A sodium-lithium mixed use starting battery with parallel connection of cells and a vehicle using the same

Abstract

The application discloses a sodium-lithium mixed use starting battery with parallel connection of electric cores and a vehicle using the battery, and belongs to the technical field of vehicle starting power sources. The starting battery comprises a battery module, wherein the battery module is formed by at least one series of mixed units connected in series; each series of the mixed units is composed of a sodium ion electric core and a lithium iron phosphate electric core; and in each series of the mixed units, the sodium ion electric core and the lithium iron phosphate electric core are connected in parallel. The starting battery can reliably start the vehicle under a low-temperature cold state and after long-time parking.

Description

Technical Field

[0001] This invention belongs to the field of vehicle starting power technology, specifically relating to a sodium-lithium hybrid starting battery with parallel cells that can reliably start in low-temperature conditions and after the vehicle has been parked for a long time, and a vehicle using the battery. Background Technology

[0002] In modern transportation, vehicle starting power supplies are an indispensable core component for internal combustion engine and hybrid vehicles. Currently, mainstream starting battery technologies mainly include lead-acid batteries and single-system lithium-ion batteries (such as lithium iron phosphate batteries). With the development of new energy vehicle technology, sodium-ion batteries, which have advantages in low-temperature performance, are also gradually entering this field.

[0003] However, all of the above-mentioned single-system batteries have insurmountable drawbacks in practical applications:

[0004] For lead-acid batteries and lithium iron phosphate batteries alone: ​​While lead-acid batteries are inexpensive, they suffer from low volumetric energy density, short cycle life, and poor low-temperature performance. Although lithium iron phosphate batteries are stable at room temperature, at low temperatures, their electrolyte viscosity increases, the lithium-ion migration rate slows down, leading to a sharp increase in internal resistance and a significant decrease in discharge power, making it impossible to drive the starter motor. Furthermore, lithium iron phosphate batteries are highly sensitive to thermal runaway; prolonged operation in the high-temperature environment of the engine compartment (80-90℃) accelerates aging, posing a safety hazard.

[0005] For sodium-ion batteries alone: ​​Sodium-ion batteries are considered a strong alternative to lead-acid batteries due to their abundant sodium reserves, excellent low-temperature performance (operating normally at -40℃), and high safety. However, the energy density (especially volumetric energy density) of sodium-ion batteries is inherently lower than that of lithium-ion batteries. For starting batteries, although their energy density is sufficient for starting requirements, their high self-discharge rate makes them prone to depletion after prolonged parking, leading to starting failures.

[0006] In summary, providing a startup battery solution that can simultaneously achieve low-temperature startup capability and long-term storage performance is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0007] The technical solution of this invention is based on the problem that vehicles are difficult to start at low temperatures and difficult to start after long-term parking.

[0008] The specific technical solution is explained below:

[0009] A sodium-lithium hybrid starting battery with cells connected in parallel, comprising:

[0010] A battery module, the battery module comprising at least one string of hybrid units;

[0011] Each of the aforementioned hybrid units consists of sodium-ion batteries and lithium iron phosphate batteries;

[0012] In each of the aforementioned hybrid units, sodium-ion batteries and lithium iron phosphate batteries are connected in parallel.

[0013] In a further embodiment, the ratio of sodium-ion cells to lithium iron phosphate cells in each string of hybrid units is 2:1.

[0014] In a further embodiment, each of the aforementioned hybrid units consists of two sodium-ion batteries and one lithium iron phosphate battery.

[0015] In a further embodiment, the positive electrode active material of the sodium ion battery cell is a Prussian blue-based compound.

[0016] In a further embodiment, a battery management system is also included, the battery management system being configured as follows:

[0017] The operating voltage range of the battery module is limited to 2.0V to 3.65V.

[0018] In a further embodiment, during charging, when the voltage of any string of hybrid units reaches the equalization threshold, the battery management system is configured to transfer the excess energy of the string of hybrid units to the hybrid units with lower voltage, until all strings of hybrid units reach a fully charged state.

[0019] In a further embodiment, in each of the hybrid units, the equivalent DC internal resistance of two sodium-ion cells connected in parallel is less than the DC internal resistance of one lithium iron phosphate cell.

[0020] In a further embodiment, at room temperature, the self-discharge rate of the lithium iron phosphate cell is <1% / month.

[0021] In a further embodiment, the total capacity of the battery module is ≥44Ah.

[0022] A vehicle comprising a starting battery as described in any of the above embodiments, the starting battery being installed in an engine compartment.

[0023] In summary, the technical solution described in this invention has the following main beneficial effects:

[0024] Compared with existing technologies, the technical solution of this invention greatly reduces the failure rate of vehicles after long-term parking, and ensures that the vehicle still has sufficient starting power after three months of parking. The failure rate of vehicles after parking is significantly lower than that of pure sodium battery solutions.

[0025] Furthermore, the technical solution of the present invention utilizes the excellent low-temperature discharge performance of Prussian blue sodium electricity and the Joule heat generated during discharge to achieve reliable starting in extremely cold environments, and can still successfully start a 3.0L displacement engine in an environment of -30℃.

