A low-temperature-startable vehicle hybrid battery pack and its use method

Abstract

The present invention provides a vehicle hybrid battery pack capable of low-temperature startup, which is composed of a sodium ion battery cell (1), a lithium iron phosphate battery cell (2), a heater (3), an electronic switch (4), a DC-DC converter (5), a vehicle powertrain (6), an ampere-hour meter (7), a thermometer (8), and a charging port (9), to solve the problem of difficulty in starting a vehicle battery pack in a low-temperature environment. The present invention also provides a method for using the above-mentioned vehicle hybrid battery pack, wherein the residual capacity of the first and second battery modules is first obtained in real time by the ampere-hour meter (7); during startup, if the temperature of the second battery module is too low, the first battery module supplies power to the heater (3) to heat it; during driving, the battery pack supplies power to the vehicle; during charging, the battery pack receives power from an external power supply; at the end of driving, if the difference between the residual capacity of the first and second battery modules is less than Q, the latter charges the former. The vehicle hybrid battery pack of the present invention has a relatively simple structure, is easy to use, is economical and applicable, does not excessively increase system complexity and cost, and is environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a low-temperature startable vehicle hybrid battery pack and a method of using the same. Background Art

[0002] Electric vehicles are gaining popularity due to their energy-saving, environmentally friendly, affordable, and comfortable advantages. Currently, electric vehicles primarily utilize ternary or lithium iron phosphate (LiFePO4) batteries connected in series and parallel to form a battery pack. However, LiFePO4 batteries have poor low-temperature charge and discharge performance, hindering their proper operation in cold environments. A key obstacle to the use of LiFePO4 batteries in vehicles is cold-weather startup: in severe cold, the LiFePO4 battery itself remains extremely cold, preventing proper discharge. To address this issue, proposals have been made to heat the LiFePO4 battery pack before startup, using internal combustion engines or supercapacitors to discharge a resistor. This allows the battery pack to heat up and start properly. Once the vehicle is started, the vehicle's thermal management system can be used to maintain the appropriate temperature during operation, consuming the battery pack's own energy. However, using an internal combustion engine for heating consumes fuel, which is not environmentally friendly or energy-efficient. The additional internal combustion engine and supercapacitors occupy excessive space and weight, adding to the vehicle's deadweight and cost. Furthermore, the need for regular or irregular refueling of the internal combustion engine or charging of the supercapacitors is inconvenient.

[0003] Therefore, in order to solve the problem of difficulty in starting vehicle battery packs in low-temperature environments, it is urgent to propose new technical solutions that are simple, convenient, economical, applicable, do not excessively increase system complexity and cost, and are green and environmentally friendly. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a vehicle hybrid battery pack that has a relatively simple structure, is easy to use, economical and applicable, does not excessively increase system complexity and cost, is environmentally friendly, and can be started at low temperatures, and provides a method for using the same.

[0005] According to one aspect of the present invention, a low-temperature startable automotive hybrid battery pack is provided, comprising a first battery module, an electronic switch, a second battery module, and a heater capable of heating the second battery module and electrically connected to the first battery module, all connected in series. The first battery module is provided with an ampere-hour meter, and the second battery module is provided with a thermometer. The first battery module and the second battery module are respectively electrically connected to a DC-DC converter. The first battery module is composed of a plurality of first battery cells connected in series, and the second battery module is composed of a plurality of second battery cells connected in series.

[0006] In the above-mentioned low-temperature startable automotive hybrid battery pack, the electronic switch is a normally closed type, and the heater and the DC-DC converter are in an inoperative disconnected state by default.

[0007] In the above-mentioned low-temperature startable vehicle hybrid battery pack, the DC-DC converter is used to enable the second battery module to charge the first battery module.

[0008] In the above-mentioned low-temperature startable automotive hybrid battery pack, the first battery unit is composed of one or more sodium-ion battery cells connected in parallel, the second battery unit is composed of one or more lithium iron phosphate battery cells connected in parallel, and the maximum capacity of the first battery unit is k times the maximum capacity of the second battery unit, where k is a capacity ratio coefficient greater than 1.

