Lithium battery pack low-temperature control system based on cooperation of electric heating and phase change heat storage

Abstract

The invention relates to the technical field of batteries, and discloses a lithium battery pack low-temperature control system based on cooperation of electric heating and phase change heat storage. The system comprises an electric heating unit, a phase change heat storage unit filled with a phase change material, a liquid cooling circulation unit with a liquid cooling pipeline and a driving pump, a mode switching unit with a manual three-way valve and a heat preservation unit wrapping the outside. By manually operating the three-way valve, the liquid cooling flow path can be switched to respectively realize electric heating and preheating, heat storage and heat preservation by using the phase change material or heat dissipation by absorbing peak heat. The system preferably adopts a paraffin-expanded graphite composite material with the phase change temperature of 20 DEG C, and state judgment can be performed through a mechanical temperature indicator. According to the invention, rapid battery starting, stable operation temperature and peak thermal load buffering can be realized in a low-temperature environment without complex electric control, and the system has the advantages of simple structure, high reliability and low cost, and is especially suitable for low-temperature application scenes such as new energy vehicles and energy storage power stations.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of batteries, in particular to a low-temperature temperature control system for a lithium battery pack based on electric heating and phase change heat storage cooperation. BACKGROUND

[0002] New energy vehicles and energy storage systems are penetrating into high-latitude and high-altitude areas at an unprecedented speed. However, the environmental temperature in these areas is often lower than -30 DEG C in winter, and the extreme record even breaks -50 DEG C. Under low-temperature environment, the electrochemical performance of lithium ion batteries declines exponentially: the ionic conductivity of electrolyte decreases by one order of magnitude, the lithium intercalation path of negative electrode graphite is partially "frozen", the charge transfer impedance increases by 5-10 times, the available capacity attenuates by 30%-50%, the charging time is prolonged by 2-3 times, and the safety hazard of lithium dendrite piercing the separator is prone to occur. According to incomplete statistics, the winter endurance complaint rate of new energy vehicles in northern China accounts for more than 45% of the annual quality complaints, and the number of events of energy storage power stations unable to be connected to the grid due to low temperature exceeds 200 times per year, with direct economic losses of more than 1 billion yuan.

[0003] In order to alleviate the low-temperature pain point, the industry generally adopts the "active electric heating" scheme: silicon rubber heating film or PTC heating plate is laid in the battery pack, and 3-5 kW power is used to preheat for 15-20 min before starting. Although this scheme is simple and easy to implement, it has three major drawbacks:

[0004] High energy consumption: 1-1.5 kWh of electricity is consumed for single preheating, which is equivalent to the driving distance of an A-class electric vehicle at room temperature for 8-10 km;

[0005] Power grid impact: if large-scale energy storage power stations start electric heating at the same time, the instantaneous power can reach MW level, which forms a severe impact on the weak power grid;

[0006] Poor thermal uniformity: the local hot spot temperature of the heating film can be 15 DEG C higher than the average value, and long-term operation aggravates the battery inconsistency and shortens the cycle life.

[0007] In recent years, the "phase change heat storage (PCM)" technology has been introduced into the field of battery low temperature. Paraffin, fatty acid, hydrated salt and other phase change materials can absorb or release a large amount of latent heat in the solid-liquid conversion process, which can theoretically realize "passive heat preservation". However, the thermal conductivity coefficient of pure PCM is only about 0.2 W / (m·K), and the heat storage and heat extraction rate is slow, which cannot meet the demand of "immediate travel" of vehicles; at the same time, the volume expansion rate of PCM is ≥10%, the packaging reliability is poor, and leakage and pulverization are prone to occur after multiple cycles. In order to improve the thermal conductivity, researchers composite expanded graphite, carbon nanotubes, metal foam and PCM, although the thermal conductivity coefficient can be increased to 5-20 W / (m·K), but the process is complex, the cost is high, and the structural contradiction of "no heat source in the preheating stage and unable to quickly dissipate heat in the heat dissipation stage" has not been solved. Summary of the Invention

[0008] This invention provides a low-temperature temperature control system for lithium battery packs based on the synergy of electric heating and phase change thermal storage, in order to solve the above-mentioned problems.

