Compact electric vehicle, lithium ion secondary battery, and swappable battery system

Abstract

To provide a compact electric vehicle that is lightweight, has an easily swappable secondary battery and has low risk of heat generation and ignition.SOLUTION: A compact electric vehicle has a power storage system that stores electricity in a lithium ion secondary battery having an internal resistance of 60 mΩ Ah or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a small electric vehicle, a lithium ion secondary battery, and a replaceable battery system. [Background technology]

[0002] In recent years, public transportation services for residents in areas without public transportation have been implemented in various places, utilizing small electric vehicles that travel at speeds of less than 20 km / h, known as green slow mobility. The power source for the Green Slow Mobility is a secondary battery installed in the vehicle body, and the secondary battery is generally charged by an external power source. The capacity and weight of this secondary battery are proportional to the distance traveled by the Green Slow Mobility. In addition, it is required that the secondary battery has stable performance in various climates, such as high temperature and humidity, and cold regions, and that there is no risk of fire. Lithium ion secondary batteries are mainly used for light weight and high capacity. Lithium-ion secondary batteries have a proven track record in a variety of applications, including electric mobility for land and sea travel, home storage batteries, and leisure power sources. However, because lithium-ion secondary batteries pose the risk of overheating and catching fire due to thermal runaway, it is necessary to manage each battery cell within the lithium-ion secondary battery, and control devices tailored to each application are required. As a result, it has become difficult to share and use lithium-ion secondary batteries among various devices.

[0003] Conventionally, technologies for the exchange, sharing, remote monitoring, etc. of secondary batteries for electric mobility and the like have been known (see, for example, Patent Documents 1 and 2). Patent Documents 1 and 2 state that batteries are shared for electric motorcycles, four-wheeled automobiles, electric wheelchairs, electric carts, smartphones, etc., but the shared use is between individual electric mobility devices or as batteries for charging smartphones. In particular, when using lithium-ion secondary batteries, they are assumed to be used with the same model, and a dedicated battery management system is required to control each cell within the battery module to protect against thermal runaway, so a dedicated battery or a dedicated battery management system is required for each of the same model. Summary of the Invention [Problem to be solved by the invention]

[0004] Since small electric vehicles have limited space for installing secondary batteries, the driving distance of a fully charged secondary battery is limited to about 50 to 80 km. In addition, charging a secondary battery takes time, and the vehicle cannot be operated during that time. To address this issue, battery replacement systems have been proposed; however, it is often difficult for elderly people and women to replace heavy secondary batteries and perform various other tasks, so there is a demand for lighter secondary batteries. Furthermore, when secondary batteries with different potentials are connected in series or parallel, a large current flows from the secondary battery with a higher potential to the secondary battery with a lower potential, which can cause heat generation and the risk of fire.

[0005] In view of the above problems, an object of the present invention is to provide a small electric vehicle that is lightweight, has an easily replaceable secondary battery, and has a low risk of heat generation and fire. [Means for solving the problem]

[0006] In order to solve the above problems, a small electric vehicle according to one embodiment of the present invention is characterized in having an electricity storage system that stores electricity in a lithium-ion secondary battery having an internal resistance of 60 mΩ·Ah or less. Effect of the Invention

[0007] According to the present invention, it is possible to provide a small electric vehicle which is lightweight, has an easily replaceable secondary battery, and has a low risk of heat generation and fire. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing an example of a connection relationship between a small electric vehicle and a lithium ion secondary battery according to an embodiment of the present invention. [Diagram 2] 1 is a schematic diagram showing an example of a connection relationship between a lithium ion secondary battery and a natural energy power generation system in a small electric vehicle according to an embodiment of the present invention. FIG. [Diagram 3] 1 is a schematic diagram showing an example of a relationship between a small electric vehicle and a charging station for an exchangeable secondary battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a small electric vehicle according to an embodiment of the present invention will be described. Fig. 1 is a schematic diagram showing an example of a connection relationship between a small electric vehicle according to an embodiment of the present invention and a lithium ion secondary battery. The small electric vehicle 100 shown in Fig. 1 has a voltage sensor 10, which is connected to a lithium ion secondary battery 20.