[0009] For the above-mentioned low-temperature startable automotive hybrid battery pack, the capacity proportional coefficient k is between 1.05 and 1.5.

[0010] According to another aspect of the present invention, a method for using the above-mentioned low-temperature startable automotive hybrid battery pack is provided, wherein the remaining capacities of the first battery module and the second battery module are respectively obtained in real time by an integration method based on an ampere-hour meter: the initial capacities of the first battery module and the second battery module are calibrated in advance; during operation, if the first battery module and the second battery module are charged and discharged synchronously, the ampere-hour meter is used to obtain the change in their capacities; if the first battery module works alone to power a heater, the ampere-hour meter is used to obtain the decrease in the power of the first battery module; if the second battery module charges the first battery module, the ampere-hour meter is used to obtain the increase in the power of the first battery module, and this value is also the decrease in the power of the second battery module.

[0011] The method for using the above-mentioned low-temperature startable vehicle hybrid battery pack also includes operating methods in the battery pack low-temperature start mode, driving mode, charging mode, and capacity compensation mode:

[0012] In the low-temperature starting mode, when the thermometer detects that the temperature of the second battery module is lower than the lower limit of its suitable operating temperature, the first battery module powers the heater to operate until the second battery module is heated to above the lower limit of its suitable operating temperature;

[0013] In driving mode, the electronic switch is closed and the battery pack as a whole provides power for vehicle operation;

[0014] In charging mode, the electronic switch is closed and the battery pack is powered by an external power source.

[0015] In the capacity compensation mode, the electronic switch is disconnected, and the second battery module charges the first battery module through the DC-DC converter.

[0016] The method for using the above-mentioned low-temperature startable automotive hybrid battery pack is as follows: when the vehicle ends the driving mode, the starting condition of the capacity compensation mode is: when the vehicle ends the driving mode, the difference between the remaining capacity of the first battery module and the remaining capacity of the second battery module is calculated. If the difference is less than Q, the compensation mode is started; and the compensation mode is terminated when the above difference is greater than or equal to Q.

[0017] In the method for using the above-mentioned low-temperature startable automotive hybrid battery pack, the capacity difference Q is the minimum amount of electricity required for the first battery module to heat the second battery module to above the lower limit of its suitable operating temperature through the heater when the battery pack is at the lowest allowable operating ambient temperature.

[0018] The principles and advantages of the technical solution of the present invention are introduced below.

[0019] Lithium-ion batteries, using lithium iron phosphate as their cathode material, currently account for the majority of automotive power battery market share. While lithium iron phosphate batteries offer advantages such as high energy density, low cost, and safety and reliability, their significant drawback is poor low-temperature performance. In environments below 0°C, as the temperature drops, their internal resistance increases dramatically, and their rate discharge capability and capacity retention decrease dramatically. While the energy density of current sodium-ion batteries is slightly lower than that of lithium iron phosphate batteries, they offer the distinct advantage of excellent low-temperature performance. Their discharge retention rate at low temperatures is much higher than that of lithium-ion batteries. This is because the liquid electrolyte used in sodium-ion batteries is generally a mixture of organic solvents and inorganic salts, which has a much lower freezing point than the mixture of organic solvents and organic salts used in lithium-ion batteries. Therefore, sodium-ion batteries can maintain a discharge retention rate of over 90% even in extremely cold environments of around -20°C, while lithium-ion batteries only achieve a discharge retention rate of less than 50%.

