Battery system, secondary battery, and electric flying body

Abstract

The battery system is mounted on the electric moving body. A battery system is provided with a secondary battery (2) and a battery control unit. The battery control unit controls the secondary battery (2) so as to perform high-rate discharge when the electric moving body is started. A positive electrode (4) of a secondary battery (2) has a first active material (41) and a second active material (42). In a high-rate discharge region, which is an SOC region of the secondary battery (2) that performs high-rate discharge at the time of startup, the second active material (42) has a high-resistance region having a higher resistance than the first active material (41). The secondary battery (2) is configured such that the utilization rate of the second active material (42) is higher than the utilization rate of the first active material (41) during high-rate discharge at the time of startup, and then the utilization rate of the first active material (41) is higher than the utilization rate of the second active material (42).

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based on Japanese application No. 2023-019462 filed on February 10, 2023, the contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a battery system, a secondary battery, and an electric flying object. Background Art

[0004] Patent Document 1 discloses an electric flying vehicle equipped with multiple secondary batteries. This electric flying vehicle is configured to perform an emergency evacuation maneuver if a secondary battery malfunctions. Furthermore, if a malfunction occurs in one secondary battery, the electric flying vehicle replenishes the power required for flight by using other secondary batteries, thereby preventing the malfunction from developing into a safety-compromising malfunction.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-196440 Summary of the Invention

[0008] Typically, an electric aircraft requires relatively high output power during startup and takeoff. Therefore, when the electric aircraft takes off, the discharge rate of the secondary battery increases, which can easily cause a deviation in the ion concentration distribution within the secondary battery. Consequently, this deviation in ion concentration distribution can cause a temporary increase in the internal resistance of the secondary battery, or temporary degradation. Therefore, even if the electric aircraft described in Patent Document 1 includes multiple secondary batteries, temporary degradation may occur in all of the multiple secondary batteries. From the perspective of ensuring the output power of the electric aircraft during startup, there is room for further improvement.

[0009] The present disclosure provides a battery system, a secondary battery, and an electric flying vehicle that can increase the output power at the time of starting an electric vehicle.

[0010] A first aspect of the present disclosure is a battery system mounted on an electric vehicle, the battery system comprising:

[0011] Secondary batteries, and

[0012] a battery control unit for controlling discharge of the secondary battery,

[0013] The battery control unit controls the secondary battery so that high-rate discharge is performed when the electric vehicle is started, wherein the high-rate discharge is higher than the discharge rate of the secondary battery during normal operation of the electric vehicle.

[0014] The positive electrode of the secondary battery has:

[0015] a first active substance, and

[0016] a second active material having a high-resistance region having a higher resistance than that of the first active material in a high-rate discharge region, wherein the high-rate discharge region is an SOC region of the secondary battery in which the high-rate discharge is performed during the startup;

[0017] The secondary battery is configured such that, after the utilization rate of the second active material becomes higher than that of the first active material during the high-rate discharge at the start-up, the utilization rate of the first active material becomes higher than that of the second active material.

[0018] A second aspect of the present disclosure is a secondary battery, characterized in that it is a secondary battery mounted on an electric flying vehicle and has a positive electrode and a negative electrode.

[0019] The positive electrode has:

[0020] a first active substance, and

[0021] The second active material has a resistance higher than that of the first active material when the SOC value of the secondary battery is a predetermined value.

[0022] The first active material is lithium nickel cobalt manganese oxide having a layered rock salt structure, and the second active material is lithium manganese iron phosphate having an olivine structure.

[0023] A third aspect of the present disclosure is an electric flying object including the battery system according to the first aspect.

[0024] A fourth aspect of the present disclosure is an electric flying object including the secondary battery according to the second aspect.

[0025] In the battery system of the first embodiment described above, the secondary battery is configured such that, during high-rate discharge at startup, after reaching a state where the utilization rate of the second active material is higher than that of the first active material, the utilization rate of the first active material is higher than that of the second active material. Therefore, by increasing the temperature of the secondary battery during startup, high-rate discharge of the secondary battery can be performed while reducing the internal resistance of the secondary battery. In other words, by suppressing temporary degradation of the secondary battery, high output power of the secondary battery can be ensured. As a result, the output power of the electric vehicle during startup can be increased.

[0026] The secondary battery of the second embodiment described above comprises a first active material and a second active material. When the SOC of the secondary battery reaches a predetermined value, the resistance of the second active material is higher than that of the first active material. Furthermore, the first active material is lithium nickel cobalt manganese oxide with a layered rock salt structure, and the second active material is lithium manganese iron phosphate with an olivine structure. Therefore, by suppressing temporary degradation of the secondary battery during startup, high output power of the secondary battery can be ensured. As a result, the output power of the electric vehicle during startup can be improved.

