Lead-sodium composite battery pack for electric vehicle

Abstract

The invention relates to the field of electric vehicle batteries, and particularly discloses a lead-sodium composite battery pack for an electric vehicle, which comprises a sodium ion battery and a lead-acid battery pack, the sodium ion battery and the lead-acid battery pack are connected in parallel, the lead-acid battery pack is formed by connecting a plurality of lead-acid batteries in series, and the initial discharge voltage of the sodium ion battery is higher than that of the lead-acid battery pack. The charging upper limit voltage of the sodium ion battery is equal to the charging upper limit voltage of the lead-acid battery pack, and a first diode is arranged between the lead-acid battery pack and the sodium ion battery. According to the prepared composite battery pack, the mass of a lead-acid battery with the same capacity can be reduced by 20% or above, the battery pack can be used under the high-power discharge requirement, the sodium ion battery with the high discharge voltage can effectively assist the lead-acid battery in full discharge, the current density borne by the lead-acid battery is effectively reduced, and the service life of the battery pack is prolonged. And the service life of the lead-acid battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of electric vehicle batteries, and in particular to a lead-sodium composite battery pack for electric vehicles. Background Art

[0002] Lead-acid batteries and sodium-ion batteries are commonly used battery components for electric vehicles on the market.

[0003] Lead-acid battery technology is mature, raw materials are abundant, prices are low and safety performance is good, but lead-acid batteries have poor low-temperature performance and short winter range; and their deep cycle life is poor, requiring replacement in about a year, making it difficult to meet long-term usage needs.

[0004] Sodium-ion batteries, especially sodium iron sulfate batteries and sodium iron pyrophosphate batteries, are safer than lithium-ion batteries under conditions of thermal abuse, mechanical abuse, overcharge and over-discharge, and their cycle life far exceeds that of lead-acid batteries, making them suitable for use in low-speed electric vehicles.

[0005] Currently, lead-acid batteries and sodium-ion batteries on the market are used separately and cannot be used simultaneously. Summary of the invention

[0006] The invention provides a lead-sodium composite battery pack for electric vehicles, which solves the problem of low service life when lead-acid batteries are used as batteries in electric vehicles.

[0007] The present invention adopts the following technical scheme: a lead-sodium composite battery pack for electric vehicles, comprising a sodium ion battery and a lead-acid battery pack, wherein the sodium ion battery and the lead-acid battery pack are connected in parallel, the lead-acid battery pack is composed of a plurality of lead-acid batteries connected in series, the initial discharge voltage of the sodium ion battery is higher than that of the lead-acid battery pack, the upper limit charging voltage of the sodium ion battery is equal to that of the lead-acid battery pack, and a first diode is arranged between the lead-acid battery pack and the sodium ion battery.

[0008] Furthermore, the initial discharge voltage of the sodium ion battery is at least 1V higher than the initial discharge voltage of the lead-acid battery pack.

[0009] Furthermore, the positive electrode of the sodium ion battery is one of layered oxide, sodium iron sulfate or sodium iron pyrophosphate.

[0010] Furthermore, the circuit of the lead-sodium composite battery pack adopts a parallel charging and series discharging method.

[0011] Furthermore, a second diode is provided between the charging input end of the lead-sodium composite battery pack and the sodium ion battery, and a starting switch controlled by the sodium ion battery is provided between the discharge output end and the lead-acid battery pack.

[0012] Furthermore, the circuit of the sodium lead-acid composite battery pack adopts a parallel charging and discharging method.

[0013] Furthermore, a second diode is provided between the charging input end of the lead-sodium composite battery pack and the sodium ion battery, and a third diode is provided between the discharging output end and the lead-acid battery pack.

[0014] Beneficial effects of the present invention:

[0015] 1. In the present invention, by combining lead-acid batteries and sodium-ion batteries, the advantages of long cycle life, rate discharge capability, low-temperature discharge capability, etc. of sodium-ion battery modules can be brought into play, and the characteristics of low cost and high recovery value of lead-acid batteries can be reflected, thereby extending the driving range and optimizing the user experience. Since the initial discharge platform of sodium-ion batteries is higher than that of lead-acid batteries, the problem of insufficient high-current discharge performance of lead-acid batteries can be solved, and high-power discharge requirements such as starting, climbing, and facing the wind of electric vehicles can be met. At the same time, the current density carried by the lead-acid battery pack can be reduced, and the attenuation rate of the lead-acid battery can be slowed down.

