Micro-channel thermosyphon self-circulation high fault-tolerant power battery thermal management system and low-cost mass production process

Abstract

This invention discloses a microchannel thermosiphon self-circulating high-fault-tolerant power battery thermal management system and process, aiming to solve the technical problems of existing fully immersed liquid cooling systems, such as high pressure and explosion susceptibility, high thermal resistance, reliance on software-based power locking, and low mass production fault tolerance. During the cell stacking or winding process, the system simultaneously embeds a micron-level microtube array in the gaps between the electrodes, constructing a physical-level heat dissipation channel directly reaching the core of the cell. The system utilizes the density difference between hot and cold fluids to generate thermosiphon power, eliminating the need for high-power water pumps. Combined with the expansion tank's air chamber buffer and the porous medium's capillary water-locking mechanism, it can maintain a gas-liquid two-phase microcirculation within the cell even when external pipelines rupture and lose pressure. This enables vehicles equipped with this system to achieve short-term limp-out evacuation at speeds of 80–100 km / h under moderate loads. In addition, the total volume of microchannels accounts for less than 1%, which has a minimal impact on the energy density of the battery cell. The microtube material has excellent electrochemical stability and flexible deformation capability, which can be seamlessly integrated into the existing pouch / hard-shell battery cell stacking and winding process, freeing it from dependence on precision water cooling system, adapting to the domestic extensive mass production environment, and achieving a balance between safety, energy consumption and manufacturing cost.

Description

Technical Field

[0001] This invention relates to the field of thermal management and electrochemical energy storage safety technology for power batteries in new energy vehicles, and particularly to a cell-embedded heat dissipation system based on thermosiphon effect and capillary water-locking mechanism, and its low-cost mass production process. This invention is applicable to pure electric passenger vehicles, commercial new energy vehicles, and stationary energy storage power stations, aiming to provide a power battery thermal management solution with zero energy consumption, high fault tolerance, intrinsic safety, and no reliance on software-based power-locking strategies. Background Technology

[0002] Lithium-ion batteries have become the mainstream energy storage medium for new energy vehicles and energy storage power stations due to their high energy density, long cycle life, and excellent rate performance. However, the charging and discharging process of lithium batteries is accompanied by significant Joule heating and reaction heat. Under high temperature, fast charging, and high rate conditions, heat is easily accumulated inside the cell, causing excessive temperature difference, hot spots, capacity decay, bulging, and even thermal runaway chain reactions. Thermal management has become a core bottleneck restricting the safety and lifespan of the industry. Existing power battery cooling solutions mainly include three types: air cooling, traditional contact liquid cooling, and fully immersed closed liquid cooling, all of which have significant technical defects: Fully immersed closed liquid cooling: The battery cells are completely immersed in insulating coolant. Although the heat transfer coefficient is high, the closed pressure accumulation characteristic introduces a fatal safety hazard. Gas generation from the battery cells, electrolyte evaporation, and thermal runaway byproducts accumulate in the closed cavity, forming a high-pressure explosion source. A collision with the internal high pressure can easily cause the battery pack to rupture and the entire vehicle to explode, seriously threatening the safety of passengers. This is a dangerous structure that is not suitable for commercial use. Traditional contact liquid cooling uses an external liquid cooling plate and a high-power water pump for forced circulation. This results in a long heat exchange path, high thermal resistance, and delayed heat removal from the core of the battery cell, creating a false sense of safety due to "external cooling and internal heating." The high-power water pump also has high parasitic power consumption, drawing energy from the power battery and exacerbating cell polarization heating, creating a positive feedback loop of "the more heat is dissipated, the more heat is generated," thus increasing the risk of thermal runaway. Air cooling has low heat dissipation efficiency, only acts on the surface of the battery cell and cannot reach the core heat source, making it difficult to meet the fast charging and high power requirements of modern electric vehicles. At the same time, the industry suffers from multiple systemic pain points: Distorted safety logic: Automakers tend to cut costs and bear the burden of compensation for low-probability accidents, rather than investing in highly redundant safety designs, forming a "cost-luck" mentality and ignoring safety throughout the entire life cycle. Mass production adaptation conflict: Domestic production lines generally have common defects such as pipe burrs, large assembly tolerances, and uneven fastener torque. The traditional "zero-tolerance" design of precision water cooling system is seriously mismatched with the reality of extensive mass production, resulting in low yield and reliability. Software dependency risk: Since 2026, OTA power-locking incidents have occurred frequently. Automakers use BMS software to limit charging and discharging power and range in order to cover up hardware safety defects, harming user rights, and cannot replace physical-level heat dissipation protection in accident conditions. In summary, existing technologies cannot simultaneously address safety, energy consumption, mass production feasibility, and user rights. There is an urgent need for a power battery thermal management solution that is inherently safe at the physical level, has zero parasitic power consumption, high fault tolerance, and does not require software-based power locking. Summary of the Invention