[0026] Furthermore, within the same size, the total capacity of the technical solution of the present invention is improved compared with the pure sodium-electric solution, providing more margin for vehicle electronic devices.

[0027] Furthermore, the technical solution of the present invention significantly simplifies the system structure, reduces costs, and improves reliability.

[0028] Further or more detailed beneficial effects will be described in conjunction with specific embodiments in the detailed implementation. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the internal structure of the battery module in a specific implementation.

[0030] Figure label:

[0031] 1: Sodium-ion battery cell; 2: Lithium iron phosphate battery cell. Detailed Implementation

[0032] The present invention will be further explained in conjunction with the embodiments:

[0033] The core technical problem faced by the technical solution of this application's embodiments stems from the inventor's accurate understanding of the prior art. Therefore, how to overcome the defects of sodium-ion battery cells and lithium iron phosphate battery cells when used alone is a technical problem that the inventor urgently needs to solve.

[0034] It should be noted that the embodiments do not constitute a limitation on the scope of protection of the claims of this invention. All technical solutions that can be reasonably expected by those skilled in the art based on the technical concepts provided / proved by the embodiments should be covered within the scope of protection of the claims of this invention.

[0035] The implementation method is detailed below:

[0036] Example 1:

[0037] This embodiment provides a sodium-lithium hybrid starting battery with cells connected in parallel. In the starting battery:

[0038] The sodium-ion battery cell uses Prussian blue analogs (PBA) as the positive electrode active material. The rated capacity of this sodium-ion battery cell is 12Ah, the charging cut-off voltage is 3.65V, and the discharging cut-off voltage is 2.0V.

[0039] The lithium iron phosphate battery cell uses a mature commercial lithium iron phosphate battery cell with a rated capacity of 20Ah, a charging cut-off voltage of 3.65V, and a discharging cut-off voltage of 2.0V.

[0040] As attached Figure 1 As shown, each hybrid unit adopts a parallel connection structure of 2 sodium-ion battery cells 1 and 1 lithium iron phosphate battery cell 2.

[0041] In this embodiment, the equivalent DC internal resistance of the two sodium-ion cells 1 connected in parallel is less than that of a single lithium iron phosphate cell 2. According to the parallel current splitting principle, during battery startup, the peak current is large, and the voltage drop of sodium-ion cell 1 is lower than that of lithium iron phosphate cell 2. At this time, sodium-ion cell 1 plays a dominant role, while lithium iron phosphate cell 2 serves as the electrical power supply during non-startup periods. In environments below -20℃, the internal resistance of lithium iron phosphate cell 2 increases sharply, making it difficult for it to generate heat through high-current discharge. Meanwhile, sodium-ion cell 1, with its relatively stable internal resistance and bearing over 90% of the current, becomes the primary heat source. The heat it generates effectively raises the temperature of lithium iron phosphate cell 2, reducing its internal resistance and restoring its discharge capacity. This creates a positive feedback loop: sodium-ion cell 1 heats up, lithium iron phosphate cell 2 heats up, lithium iron phosphate cell 2 outputs better, and overall output is enhanced. This embodiment utilizes the battery's own discharge energy and physical heat conduction, eliminating components such as heating films and temperature switches found in traditional solutions, thus reducing system costs and potential failure points.

[0042] Example 2:

[0043] This embodiment relates to the module assembly and heat distribution structure of the starting battery described in Embodiment 1:

[0044] The selected battery cells are arranged in the module bracket in the order of sodium-ion battery cell - lithium iron phosphate battery cell - sodium-ion battery cell, with thermally conductive silicone pads filling the spaces between the cells. Using laser welding, the negative electrode tabs of two sodium-ion battery cells and the negative electrode tab of one lithium iron phosphate battery cell are simultaneously welded to the same copper busbar; the positive electrode is treated similarly.

[0045] This thermally conductive silicone pad not only serves as insulation but also forms a low thermal resistance channel between the sodium-ion battery cell and the lithium iron phosphate battery cell. As can be seen from Example 1 above, when the sodium-ion battery cell generates Joule heat during high-current discharge, the heat can be rapidly conducted to the lithium iron phosphate battery cell through the silicone pad. This utilizes physical heat conduction to replace the traditional heating film, thus eliminating the need for a heating component, achieving structural simplification and improved thermal efficiency.

[0046] Example 3:

[0047] This embodiment relates to the BMS control logic, electrical parameters, and assembly of the starting battery described in Embodiment 1:

[0048] Because the starting battery uses Prussian blue sodium-ion cells, the upper voltage limit of this type of sodium-ion cell is essentially the same as the charging cutoff voltage of lithium iron phosphate batteries, both being 3.65V. Therefore, by simply setting the protection parameters from 2.0 to 3.65V uniformly in the BMS, both batteries can safely work together. This setup eliminates the need for a DC-DC voltage converter required in existing technologies, thus reducing system costs.