[0010] The voltage sensor 10 is a device having a mechanism for opening and closing a circuit in response to a change in voltage.

[0011] The lithium ion secondary battery 20 has an internal resistance of 60 [mΩ·Ah] or less, preferably 45 [mΩ·Ah] or less and 15 [mΩ·Ah] or more. If the internal resistance is 60 [mΩ·Ah] or less, heat generation due to charging and discharging can be suppressed, heat generation of the secondary battery can be suppressed and thermal stability can be improved, and the risk of smoke and fire due to overcharging and overdischarging can be reduced. In addition, by setting the internal resistance to 60 [mΩ·Ah] or less, loss due to internal resistance can be suppressed, and the secondary battery can be charged well even if the charging current flowing through the secondary battery is small.

[0012] The lithium ion secondary battery 20 is not particularly limited and may be appropriately selected depending on the purpose, and examples thereof include a manganate lithium ion secondary battery, a cobalt oxide lithium ion secondary battery, a lithium iron phosphate ion secondary battery, a ternary lithium ion secondary battery, a nickel-based lithium ion secondary battery, etc. Among these, a manganate lithium ion secondary battery is preferable because it has a small self-discharge and does not require cell balance control of serial cells for protecting the secondary battery.

[0013] The positive electrode of the lithium ion secondary battery 20 is preferably an active material having a spinel structure or an olivine structure. Even if the positive electrode is in a lithium-free (Li) state, the crystal structure is not broken, so the risk of smoke and fire is reduced. In addition, since the positive electrode has a spinel structure, a protection circuit is not required, and the cost and internal resistance of the power storage system can be reduced.

[0014] Considering heat generation due to inrush current, a lithium manganate ion secondary battery using lithium manganate with a spinel structure, which has low internal resistance, as the positive electrode material is preferable as the lithium ion secondary battery 20. The crystals of the positive electrode material of the lithium manganate ion secondary battery are stable against fluctuations in the amount of Li and heat, and are stable and safe against heat generation due to inrush current that is likely to occur when replacing the unit and physical shocks when replacing the unit.

[0015] The lithium-ion secondary battery 20 is made of a general ternary positive electrode material, cobalt acid positive electrode material, and nickel-based positive electrode material, and since the positive electrode has a layered crystal structure, there is a risk of thermal runaway, so the charging current and charging voltage are strictly limited. For this reason, it is necessary to attach a protection circuit to each cell in the battery module, but this circuit increases the internal resistance of the charging / discharging system and reduces the charging / discharging efficiency. By using lithium manganate positive electrode material with a spinel structure, which has a low risk of smoke and fire, or phosphate-based positive electrode material with an olivine structure, the need for individual cell protection circuits is eliminated, reducing costs and the internal resistance of the energy storage system. Furthermore, since the self-discharge rate of lithium manganate positive electrodes is extremely low, there is almost no voltage fluctuation due to self-discharge, and balancing circuits between cells are not required. This makes it possible to connect secondary batteries without the voltage of the generator (panel) passing through various protection circuits, and by connecting the generator in parallel with the power generation device, the power generation device is fixed at the battery voltage, so the current generated by the generator flows directly into the batteries connected in parallel, eliminating losses due to resistance and improving charge and discharge efficiency.

[0016] Furthermore, manganese, phosphorus and iron are abundant materials and do not have resource problems as with cobalt used in ternary systems, making this system extremely beneficial for widespread worldwide adoption.

[0017] The lithium ion secondary battery 20 is not particularly limited and can be appropriately selected depending on the purpose, but it is preferable to have a replaceable system. By easily replacing a pre-charged secondary battery, the use and operation downtime of the small electric vehicle due to charging is shortened, improving the operation efficiency.