[0020] The present invention connects a first battery module composed of sodium ion batteries and a second battery module composed of lithium iron phosphate batteries in series to form a hybrid battery pack, and designs corresponding usage methods for the battery pack in different operating scenarios: in a low-temperature starting mode, the first battery module with better low-temperature performance powers a heater to heat the second battery module with poorer low-temperature performance; in a driving mode, the electronic switch is closed, and the battery pack composed of the first and second battery modules supplies power to the vehicle as a whole, that is, the first battery module does not only work in a low-temperature starting environment, but both supply energy to the vehicle during normal driving, thereby ensuring the effective energy density and volume density of the battery pack; in a charging mode, the electronic switch is closed, and the battery pack as a whole receives power from an external power supply; in a capacity compensation mode, the electronic switch is disconnected, and the second battery module charges the first battery module through a DC-DC converter, so that the remaining capacity of the first battery module is always more than 1000W than the remaining capacity of the second battery module, thereby ensuring that the first battery module can maintain a remaining capacity not less than that of the second battery module after a low-temperature starting heating discharge, thereby avoiding a power shortage of the first battery module during subsequent driving and ensuring the vehicle's mileage.

[0021] The technical solution of the present invention is fully compatible with existing electric vehicle design and usage specifications. On the basis of the current lithium iron phosphate lithium-ion battery pack, it is only necessary to replace some lithium-ion batteries with sodium-ion batteries, and add electronic switches, DC-DC converters (also known as "DC / DC converters") and heaters. The electrical connection relationship between the battery pack as a whole and the motor and charging pile will not be changed, and the vehicle driving and charging modes will not be changed. The special low-temperature starting mode and capacity compensation mode are only triggered during the starting process before the vehicle is driven and when the vehicle ends driving. During the vehicle driving and charging process, the first battery module and the second battery module are in series, so the battery pack has a sufficient total voltage, which can ensure sufficient power output and input capabilities, and has good electrical compatibility with existing motors and charging piles. Due to the design of the capacity compensation mode, no matter what kind of charging or driving operation the vehicle has performed in the past (for example, it has been driving at a constant speed), it can be guaranteed that the first battery module will have a residual capacity no less than that of the second battery module after the next low-temperature start-up discharge.

[0022] Furthermore, considering that ampere-hour meters are precision instruments and expensive, despite the existence of two special operating modes (low-temperature startup and capacity compensation), the technical solution of the present invention uses only one ampere-hour meter connected in series within the first battery module to simultaneously measure the remaining capacity of the first and second battery modules, without having to install separate ampere-hour meters for each. The initial capacity of each battery module is calibrated in advance. During operation, if the two modules are charged and discharged synchronously, the ampere-hour meter is used to obtain the change in their capacity. If the first battery module operates independently to power the heater, the ampere-hour meter is used to obtain the decrease in the capacity of the first battery module. If the second battery module charges the first battery module, the ampere-hour meter is used to obtain the increase in the capacity of the first battery module. Naturally, this increase also represents the decrease in the capacity of the second battery module. This helps control costs.

[0023] Therefore, the above-mentioned low-temperature startable automotive hybrid battery pack and its use method have the advantages of simple battery pack structure, easy use, good economy and applicability, no excessive increase in system complexity and cost, and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the battery pack in an embodiment of the present invention. In the figure, 1 is a sodium ion battery cell, 2 is a lithium iron phosphate battery cell, 3 is a heater, 4 is an electronic switch, 5 is a DC-DC converter, 6 is a vehicle powertrain, 7 is an ampere-hour meter, 8 is a thermometer, and 9 is a charging port. For ease of expression, Figure 1 The ellipsis "..." is used to represent the omission of repeated battery cells and their connecting lines at the corresponding positions. Figure 1 Rectangular and rounded rectangles are used to distinguish different types of battery cells. DETAILED DESCRIPTION

[0025] The following is combined with Figure 1 The present invention is further illustrated with reference to the accompanying drawings and examples.

[0026] A low-temperature startable automotive hybrid battery pack includes a first battery module, an electronic switch 4, a second battery module, and a heater 3 connected in series, capable of heating the second battery module and electrically connected to the first battery module; an ampere-hour meter 7 is provided in the first battery module, and a thermometer 8 is provided in the second battery module; the first battery module and the second battery module are respectively electrically connected to a DC-DC converter 5; the first battery module is composed of a plurality of first battery cells connected in series, and the second battery module is composed of a plurality of second battery cells connected in series.