[0027] The third embodiment of the electric flying vehicle includes the battery system of the first embodiment. Therefore, during startup, temporary degradation of the secondary battery can be suppressed, ensuring high output power from the secondary battery. Consequently, the output power of the electric flying vehicle during startup can be increased.

[0028] The electric flying object of the fourth embodiment includes the secondary battery of the second embodiment. Therefore, by suppressing temporary degradation of the secondary battery during startup, high output power of the secondary battery can be ensured. Consequently, the output power of the electric flying object during startup can be increased.

[0029] As described above, according to the above aspects, it is possible to provide a battery system, a secondary battery, and an electric flying vehicle that can increase the output power when starting an electric vehicle.

[0030] It should be noted that the symbols in parentheses described in the claims indicate the corresponding relationship with the specific means described in the embodiments described later, and do not limit the technical scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above-mentioned objects and other objects, features and advantages of the present disclosure will become more apparent through reference to the accompanying drawings and the following detailed description.

[0032] [ Figure 1 ] Figure 1 This is an external view of an electric flying vehicle equipped with a battery system in Embodiment 1;

[0033] [ Figure 2 ] Figure 2 is a cross-sectional view of the secondary battery in Embodiment 1;

[0034] [ Figure 3 ] Figure 3 is a diagram showing the relationship between the SOC and the voltage of the secondary battery in the first embodiment;

[0035] [ Figure 4 ] Figure 4 is a diagram showing the relationship between the SOC and voltage of the secondary battery in Comparative Example 1;

[0036] [ Figure 5 ] Figure 5 is a diagram showing the relationship between the SOC and voltage of the secondary battery in Comparative Example 2;

[0037] [ Figure 6 ] Figure 6 This is a flowchart showing the flow from charging of the secondary battery to discharging during normal operation in the first embodiment;

[0038] [ Figure 7 ] Figure 7 This is a diagram showing the magnitude of output power at takeoff, normal operation, and landing in Embodiment 1;

[0039] [ Figure 8 ] Figure 8 is a graph showing the relationship between the discharge rate, the temperature of the secondary battery, and the internal resistance of the secondary battery in Embodiment 1 and Comparative Example 1;

[0040] [ Figure 9 ] Figure 9 This is a scanning electron microscope photograph of a cross section of the secondary battery in Example 1. DETAILED DESCRIPTION

[0041] (Implementation 1)

[0042] Reference Figures 1 to 8 Embodiments related to a battery system, a secondary battery, and an electric flying vehicle will be described.

[0043] like Figure 1 As shown, a battery system 1 of this embodiment is mounted on an electric vehicle 10. The battery system 1 includes a secondary battery 2 and a battery control unit 3 that controls the discharge of the secondary battery 2. The battery control unit 3 controls the secondary battery 2 so that it performs high-rate discharge when the electric vehicle 10 is started. High-rate discharge is discharge at a higher rate than the discharge rate of the secondary battery 2 during normal operation of the electric vehicle 10.

[0044] like Figure 2As shown, the positive electrode 4 of the secondary battery 2 includes a first active material 41 and a second active material 42. In the high-rate discharge region, i.e., the SOC (State of Charge) region of the secondary battery 2 during high-rate discharge at startup, the second active material 42 has a higher resistance than the first active material 41.

[0045] Secondary battery 2 is configured so that, during high-rate discharge at startup, the utilization rate of second active material 42 becomes higher than that of first active material 41, and then the utilization rate of first active material 41 becomes higher than that of second active material 42. In this embodiment, the high-rate discharge range can be set, for example, from the SOC value of secondary battery 2 at the start of high-rate discharge (i.e., the starting SOC value) to an SOC value 20 percentage points lower than the starting SOC value. For example, if the starting SOC value is 90%, the SOC range of 70-90% can be set as the high-rate discharge range. Furthermore, high-rate discharge can be set to continue within the SOC range of 70-90%.

[0046] For example, the battery system 1 of this embodiment can be used as a means for controlling discharge during movement of the electric vehicle 10 by being mounted on the electric vehicle 10. Examples of the electric vehicle 10 include electric vertical take-off and landing aircraft (eVTOL), electronic short-distance take-off and landing aircraft (eSTOL), and drones. In this embodiment, the electric vehicle 10 is an electric vertical take-off and landing aircraft.

[0047] like Figure 1 As shown, the electric aircraft 100 includes a battery system 1. That is, the electric aircraft 100 includes a secondary battery 2. The secondary battery 2 stores electric power for driving a motor (not shown) mounted on the electric aircraft 100. In this embodiment, the secondary battery 2 is a lithium-ion battery.