[0003] The technical problem to be solved by the present invention This invention aims to overcome the following shortcomings of the prior art: Thermal runaway protection failure: Risk of high-pressure explosion in fully immersed liquid cooling; high thermal resistance of traditional liquid cooling; external cooling and internal heating. Paradox of paradoxical power consumption: Water pumps consume electricity and generate heat, exacerbating the temperature rise of battery cells; The industry's security logic has become distorted: relying on software to lock power and harming user rights; Poor mass production adaptability: The precision design is mismatched with the rough mass production environment; Poor survivability under extreme conditions: After a failure, it loses its heat dissipation capacity and has no escape route. The core technical solution of this invention To achieve the above objectives, this invention provides a high-fault-tolerant power battery thermal management system with in-cell microchannel thermosiphon self-circulation, comprising a cell body, an embedded microchannel array, a voltage-stabilizing buffer current collector structure, a dual power circulation loop, and a packaging structure, as detailed below: Embedded microchannel array During the cell stacking or winding process, multiple longitudinal microtubes are pre-embedded simultaneously, preferably nine in a 3×3 matrix arrangement. The microtubes are made of polyimide, PP / PE composite material, or thin-walled stainless steel, with an inner diameter of 50–200 μm. The interior of the microtubes is filled with a hydrophilic porous medium with a porosity of 80%–95%, providing capillary suction functionality. The microtubes are implanted along the gaps between electrodes or between the separator layers, preferentially occupying the inherent gap space inside the cell. The cross-sectional area of ​​a single microtube is 0.002–0.03 mm², and the total cross-sectional area of ​​the nine microtubes is 0.018–0.28 mm², accounting for a volume fraction far less than 1%, thus having a controllable impact on the cell's energy density. Voltage stabilizing buffer current collection structure The battery cell has an upper cover and upper expansion tank at the top, and a lower cover and lower expansion tank at the bottom. Both expansion tanks have a reserved gas cavity of at least 30% for pressure stabilization, venting, and absorbing the thermal expansion of the coolant. An upper connecting pipe connects the upper end of the microtube to the upper expansion tank, and a lower connecting pipe connects the lower end of the microtube to the lower expansion tank. The system's rated internal pressure is ≤500Pa to eliminate the risk of high-pressure explosion. An vent valve is located at the top of the upper expansion tank to release air from the circuit. Dual-power circulation loop The system forms a closed loop by connecting the upper and lower expansion tanks through a circulation pipe. It utilizes the thermosiphon effect as the primary driving force, supplemented by a 10–100mW micro auxiliary water pump. This micro pump is located in the main inlet pipe or the lower expansion tank, activating in extremely cold conditions (<-20℃) or high-temperature, high-rate conditions, and otherwise operating in sleep mode with zero power consumption. Multiple battery cells are fluidly connected through a secondary connecting pipe. The main outlet pipe and main inlet pipe are connected in parallel or series at the module level. Parallel connection is suitable for high-power fast charging, while series connection is suitable for space-constrained scenarios. Three-state adaptive operation logic High-voltage operation: When the external pressure increases, the 9 tubes are connected in parallel to divert the flow, and the expansion tank air chamber absorbs the impact energy to maintain the internal low-pressure steady state and protect the battery cell from deformation. Low-pressure operation: When the thermosiphon power is insufficient, the micro water pump intervenes to supplement the pressure, maintain stable flow, and prevent local boiling; Zero-pressure / damage conditions: When there is external pressure loss or coolant leakage, the porous medium capillary water retention maintains the microcirculation inside the core and delays thermal runaway. Packaging structure The cell is coated with a 45℃ paraffin-based PCM phase change material layer to aid in temperature uniformity and heat dissipation; the end caps, terminals and pipe interfaces are encapsulated with thermally conductive epoxy potting compound to form a sealed insulation layer. The process is compatible with existing soft-pack / hard-shell cell production lines and does not require additional high-cost equipment. Engineering Principles and Boundary Conditions Microchannels and energy density, material compatibility The microtubes are implanted at a low micrometer-scale proportion, preferentially occupying the electrode gaps, with energy density loss controlled within 2%, making them engineering-friendly. The microtubes are made of chemically stable materials suitable for lithium-ion batteries, exhibiting a swelling rate of <3% and metal ion deposition <ppm level under long-term immersion in carbonate electrolyte at 60℃. The interface employs triple redundancy: capillary seal + structural seal + adhesive seal, buffering interface stress under temperature cycling from -40℃ to 85℃ to reduce the risk of debonding and leakage. The microtubes are flexibly constrained within the stack, deforming synchronously with the cell's charging and discharging deformation, avoiding rigid stress concentration. The porous medium resists detachment and collapse. Actual lifespan needs to be verified based on cell formulation, operating conditions, and cycle count. This invention does not exclude the possibility of localized aging or leakage under extreme abnormal operating conditions. Microchannel flow resistance, clogging and capillary water retention durability The microchannels feature large pore sizes (50–200 μm), short flow channels, and a parallel flow distribution structure, resulting in low Reynolds numbers, laminar flow stability, and reduced sedimentation. Nine parallel channels amplify the flow cross-sectional area, and the main channel exhibits strong self-cleaning properties. The porous medium, with an 80%–95% porosity interconnected network, enables capillary transport and impurity filtration and classification. Small particles pass through with the liquid flow, while larger particles are retained on the surface, reducing the risk of deep clogging. However, gradual clogging may still occur under long-term high-impurity conditions (severe lithium plating, electrolyte deterioration), requiring optimization through filtration and maintenance strategies. Capillary water retention is determined by the Laplace equation. After hydrophilic treatment of the medium, the contact angle θ < 30°, spontaneous