[0027] In the above-mentioned low-temperature startable vehicle hybrid battery pack, the electronic switch 4 is a normally closed type, and the heater 3 and the DC-DC converter 5 are in an inoperative disconnected state by default.

[0028] In the above-mentioned low-temperature startable vehicle hybrid battery pack, the DC-DC converter 5 is used to enable the second battery module to charge the first battery module.

[0029] In the above-mentioned low-temperature startable automotive hybrid battery pack, the first battery unit is composed of one or more sodium-ion battery cells 1 connected in parallel, and the second battery unit is composed of one or more lithium iron phosphate battery cells 2 connected in parallel, and the maximum capacity of the first battery unit is k times the maximum capacity of the second battery unit, where k is a capacity ratio coefficient greater than 1.

[0030] For the above-mentioned low-temperature startable automotive hybrid battery pack, the capacity proportional coefficient k is between 1.05 and 1.5.

[0031] Preferably, under the premise of meeting the low-temperature starting discharge requirements, in order to ensure the overall energy density of the battery pack, the number of second battery cells with relatively higher energy density should be as large as possible, and the number of first battery cells should be 1 / 20 to 1 / 10 of the number of second battery cells.

[0032] The electronic switch 4, heater 3, ampere-hour meter 7, thermometer 8 and DC-DC converter 5 are all electrically connected to the controller to achieve two-way communication; when the heater 3 and DC-DC converter 5 are not working, the series circuit in which the two are located is in an open circuit state.

[0033] The ampere-hour meter 7 is located inside the first battery module and is connected in series with the first battery unit inside the first battery module. Regardless of the operating mode of the battery pack, the ampere-hour meter 7 can directly measure the change in the power of the first battery module.

[0034] A method for using the above-mentioned low-temperature startable automotive hybrid battery pack is as follows: the first battery module and the second battery module each obtain their respective remaining capacities in real time using an integration method based on an ampere-hour meter 7: the initial power of the first battery module and the second battery module are calibrated in advance; during operation, if the first battery module and the second battery module are synchronously charged and discharged, the ampere-hour meter 7 is used to obtain the change in power of the two; if the first battery module works alone to power the heater 3, the ampere-hour meter 7 is used to obtain the power reduction of the first battery module; if the second battery module charges the first battery module, the ampere-hour meter 7 is used to obtain the power increase of the first battery module, and this value is also the power reduction of the second battery module.

[0035] The method for using the above-mentioned low-temperature startable vehicle hybrid battery pack also includes operating methods in the battery pack low-temperature start mode, driving mode, charging mode, and capacity compensation mode:

[0036] In the low-temperature starting mode, when the thermometer 8 detects that the temperature of the second battery module is lower than the lower limit of its suitable operating temperature, the first battery module supplies power to the heater 3 to operate until the second battery module is heated to above the lower limit of its suitable operating temperature;

[0037] In driving mode, the electronic switch 4 is closed and the battery pack as a whole provides power for vehicle operation;

[0038] In charging mode, the electronic switch 4 is closed, and the battery pack as a whole receives power from the external power supply;

[0039] In the capacity compensation mode, the electronic switch 4 is disconnected, and the second battery module charges the first battery module through the DC-DC converter 5 .

[0040] The method for using the above-mentioned low-temperature startable automotive hybrid battery pack is as follows: when the vehicle ends the driving mode, the starting condition of the capacity compensation mode is: when the vehicle ends the driving mode, the difference between the remaining capacity of the first battery module and the remaining capacity of the second battery module is calculated. If the difference is less than Q, the compensation mode is started; and the compensation mode is terminated when the above difference is greater than or equal to Q.

[0041] In the method for using the above-mentioned low-temperature startable automotive hybrid battery pack, the capacity difference Q is the minimum amount of electricity required for the first battery module to heat the second battery module to above the lower limit of its suitable operating temperature through the heater 3 when the battery pack is at the lowest allowable operating ambient temperature.