[0048] like Figure 2 As shown, the secondary battery 2 mounted on the electric aircraft 100 includes a positive electrode 4 and a negative electrode 5. The positive electrode 4 and the negative electrode 5 have current collectors 43 and 52, respectively. By electrically connecting a load or a power generation device to these current collectors 43 and 52, the secondary battery 2 can be discharged or charged. For example, conductive materials such as metal foil and metal plates can be used as the current collectors 43 and 52.

[0049] Secondary battery 2 includes a separator 6. Separator 6 is disposed between positive electrode 4 and negative electrode 5, separating the positive electrode 4 and negative electrode 5. Separator 6 is lithium-ion permeable. In this embodiment, separator 6 is sheet-shaped and has a porous structure. For example, a separator made of a polyolefin such as polyethylene or polypropylene can be used.

[0050] The secondary battery 2 includes an electrolyte 20. In this embodiment, the electrolyte 20 is impregnated in the positive electrode 4, the negative electrode 5, and the separator 6, respectively. The electrolyte 20 may contain, for example, a non-aqueous solvent and a lithium salt. The non-aqueous solvent may be, for example, dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, or a mixture thereof. The lithium salt may be, for example, LiPF6, LiBF4, LiClO4, or a mixture thereof. The electrolyte 20 may also contain, for example, vinylene carbonate as an additive.

[0051] In addition, a solid electrolyte may be used as the electrolyte 20 of the secondary battery 2. The solid electrolyte may be, for example, a polymer solid electrolyte such as polyethylene oxide, a sulfide solid electrolyte, or an oxide solid electrolyte. In addition, as a sulfide solid electrolyte, for example, a solid electrolyte having an argyrodite structure such as Li6PS5Cl or a solid electrolyte having a sulfide structure such as Li6PS5Cl may be used. 10 GeP2S 12 As an oxide-based solid electrolyte, for example, Li 1.25 La 0.58 Solid electrolytes with pyrochlore structures such as Nb2O6F, Li7La3Zr2O 12 Solid electrolytes with garnet structure, Li 1.4 Al 0.4 Ti 1.6 (PO4)3 and other solid electrolytes with NASICON structure, La 0.57 Li 0.29 A solid electrolyte having a perovskite structure, such as TiO3, may be used. Alternatively, the electrolyte 20 may be a mixture of two or more of the solid electrolytes listed above. Alternatively, the solid electrolytes listed above may be contained in the positive electrode 4 and the negative electrode 5.

[0052] Positive electrode 4 and negative electrode 5 are provided on the surfaces of current collectors 43 and 52, respectively, and have active material layers 40 and 50 containing active materials. Active material layers 40 and 50 may contain, for example, a conductive material, a binder, and the like in addition to the active material.

[0053] As the active material 51 contained in the active material layer 50 of the negative electrode 5 , for example, graphite, silicon, lithium metal, or LTO (lithium titanate)-based active materials can be used.

[0054] The active material layer 40 of the positive electrode 4 includes a first active material 41 and a second active material 42. In this embodiment, the first active material 41 is lithium nickel cobalt manganese oxide having a layered rock salt structure. The second active material 42 is lithium manganese iron phosphate having an olivine structure. The energy density of lithium nickel cobalt manganese oxide, the first active material 41, is greater than the energy density of lithium manganese iron phosphate, the second active material 42. It should be noted that the active material layer 40 of the positive electrode 4 may also contain active materials other than the first active material 41 and the second active material 42.

[0055] In this embodiment, the higher the SOC of the secondary battery 2, the lower the resistance of the first active material 41. Furthermore, the lithium nickel cobalt manganese oxide serving as the first active material 41 can be represented by the following formula (1). Furthermore, in this embodiment, the lithium nickel cobalt manganese oxide serving as the first active material 41 can be represented by the following formula (2). In the following formula (1), x+y+z=1, 0.6≤x<1, 0.02≤y≤0.2, and 0.02≤z≤0.2.

[0056] LiNi x Co y Mn z O2···(1)

[0057] LiNi 0.8 Co 0.1 Mn 0.1 O2···(2)

[0058] When the SOC value of the secondary battery 2 is a predetermined value, the resistance of the second active material 42 is higher than the resistance of the first active material 41. That is, as described above, in the high-rate discharge region, the second active material 42 has a high-resistance region in which the resistance is higher than that of the first active material 41. The lithium manganese iron phosphate serving as the second active material 42 can be expressed by the following formula (3). In this embodiment, the lithium manganese iron phosphate serving as the second active material 42 can be expressed by the following formula (4). In the following formula (3), x>0.5.