[0018] It is preferable that the lithium ion secondary battery 20 can be commonly used in electrical products. This allows the control device for the lithium ion secondary batteries configured in series to be installed in other small electric vehicles such as two-wheeled, three-wheeled, and four-wheeled vehicles and used. The electrical appliance is not particularly limited and can be appropriately selected depending on the purpose. Examples of the electrical appliance include batteries for electric motorcycles, four-wheeled automobiles, electric wheelchairs, electric carts, and smartphones.

[0019] It is preferable that the lithium ion secondary batteries 20 can be used in series or parallel connection. Since it is necessary to manage only the total voltage of the lithium ion secondary batteries configured in series, the lithium ion secondary batteries configured in series can be freely combined in series or parallel, and a certain charge balance can be ensured by managing the charge.

[0020] No special control is required on the side that uses the power from the lithium-ion secondary batteries configured in series in the small electric vehicle. On the charging side, charging via a balancing circuit or a system that manages each battery connected in series is required, but when using batteries that use lithium manganate, self-discharge is extremely small, so charging that manages the voltage of the entire module is possible and a balancing circuit is not required.

[0021] In addition, although chemical batteries such as lead secondary batteries and redox flow batteries can be charged and discharged at the same time, there is a reverse polarization (hysteresis) in the chemical reactions during charging and discharging, so a reverse voltage is applied to the electrode surface where the reaction occurs depending on the charge / discharge current balance. This causes damage to the reaction interface of the battery, shortening the battery life. For this reason, the battery voltage of the secondary battery is applied to the generator (panel) to fix the generated voltage, and by using a chemical battery in this embodiment, there is a risk that the life of the secondary battery will be shortened.

[0022] The lithium ion secondary battery 20 is a "non-chemical battery" that has a higher capacity density than a lead acid battery, has a voltage corresponding to the charge amount in a narrow range, and has an operating principle in which the charge movement of a capacitor is replaced by the movement of lithium ions. In addition, in a lithium ion secondary battery, if the charge amount is 20 to 80%, Li is easily moved, so the internal resistance is almost constant and it follows even rapid fluctuations in the charging current. In addition, the charging of lithium ions depends on the current, and the charging amount depends on the voltage. By charging the modules until the battery voltage reaches a certain voltage, the charging state of the batteries can be made uniform, making it possible to use them in a parallel combination. In addition, when the target module reaches a certain voltage, the connection is switched to the module to be charged, and the panel voltage is switched to the new target battery voltage, and charging begins at the optimal voltage for the target module. By performing this switching sequentially, charging without waste is possible.

[0023] In the relationship between the small electric vehicle and the secondary battery, power is supplied from the secondary battery to the small electric vehicle.

[0024] When a small electric vehicle is traveling uphill, in particular, it is necessary to supply a larger current to the motor in order to increase the motor torque of the small electric vehicle.

[0025] In addition, no protection circuit is required for charging control during charging, and if lithium manganese oxide positive electrode material is used, the cell balance circuit can also be eliminated.

[0026] Fig. 2 is a schematic diagram showing an example of the connection relationship between a lithium ion secondary battery and a natural energy power generation system in a small electric vehicle according to an embodiment of the present invention. A generator 30 using natural energy shown in Fig. 2 has a voltage sensor 10 and is connected to a lithium ion secondary battery 20 according to the present invention.

[0027] The power generation method of the generator 30 using natural energy is not particularly limited and can be appropriately selected depending on the purpose, and examples include power generation using natural energy such as solar, hydroelectric, wind, geothermal, tidal, etc. This makes it possible to provide an off-grid system in which power is generated using natural energy so that the power storage system can be used even in places without grid power lines, and the generated power is used for charging.

[0028] The power storage system is preferably a replaceable battery system, and more preferably a replaceable battery system capable of remotely monitoring the amount of power in the lithium-ion secondary battery. By remote monitoring, secondary battery information can be checked in real time using a smartphone or the like.

[0029] Conventional lithium ion secondary batteries are paired with the target product, because it is necessary to control or manage the input and output of the same voltage and current values ​​for each battery cell to prevent heat generation and fire in the lithium ion secondary battery. For this reason, it is difficult to use conventional lithium ion secondary batteries in different product groups or from different manufacturers. In the replaceable battery system according to the present invention, the lithium ion secondary battery can be used in a variety of products and is replaceable.