[0042] Example

[0043] Please refer to Figure 1 Understand this embodiment.

[0044] A certain automotive battery pack consists of eight sodium-ion battery cells (1) with a maximum capacity of 130Ah and a rated voltage of 3.0V connected in series to form the first battery module. The second battery module consists of 120 lithium iron phosphate lithium-ion battery cells (1) with a maximum capacity of 100Ah and a rated voltage of 3.2V connected in series. The lower limit of the suitable operating temperature of the second battery module is 10°C, and the battery pack's lowest low-temperature startup temperature can reach -30°C.

[0045] In this embodiment, the heater 3 is in the form of a resistance heating wire arranged on the surface of the battery, which directly provides heating for the battery.

[0046] One day, the battery pack draws power from a charging station via charging port 9, undergoes a 100A constant-current fast charge to a total voltage of 470V, and is parked outdoors. The next morning, the user attempts to start the vehicle, initiating a cold start mode. Thermometer 8 detects the second battery module's temperature at -25°C, below its lower operating temperature. Therefore, the first battery module powers heater 3, causing it to heat the second battery module to a temperature above 10°C.

[0047] The driving mode is then started, the electronic switch 4 is closed, and the battery pack as a whole supplies power to the vehicle powertrain 6 to meet the normal operation needs of the vehicle. During the operation of the vehicle, its battery thermal management system also obtains electrical energy from the battery pack as a whole.

[0048] After a vehicle travels a long distance at a constant speed on a highway, the vehicle ends its journey. The battery pack immediately determines whether to activate capacity compensation mode. Calculations reveal that the difference between the remaining capacity of the first battery module and the remaining capacity of the second battery module at the end of the journey is 5 Ah. The pre-set capacity difference Q is 15 Ah. Therefore, compensation mode is activated, electronic switch 4 opens, and the second battery module, through DC-DC converter 5, changes its output voltage and charges the first battery module until the difference between the remaining capacity of the first battery module and the remaining capacity of the second battery module reaches 15 Ah.

[0049] The capacity difference Q is pre-calibrated by experiments: when the battery pack is at the lowest allowable operating ambient temperature, under the most unfavorable conditions, the minimum amount of electricity required for the first battery module to heat the second battery module to above the lower limit of its suitable operating temperature through heater 3 is the capacity difference Q.

[0050] In this embodiment, a first battery module composed of sodium ion batteries and a second battery module composed of lithium iron phosphate batteries are connected in series to form a hybrid battery pack, and corresponding usage methods are designed for the battery pack to work in different scenarios: in low-temperature starting mode, the first battery module with better low-temperature performance supplies power to the heater 3 to heat the second battery module with poor low-temperature performance; in driving mode, the battery pack composed of the first battery module and the second battery module supplies power to the vehicle as a whole, ensuring the effective energy density and volume density of the battery pack; in charging mode, the battery pack as a whole receives power from an external power supply; in capacity compensation mode, the electronic switch 4 is disconnected, and the second battery module charges the first battery module through the DC-DC converter 5, so that the remaining capacity of the first battery module is always more than 1000W than the remaining capacity of the second battery module, thereby meeting the requirement that the first battery module can maintain a remaining capacity not less than that of the second battery module after a low-temperature starting heating discharge, so as to avoid a power shortage of the first battery module during subsequent driving and ensure the vehicle's mileage.

[0051] The technical solution of this embodiment is fully compatible with existing electric vehicle design and usage specifications. The addition of new components is limited and does not alter the electrical connections between the battery pack, the motor, or the charging station. The vehicle's driving and charging modes remain unchanged, with the special low-temperature startup mode and capacity compensation mode triggered only during the vehicle's startup process before travel and at the end of travel. During vehicle travel and charging, the first and second battery modules are connected in series, providing the battery pack with a sufficient total voltage, ensuring adequate power output and input capabilities, and excellent electrical compatibility with existing motors and charging stations. Furthermore, this technical solution simultaneously measures the remaining capacity of both the first and second battery modules using only a single ampere-hour meter 7 connected in series within the first battery module, eliminating the need for separate ampere-hour meters 7 for each, which helps control costs.