[0059] LiMn x Fe 1-x PO4···(3)

[0060] LiMn 0.6 Fe 0.4 PO4···(4)

[0061] The ratio of the first active material 41 to the total active material of the positive electrode 4 is 50-95% by weight, and the ratio of the second active material 42 to the total active material of the positive electrode 4 is 5-50% by weight. Furthermore, when the initial SOC value is set to a relatively high value of approximately 90%, the ratio of the second active material 42 to the total active material of the positive electrode 4 is preferably 5-20% by weight, and the ratio of the first active material 41 to the total active material of the positive electrode 4 is preferably 80-95% by weight. Furthermore, the ratio of the first active material 41 to the total active material of the positive electrode 4 is more preferably 90% by weight or greater, and the ratio of the second active material 42 to the total active material of the positive electrode 4 is more preferably 10% by weight or less. Furthermore, the ratio of the second active material 42 to the total active material of the positive electrode 4 is even more preferably 9% by weight or less. Furthermore, when the initial SOC value is set to a relatively low value of approximately 60%, the ratio of the second active material 42 to the total active material of the positive electrode 4 is preferably 40-50% by weight, and the ratio of the first active material 41 to the total active material of the positive electrode 4 is preferably 50-60% by weight.

[0062] In this embodiment, the average particle size of the first active material 41 is larger than the average particle size of the second active material 42. In other words, the average particle size of the second active material 42 is smaller than the average particle size of the first active material 41. However, whether the average particle size of the first active material 41 is larger than the average particle size of the second active material 42 or smaller than the average particle size of the second active material 42, the output power during startup of the electric vehicle 10 can be increased. The average particle size of the first active material 41 can be, for example, 5 to 15 μm, and the average particle size of the second active material 42 can be, for example, 0.1 to 20.0 μm.

[0063] Next, the characteristics of the secondary battery 2 of this embodiment will be described.

[0064] like Figure 3 As shown, the voltage of the secondary battery 2 of this embodiment changes as the SOC value changes. Specifically, the smaller the SOC value of the secondary battery 2, the smaller the potential difference between the positive electrode 4 and the negative electrode 5, that is, the voltage of the secondary battery 2. In addition, as described later, the utilization rate of the first active material 41 and the utilization rate of the second active material 42 change according to the voltage of the secondary battery 2. In this embodiment, the utilization rate of the first active material 41 refers to the ratio of lithium ions stored in the first active material 41 of the positive electrode 4 to the total lithium ions stored in the active material during discharge. In addition, the utilization rate of the second active material 42 refers to the ratio of lithium ions stored in the second active material 42 of the positive electrode 4 to the total lithium ions stored in the active material during discharge.

[0065] In this embodiment, the reaction during charge and discharge at around 3.4V is mainly related to Fe (i.e., iron) of the lithium manganese iron phosphate as the second active material 42. On the other hand, the reaction during charge and discharge at around 4.0V is mainly related to Mn (i.e., manganese) of the lithium manganese iron phosphate as the second active material 42. Therefore, Figure 5 As shown, in the case of the secondary battery of Comparative Example 2, which has only lithium manganese iron phosphate as the active material of the positive electrode, a flat voltage curve is formed at around 3.4 V and around 4.0 V, and charging and discharging are mainly carried out in the potential range around 3.4 V and around 4.0 V. That is, in this example, the second active material 42 mainly reacts during charging and discharging in the potential range around 3.4 V and around 4.0 V. Therefore, in this example, Figure 3 As shown, when the voltage of the secondary battery 2 is around 3.4V and around 4.0V, there is a region where the utilization rate of the second active material 42 is higher than the utilization rate of the first active material 41, namely the second highest utilization region. In addition, when the SOC value of the secondary battery 2 is around 10% and around 80-90%, it becomes the second highest utilization region. Moreover, in these second highest utilization regions, the second active material 42 is mainly related to the reaction during charging and discharging. That is, the secondary battery 2 is configured to have a second highest utilization region in a low SOC region where the SOC value of the secondary battery 2 is lower than a specified value. The low SOC region can be, for example, a region where the SOC value is below 30%. It should be noted that an SOC of 0% refers to a state in which the secondary battery 2 is fully discharged, and an SOC of 100% refers to a state in which the secondary battery 2 is fully charged.

[0066] In addition, in this method, if Figure 3 As shown in FIG, except for the two second high utilization areas, the utilization rate of the first active material 41 is higher than that of the second active material 42. In the first high utilization area, the first active material 41 is mainly used for the reaction during charge and discharge. Figure 4 As shown, in the case of the secondary battery of Comparative Example 1 using only lithium nickel cobalt manganese oxide, which is the same as the first active material, as the positive electrode active material, the voltage curve becomes lower as the SOC value decreases.