[0049] In contrast, other mainstream sodium-ion cathode systems exhibit significant differences in voltage windows:

[0050] For example, layered oxide systems have a voltage limit of up to 3.9V, far exceeding the 3.65V of lithium iron phosphate. If directly connected in parallel, it will lead to long-term overcharging of lithium iron phosphate, causing safety risks.

[0051] For example, polyanionic systems have a voltage limit of only 3.45V, which is lower than the full-charge voltage of lithium iron phosphate. If used in parallel, lithium iron phosphate cannot be fully charged, resulting in a significant reduction in capacity utilization.

[0052] Meanwhile, in this embodiment, the BMS is set to monitor the total voltage of each string of hybrid units in real time. When the voltage of any string of hybrid units reaches 3.4V, passive equalization is initiated to transfer the excess energy of that string to the string with lower voltage until the voltage of each string is consistent.

[0053] This design solves the voltage dispersion problem caused by different self-discharge rates in hybrid cells, ensuring improved overall system capacity utilization.

[0054] The above modules are assembled into a high-strength aluminum alloy enclosure, and the BMS mainboard and high and low voltage wiring harnesses are installed. The enclosure protection level reaches IP67. The final specifications of the starting battery are: a 12V system consisting of 4 series hybrid cells, with a total capacity of 44Ah, which is 22% higher than the pure sodium-ion cell solution. The size is the same as that of traditional lead-acid batteries, and it can be directly replaced and installed in the engine compartment of the vehicle.

[0055] In extremely cold environments, the internal resistance of the lithium iron phosphate (LFP) battery cells described in the above embodiments surges to the milliohm level or higher, almost losing their discharge capability. At this time, the internal resistance of the sodium-ion battery cells changes relatively little. During startup, because the internal resistance of the sodium-ion cells is much lower than that of the LFP cells, the vast majority of the current is supplied by the sodium-ion cells. The heat generated by the high-current discharge of the sodium-ion cells rapidly heats the LFP cells. When the temperature of the LFP cells rises above -10°C, their internal resistance returns to normal, and they begin to output power collaboratively.

[0056] The starting battery described in the above embodiment can successfully cold start a 3.0L diesel engine at -30℃, while a starting battery with pure lithium iron phosphate cells cannot ignite.

[0057] Corresponding to the vehicle being turned off and parked, under the long-term static condition of 3 months described in the above embodiment, since the self-discharge rate of lithium iron phosphate cells (<1% / month) is much lower than that of sodium-ion cells (about 3~5% / month), over time, sodium-ion cells may have self-discharged to a low charge state, but lithium iron phosphate cells still retain most of their charge. Through a parallel circuit, a small amount of charge can be added to sodium-ion cells to maintain the voltage level of the entire module and avoid the inability to start due to sodium-ion cells being depleted.

[0058] The starting battery described in the above embodiment stabilizes at a voltage above 3.0V after being left to stand for 3 months, and the failure rate due to low power is significantly reduced; while the starting battery with pure sodium-ion cells drops to the critical value where it cannot start.

[0059] In the description of this specification, the references to terms such as "embodiment," "basic embodiment," "preferred embodiment," "other embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0060] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0061] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A sodium-lithium hybrid starting battery with cells connected in parallel, characterized in that, include: The battery module includes at least one string of hybrid units; Each of the aforementioned hybrid units consists of sodium-ion batteries and lithium iron phosphate batteries; In each of the aforementioned hybrid units, sodium-ion batteries and lithium iron phosphate batteries are connected in parallel.

2. The starting battery according to claim 1, characterized in that: In each of the aforementioned hybrid units, the ratio of sodium-ion cells to lithium iron phosphate cells is 2:

1.

3. The starting battery according to claim 2, characterized in that: Each of the aforementioned hybrid units consists of two sodium-ion batteries and one lithium iron phosphate battery.

4. The starting battery according to any one of claims 1 to 3, characterized in that: The positive electrode active material of the sodium-ion battery cell is a Prussian blue compound.

5. The starting battery according to claim 4, characterized in that: It also includes a battery management system, which is configured as follows: The operating voltage range of the battery module is limited to 2.0V to 3.65V.

6. The starting battery according to claim 5, characterized in that: During charging, when the voltage of any string of hybrid units reaches the equalization threshold, the battery management system is configured to transfer the excess energy of the string of hybrid units to the hybrid units with lower voltage, until all strings of hybrid units reach full charge.

7. The starting battery according to claim 3, characterized in that: In each of the aforementioned hybrid units, the equivalent DC internal resistance of two sodium-ion cells connected in parallel is less than the DC internal resistance of one lithium iron phosphate cell.

8. The starting battery according to claim 1, characterized in that: At room temperature, the self-discharge rate of the lithium iron phosphate battery cell is <1% / month.

9. The starting battery according to claim 1, characterized in that: The total capacity of the battery module is ≥44Ah.

10. A vehicle, characterized in that: Includes a starting battery as described in any one of claims 1 to 9, wherein the starting battery is installed in the engine compartment.

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