wetting occurs, and the capillary rise height is greater than the cell height. Microchannels and porous media form a continuous capillary network. In the event of external pressure loss / leakage, residual liquid is locked in the porous framework, maintaining the microcirculation liquid film within the cell. The coolant is preferably a low surface tension, high boiling point, and low volatility system to reduce the evaporation and depletion rate. The capillary water retention capability depends on the hydrophilicity of the medium, the coolant formulation, temperature, and the amount of residual liquid. This invention provides a short-term (minutes to tens of minutes) physical mechanism for microcirculation within the cell, but does not guarantee permanent water retention for unlimited duration or under arbitrary leakage. Thermosiphon drive force is suitable for high magnification, high altitude and extremely cold conditions. Thermosiphon head formula: ΔP t =(ρ_c−ρ_h)gh, where ρ_c is the density at the cold end, ρ_h is the density at the hot end, g is the acceleration due to gravity, and h is the height difference between the cold and hot ends. Under 1°C operating conditions, the temperature rise is 5–8 K, Δρ≈15 kg / m³, h≈0.2 m, ΔP t ≈14.7Pa, capable of driving a basic cycle; temperature rise of 15–25K under 3C–4C fast charging conditions, Δρ can reach 40–70kg / m³, ΔP t The driving force can reach 40–140 Pa, significantly improving performance. For high-height cells (h=0.3–0.4m), the driving force increases linearly with h, which is more conducive to thermosiphoning. In extremely cold conditions (<-20℃), the coolant viscosity increases and the density difference decreases, resulting in insufficient pure thermosiphoning power. A micro-pump is forced to start to provide initial flow. After the cell generates heat and establishes a temperature difference, it automatically switches to thermosiphoning as the dominant force and the pump goes into sleep mode. The thermosiphoning capacity is affected by the scaling factor, temperature rise, height, and viscosity. This invention provides sufficient driving force under normal and high-scaling conditions, while relying on an auxiliary pump for compensation in extremely cold conditions. It is an engineering-feasible adaptive driving solution. Mechanism and Boundaries of Zero External Pressure Limping Capability After zero external pressure / external pipe rupture, the system enters a capillary self-sustaining microcirculation mode: the porous medium capillary water-locking retains the thin liquid film inside the core and the connecting liquid channels. The heat generated by the battery cell causes the liquid film inside the microchannel to evaporate. The vapor rises to the top water tank, condenses, and flows back along the wall, forming a local gas-liquid two-phase microcirculation. This continuously removes heat from the hot spots inside the core, delaying thermal runaway and controlling the rate of temperature rise. Under medium load (1 / 3 to 1 / 2 rated power), ambient temperature <45℃, and no serious internal short circuit, simulation and principle analysis show that the system has the potential to maintain heat dissipation for a short time and support limp-out at medium speeds (approximately 80–100 km / h). The actual duration, upper speed limit, and operating condition boundaries need to be confirmed through bench and vehicle tests in conjunction with battery cell parameters, coolant formulation, leakage degree, and environmental conditions. This invention does not constitute an absolute guarantee of limp-out capability under any fault scenario. Beneficial effects Compared with the prior art, the present invention has the following beneficial effects: Physical-grade thermal safety and high-voltage immunity: Microchannels within the battery cell are directly connected to the core heat source, eliminating the thermal resistance of traditional liquid cooling; Low-voltage stabilization design prevents high-voltage explosion, ensuring inherent safety. Breaking the paradox of zero parasitic power consumption and energy consumption: driven primarily by thermosiphon, the micro water pump consumes only 10–100mW, eliminating the pump heat feedback cycle and indirectly improving battery life; High tolerance for mass production: The low-pressure, high-flow characteristics accommodate defects such as pipe burrs, assembly tolerances, and inferior parts, making it suitable for the domestic low-cost manufacturing environment. No software power-locking requirement: The physical structure ensures inherent safety, eliminates the need for BMS to limit performance, prevents power-locking disputes, and protects user rights; Strong survivability under fault conditions: It maintains microcirculation within the core during car accidents and coolant leaks, and has the potential for short-term limp evacuation, transforming safety from probabilistic assurance to physical assurance. Low cost and easy maintenance: Standard parts design, simple process, no high-speed rotating parts, low operation and maintenance costs, and damaged parts can be quickly replaced. Engineering Boundaries and Verification Specifications The description of the structure and effects of this invention is based on principle analysis and well-known principles, including fluid mechanics, thermosiphon, capillary action, phase change heat transfer, low-pressure stabilization and the basic theory of two-phase flow. It can be understood and implemented by those skilled in the art without relying on specific experimental data. The thermosiphon driving force, capillary water-locking ability, microchannel flow characteristics, low-pressure stabilization mechanism, and PCM temperature equalization mechanism involved in this invention are all publicly disclosed and mature known principles. The core of this invention lies in structural innovation and system combination, which integrates known physical effects in the microscale space inside the battery cell to form a thermal management architecture with high fault tolerance, self-circulation and intrinsic safety. Actual performance (energy density loss, long-term reliability, clogging cycle, capillary durability, limp time, etc.) is affected by a combination of factors such as cell formulation, size, rate, temperature, coolant system, manufacturing tolerance, and impurity level. Before industrialization, it is necessary to conduct special bench tests for specific cell specifications and vehicle operating conditions, including cycle, temperature, vibration, leakage and thermal runaway triggering tests, to determine the optimal parameter range and safety boundaries. This invention discloses the core structure, mechanism and design principles, aiming to reduce software power-lock dependence and improve physical safety fault tolerance, but is not an absolute commitment to no faults, no degradation and no risks under all operating conditions. Attached Figure Description