[0016] 2. The arrangement of the diode in the present invention solves the problem of reverse charging of the lead-acid battery by the sodium-ion battery, so that the sodium-ion battery can assist the lead-acid battery in discharging to the maximum extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a comparison diagram of discharge curves of the lead-acid battery, sodium-ion battery, and lead-sodium composite battery pack of the present invention;

[0018] Figure 2 It is a comparison diagram of charging curves of the lead-acid battery, sodium-ion battery, and lead-sodium composite battery pack of the present invention;

[0019] Figure 3 A schematic diagram of the electrical connection of the composite battery pack of the present invention for parallel charging and serial discharging for charging and discharging;

[0020] Figure 4 It is a schematic diagram of the electrical connection of charging and discharging of the composite battery pack of the present invention.

[0021] Reference numerals:

[0022] First diode 1, second diode 2, third diode 3 DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0024] Embodiment 1:

[0025] Four 12Ah lead-acid batteries are connected in series, and then connected in parallel with 14 strings of 12Ah sodium iron sulfate batteries to form a composite battery pack.

[0026] The initial discharge voltage of 14 strings of 12Ah sodium iron sulfate batteries is 57.4V (4.1V*14=57.4V), and the initial discharge voltage of lead-acid batteries is 53.2V (13.3V*4=53.2V). The initial discharge voltage of sodium iron sulfate batteries is 4.2V higher than that of lead-acid batteries. As the discharge progresses, the voltage difference will gradually decrease; but it is the high voltage of sodium iron sulfate batteries in the early stage that makes the power or current shared by lead-acid batteries smaller than that of sodium iron sulfate batteries. The upper limit voltage of sodium iron sulfate batteries and lead-acid battery packs is the same, both 59V.

[0027] A first diode 1 is connected in series between the positive electrode or the negative electrode of the battery, and the first diode 1 conducts unidirectionally from the lead-acid battery to the sodium iron sulfate battery.

[0028] like Figure 3 As shown, in the charging circuit, a second diode 2 is connected between the charging input terminal and the positive electrode or negative electrode of the sodium iron sulfate battery, and the second diode 2 is unidirectionally conducted from the charging input terminal to the sodium iron sulfate battery. In the discharging circuit, a switch is connected between the discharging output terminal and the positive electrode or negative electrode of the lead-acid battery. When the sodium iron sulfate battery is discharged to a set cut-off voltage, the switch is turned on by the BMS battery management system of the sodium ion battery, and the lead-acid battery continues to supply power to the load.

[0029] Embodiment 2:

[0030] Four 12Ah lead-acid batteries are connected in series, and then connected in parallel with 16 strings of 12Ah nickel-iron-manganese-sodium batteries to form a composite battery pack.

[0031] The initial discharge voltage of 16 strings of 12Ah sodium nickel-iron-manganese batteries is 56V (3.5V*16=56V), and the initial discharge voltage of lead-acid batteries is 53.2V (13.3V*4=53.2V). The initial discharge voltage of sodium nickel-iron-manganese batteries is 2.8V higher than that of lead-acid batteries. As the discharge progresses, the voltage difference will gradually decrease; but it is the high voltage of sodium nickel-iron-manganese batteries in the early stage that makes the power or current shared by lead-acid batteries smaller than that of sodium nickel-iron-manganese batteries. The upper limit voltage of charging for sodium nickel-iron-manganese batteries and lead-acid battery packs is the same, 59.2V.

[0032] A first diode 1 is connected in series between the positive electrode or the negative electrode of the lead-acid battery and the nickel-iron-manganese-sodium battery. The first diode 1 conducts unidirectionally from the lead-acid battery to the nickel-iron-manganese-sodium battery and does not conduct in the opposite direction.

[0033] like Figure 4 As shown, in the charging circuit, a second diode 2 is connected between the charging input end and the positive electrode or negative electrode of the nickel-iron-manganese-sodium battery, and the second diode 2 is unidirectionally conducted from the charging input end to the nickel-iron-manganese-sodium battery. In the discharging circuit, a third diode 3 is connected between the discharging output end and the positive electrode or negative electrode of the lead-acid battery, and the third diode 3 is conducted from the lead-acid battery to the output end.