[0067] In addition, the resistance of the first active material 41 and the second active material 42 are different from each other. In addition, the internal resistance of the secondary battery 2 and the resistance of the active material change according to the state of charge of the secondary battery 2, that is, the value of the SOC. In this embodiment, in the low SOC region, the resistance of the second active material 42 is smaller than the resistance of the first active material 41. In addition, the resistance of the first active material 41 in the low SOC region is larger than the resistance in other SOC regions. Therefore, Figure 4 As shown, the internal resistance of Comparative Example 1 in the low SOC region is also larger than the internal resistance in other SOC regions.

[0068] In addition, in this embodiment, in the high-rate discharge region with an SOC value ranging from 70% to 90%, the second active material 42 has a high-resistance region in which the resistance is greater than that of the first active material 41. Here, the magnitude of the resistance of the first active material 41 and the second active material 42 can be measured, for example, by measuring the direct current resistance at various SOC values ​​of the secondary battery 2 using a DCIR (Direct Current Internal Resistance) measurement, or measuring the alternating current resistance at various SOC values ​​of the secondary battery 2 using an AC internal resistance measurement. Furthermore, whether the internal resistance of the secondary battery 2 measured by these measurement methods originates from the first active material 41 or the second active material 42 can be determined based on a secondary battery using only the same active material as either the first active material or the second active material as the active material of the positive electrode. Specifically, the resistance of the first active material 41 and the second active material 42 can be determined by referring to the internal resistance at SOC of a secondary battery using only the same active material as the first active material as the positive electrode active material and a secondary battery using only the same active material as the second active material as the positive electrode active material. For example, by referring to a secondary battery having a flat voltage curve around 4.0 V, the internal resistance at SOC can be determined. Figure 5 Comparison of the curve of method 2 and the curve that does not have a flat voltage curve near 4.0V Figure 4 By comparing the curve of the first embodiment with the curve of the second embodiment, the resistance of the second active material 42 in the secondary battery 2 of this embodiment can be obtained. Figure 3 As shown in the curve, by referring to Figure 4 Comparison of the curves of method 1 and Figure 5 Comparing the curve of form 2, it can be seen that the internal resistance of the secondary battery 2 in the second highest utilization range with an SOC value of approximately 80% and a voltage of approximately 4.0 V is mainly due to the resistance of the second active material 42 .

[0069] Next, the electric flying object 100 of this embodiment will be described.

[0070] like Figure 1 As shown, the electric flying object 100 of this embodiment includes a main body 102, fixed wings, and rotary wings 101. The main body 102 may include, for example, a storage space for transported cargo. Furthermore, in this embodiment, the fixed wings used to generate lift include a main wing 103 and a tail wing 104. Electric flying object 100 may be, for example, a manned aircraft or an unmanned aircraft.

[0071] Furthermore, the electric aircraft 100 includes multiple rotors 101 and multiple electric motors (not shown) that rotate each of the rotors 101. The electric motors are driven by electricity from a secondary battery 2. In this embodiment, the rotors 101 are provided in a main body 102 and a main wing 103. Rotating the rotors 101 using the electric motors generates lift or thrust, enabling the electric aircraft 100 to fly.

[0072] The electric flying object 100 is configured to be movable in a vertical direction and a horizontal direction. Furthermore, the electric flying object 100 may be configured to be movable in a direction that includes both vertical and horizontal components, that is, in a direction that is inclined relative to the horizontal direction.

[0073] Furthermore, the electric flying vehicle 100 of this embodiment is equipped with a plurality of secondary batteries 2. The plurality of secondary batteries 2 can be connected in series or in parallel, for example. In this embodiment, the electric flying vehicle 100 is equipped with a battery module modularized by connecting the plurality of secondary batteries 2 in series and in parallel.

[0074] The electric aircraft 100 of this embodiment includes an aircraft control unit 105 for controlling the flight of the electric aircraft 100. The aircraft control unit 105 may include, for example, a processor, memory, and a communication circuit for wireless communication. The processor, for example, executes a control program pre-stored in the memory to control the takeoff and landing, as well as normal operations, of the electric aircraft 100. Furthermore, the takeoff and landing, as well as normal operations of the electric aircraft 100, may be performed based on information about a pre-set flight path, or based on commands from outside the electric aircraft 100.

[0075] In the battery system 1 mounted on the electric aircraft 100, the battery control unit 3 includes a processor and memory. The processor of the battery control unit 3 controls the discharge of the secondary battery 2 by, for example, executing a control program pre-stored in the memory. In this embodiment, the battery system 1 is also part of the aircraft control unit 105.

[0076] Next, refer to Figure 6 The flowchart of FIG. 1 illustrates the process from charging the electric flying object 100 to performing normal operation.