[0009] In a first aspect, the present invention provides a low-temperature temperature control system for lithium battery packs based on the synergy of electric heating and phase change thermal storage, comprising:

[0010] Electric heating unit;

[0011] Phase change thermal storage unit, which is filled with phase change material;

[0012] A liquid cooling circulation unit includes liquid cooling pipes and a drive pump. The liquid cooling pipes pass through the phase change thermal storage unit and are used to contact the battery.

[0013] The mode switching unit includes a manual three-way valve installed on the liquid cooling pipeline; and

[0014] An insulation unit that at least partially covers the battery, the phase change thermal storage unit, and the liquid cooling pipeline;

[0015] The manual three-way valve can be operated to switch the flow path of the liquid cooling circulation unit, so as to preheat the battery via the electric heating unit or use the phase change heat storage unit to keep the battery warm or dissipate heat.

[0016] When starting the battery in a low-temperature environment, the operator manually switches the three-way valve to the preheating path. At this time, the drive pump starts, the electric heating unit operates, and the heated coolant flows through the liquid cooling pipeline, directly heating the battery in contact with it and transferring some heat to the phase change material in the phase change energy storage unit, allowing it to store latent heat. Once the battery is started and in operation, the three-way valve can be manually switched according to its heat generation. If the battery generates little heat and there is a risk of temperature drop, switch to the insulation path. In this case, the electric heating unit can be turned off, and the circulating coolant mainly absorbs heat from the already stored phase change material to maintain the battery temperature. If the battery generates a lot of heat and there is a risk of overheating, switch to the heat dissipation path. The heat generated by the battery is carried away by the coolant and transported to the phase change energy storage unit, where the phase change material absorbs this heat, thereby suppressing the rapid rise in battery temperature.

[0017] In one alternative embodiment, the phase change material is a composite material of paraffin and expanded graphite, wherein the expanded graphite accounts for 18% to 22% by mass.

[0018] The main component of the phase change material is paraffin wax, which, as the working fluid, can absorb or release a large amount of latent heat near the phase change temperature. To improve the poor thermal conductivity of pure paraffin wax, expanded graphite is added as an additive. Expanded graphite has a well-developed porous network structure. When its mass percentage is controlled within the range of 18% to 22%, it can form continuous and efficient thermal conductivity pathways in the paraffin wax, significantly improving the overall thermal conductivity of the composite material and thus accelerating the heat transfer rate between the thermal storage unit and the liquid cooling pipeline. Simultaneously, this proportion of expanded graphite can be well wetted by the paraffin wax, ensuring good thermal conductivity enhancement while also considering the thermal storage density and shape stability of the composite material.

[0019] In one alternative embodiment, the phase transition temperature of the paraffin is 20°C.

[0020] During the low-temperature preheating stage, the system aims to heat the battery from an ambient temperature below 0°C to the ideal operating temperature. A phase change point of 20°C means that when the electric heating unit transfers heat through the liquid cooling system, the phase change material (PCM) will begin to absorb heat and melt significantly when the temperature reaches or slightly exceeds 20°C, thus efficiently storing thermal energy. When the battery operates under low load and heat generation is insufficient, the battery and coolant temperatures tend to decrease. When the temperature approaches 20°C, the melted PCM begins to solidify and release its stored latent heat, preventing further temperature drops and maintaining the battery temperature within a reasonable range based on 20°C. When the battery operates under high load and heat generation surges, the battery and coolant temperatures rise. If the temperature exceeds 20°C, the PCM can absorb heat and melt again, thus buffering the rate of temperature rise.

[0021] In one optional embodiment, the manual three-way valve has a preheating setting, a heat preservation setting, and a heat dissipation setting;

[0022] When in the preheating state, the liquid cooling pipeline connects the electric heating unit and the phase change thermal storage unit;

[0023] When the battery is in the heat preservation mode, the electric heating unit is cut off, and the liquid cooling pipeline forms a loop between the battery and the phase change heat storage unit.

[0024] When in the heat dissipation mode, the liquid cooling pipeline directs the heat absorbed by the battery to the phase change thermal storage unit.

[0025] In one optional embodiment, the mode switching unit further includes a temperature indicator plate affixed to the surface of the battery. The temperature indicator plate is based on the bimetallic strip temperature measurement principle and uses color to indicate the temperature range.