[0052] Therefore, the low-temperature startable automotive hybrid battery pack and its use method in this embodiment have the advantages of simple battery pack structure, easy use, good economy and applicability, no excessive increase in system complexity and cost, and environmental protection.

Claims

1. A method for using a low-temperature startable vehicle hybrid battery pack, characterized in that: The battery pack comprises a first battery module, an electronic switch (4), a second battery module, and a heater (3) which is capable of heating the second battery module and is electrically connected to the first battery module. The first battery module is provided with an ampere-hour meter (7), and the second battery module is provided with a thermometer (8). The first battery module and the second battery module are electrically connected to a DC-DC converter (5), respectively. The first battery module is composed of a plurality of first battery cells connected in series, and the second battery module is composed of a plurality of second battery cells connected in series. The method of use is: The first battery module and the second battery module both obtain their remaining capacities in real time through an integration method based on an ampere-hour meter (7): the initial electric capacity of the first battery module and the second battery module is calibrated in advance; during operation, if the first battery module and the second battery module are synchronously charged and discharged, the electric capacity change of the two is obtained using the ampere-hour meter (7); if the first battery module works alone to supply power to the heater (3), the electric capacity reduction of the first battery module is obtained using the ampere-hour meter (7); if the second battery module charges the first battery module, the electric capacity increase of the first battery module is obtained using the ampere-hour meter (7), and this value is also the electric capacity reduction of the second battery module.

2. The method for using the low-temperature startable vehicle hybrid battery pack according to claim 1, characterized in that: The electronic switch (4) is of a normally closed type, and the heater (3) and the DC-DC converter (5) are in an inoperative disconnected state by default.

3. The method for using the low-temperature startable vehicle hybrid battery pack according to claim 1, characterized in that: The DC-DC converter (5) is used to enable the second battery module to charge the first battery module.

4. The method for using the low-temperature startable vehicle hybrid battery pack according to claim 1, characterized in that: The first battery unit is composed of one or more sodium ion battery cells (1) connected in parallel, the second battery unit is composed of one or more lithium iron phosphate battery cells (2) connected in parallel, and the maximum capacity of the first battery unit is k times the maximum capacity of the second battery unit, wherein k is a capacity proportional coefficient greater than 1.

5. The method for using the low-temperature startable vehicle hybrid battery pack according to claim 4, characterized in that: The capacity proportionality coefficient k is between 1.05 and 1.

5.

6. The method for using the low-temperature startable vehicle hybrid battery pack according to claim 1, characterized in that: The method also includes operating methods in the battery pack low-temperature starting mode, driving mode, charging mode, and capacity compensation mode: In the low-temperature starting mode, when the temperature of the second battery module is detected by the thermometer (8) to be lower than the lower limit of its suitable operating temperature, the first battery module supplies power to the heater (3) to operate until the second battery module is heated to above the lower limit of its suitable operating temperature; In the driving mode, the electronic switch (4) is closed, and the battery pack as a whole provides power for the vehicle operation; In the charging mode, the electronic switch (4) is closed, and the battery pack as a whole receives power from an external power source; In the capacity compensation mode, the electronic switch (4) is disconnected, and the second battery module charges the first battery module via the DC-DC converter (5).

7. The method for using the low-temperature startable vehicle hybrid battery pack according to claim 6, characterized in that: The starting condition of the capacity compensation mode is: when the vehicle ends the driving mode, the difference between the remaining capacity of the first battery module and the remaining capacity of the second battery module is calculated. If the difference is less than Q, the compensation mode is started; the compensation mode is terminated until the above difference is greater than or equal to Q.

8. The method for using the low-temperature startable vehicle hybrid battery pack according to claim 7, characterized in that: The capacity difference Q is the minimum amount of electricity required for the first battery module to be heated to above the lower limit of its suitable operating temperature by the heater (3) when the battery pack is at the lowest permissible operating ambient temperature.

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