optimal storage temperature, and

[0010] b) In response to determining that the main cooling system is insufficient, an auxiliary cooling system including a compressor is used to maintain the temperature of the battery at or below the optimal storage temperature of the battery, wherein the optimal storage temperature of the battery is determined based on the effort to cool the battery and the degradation of the battery.

[0011] In a second aspect, a cooling system for a lithium-ion battery is provided, the lithium-ion battery providing backup power for information technology (IT) equipment, the cooling system comprising:

[0012] Main cooling system;

[0013] Auxiliary cooling system; and

[0014] A controller coupled to the main cooling system and the auxiliary cooling system, the controller being configured to perform operations including:

[0015] It is determined that the lithium-ion battery is currently in an inactive state, and

[0016] In response to determining that the lithium-ion battery is currently in an inactive state

[0017] a) Use the main cooling system to maintain the battery temperature at or below the battery's optimal storage temperature, and

[0018] b) In response to the determination that the main cooling system is insufficient, an auxiliary cooling system, including a compressor, is used to maintain the battery temperature at or below the battery's optimal storage temperature, wherein the optimal storage temperature of the battery is determined based on the effort to cool the battery and the battery's degradation.

[0019] Thirdly, a data center is provided, including:

[0020] Lithium-ion batteries coupled to information technology (IT) equipment; and

[0021] The cooling system as described in the second aspect.

[0022] According to this disclosure, optimal management of lithium-ion backup batteries in data centers can be achieved, thereby minimizing the total cost of battery management. Attached Figure Description

[0023] These aspects are shown by way of example and are not limited to the figures in the accompanying drawings, in which the same reference numerals denote similar elements. It should be noted that references to “a” or “an” aspect of this disclosure do not necessarily refer to the same aspect; they mean at least one. Furthermore, for the sake of brevity and to reduce the total number of figures, a given figure may be used to illustrate features of more than one aspect, and not all elements in the figure may be necessary for a given aspect.

[0024] Figure 1 The relationship between cooling effort and battery compartment temperature is shown.

[0025] Figure 2 The relationship between battery storage capacity, ambient temperature, and storage time is illustrated according to some embodiments.

[0026] Figure 3 The relationship between charging or discharging capacity and battery temperature is shown.

[0027] Figure 4 A data center according to some embodiments is shown.

[0028] Figure 5 A method for managing battery status according to some embodiments is shown.

[0029] Figure 6 A flowchart illustrating the management of battery status according to some embodiments is shown. Detailed Implementation

[0030] Several aspects of this disclosure will now be explained with reference to the accompanying drawings. Where the shape, relative position, and other aspects of the components described in a given aspect are not explicitly defined, the scope of this disclosure is not limited to the components shown for illustrative purposes only. Furthermore, while many details are set forth, it should be understood that certain aspects can be practiced without these details. In other instances, well-known circuits, structures, and techniques have not been shown in detail so as not to obscure the understanding of this description. Moreover, unless there is a clear contrary meaning, all scopes listed herein are to be considered to include the endpoints of each scope.

[0031] In this specification, references to "an embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this disclosure. The phrase "in an embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment.

[0032] Optimal battery storage and operating temperatures can be maintained to achieve optimal management of lithium-ion backup batteries in data centers, thereby minimizing the total cost of battery management. The total cost of lithium-ion battery use in a data center can be determined based on 1) the cost of cooling the battery storage room, 2) the cost due to battery degradation, and 3) the cost of cooling the battery when it is active (e.g., charging or discharging). Each “cost” can be described as power consumption (e.g., the power required to operate cooling equipment such as fans, pumps, or compressors), monetary value, and / or a standardized value indicating general effort or damage.

[0033] The optimal storage temperature is determined by considering the trade-off between the cost of cooling facilities used for storage and battery degradation. Maintaining the battery temperature at its upper limit allows for the lowest possible cost of cooling the battery during charging or discharging. Real-time battery compartment ambient temperature and battery temperature can be monitored from multiple locations. The main cooling system, such as a fan or coolant-based system, can then be controlled to adequately cool the battery during operation, thereby maintaining the battery temperature at its upper limit. This temperature limit may vary depending on battery specifications (e.g., cell structure and chemistry) and is typically provided by the cell or module manufacturer.