[0004] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort. Figure 1 is a schematic diagram of the overall structure of the three sets of batteries in parallel in an embodiment of the present invention; it shows the overall connection layout of the battery cell (1) with the top collecting pipe (2), bottom collecting pipe (3), side return pipe (4), main outlet pipe (5) and main inlet pipe (6) in the parallel topology. Figure 2 is a three-dimensional top view of a single battery cell; it shows the overall outline of the battery cell (1), the packaging form of the top manifold (2), and the layout structure of the external pipeline. Figure 3 shows the internal structure of the battery cell after the outer casing has been removed; it shows the internal layout and spatial orientation of the top manifold (14), the main outlet pipe (15), the upper end hole of the microtube (16), the lateral return pipe (17), and the battery cell body (18). Figure 4 is a bottom view of the battery cell; it shows the bottom layout structure of the bottom manifold (14), inflow interface (15), microtube lower end hole (161), micro water pump (171) and battery cell body (18). Figure 5 is a schematic diagram of the longitudinal cross-sectional structure of the battery cell; it shows the embedded relationship between the stacked battery cell (11) and the nine longitudinal microtubes (14), highlighting the connection path and axial depth between the longitudinal microtubes (14) and the bottom manifold (141). Figure 6 is a schematic diagram of the transverse cross-sectional structure of the battery cell; it clearly shows the cross-sectional arrangement and spatial relationship of the three longitudinal microtubes (14) inside the stacked battery cell (11). Figure 7 is a schematic diagram of the overall structure of the three sets of batteries in series in an embodiment of the present invention; it shows the series circuit structure formed by the battery cell (1) being connected end to end through the top collector tube (2) and the bottom collector tube (3) in series topology. Figure 8 is a cross-sectional view of the series mode; it shows the internal coordination structure and fluid communication path of the cell, longitudinal microtube, and upper and lower manifold in the series mode. Detailed Implementation