[0030] Fig. 3 is a schematic diagram showing an example of the relationship between a small electric vehicle and a charging station for replaceable secondary batteries according to an embodiment of the present invention. Electricity obtained from natural energy is supplied to and stored in a replaceable secondary battery installed in the battery station, and the charge amount of the replaceable secondary battery can be remotely managed and confirmed. The replaceable secondary battery of the small electric vehicle is replaced with a replaceable secondary battery installed in a battery station, allowing the small electric vehicle to continue traveling without waiting for the time required for charging. In addition, this replaceable secondary battery does not require management of each battery cell as with conventional lithium-ion secondary batteries, and there is no need for unique control equipment for each product, so it can be used as a power source for a variety of small electric vehicles and outdoor use. EXAMPLES

[0031] Next, a verification test carried out by the applicant will be described as an example.

[0032] Example 1 In Example 1, a lithium manganate secondary battery in which the positive electrode is an active material having a spinel structure was used as the battery module. The battery module had a nominal battery voltage of 24 [VDC] and an internal resistance of 60 [mΩ·Ah]. In Example 1, the system shown in Fig. 2 was used to charge a lithium-ion secondary battery using a solar panel as a generator using natural energy. The lithium-ion secondary battery was not provided with a battery management system that monitors the current and voltage of each secondary battery cell in the battery module, and charging control was performed by controlling only the voltage of the entire secondary battery. Charging was performed for 30 minutes, and the open circuit voltage of the secondary battery after charging was 25.80 [VDC]. The charged secondary batteries were then attached to a four-wheeled electric cart. The electric cart had four secondary batteries connected in a two-series, two-parallel configuration, and was equipped with a voltage sensor to collectively protect the four secondary batteries, and a plug to allow the secondary batteries to be removed. The DC voltage of the two-series, two-parallel charged secondary batteries attached to the four-wheeled electric cart was 51.60 VDC. After that, the electric cart was started by turning on the start switch, and was driven for 30 minutes at the maximum speed [19 km / h] outdoors at an outside temperature of 20°C. The instantaneous value of the DC current when starting was measured to be 192 [A], and the instantaneous value of the DC current while driving was measured to be 113 [A]. The surface temperature of the lithium-ion secondary battery was measured to be 23°C. After that, the secondary battery's DC voltage was stable up to 40 [VDC] and could be used over a range of 11.6 [VDC].

[0033] Next, we replaced the lithium manganese oxide secondary batteries in a four-wheeled electric cart. Each secondary battery module weighed 5 kg, and the total replacement time for the four secondary battery modules was less than one minute. Next, the lithium-ion secondary battery, which had been charged using power supplied from a solar panel, was connected to an electric kick scooter and the scooter was driven. The open-circuit voltage of the secondary battery after charging was 25.80 [VDC]. The secondary battery after charging was attached to the electric kick scooter, the start switch was turned on, and the scooter was started by using the accelerator, and the scooter was confirmed to start moving. The scooter reached a speed of [14.6 km / h]. The instantaneous DC current value at startup was measured at 19A. The instantaneous DC current value while driving was measured at 6A. The vehicle was driven for 30 minutes outdoors at an outside temperature of 20°C, and the surface temperature of the secondary battery was measured, finding it to be 20.5°C. After that, the vehicle was able to run stably up to a DC voltage of 40 VDC from the secondary battery.