[0077] First, in step S1, the secondary battery 2 mounted on the electric aircraft 100 is charged to ensure a sufficient cruising range for the electric aircraft 100. In this method, the secondary battery 2 is charged using an external charging device (not shown). Furthermore, in this method, charging is continued until the state of charge (SOC) of the secondary battery 2 reaches 90%. Then, in step S2, charging and discharging of the secondary battery 2 are stopped until the electric aircraft 100 begins flight. It should be noted that after charging the secondary battery 2, the electric aircraft 100 can also begin flight immediately without stopping.

[0078] Next, in step S3, the electric flying object 100 is started and the high rate discharge of the secondary battery 2 is started. When the electric flying object 100 of this embodiment is started, it takes off by driving the rotor 101 and reaches a place at a predetermined height. Figure 7 As shown, during startup and takeoff, the electric aircraft 100 requires higher output power than during normal operation. Therefore, under the control of the battery control unit 3, the secondary battery 2 is discharged at a high rate, driving the electric motor with high output power to rotate the rotor 101. In this embodiment, high-rate discharge is performed at a discharge rate of, for example, 4 to 12C (Capacity). Furthermore, in this embodiment, high-rate discharge begins when the state of charge (SOC) of the secondary battery 2 is at least 80%. Furthermore, in this embodiment, normal operation refers to the cruising of the electric aircraft 100 from the point immediately after takeoff at a predetermined altitude (i.e., the normal operation start point, described later) until it reaches the airspace above the destination. In other words, normal operation refers to the movement of the electric aircraft 100 that does not include takeoff and landing. Takeoff and landing of the electric aircraft 100 primarily involve movement in the vertical direction.

[0079] Then, by performing high rate discharge, Figure 6 In step S4, the secondary battery 2 is heated. During this heating step in step S4, the temperature of the secondary battery 2 can be raised to, for example, 45°C or higher. Specifically, during this heating step in step S4, the secondary battery 2 is heated by performing high-rate discharge in the high-resistance region and the second high-utilization region. During this heating step in step S4, the second active material 42 is primarily utilized. In this embodiment, the heating step is performed in the SOC region of the secondary battery 2, where the SOC is 70% or higher.

[0080] In addition, by implementing the heating step of step S4, as Figure 8 As shown in FIG. 1 , as the temperature of the secondary battery 2 rises, the internal resistance of the secondary battery 2 decreases. Figure 6As shown, in step S5 after the heating step, high-rate discharge is performed in a state where the internal resistance of the secondary battery 2 is low. Thus, high-output power discharge based on the secondary battery 2 can be performed. Then, in the high-output power step of step S5, the electric motor is driven based on the high-rate discharge of the secondary battery 2, so that the electric flying body 100 rises to a location at a predetermined height. In addition, in the high-output power step of step S5, the output power of the secondary battery 2 is performed in the first high utilization area where the utilization rate of the first active material 41 is higher than the utilization rate of the second active material 42. And, in the high-output power step, the first active material 41 is mainly utilized. Furthermore, the high-output power step is performed in an area where the resistance of the first active material 41 is lower than the resistance of the second active material 42.

[0081] In steps S3 to S5, continuous high output power is required from the secondary battery 2 from the start of high-rate discharge to the time when the electric aircraft 100 reaches the normal operation start point. That is, during steps S3 to S5, the secondary battery 2 continuously performs high-rate discharge. In this method, the time for high-rate discharge is shorter than the time for discharge during normal operation. That is, during takeoff at startup, the time for the secondary battery 2 to continuously perform high-rate discharge is shorter than the time for normal operation. In this method, the normal operation start point indicates a point at an altitude at which normal operation is started. In addition, startup indicates the period from the start of movement of the electric aircraft 100 as the electric mobile body 10 to the start of normal operation.

[0082] In step S5, after the electric aircraft 100 reaches the normal operation start point, in step S6, the battery control unit 3 controls the discharge of the secondary battery 2 so that the electric aircraft 100 can cruise to the target point during normal operation. The normal operation of the electric aircraft 100 cruises mainly in the horizontal direction. Therefore, Figure 7 As shown in FIG, the amount of power required is significantly reduced compared to the amount of power required for takeoff at startup. Figure 8 As shown, the internal resistance of the secondary battery 2 is also likely to be lower than in the heating step. Therefore, the temperature of the secondary battery 2 gradually decreases. In normal discharge, which is the discharge of the secondary battery 2 during normal operation, the discharge rate can be, for example, 0.3 to 1.0C.

[0083] In addition, Figure 6 While the steps after step S6 are omitted in the flowchart, in step S6, after the electric aircraft 100 is operated normally to the air above the destination, it is then descended from a predetermined altitude to the landing site and landed. Landing requires higher output power than normal operation. Therefore, when landing the electric aircraft 100, the battery control unit 3 controls the secondary battery 2 to discharge at a high rate.

[0084] Next, the effects of this embodiment will be described.