[0034] In some embodiments, the data center includes lithium-ion backup batteries, which may include one or more battery modules, each containing multiple lithium-ion batteries. The batteries may be stored in a battery room for centralized management. The cost of maintaining the batteries at the desired temperature can be determined based on the power consumption required by fans, compressors, or pumps in a coolant-based cooling system. Such costs can vary based on the data center facility's infrastructure, the number of batteries, the size of the battery room, and the outside air temperature. Typically, the cost of cooling facilities increases as the desired temperature decreases.

[0035] For a given data center, it can be assumed that the outdoor air temperature is consistent with historical data. Therefore, the annual operating cost of the facility can be considered as a function of battery storage temperature, given by the following formula:

[0036] C facility (T storage ) = C fan (T storage )+C compressor (T storage )

[0037] Where T storage It is the ambient temperature of the battery compartment, C facility It is facility cooling, C fan (T storage ) is to operate the fan to maintain T storage Cost, C compressor (T storage () is the operation of the compressor to maintain the ambient temperature at T. storage The cost. As discussed, in some instances, the system may include a coolant-based cooling system instead of a fan, which includes a pump that circulates coolant through a cold plate that transfers heat from the battery.

[0038] Figure 1A graph depicting the relationship between annual effort (e.g., cost) and battery room temperature is shown. As the graph illustrates, the lower the temperature setpoint, the greater the effort required to cool the battery room. Conversely, as the temperature setpoint increases, the effort required to cool the battery room decreases. In data centers, lithium-ion batteries can be stored in a shared battery room for centralized management. The ambient temperature of the battery room is controlled by the facility's cooling system.

[0039] Figure 2 The graph illustrates the relationship between battery capacity (how much energy a battery can store), ambient temperature during battery storage, and total storage time. Several observations can be made based on the graph.

[0040] First, the discharge capacity of lithium-ion batteries decreases during storage. Even when not in use, each battery will degrade over time. Eventually, the battery capacity will become too low to meet the requirements of a data center. For example, a data center may need energy storage capable of providing 24-hour backup. After a certain number of days, the batteries will need to be replaced due to degradation.

[0041] Secondly, lower ambient temperatures help extend battery storage time. Typically, lithium-ion batteries have a lifespan of 15 years. However, higher ambient temperatures during battery storage significantly shorten this lifespan. Therefore, although this increases the power consumption for cooling the battery compartment, it is more economical in terms of improving battery condition.

[0042] One way to capture the cost of battery degradation is as a capital expenditure. Battery capital expenditure is denoted as C. battery,capex The nominal lifespan is denoted as t. battery,nominal (e.g. t) battery,nominal =15 years), the actual lifespan of the battery is denoted as η·t battery,nominal η is a coefficient representing the effect of storage temperature on battery life. η is a function of temperature (e.g., storage temperature), and η = 1 can be defined using a nominal storage temperature of 20°C.

[0043] For example, when battery capacity drops below 70% of its initial capacity (the amount depends on specific technical requirements), the company needs to replace the batteries. Taking into account the effect of storage temperature, battery life can be expressed as η·t. battery,nominal To describe. Therefore, due to battery degradation C battery,degrade The resulting annual expenses can be expressed as

[0044]

[0045] As mentioned earlier, η is the storage temperature T. storage The value of η is a function of the battery's internal structure, and decreases as the battery storage temperature increases. Therefore, higher annual battery costs lead to higher storage temperatures.

[0046] As mentioned above, Figure 2 The relationship between battery storage time, storage temperature, and remaining battery energy storage capacity is shown. For different ambient storage temperatures (e.g., 20°C, 30°C, 40°C, etc.), a unique relationship may exist between storage time and storage capacity.

[0047] Figure 3 This illustrates the relationship between battery capacity and battery temperature during operation. Generally, battery capacity increases with increasing battery temperature during operation. In other words, battery performance can benefit from higher battery temperatures. Therefore, during operation, cooling efforts can be minimized to keep the battery below thresholds such as the battery's upper temperature limit. The upper temperature limit can be a manufacturer-defined temperature that allows the battery to operate without the risk of overheating. The upper temperature limit can be determined through testing and replication and is typically provided by the battery manufacturer.