[0034] Comparative Example:

[0035] All are made of 48V24Ah lead-acid batteries.

[0036] The battery performance of the battery packs in Example 1 and Example 2 and the battery pack composed of the comparative example was tested, and the results are shown in Table 1.

[0037] Table 1 Battery performance table

[0038] Mass specific energy Wh / kg Low temperature capacity / Ah Embodiment 1 52.8 19.2 Embodiment 2 57.9 19.2 Comparative Example 41.1 16.8

[0039] As shown in Table 1, when the upper charging limit voltage and capacity of the composite battery pack prepared by the present invention are equal, the mass specific energy of the composite battery pack is increased by more than 25% compared with the lead-acid battery, and the low-temperature capacity is increased by more than 15%. This shows that the composite battery pack of the present invention can be used in electric vehicles for a longer battery life, reduce the charging frequency, and has a better market application prospect.

[0040] The weight of the battery pack is reduced by combining lead-acid batteries with sodium-ion batteries. For example, the weight of a 48V24Ah lead-acid battery is about 28kg, the weight of a 48V12Ah lead-acid battery is about 15.2kg, and the weight of a 4812 sodium iron sulfate battery is about 6.6kg. If a lead-acid battery and a sodium iron sulfate battery are used in combination, the weight of the combined 4824 battery module is about 21.8kg, which is about 22% lower than the 28kg of a 48V24Ah lead-acid battery.

[0041] like Figure 1 and Figure 2 It can be seen that the discharge curves and charge curves of Example 1, Example 2 and the comparative example.

[0042] For sodium-ion batteries and lead-acid batteries with the same upper limit of charging voltage, during the discharge process, the sodium-ion battery bears a larger discharge current or output power, which reduces the burden on the lead-acid battery and can extend the service life of the lead-acid battery. Because the lead-acid battery is in a state of deep discharge and insufficient charging in actual application scenarios, after being used in combination with the sodium-ion battery, the sodium-ion battery bears the power output within a certain discharge time, which not only reduces the discharge depth of the lead-acid battery, but also allows the sodium-ion battery to bear a larger proportion of the output power when high power output is achieved, reduces the discharge current density borne by the lead-acid battery, and slows down the aging rate of the lead-acid battery.

Claims

1. A lead-sodium composite battery pack for electric vehicles, characterized in that: The invention comprises a sodium ion battery and a lead-acid battery group, wherein the sodium ion battery and the lead-acid battery group are connected in parallel, the lead-acid battery group is composed of a plurality of lead-acid batteries connected in series, the initial discharge voltage of the sodium ion battery is higher than that of the lead-acid battery group, the upper charging limit voltage of the sodium ion battery is equal to that of the lead-acid battery group, and a first diode is arranged between the lead-acid battery group and the sodium ion battery.

2. The lead-sodium composite battery pack for electric vehicles according to claim 1, characterized in that: The initial discharge voltage of the sodium ion battery is at least 1V higher than the initial discharge voltage of the lead-acid battery pack.

3. The lead-sodium composite battery pack for electric vehicles according to claim 2, characterized in that: The positive electrode of the sodium ion battery is one of layered oxide, sodium iron sulfate or sodium iron pyrophosphate.

4. The lead-sodium composite battery pack for electric vehicles according to claim 3, characterized in that: The circuit of the lead-sodium composite battery pack adopts a parallel charging and serial discharging method.

5. The lead-sodium composite battery pack for electric vehicles according to claim 4, characterized in that: A second diode is arranged between the charging input end of the lead-sodium composite battery pack and the sodium ion battery, and a starting switch controlled by the sodium ion battery is arranged between the discharge output end and the lead-acid battery pack.

6. The lead-sodium composite battery pack for electric vehicles according to claim 3, characterized in that: The circuit of the sodium lead-acid composite battery pack adopts a parallel charging and discharging method.

7. The lead-sodium composite battery pack for electric vehicles according to claim 6, characterized in that: A second diode is arranged between the charging input end of the lead-sodium composite battery pack and the sodium ion battery, and a third diode is arranged between the discharging output end and the lead-acid battery pack.

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