[0034] Example 2 The secondary batteries used were four lead-acid batteries connected in series, each with a rated voltage of 12 VDC and an internal resistance of 226.8 mΩ·Ah. The lithium-ion secondary batteries in Figure 2 were replaced with lead-acid secondary batteries, and charging was performed using a solar panel as a natural energy generator. After charging for 10 hours, the open-circuit voltage of the four lead-acid secondary batteries connected in series was 51.60 VDC. After that, the electric cart was turned on and started moving, reaching the upper limit of speed [19km / h]. The instantaneous DC current value at startup was measured at 141A. The instantaneous DC current value while driving was measured at 82A. The vehicle was driven for 30 minutes outdoors at an outside temperature of 20°C, and the surface temperature of the lead secondary battery was measured, finding it to be 26.5°C. After that, the vehicle was able to run stably up to a DC voltage of 43 VDC from the lead secondary battery. It was available with a width of 8.6 [VDC]. Next, we replaced the lead-acid battery connected to the four-wheel electric cart. The weight of one lead-acid secondary battery module was 11 kg, and the total replacement time for the four secondary battery modules was 15 minutes. Next, we connected the electric kick scooter to the secondary battery. The lithium-ion secondary battery in Figure 2 was replaced with a lead secondary battery, and the natural energy generator was replaced with a solar panel for 10 hours of charging. After charging, the lead secondary battery had an open voltage of 12.8 [VDC]. Two lead secondary batteries were connected in series to give an open voltage of 25.6 [VDC], and an attempt was made to install them on an electric kick scooter. The lead storage battery was large in volume, making it difficult to fit it in the space for installing the secondary battery on the kick scooter, so installation was abandoned.

[0035] For example, aspects of the present invention are as follows. <1> This small electric vehicle is characterized by having an electricity storage system that stores electricity in a lithium-ion secondary battery with an internal resistance of 60 mΩ·Ah or less. <2> The positive electrode of the lithium ion secondary battery is an active material having a spinel structure or an olivine structure. <1> 2. A small electric vehicle according to claim 1. <3> The lithium ion secondary battery has a replaceable system. <1> from <3> 13. The small electric vehicle according to claim 12, <4> The lithium ion secondary batteries can be used in series or parallel connection. <1> from <4> 13. The small electric vehicle according to claim 12, <5> The power storage system stores power using at least one natural energy source selected from solar power, hydraulic power, wind power, geothermal power, and tidal currents. <1> from <5> 13. The small electric vehicle according to claim 12, <6> The internal resistance is 60mΩ·Ah or less. This is a lithium-ion secondary battery that can be commonly used in small electric vehicles. <7> The above can be used for all electrical appliances. <6> The lithium ion secondary battery is as described above. <8> The above <6> from <7> 1 is a replaceable battery system capable of remotely monitoring the amount of electric power of the lithium ion secondary battery according to any one of claims 1 to 9.

[0036] Although the present invention has been described above based on the embodiments, the present invention is not limited to the requirements shown in the above embodiments. These points can be changed without departing from the spirit of the present invention, and can be appropriately determined according to the application form. [Explanation of symbols]

[0037] 10 Voltage Sensor 20 Lithium-ion secondary battery 30 Natural energy generator 100 Small electric vehicles [Prior art documents] [Patent documents]

[0038] [Patent Document 1] Patent Application No. 2020-194604 [Patent Document 2] Patent Application No. 2020-501736

Claims

1. A small electric vehicle comprising an electricity storage system for storing electricity in a lithium ion secondary battery having an internal resistance of 60 mΩ·Ah or less.

2. 2. The small electric vehicle according to claim 1, wherein the positive electrode of the lithium ion secondary battery is an active material having a spinel structure or an olivine structure.

3. The small electric vehicle according to claim 1 or 2, wherein the lithium ion secondary battery has a replaceable system.

4. 3. The small electric vehicle according to claim 1, wherein the lithium ion secondary batteries can be used in a series or parallel connection.

5. 3. The small electric vehicle according to claim 1, wherein the power storage system stores power using at least one natural energy source selected from the group consisting of solar power, hydroelectric power, wind power, geothermal power, and tidal currents.

6. The internal resistance is 60 mΩ·Ah or less, A lithium-ion secondary battery that can be commonly used in small electric vehicles.

7. 7. The lithium ion secondary battery according to claim 6, which can be commonly used in electrical products.

8. 8. A replaceable battery system capable of remotely monitoring the amount of electric power of the lithium ion secondary battery according to claim 6.

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