[0048] The operating cost of using lithium-ion batteries can be determined as the cost of cooling the battery during charging / discharging. This can be accomplished using primary cooling equipment such as fans or liquid / cold plate technology. Operating costs can also be the power consumption of the primary cooling system, such as the power consumption of the fans or pumps used to circulate the coolant. The primary cooling system should be applied at the lowest possible settings to keep the battery below its maximum permissible temperature. This is because higher battery temperatures increase the battery's charge / discharge capacity, thus effectively improving performance while minimizing cooling effort.

[0049] Therefore, based on the above, the total cost of battery operation C total The following can be determined:

[0050] C total =C facility +C battery,degrade +C operation .

[0051] In other words, the total cost depends on a) the cooling cost when the battery is in an inactive state (not charging / discharging), b) the cost of battery degradation, and c) the cost of cooling the battery when it is in an active state. Higher storage temperatures result in lower C. facility But increase C battery,degrade On the other hand, lower storage temperatures lead to higher C values. facility But lowering C battery,degrade For C operation Higher battery temperatures result in higher battery charge / discharge capacity, thus improving performance. Please note that battery temperature should be kept below its upper limit to prevent overheating.

[0052] In some embodiments, the optimized storage temperature T storageThe goal is to minimize the sum of a) the effort or cost of cooling the battery compartment and b) the effort or cost due to battery degradation. Battery degradation can be fitted to the following analytical relationship: y = A·exp(-x / B), where x is the storage time and y is the remaining battery capacity. Historical data such as the remaining battery capacity y and the storage time x can be collected through testing. This data can be used to apply the least squares method to fit constants A and B. Using this equation, the actual lifespan of the battery can be predicted, and η can be obtained.

[0053] Then, the sum of the facility cooling cost and the battery degradation cost for each possible temperature setting of the battery compartment can be obtained. An example is shown below, where there are corresponding facility cooling costs and corresponding costs due to battery degradation for different storage temperatures.

[0054] T storage,1 :C facility,1 +C battery,degrade,1

[0055] T storage,2 :C facility,2 +C battery,degrade,2

[0056] …

[0057] T storage,10 :C facility,10 +C battery,degrade,10

[0058] Based on different values ​​for different storage temperatures, an optimal storage temperature can be selected. This optimal storage temperature is the storage temperature that results in the lowest cost (e.g., calculated as the sum of cooling costs and battery degradation). Figure 2 The relationships shown can be found in the manufacturer's battery specifications and can then be used to obtain optimal results. In some embodiments where establishing a relationship is not readily available, the number of unused batteries can be monitored over time at different storage temperatures to establish a correspondence between storage capacity and storage time at a given storage temperature. In any case, this can be achieved with minimal combined cost (C facility +C battery,degrade Achieve optimal storage temperature

[0059] In other words, the optimal storage temperature of a battery can be determined by minimizing the sum of a) the effort to cool the battery (when inactive) and b) battery degradation, which is a function of the battery storage temperature. The effort to cool the battery can be the sum of a) the estimated operating effort of the main cooling system (such as a fan or a coolant-based system) and b) the compressor. Furthermore, battery degradation is determined at least based on the nominal battery temperature (e.g., 20°C) and the optimal storage temperature, as discussed in other sections regarding the relationship.

[0060]

[0061] Optimal control of the main cooling system (e.g., optimal fan or pump speed) can be determined and applied during battery activity (e.g., charging / discharging). This optimal control over the duration of activity contributes to the total operating cost of the lithium-ion battery. Real-time battery temperature can be monitored at multiple locations. For example, temperature sensors may be located on one or more battery cells, the battery casing, the chassis, a hot plate, etc. In some embodiments, the highest temperature value can be used to perform control of the cooling system. The main cooling system is controlled to keep the battery temperature below the upper limit of the battery's temperature range.

[0062] Figure 4 A block diagram of a data center 400 according to some embodiments is shown. The data center may include a cooling system comprising a controller 401, a main cooling system 414, and an auxiliary cooling system 404. The main cooling system may include technologies that are less expensive and / or more efficient than the auxiliary cooling system. Thus, the main cooling system serves as the default cooling system, while the auxiliary cooling system serves as a supplement (e.g., when the main cooling system is insufficient or requires assistance).