[0026] This temperature indicator provides operators with an intuitive visual temperature reference that requires no power supply or cables. In systems that use a manual three-way valve for mode switching, operators can quickly and intuitively determine the approximate temperature status of the battery based on the colors displayed on the indicator, and then decide whether to switch the three-way valve to the "preheat," "keep warm," or "dissipate heat" setting. It replaces complex electronic temperature sensors and displays, eliminating the risk of temperature information loss due to circuit failures, electromagnetic interference, or power outages, and greatly enhancing the robustness and ease of operation of the entire thermal management system in harsh environments.

[0027] In one optional embodiment, the insulation unit includes an aluminum foil reflective layer and a polyurethane foam layer arranged sequentially from the inside to the outside.

[0028] These two layers of materials are physically combined (such as through adhesive bonding, hot pressing, or lamination) to form a unified insulation shell. Their working principle is synergistic: the aluminum foil reflective layer primarily targets radiative heat dissipation, while the polyurethane foam layer primarily targets conductive heat dissipation. Together, they form a dual barrier of "radiation reflection" and "physical barrier." Compared to single-material insulation solutions, this composite structure more effectively reduces heat loss in low-temperature environments, especially significantly improving the utilization rate of electric heating energy during the preheating stage. During operation, it helps maintain stable internal system temperature and reduces fluctuations.

[0029] In one alternative embodiment, the electric heating unit includes a PTC heater and a temperature self-limiting controller electrically connected to the PTC heater, the temperature self-limiting controller being configured to reduce the heating power of the PTC heater when it detects that the target heating temperature has reached a preset value.

[0030] During the low-temperature start-up preheating phase, the controller controls the PTC heater to operate at high power (or rated power) to rapidly increase the coolant temperature. When the controller detects that the coolant temperature has reached a preset "target temperature value" (e.g., 25°C) through its sensing component, its logic control component outputs a control signal to actively reduce the operating voltage or current applied to the PTC heater, or change its operating mode (e.g., from continuous heating to pulse heating), thereby significantly reducing its heating power. This design allows the electric heating unit to perform "on-demand heating" according to the actual needs of the system, meeting the requirements of rapid preheating while automatically switching to a low-power maintenance state or near-shutdown state after reaching the appropriate temperature. This avoids energy waste and potential overheating risks caused by continuous full-power heating, improving the economy and safety of the preheating process.

[0031] In one optional embodiment, a safety protection unit is also included, which includes a pressure relief valve disposed on the liquid cooling circulation unit and a temperature fuse connected in series with the electric heating unit circuit.

[0032] In one alternative embodiment, the liquid cooling pipeline is a serpentine metal tube made of 304 stainless steel.

[0033] In one alternative embodiment, the phase change thermal storage unit is a honeycomb structure wrapped around the liquid cooling pipeline.

[0034] The honeycomb structure provides a significantly larger internal surface area than solid blocks, allowing the phase change material (PCM) filling it to exchange heat with the liquid cooling pipe walls and structural skeleton through a thinner layer. This significantly shortens the heat transfer path and greatly improves the response speed of heat storage and release. The metal honeycomb skeleton itself forms a highly efficient three-dimensional heat-conducting network, which can quickly and evenly transfer the heat absorbed from the liquid cooling pipes to the PCM in all the channels, or rapidly collect the heat released by the PCM to the liquid cooling pipes, effectively avoiding localized hot or cold spots caused by the poor thermal conductivity of the PCM. Attached Figure Description

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of a low-temperature temperature control system for a lithium battery pack based on the synergy of electric heating and phase change thermal storage, according to an embodiment of the present invention.