[0005] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Example 1: Fabrication of battery cell and embedded microchannel array This embodiment provides a single cell structure fabricated using a stacking process. During the sequential stacking of the positive electrode, negative electrode, and separator, nine longitudinal microtubes are simultaneously embedded, arranged in a 3×3 matrix within the gaps between the cell stacks. The microtubes are made of thin-walled polyimide (PI) tubing with an inner diameter of 50–200 μm, preferably 100 μm. The tubing is filled with hydrophilic polyurethane foam as a porous medium, with a porosity controlled at 80%–95%, preferably 90%. The microtubes penetrate the entire stack along the cell height, preferentially occupying the inherent gaps between the electrodes and separator within the cell, without encroaching on the space of the active material. The overall cell thickness increase is ≤2%, and the impact on energy density is controllable. The cell is externally coated with a 45℃ paraffin-based PCM phase change material layer for auxiliary temperature uniformity and heat dissipation. Example 2: Assembly of voltage stabilizing and buffering current collector structure The top of the battery cell is equipped with an upper cover and an upper expansion tank, and the bottom is equipped with a lower cover and a lower expansion tank. The upper and lower expansion tanks have a gas cavity of no less than 30%, preferably 35%, which is used to absorb the volume of the coolant when heated, buffer pressure pulsation, and discharge air in the circuit. The upper connecting pipe connects the upper end of the microtube to the upper expansion tank, and the lower connecting pipe connects the lower end of the microtube to the lower expansion tank; a manual or automatic air vent valve is installed on the top of the upper expansion tank. After assembly, the overall rated internal pressure of the system is controlled within 500Pa to avoid the risk of high-pressure explosion, forming a low-pressure stabilizing structure. Example 3: Module serial-parallel integration A battery module is formed by three of the above-mentioned cells, and the topology can be either parallel or series, depending on the requirements of the vehicle. Parallel mode (corresponding to Figure 1): The main inlet pipe is connected to the lower connecting pipe of each cell through the secondary connecting pipe, and the main outlet pipe is connected to the upper connecting pipe of each cell through the secondary connecting pipe; the coolant is evenly distributed to the microchannels of each cell, which is suitable for high-power fast charging scenarios and improves heat dissipation uniformity. Series mode (corresponding to Figures 7 and 8): The main outlet pipe of the first cell is connected to the main inlet pipe of the second cell, and the two are connected end to end in sequence. The coolant flows through the microchannels of each cell in a series circuit, which is suitable for scenarios with limited space and low flow and high heat dissipation requirements. Example 4: Construction of a Dual-Power Circulation System The system forms a closed loop with upper and lower expansion tanks and circulation pipelines, and adopts a dual-power drive scheme with thermosiphon self-circulation as the main method and micro water pump as the auxiliary method. Thermosiphon Drive: Based on the principle of fluid density difference, the heat generated during the charging and discharging of the battery cell raises the temperature and decreases the density of the coolant in the microchannel, causing it to flow upwards. After being cooled by the top water tank, the density increases, and it flows downwards along the loop, forming a natural circulation. Under 1C discharge conditions, the density difference between the hot and cold ends is ≥15kg / m³, and the driving pressure head is ≥14.7Pa, allowing for stable circulation without a water pump. Under 3C–4C high-rate fast charging conditions, the density difference between the hot and cold ends can reach 40–70kg / m³, and the driving pressure head can reach 40–140Pa, significantly enhancing the driving force. Miniature water pump assistance: A 10–100mW miniature DC water pump, preferably 3V / 50mW, is installed at the main inlet pipe or lower expansion tank. In extremely cold conditions (ambient temperature < -20℃), the coolant viscosity increases and the thermosiphon power is insufficient. The miniature water pump starts to provide initial