[0063] The main cooling system 414 may include one or more fans 416 that blow air across the battery compartment 402 where the lithium battery 404 is located. Alternatively or additionally, the main cooling system includes a pump 418 that circulates coolant to and from the battery. For example, the coolant may be thermally coupled to a cold plate 403 to absorb heat from the battery.

[0064] The auxiliary cooling system 404 may include a compressor and other standard air conditioning components that use compressor / condenser technology to cool the air in the battery compartment. As previously mentioned, this auxiliary cooling system often requires more effort (e.g., power consumption) than the main cooling system and therefore serves as a backup in addition to the main cooling system. In some embodiments, instead of a compressor, an alternative facility cooling solution is used, such as, for example, IDEC (indirect evaporative cooling). In some embodiments, any auxiliary cooling system that produces air colder than the outside air temperature can be used.

[0065] Sensor 406 may include one or more temperature sensors that monitor the temperature of the battery cell and / or the ambient temperature of the battery compartment. The sensor may also include other information, such as voltage, current, and / or other telemetry data.

[0066] Controller 401 may include components configured to execute this document (e.g., Figure 5The controller may include a combination of hardware (e.g., a processor, a programmable logic array, a computer-readable memory) for the control operations described in the diagram. The controller may include one or more output signals that control the main cooling system and auxiliary cooling system (e.g., command them to turn on / off, or at different speeds or efforts) based on inputs received from sensor 406. Inputs may include sensed battery cell temperatures and current measurements to determine whether the battery is active (e.g., charging or discharging) or inactive (not charging and not discharging). Inputs and outputs may communicate using known technologies such as TCP / IP, RS232, RS485, CAN-BUS, Wi-Fi, LTE, etc.

[0067] In some embodiments, the primary cooling system and / or auxiliary cooling system may have variable control levels. For example, the primary cooling system may have variable fan speed or pump speed. Similarly, the auxiliary cooling system may have variable compressor speed control. In other embodiments, the primary cooling system and / or auxiliary cooling system have a simple binary bit control (e.g., on / off) interface.

[0068] It should be understood that battery 404 may include multiple battery modules. Each battery module may include multiple lithium battery cells. The battery may be electrically connected to IT equipment 410 as a backup power source in case of loss of main power (e.g., the power grid). In some embodiments, although not shown, the battery may be connected to a power inverter to convert DC to AC (e.g., 120VAC, 240VAC, etc.) to power the IT equipment.

[0069] Figure 5 A method is shown for managing a battery system arranged as a backup power source for information technology (IT) equipment, which can be performed by a cooling system controller such as controller 401.

[0070] In Operation 501, the battery is determined to be active. For example, information from one or more current sensors can be used to determine whether the battery is charging, discharging, or idle. In other words, if the current is zero, the battery is inactive. If the current is greater than or less than zero, the battery is discharging or charging (active).

[0071] In response to the lithium-ion battery being currently inactive, the method may proceed to operation 502. In operation 502, the method includes using the main cooling system to maintain the battery temperature at or below the battery's optimal storage temperature. For example, the controller may command a fan (or pump) to operate at maximum speed until the battery temperature is at or below the optimal storage temperature. When the optimal storage temperature is reached, the fan may be turned off or its speed reduced, and control may proceed to operation 101 to repeat the cycle of maintaining the optimal storage temperature.

[0072] In some embodiments, a speed control command can be given to the fan or pump, proportional to the difference between the battery temperature and the optimal storage temperature. For example, if the battery temperature is only slightly above the optimal storage temperature (e.g., 1 degree, 2 degrees), the fan or pump can operate at a lower setting (e.g., 25%, 50%). If the battery temperature is significantly above the optimal storage temperature (e.g., 5 degrees or higher), the fan or pump can be commanded to adjust to a higher setting (e.g., 80% or 100%). The battery temperature can be determined based on the hottest temperature among multiple temperatures obtained at different battery cells or a weighted average of the battery cells.

[0073] In certain situations, such as when the outside air is very hot, a fan or pump alone may not be sufficient to cool the battery. Battery temperature can be monitored so that if it does not decrease or does not decrease at the desired rate, the main cooling system can be considered insufficient to maintain the optimal storage temperature. If the main cooling system is deemed insufficient, the process can proceed to block 503.