[0037] Explanation of reference numerals in the attached figures:

[0038] 11. PTC heater; 12. Temperature self-limiting controller;

[0039] 21. Phase change materials;

[0040] 31. Liquid cooling piping; 32. Drive pump; 33. Coolant tank;

[0041] 41. Manual three-way valve; 42. Temperature indicator;

[0042] 51. Pressure relief valve; 52. Fusible link;

[0043] 6. Battery. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] New energy vehicles and energy storage systems are penetrating high-latitude and high-altitude regions at an unprecedented rate. However, winter temperatures in these areas often fall below -30°C, with extreme records even exceeding -50°C. Under low-temperature conditions, the electrochemical performance of lithium-ion batteries deteriorates exponentially: the electrolyte's ionic conductivity decreases by an order of magnitude, the lithium intercalation pathway in the graphite of the negative electrode partially "freezes," and the charge transfer impedance increases by 5 to 10 times, resulting in a 30% to 50% reduction in usable capacity, a 2 to 3-fold increase in charging time, and a high risk of lithium dendrites piercing the separator. According to incomplete statistics, complaints about the winter range of new energy vehicles in northern my country account for more than 45% of all annual quality complaints, and there are more than 200 incidents annually where energy storage power stations cannot connect to the grid due to low temperatures, resulting in direct economic losses exceeding one billion yuan.

[0046] To alleviate the problem of low temperatures, the industry generally adopts an "active electric heating" solution: a silicone rubber heating film or PTC heating plate is laid inside the battery pack, and preheating is performed at a power of 3~5 kW for 15~20 minutes before startup. While this solution is simple and easy to implement, it has three major drawbacks:

[0047] High energy consumption: a single preheating cycle consumes 1~1.5 kWh of electricity, which is equivalent to the electricity consumption of an A-class electric vehicle to travel 8~10 km at room temperature;

[0048] Grid impact: If large-scale energy storage power stations start electric heating at the same time, the instantaneous power can reach the MW level, which will cause a severe impact on the weak power grid.

[0049] Poor thermal uniformity: The temperature of local hot spots in the heating film can be more than 15°C higher than the average value. Long-term operation exacerbates battery inconsistency and shortens cycle life.

[0050] In recent years, phase change thermal energy storage (PCM) technology has been introduced into the low-temperature battery field. Phase change materials such as paraffin, fatty acids, and hydrated salts can absorb or release a large amount of latent heat during solid-liquid conversion, theoretically achieving "passive insulation." However, pure PCM has a thermal conductivity of only about 0.2 W / (m·K), resulting in slow heat storage and extraction rates, which cannot meet the "instant travel" requirements of vehicles. Simultaneously, PCM has a volume expansion rate ≥10%, leading to poor encapsulation reliability and a tendency to leak and pulverize after multiple cycles. To improve thermal conductivity, researchers have combined expanded graphite, carbon nanotubes, and metal foam with PCM. While this can increase the thermal conductivity to 5~20 W / (m·K), the process is complex and costly, and it still fails to resolve the structural contradiction of "no heat source during preheating and inability to quickly dissipate heat during heat dissipation."

[0051] The following is combined Figure 1 The following describes embodiments of the present invention.

[0052] According to an embodiment of the present invention, a low-temperature temperature control system for six lithium batteries based on the synergy of electric heating and phase change thermal storage is provided. The system includes an electric heating unit, a phase change thermal storage unit, a liquid cooling circulation unit, a mode switching unit, and a heat preservation unit. The phase change thermal storage unit is filled with a phase change material 21. The liquid cooling circulation unit includes a liquid cooling pipe 31, a drive pump 32, and a coolant tank 33. The liquid cooling pipe 31 passes through the phase change thermal storage unit and is used to contact the battery 6. The mode switching unit includes a manual three-way valve 41 disposed on the liquid cooling pipe 31. The heat preservation unit at least partially covers the battery 6, the phase change thermal storage unit, and the liquid cooling pipe 31. By operating the manual three-way valve 41, the flow path of the liquid cooling circulation unit can be switched to respectively achieve preheating of the battery 6 via the electric heating unit, or heat preservation or heat dissipation of the battery 6 using the phase change thermal storage unit.

[0053] In this embodiment, the system as a whole constitutes an integrated thermal management module. An electric heating unit serves as an active heat source connected to the liquid cooling circulation unit. The phase change thermal storage unit is a container or structure housing the phase change material 21, through which the liquid cooling pipe 31 passes, enabling efficient heat exchange between the coolant and the phase change material 21. The liquid cooling pipe 31 is also arranged to be in close contact with the battery pack 6, for example, attached to the side or bottom of the battery module 6, to achieve heat conduction between them. A drive pump 32 provides the power for coolant circulation, and a coolant tank 33 stores coolant for the cold circulation unit.