circulation power. After the battery cells generate heat and establish a stable temperature difference, the water pump automatically goes into sleep mode and returns to the thermosiphon self-circulation mode, reducing parasitic power consumption. The coolant is a mixture of deionized water and ethylene glycol, which takes into account the characteristics of low freezing point, low volatility, and high boiling point, and is suitable for wide temperature range operation. Example 5: Three-state adaptive operation control The system of this invention has the ability to adaptively adjust to three working conditions: high pressure, low pressure, and zero pressure / damage. It does not require additional complex control strategies and responds automatically by relying on physical mechanisms. High-voltage operation: When the external circuit pressure increases, the nine microtubes are connected in parallel to divert the flow and reduce the flow rate of a single tube; the gas cavity in the expansion tank absorbs the pressure shock and maintains the low-pressure steady state inside the microchannel, avoiding cell deformation and diaphragm damage due to pressure. Low-pressure operation: When the system pressure is low and the thermosiphon power is insufficient, the micro water pump automatically intervenes to replenish the pressure, maintain a stable flow rate of coolant, and prevent local boiling and air blockage in the microchannel. Zero-pressure / Breakage Condition: In the event of a vehicle accident, external pipeline rupture, or coolant leakage, the external pressure drops to zero. The porous medium within the microchannels, relying on capillary action, locks residual coolant within the pore network, maintaining a two-phase gas-liquid microcirculation within the core. This continuously removes heat from the cell's hot spots, delaying thermal runaway. Under moderate load (1 / 3 to 1 / 2 rated power), ambient temperature <45℃, and without severe internal short circuits, the system can maintain heat dissipation for a short period, supporting the vehicle's limp-away to a safe area at 80–100 km / h. Actual duration and maximum vehicle speed need to be verified through testing under specific operating conditions. Example 6: Packaging and Mass Production Process After the battery cell is assembled, thermally conductive epoxy potting compound is used to encapsulate the end caps, terminals, microtube interfaces, and pipeline connections to form a sealed insulation layer, thereby achieving structural reinforcement, insulation protection, and enhanced interface thermal conductivity. The microtube pre-embedding process is fully compatible with existing soft-pack / rigid-shell cell stacking and winding processes, requiring no additional high-precision equipment. The overall assembly and potting process can be seamlessly integrated with existing power battery production lines, resulting in high yield and controllable manufacturing costs. After encapsulation, the cells undergo temperature cycling, vibration, leakage, and insulation tests to meet the reliability requirements for automotive environments. The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A microchannel thermosiphon self-circulating high-fault-tolerant power battery thermal management system, characterized in that, include: The battery cell body is fabricated using a stacked or wound structure. An embedded microchannel array is pre-embedded inside the cell during fabrication, comprising multiple longitudinal microtubes, preferably nine arranged in a 3×3 matrix. The microtubes are filled with a hydrophilic porous medium and are arranged along the electrode gaps or diaphragm layers. The inner diameter of a single microtube is 50–200 μm, and the total flow cross-sectional area accounts for less than 1% of the usable internal space of the cell. A voltage-stabilizing and buffering current-collecting structure includes an upper expansion tank at the top of the cell and a lower expansion tank at the bottom. Both expansion tanks have a reserved gas cavity of no less than 30%, and the system's rated internal pressure is ≤500 Pa. A dual-power circulation loop connects the upper and lower expansion tanks through a circulation pipe to form a closed flow path, using thermosiphon effect as the main driving force, and is equipped with a micro auxiliary water pump with a power consumption of 10–100 mW. The encapsulation structure provides sealing and insulation for the cell end caps, terminals, and pipe interfaces.