[0085] In the battery system 1 described above, the secondary battery 2 is configured such that, during high-rate discharge at startup, after the utilization rate of the second active material 42 reaches a higher level than that of the first active material 41, the utilization rate of the first active material 41 then becomes higher than that of the second active material 42. Therefore, during startup, by raising the temperature of the secondary battery 2, high-rate discharge of the secondary battery 2 can be performed while reducing the internal resistance of the secondary battery 2. In other words, by suppressing temporary degradation of the secondary battery 2, high output power of the secondary battery 2 can be ensured. Consequently, the output power of the electric vehicle can be increased during startup.

[0086] Typically, electric aircraft take off during startup, requiring high output power. Therefore, during takeoff, the secondary battery 2 undergoes high-rate discharge. Here, an electric aircraft is assumed not to undergo a heat generation step before the high-output step. In this case, during takeoff, the high-rate discharge could cause a deviation in the lithium ion concentration distribution within the secondary battery. If this deviation occurs, even if the secondary battery's SOC is sufficiently high, discharge is restricted, potentially causing temporary degradation of the secondary battery. Therefore, in the battery system 1 of this embodiment, control is performed so that the heat generation step is performed before the high-output step. Specifically, during startup, the high-rate discharge region is set to a high-resistance region and the second-highest utilization region, raising the temperature of the secondary battery 2. This facilitates the movement of lithium ions within the secondary battery 2, minimizing deviations in the lithium ion concentration distribution. As a result, temporary degradation of the secondary battery 2 can be suppressed, allowing the high-output step to be performed while the internal resistance of the secondary battery 2 is sufficiently low. Furthermore, during the high-output step following the heat generation step, the utilization rate of the first active material 41 is higher than that of the second active material 42. Furthermore, in the SOC region where the high-output step occurs, the resistance of the first active material 41 tends to be lower than that of the second active material 42. Therefore, the high output of the secondary battery 2 can be reliably ensured. Consequently, output performance can be improved throughout the entire high-rate discharge period.

[0087] Next, the present embodiment will be described while comparing it with Comparative Embodiment 1. In the present embodiment, the secondary battery 2 includes both the first active material 41 and the second active material 42 in the active material layer 40 of the positive electrode 4. Figure 8As shown, compared to Comparative Embodiment 1, which contains only lithium nickel cobalt manganese oxide as the positive electrode active material, this embodiment, which includes the second active material 42, can increase the internal resistance of the secondary battery 2 in the SOC region during the heat generation step. Therefore, the temperature of the secondary battery 2 can be reliably raised, and the internal resistance of the secondary battery 2 can be reliably reduced in the SOC region of the high output power step after the heat generation step. In other words, in this embodiment, the temperature of the secondary battery 2 can be raised when high output power is required, further increasing the utilization rate of the low-resistance first active material 41. As a result, high output power can be maintained while significantly reducing the internal resistance of the secondary battery 2.

[0088] In addition, generally, when a secondary battery is used as a battery module, depending on the constraint method using a constraint component for multiple secondary batteries, there may be a situation where the amount of electrolyte in the electrode is reduced due to the electrolyte being squeezed out of the electrode. In such a case, temporary degradation of the secondary battery due to the implementation of high-rate discharge may be easily generated. In addition, even in the case of so-called electrode expansion caused by the volume change of the active material, temporary degradation of the secondary battery due to the implementation of high-rate discharge may be easily generated. In contrast, in this method, it is configured to perform a high-output power step after the heat generation step. Therefore, even in a state where the electrolyte is squeezed out of the electrode due to the constraint of the secondary battery 2, etc., it is easy to suppress temporary degradation of the secondary battery 2. As a result, the high output power of the secondary battery 2 can be reliably ensured.

[0089] As the SOC of secondary battery 2 increases, the resistance of first active material 41 decreases. Therefore, in the SOC region where high-output steps are performed, the resistance of first active material 41 tends to decrease further. Consequently, in high-output steps where the utilization rate of first active material 41 is high, the high output of secondary battery 2 can be further ensured.

[0090] The ratio of the first active material 41 to the total active material in the positive electrode 4 is 50 to 95% by weight, and the ratio of the second active material 42 to the total active material in the positive electrode 4 is 5 to 50% by weight. Therefore, by adjusting the ratio of the first active material 41 to the second active material 42 in the positive electrode 4 within the above range, the SOC range that constitutes the second highest utilization region can be adjusted. Therefore, it is possible to adjust the SOC range where the heating step is to be performed so that it falls within the second highest utilization region. As a result, the heating step can be performed for an appropriate period of time, consistent with any starting SOC value.