[0054] The core of the mode switching unit is a manual three-way valve 41 installed on the liquid cooling pipeline 31. This valve can guide the coolant to circulate along different paths by changing the connection relationship of its internal channels. The insulation unit, as a heat-insulating shell, encloses the battery 6, the heat storage unit, and the main liquid cooling pipeline 31, forming a relatively closed thermal management cavity to reduce heat loss from the external low-temperature environment.

[0055] When battery 6 needs to be started in a low-temperature environment, the operator switches the manual three-way valve 41 to the preheating flow path. At this time, the drive pump 32 starts, the electric heating unit works, and the heated coolant flows through the liquid cooling pipe 31, directly heating the battery 6 in contact with it, and transferring some heat to the phase change material 21 in the phase change heat storage unit, allowing it to store latent heat. After battery 6 starts and enters the operating state, the three-way valve can be manually switched according to its heat generation. If battery 6 generates less heat and there is a risk of temperature drop, the flow path is switched to the heat preservation flow path. At this time, the electric heating unit can be turned off, and the circulating coolant mainly absorbs heat from the already stored heat in the phase change material 21 to maintain the temperature of battery 6. If battery 6 generates more heat and there is a risk of overheating, the flow path is switched to the heat dissipation flow path. The heat generated by battery 6 is carried away by the coolant and transported to the phase change heat storage unit, where the phase change material 21 absorbs this heat, thereby suppressing the rapid rise in the temperature of battery 6.

[0056] The system provided in this embodiment integrates preheating, heat preservation and heat dissipation functions through a simple mechanical manual valve, without the need for a complex electronic control system and sensors, which improves reliability in harsh low-temperature environments. Furthermore, it utilizes a phase change thermal storage unit to achieve spatiotemporal transfer and buffering of heat, effectively improving the performance and lifespan of battery 6 in low-temperature environments.

[0057] In one embodiment, the phase change material 21 is a composite material of paraffin wax and expanded graphite, wherein the expanded graphite accounts for 18% to 22% by mass.

[0058] In this embodiment, the phase change material 21 is primarily paraffin wax, which, as the working fluid, can absorb or release a large amount of latent heat near the phase change temperature. To improve the poor thermal conductivity of pure paraffin wax, expanded graphite is added as an additive. Expanded graphite has a well-developed porous network structure, and when its mass percentage is controlled within the range of 18% to 22%, it can form continuous and efficient thermal conductivity pathways within the paraffin wax, significantly improving the overall thermal conductivity of the composite material and thus accelerating the heat transfer rate between the heat storage unit and the liquid cooling pipe 31. Simultaneously, this proportion of expanded graphite can be well wetted by the paraffin wax, ensuring both good thermal conductivity enhancement and good heat storage density and shape stability of the composite material.

[0059] In one embodiment, the phase transition temperature of the paraffin is 20°C.

[0060] In this embodiment, the paraffin component in the composite material is selected or formulated so that the temperature at which it undergoes a solid-liquid phase transition (i.e., the phase transition temperature) is precisely set to 20°C. This temperature value is based on the lower limit of the typical temperature range for efficient and safe operation of the lithium battery 6 in low-temperature environments (it is generally believed that performance improves significantly above 0°C, and reaches a better balance in the 15-25°C range). Setting the phase transition temperature of the thermal storage unit to 20°C makes it an ideal heat "buffer zone" and "transfer station".

[0061] Specifically, during the low-temperature preheating stage, the system aims to heat battery 6 from an ambient temperature below 0°C to the ideal operating temperature. The 20°C phase change point means that when the electric heating unit transfers heat through the liquid cooling pipe 31, the phase change material 21 will begin to absorb heat and melt significantly when the temperature reaches and slightly exceeds 20°C, thus efficiently storing thermal energy. When battery 6 operates under low load and heat generation is insufficient, the temperature of battery 6 and the coolant tends to decrease. When the temperature approaches 20°C, the melted phase change material 21 will begin to solidify and release the stored latent heat, preventing the temperature from falling further and maintaining the battery 6 temperature within a reasonable range based on 20°C. When battery 6 operates under high load and heat generation surges, the temperature of battery 6 and the coolant rises. If the temperature exceeds 20°C, the phase change material 21 can absorb heat and melt again, thus buffering the rate of temperature rise.