[0074] In block 503, the method includes using an auxiliary cooling system, such as a compressor or other equivalent air cooling technology, to maintain the battery temperature at or below the battery's optimal storage temperature. At this stage, both the main cooling system and the auxiliary cooling system can operate to maintain the battery's optimal storage temperature. The battery temperature can be monitored over time, and if the battery temperature drops to or below the optimal storage temperature, the auxiliary cooling system can be shut down or reduced. The main cooling system can also be shut down or reduced. The method can proceed to operation 501, thereby repeating the process of maintaining the optimal storage temperature. If the battery temperature does not decrease or does not decrease at a satisfactory rate, the system can proceed to fault handling operation 504.

[0075] At block 505, in response to the battery being considered active, the method includes using minimal effort from the main cooling system to maintain the battery temperature at the upper limit of the battery temperature. In other words, the system can use the minimum fan or pump speed required to maintain the battery under safe operating conditions. This reduces cooling effort (e.g., cost, power consumption) while also increasing the battery's charge and discharge capacity. In some embodiments, if the upper temperature limit is exceeded, the method may proceed to block 504 to perform fault handling. Otherwise, the method may return to operation 501 to repeatedly maintain the upper limit battery temperature when the battery is active.

[0076] In this way, the method uses a main cooling system (e.g., a fan or pump) to maintain the storage temperature, and only uses the compressor when necessary, such as when the optimal storage temperature is below the outside air temperature and the facility fan speed is at its maximum. The compressor is then started, with its operating frequency kept as low as possible to maintain the optimal storage temperature.

[0077] As described above, the optimal storage temperature of the battery is determined based on a) the effort to cool the battery and b) the battery degradation. Considering that the effort to cool the battery increases as the optimal storage temperature decreases, but the battery degradation increases as the optimal storage temperature increases, the optimal storage temperature results in the minimum sum of cooling effort and degradation. This optimal storage temperature can be determined in operation 530 and / or stored as a setting in the controller's computer-readable memory, and the operation can be performed offline at any time.

[0078] In operation 504, the method may include responding to a) when the battery's temperature limit is exceeded or b) when the battery's optimal storage temperature is exceeded while the compressor and main cooling system are operating, by reporting a battery error (e.g., logging the fault to a fault log and / or the cloud) or performing a system shutdown. System shutdown may include cutting off power to the IT equipment, which can prevent the battery from overheating. If the battery is not active, only an error report is needed. In some embodiments, a remedial response may include requesting an immediate response from the operator (e.g., via electronic notification).

[0079] Figure 6 A flowchart for managing battery status is shown according to some embodiments. The battery system can be configured as a power source for IT devices. In operation 601, the method includes determining that the lithium-ion battery is currently inactive. In operation 602, the method includes, in response to the lithium-ion battery being currently inactive, using a main cooling system to maintain the battery temperature at or below the battery's optimal storage temperature. In operation 603, the method includes, in response to determining that the main cooling system is insufficient, using an auxiliary cooling system including a compressor to maintain the battery temperature at or below the battery's optimal storage temperature. The optimal storage temperature of the battery can be determined based on cooling efforts and battery degradation, as described in other sections.

[0080] Some embodiments may include a non-transitory machine-readable medium (such as a microelectronic memory) having instructions stored thereon that program one or more data processing components (generally referred to herein as a "processor") to perform temperature control operations. In some embodiments, known control techniques may be used to perform the temperature control operations, such as proportional-integral (PI) controllers, proportional-integral-derivative (PID) controllers, or other equivalent control techniques that utilize battery temperature as feedback.

[0081] In some embodiments, the optimal battery storage temperature is configurable (e.g., it is stored as a setting in computer-readable storage). In some embodiments, some of these operations may be performed by specific hardware components containing hard-wired logic. Those operations may alternatively be performed by any combination of programmed data processing components and fixed hard-wired circuit components.

[0082] In the foregoing description, embodiments of the present disclosure have been described with reference to specific exemplary embodiments. It will be apparent that various modifications may be made thereto without departing from the broader spirit and scope of the present disclosure as set forth in the appended claims. Therefore, the description and drawings are to be considered illustrative rather than restrictive.