2. The system according to claim 1, characterized in that, The number of microtubes is 2–16, arranged in a matrix, ring, or staggered pattern; the porosity of the porous medium is 80%–95%, and after hydrophilization treatment, the contact angle θ < 30°, and the capillary rise height is greater than or equal to the cell height, so as to achieve water retention by relying on Laplace capillary force when the external pressure is lost.

3. The system according to claim 1, characterized in that, The upper expansion tank is equipped with an exhaust valve at the top. The upper and lower expansion tanks together form a pressure buffer and coolant thermal expansion absorption space. When the external pressure increases, the impact energy is absorbed by the air chamber compression, maintaining a low-pressure steady state inside the microchannel and preventing the battery cell from being deformed by force.

4. The system according to claim 1, characterized in that, The dual-power circulation loop achieves a fluid density difference Δρ ≥ 15 kg / m³ between the hot and cold ends under 1C discharge conditions, and a thermosiphon drive pressure head ΔPt ≥ 14.7 Pa. Under 3C–4C fast charging conditions, Δρ can reach 40–70 kg / m³, and ΔPt can reach 40–140 Pa, realizing pump-free self-circulation. Under extremely cold conditions, the initial flow rate is provided by a micro auxiliary water pump, and the flow rate switches back to the thermosiphon-dominated mode after the temperature difference is established.

5. The system according to claim 1, characterized in that, The dual-power circulation loop has a three-state adaptive operation logic: under high pressure, the microtubes are connected in parallel to divert the flow, and the expansion chamber absorbs pressure pulsation; under low pressure, the micro auxiliary water pump automatically intervenes to replenish pressure and prevent local boiling; under zero pressure or damage conditions, the porous medium locks in water to maintain the gas-liquid two-phase microcirculation in the core.

6. The system according to claim 5, characterized in that, The microcirculation within the core under zero-pressure or damaged conditions provides a physical basis for vehicles equipped with this system to limp away at a speed of 80–100 km / h for a short time after external pipeline failure, under moderate load, ambient temperature below 45°C, and without serious internal short circuits.

7. The system according to claim 1, characterized in that, The encapsulation structure also includes a 45°C paraffin-based PCM phase change material layer covering the outside of the cell; the interface between the microtube and the cell adopts a triple redundant sealing structure of "capillary seal + structural seal + adhesive seal"; the swelling rate of the microtube material after long-term immersion in carbonate electrolyte at 60°C is <3%, and the concentration of metal ion precipitation is <ppm level; the microtube is flexibly constrained by the electrode and the separator inside the cell, and can deform synchronously with the thickness change during the charging and discharging process of the cell.

8. The system according to claim 1, characterized in that, Multiple battery cells are integrated at the module level through secondary connecting pipes: In parallel mode, the main inlet pipes are connected to the lower connecting pipes of each battery cell, and the main outlet pipes are connected to the upper connecting pipes of each battery cell, which is suitable for high-power fast charging scenarios; in series mode, each battery cell is connected end to end to form a step-by-step flow loop, which is suitable for space-constrained scenarios.

9. The system according to claim 1, characterized in that, The coolant is a mixture of deionized water and ethylene glycol with low surface tension, high boiling point, and low volatility. It maintains stable physical properties in a temperature range of -20℃ to 85℃ and flows in a laminar flow state within the microchannel, exhibiting a self-cleaning effect.

10. A low-cost mass production process for a microchannel thermal management system within a battery cell, applicable to the system described in any one of claims 1 to 9, characterized in that, The process includes the following steps: S1, pre-embedding microtubes during the cell stacking or winding process to form an embedded microchannel array; S2, assembling upper and lower expansion tanks and connecting pipes, reserving a gas cavity of no less than 30%; S3, performing thermally conductive epoxy potting on the entire cell to complete the sealing and insulation of the end caps, terminals, and pipe interfaces; S4, integrating multiple cells in parallel or series topology to complete liquid injection and venting; S5, conducting temperature cycling, vibration, leakage, and insulation tests on the finished product to meet the reliability requirements of automotive environments.

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