[0062] In one embodiment, the manual three-way valve 41 has a preheating setting, a heat preservation setting, and a heat dissipation setting;

[0063] When in the preheating state, the liquid cooling pipeline 31 connects the electric heating unit and the phase change heat storage unit;

[0064] When the heat preservation setting is engaged, the electric heating unit is cut off, and the liquid cooling pipeline 31 forms a loop between the battery 6 and the phase change heat storage unit.

[0065] When in the heat dissipation mode, the liquid cooling pipe 31 directs the heat absorbed by the battery 6 to the phase change thermal storage unit.

[0066] In this embodiment, the manual three-way valve 41 is a purely mechanically operated component. By rotating the valve core or moving the valve stem, the connection mode of its internal flow channels is changed, thereby achieving flow path switching for three predetermined functions. In the "preheating" position, the coolant circulation path is forced through the electric heating unit and the phase change heat storage unit. This is to quickly provide heat to the battery 6 and the heat storage medium using external electrical energy during the initial system startup. When switched to the "heat preservation" position, the electric heating unit is excluded from circulation, and the coolant circulates only between the battery 6 area and the phase change heat storage unit. At this time, the system relies on the latent heat stored in the heat storage unit to compensate for the heat loss of the battery 6 and maintain its temperature. When switched to the "heat dissipation" position, the coolant circulation path is guided to carry the excess heat generated by the battery 6 during operation to the phase change heat storage unit, where the latter absorbs this heat to buffer the temperature rise of the battery 6.

[0067] In one embodiment, the mode switching unit further includes a temperature indicator 42 affixed to the surface of the battery 6. The temperature indicator 42 is based on the bimetallic strip temperature measurement principle and indicates the temperature range by color.

[0068] In this embodiment, the temperature indicator 42 is a passive mechanical temperature sensor, the core component of which is a bimetallic strip made of one or more metals with different coefficients of thermal expansion bonded together. This bimetallic strip bends and deforms due to temperature changes, and this deformation drives a displacement of an indicator component (such as a color wheel, color strip, or coated window) with different color areas via a mechanical linkage mechanism (such as a lever or pointer), thereby revealing the color corresponding to the current temperature range. For example, it can be configured to display red for low-temperature ranges (such as below 10°C), green for suitable temperature ranges (such as 10°C to 35°C), and yellow or orange for high-temperature ranges (such as above 35°C). This indicator is directly attached or fixed to the surface of the battery module 6 casing to sense its surface temperature.

[0069] The temperature indicator 42 provides operators with an intuitive visual temperature reference that requires no power supply or connecting cables. In a system based on manual three-way valve 41 for mode switching, operators can intuitively and quickly determine the approximate temperature status of battery 6 based on the colors displayed on the indicator, and then decide whether to switch the three-way valve to the "preheat," "insulate," or "dissipate" setting. It replaces complex electronic temperature sensors and display instruments, eliminating the risk of temperature information loss due to circuit failure, electromagnetic interference, or power failure, and greatly enhancing the robustness and ease of operation of the entire thermal management system in harsh environments.

[0070] In one embodiment, the insulation unit includes an aluminum foil reflective layer and a polyurethane foam layer arranged sequentially from the inside out.

[0071] In this embodiment, the insulation unit adopts a composite double-layer structure to achieve efficient heat insulation. The aluminum foil reflective layer is located on the inner side, directly facing or close to the internal heat-generating or heat-storing components such as the battery group 6, the phase change heat storage unit, and the liquid cooling pipeline 31. Its main function is to utilize its high reflectivity to reflect most of the infrared radiation heat (i.e., radiative heat transfer) emitted from the surface of the internal components back, thereby effectively suppressing heat loss to the outside through radiation.

[0072] The polyurethane foam layer is placed on the outside of the aluminum foil reflective layer, serving as the main structural insulation layer. It has an extremely low thermal conductivity and a closed-cell structure, effectively blocking heat conduction caused by temperature differences between the internal and external environments. Simultaneously, its closed-cell structure also provides moisture insulation.