[0083] While certain aspects have been described and illustrated in the accompanying drawings, it should be understood that these aspects are merely exemplary and not intended to limit the broad disclosure, and that this disclosure is not limited to the specific constructions and arrangements shown and described, as various other modifications will be apparent to those skilled in the art. Therefore, the description is to be considered illustrative rather than restrictive.

[0084] In some aspects, this disclosure may include languages ​​such as "at least one of [element A] and [element B]". Such language may refer to one or more elements. For example, "at least one of A and B" could mean "A", "B", or "A and B". Specifically, "at least one of A and B" could mean "at least one of A and at least one of B", or "at least one of A or B". In some aspects, this disclosure may include languages ​​such as "[element A], [element B], and / or [element C]". Such language can refer to any one element or any combination thereof. For example, "A, B, and / or C" could mean "A", "B", "C", "A and B", "A and C", "B and C", or "A, B, C".

Claims

1. A method for managing a battery system in an information technology (IT) device, comprising: Determine that the lithium-ion battery is currently inactive; as well as In response to the lithium-ion battery being in an inactive state, a) Use the main cooling system to maintain the battery temperature at or below the battery's optimal storage temperature, and b) In response to determining that the main cooling system is insufficient, an auxiliary cooling system including a compressor is used to maintain the temperature of the battery at or below the optimal storage temperature of the battery, wherein the optimal storage temperature of the battery is determined based on the effort to cool the battery and the degradation of the battery; The optimal storage temperature of the battery is determined by minimizing the sum of a) the effort to cool the battery and b) the degradation of the battery, wherein the degradation of the battery is the ratio of battery capital expenditure to the nominal battery life after correction using a coefficient of influence of storage temperature on battery life, the coefficient of influence being a function of battery storage temperature and decreasing as the battery storage temperature increases. The effort to cool the battery is the sum of the estimated operating efforts of a) the main cooling system and b) the compressor.

2. The method according to claim 1, further comprising: In response to the battery being currently active, the temperature of the battery is maintained at the upper limit of the battery temperature using the minimum effort of the main cooling system.

3. The method according to claim 1, wherein, The main cooling system includes either a) a fan or b) a cold plate that circulates the coolant.

4. The method of claim 1, further comprising reporting a battery error or performing a system shutdown in response to a) exceeding the upper limit of battery temperature or b) exceeding the optimal storage temperature of the battery while the compressor and the main cooling system are operating.

5. A cooling system for a lithium-ion battery that provides backup power for information technology (IT) equipment, the cooling system comprising: Main cooling system; Auxiliary cooling system; as well as A controller coupled to the main cooling system and the auxiliary cooling system, the controller being configured to perform operations including: It is determined that the lithium-ion battery is currently in an inactive state, and In response to determining that the lithium-ion battery is currently in an inactive state a) Use the main cooling system to maintain the battery temperature at or below the battery's optimal storage temperature, and b) In response to the determination that the main cooling system is insufficient, an auxiliary cooling system including a compressor is used to maintain the battery temperature at or below the battery's optimal storage temperature, wherein the optimal storage temperature of the battery is determined based on the effort to cool the battery and the battery's degradation. The optimal storage temperature of the battery is determined by minimizing the sum of a) the effort to cool the battery and b) the battery degradation, wherein the battery degradation is the ratio of battery capital expenditure to the nominal battery life after correction using the influence coefficient of storage temperature on battery life, the influence coefficient being a function of battery storage temperature and decreasing as the battery storage temperature increases. The effort to cool the battery is the sum of the estimated operating efforts of a) the main cooling system and b) the compressor.

6. The cooling system of claim 5, wherein the operation further comprises, in response to the battery being currently active, maintaining the temperature of the battery at the upper limit of the battery temperature using minimal effort of the main cooling system.

7. The cooling system of claim 5, wherein the main cooling system comprises a) a fan or b) a cold plate for circulating coolant.

8. The cooling system of claim 5, wherein the operation further comprises reporting a battery error or performing system shutdown in response to a) exceeding the upper limit of battery temperature or b) exceeding the optimal storage temperature of battery while the compressor is operating.

9. A data center, comprising: Lithium-ion batteries coupled to information technology (IT) equipment; as well as The cooling system as described in any one of claims 5 to 8.

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