[0073] These two layers of materials are physically combined (such as through adhesive bonding, hot pressing, or lamination) to form a unified insulation shell. Their working principle is synergistic: the aluminum foil reflective layer primarily targets radiative heat dissipation, while the polyurethane foam layer primarily targets conductive heat dissipation. Together, they form a dual barrier of "radiation reflection" and "physical barrier." Compared to single-material insulation solutions, this composite structure more effectively reduces heat loss in low-temperature environments, especially significantly improving the utilization rate of electric heating energy during the preheating stage. During operation, it helps maintain stable internal system temperature and reduces fluctuations.

[0074] In one embodiment, the electric heating unit includes a PTC heater 11 and a temperature self-limiting controller 12 electrically connected to the PTC heater 11. The temperature self-limiting controller 12 is configured to reduce the heating power of the PTC heater 11 when it detects that the target heating temperature has reached a preset value.

[0075] In this embodiment, the electric heating unit employs a heating scheme with active power regulation. The PTC (Positive Temperature Coefficient) heater, as the core heating element, exhibits a self-limiting temperature characteristic as its resistance increases with its temperature. To further achieve precise and safe temperature control, an independent temperature self-limiting controller 12 is additionally provided. This controller is electrically connected to the PTC heater 11 and typically includes a temperature sensing component (such as a thermistor or thermocouple) and a logic control component. The temperature sensing component is positioned to reflect the system's target heating temperature, for example, installed on the liquid cooling pipeline 31 near the outlet of the electric heating unit, for directly monitoring the temperature of the heated coolant.

[0076] During the low-temperature start-up preheating phase, the controller controls the PTC heater 11 to operate at high power (or rated power) to rapidly increase the coolant temperature. When the controller detects through its sensing section that the coolant temperature has reached a preset "target temperature value" (e.g., 25°C), its logic control section outputs a control signal to actively reduce the operating voltage or current applied to the PTC heater 11, or change its operating mode (e.g., from continuous heating to pulse heating), thereby significantly reducing its heating power. This design allows the electric heating unit to perform "on-demand heating" according to the actual needs of the system, satisfying the requirements of rapid preheating while automatically switching to a low-power maintenance state or near-shutdown state after reaching a suitable temperature. This avoids energy waste and potential overheating risks caused by continuous full-power heating, improving the economy and safety of the preheating process.

[0077] In one embodiment, the lithium battery group 6-group low temperature control system based on the synergy of electric heating and phase change thermal storage also includes a safety protection unit, which includes a pressure relief valve 51 disposed on the liquid cooling circulation unit and a temperature fuse 52 connected in series with the electric heating unit circuit.

[0078] In this embodiment, the safety protection unit is a purely mechanical or passive protection measure designed to address potential risks such as abnormal pressure, electrical overheating, and fluid leakage in the system. The pressure relief valve 51 is installed on the pipeline or coolant tank 33 of the liquid cooling circulation unit and has a pre-compressed spring mechanism inside. When the internal pressure of the circulation pipeline exceeds the preset opening pressure of the valve (e.g., 0.8 MPa) due to the thermal expansion of the coolant or air resistance, the valve core opens under the action of pressure difference, overcoming the spring force, and automatically releases part of the fluid or gas until the pressure drops below the closing pressure. The valve then automatically resets, thereby preventing the pipeline or container from rupturing due to overpressure.

[0079] The temperature fuse 52 is a one-time overheat protection element connected in series in the power supply circuit of the electric heating unit (such as the PTC heater 11). The fuse is made of an alloy material with a specific melting point. When the electric heating unit or its control malfunctions, causing the temperature of the protected point to rise abnormally and exceed the fuse's set melting temperature (e.g., 55°C), the fuse will physically melt, permanently cutting off the power supply to the electric heating unit and fundamentally eliminating the overheating hazard that may result from continuous heating.

[0080] In one embodiment, the liquid cooling pipeline 31 is a serpentine metal pipe made of 304 stainless steel.

[0081] In one embodiment, the phase change thermal storage unit is a honeycomb structure wrapped around the liquid cooling pipeline 31.

[0082] The honeycomb structure provides a significantly larger internal surface area than a solid block, allowing the phase change material 21 filling it to exchange heat with the walls of the liquid cooling pipes 31 and the structural skeleton through a thinner layer. This significantly shortens the heat transfer path and greatly improves the response speed of heat storage and release. The metal honeycomb skeleton itself constitutes a highly efficient three-dimensional heat conduction network, which can quickly and evenly transfer the heat absorbed from the liquid cooling pipes 31 to the phase change material 21 in all the channels, or rapidly collect the heat released by the phase change material 21 to the liquid cooling pipes 31, effectively avoiding local hot or cold spots caused by the poor thermal conductivity of the phase change material 21.

[0083] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A low-temperature temperature control system for lithium battery packs based on the cooperation of electric heating and phase change heat storage, characterized in that, The application relates to a battery thermal management system, comprising: an electric heating unit; a phase change heat storage unit filled with a phase change material (21); a liquid cooling circulation unit comprising a liquid cooling pipeline (31) and a driving pump (32), the liquid cooling pipeline (31) being arranged in the phase change heat storage unit and used for contacting a battery (6); a mode switching unit comprising a manual three-way valve (41) arranged on the liquid cooling pipeline (31); and a heat preservation unit at least partially covering the battery (6), the phase change heat storage unit and the liquid cooling pipeline (31); wherein by operating the manual three-way valve (41), the flow path of the liquid cooling circulation unit can be switched to realize preheating of the battery (6) through the electric heating unit, or heat preservation or heat dissipation of the battery (6) through the phase change heat storage unit.

2. The low-temperature temperature control system for lithium battery pack based on electric heating and phase change heat storage cooperation according to claim 1, characterized in that, The phase change material (21) is a composite material of paraffin and expanded graphite, wherein the mass percentage of the expanded graphite is 18-22%.

3. The low-temperature temperature control system for lithium battery pack based on electric heating and phase change heat storage cooperation according to claim 2, characterized in that, The phase change temperature of the paraffin is 20 DEG C.

4. The low-temperature temperature control system for lithium battery pack based on electric heating and phase change heat storage cooperation of claim 1, characterized in that, The manual three-way valve (41) has a preheating gear, a heat preservation gear and a heat dissipation gear; when in the preheating gear, the liquid cooling pipeline (31) connects the electric heating unit and the phase change heat storage unit; when in the heat preservation gear, the electric heating unit is cut off, and the liquid cooling pipeline (31) forms a circulation between the battery (6) and the phase change heat storage unit; when in the heat dissipation gear, the liquid cooling pipeline (31) guides the heat absorbed by the battery (6) to the phase change heat storage unit.

5. The low-temperature temperature control system for lithium battery pack based on electric heating and phase change heat storage cooperation of claim 1, characterized in that, The mode switching unit further comprises a temperature indicator (42) attached to the surface of the battery (6), the temperature indicator (42) indicating the temperature interval through color based on the bimetallic strip temperature measurement principle.

6. The low-temperature temperature control system for lithium battery pack based on electric heating and phase change heat storage cooperation of claim 1, characterized in that, The heat preservation unit comprises an aluminum foil reflection layer and a polyurethane foaming layer arranged in sequence from inside to outside.

7. The low-temperature temperature control system for lithium battery pack based on electric heating and phase change heat storage cooperation of claim 1, characterized in that, The electric heating unit comprises a PTC heater (11) and a temperature self-limiting controller (12) electrically connected with the PTC heater (11), the temperature self-limiting controller (12) being configured to reduce the heating power of the PTC heater (11) when detecting that the heating target temperature reaches a preset value.

8. The low-temperature temperature control system for lithium battery pack based on electric heating and phase change heat storage cooperation of claim 1, characterized in that, The application further comprises a safety protection unit, the safety protection unit comprising a pressure relief valve (51) arranged on the liquid cooling circulation unit and a temperature fuse (52) connected in series with the electric heating unit circuit.

9. The low-temperature temperature control system for lithium battery pack based on electric heating and phase change heat storage cooperation of claim 1, characterized in that, The liquid cooling pipeline (31) is a metal pipeline arranged in a snake shape and made of 304 stainless steel.

10. The low-temperature temperature control system for lithium battery pack based on electric heating and phase change heat storage cooperation of claim 1, characterized in that, The phase change heat storage unit is a honeycomb structure wrapped outside the liquid cooling pipeline (31).

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