[0091] When the initial SOC value is relatively high, the ratio of the first active material 41 to the total active material of the positive electrode 4 is preferably 80-95% by weight, and the ratio of the second active material 42 to the total active material of the positive electrode 4 is preferably 5-20% by weight. In this case, the heat generation step and the high-output step can be carried out efficiently. That is, when the initial SOC value is relatively high, if the ratio of the second active material 42 is higher than the above ratio, the heat generation step will be too long, and there is a possibility that the heat generation step and the high-output step will not be carried out efficiently. On the other hand, if the ratio of the second active material 42 to the total active material of the positive electrode 4 is lower than the above ratio, the heat generation step may not be carried out sufficiently. Therefore, when the initial SOC value is relatively high, the ratio of the second active material 42 to the total active material of the positive electrode 4 is preferably set to 5-20% by weight. This allows the heat generation step and the high-output step to be carried out efficiently. On the other hand, if the ratio of the first active material 41 is higher than the above ratio, there is a possibility that the ratio of the second active material 42 will be too low when the initial SOC value is relatively high, and there is a possibility that the heat generation step will not be carried out sufficiently. If the proportion of first active material 41 is lower than the above ratio, the proportion of second active material 42 may become excessively high when the initial SOC value is relatively high. Therefore, when the initial SOC value is relatively high, the proportion of first active material 41 relative to the total active material of positive electrode 4 is preferably set to 80-95% by weight. In this case, the heat generation step and the high-output step can be carried out efficiently, resulting in further increased output power during startup.

[0092] Furthermore, when the initial SOC value is set to be relatively low, the ratio of the second active material 42 to the total active material of the positive electrode 4 is preferably 40 to 50% by weight, and the ratio of the first active material 41 to the total active material of the positive electrode 4 is preferably 50 to 60% by weight. In this case, the heat generation step and the high output step can be efficiently performed at a relatively low initial SOC value.

[0093] When the initial SOC value is relatively high, the ratio of the second active material 42 to the total active material of the positive electrode 4 is preferably 10% by weight or less. In this case, the heat generation step and the high-output step can be performed reliably and efficiently. Furthermore, when the initial SOC value is relatively high, the ratio of the second active material 42 to the total active material of the positive electrode 4 is preferably 9% by weight or less. In this case, the heat generation step and the high-output step can be performed more reliably and efficiently.

[0094] The first active material 41 is lithium nickel cobalt manganese oxide having a layered rock salt structure. The second active material 42 is lithium manganese iron phosphate having an olivine structure. Therefore, the heat generation step and the high output power step can be reliably and effectively implemented. As a result, temporary degradation of the secondary battery 2 can be reliably suppressed, and high output power can be reliably ensured. In addition, it is easy to set up a second high utilization area in both the high rate discharge area at startup and the low SOC area. In addition, it is easy to set up a high resistance area in the high rate discharge area at startup, and in the low SOC area, the second active material 42 can easily have an area with a resistance lower than that of the first active material 41. Therefore, it is easy to reliably implement the heat generation step in the high rate discharge area at startup, and it is easy to reliably ensure high output power in the low SOC area. As a result, it is possible to reliably ensure high output power of the secondary battery 2 both at takeoff and landing.

[0095] Furthermore, lithium manganese iron phosphate as the second active material 42 is less susceptible to particle breakage and surface degradation than lithium nickel cobalt manganese oxide as the first active material 41. Therefore, the durability of the secondary battery 2 can be improved, resulting in a longer lifespan for the secondary battery 2.

[0096] In this embodiment, the average particle size of the first active material 41 is larger than the average particle size of the second active material 42. Therefore, the degradation of the first active material 41 can be reliably suppressed. That is, the first active material 41 reacts more easily with the electrolyte 20 on its surface than the second active material 42. Moreover, through the reaction at this time, a film may be formed on the surface of the first active material 41, causing the first active material 41 to degrade. Therefore, in this embodiment, the average particle size of the first active material 41 is made larger than the average particle size of the second active material 42. As a result, the surface area of ​​the first active material 41 contained in the positive electrode 4 can be reduced as a whole. That is, the area of ​​the surface of the first active material 41 as a whole that contacts the electrolyte 20 can be reduced. Therefore, the reaction between the first active material 41 and the electrolyte 20 can be suppressed, and the degradation of the first active material 41 can be reliably suppressed. As a result, the life of the secondary battery 2 can be extended.

[0097] The average particle size of the second active material 42 is smaller than the average particle size of the first active material 41. Therefore, the particle breakage of the second active material 42 can be further suppressed, the life of the secondary battery 2 can be reliably extended, and the temporary degradation of the secondary battery 2 can be reliably suppressed. In addition, the smaller the average particle size of the second active material 42, the easier it is to reduce the resistance of the second active material 42. In addition, since it is easy to evenly distribute the second active material 42 in the positive electrode 4, it is easy to improve the safety of the secondary battery 2. Among them, if the particle size of the second active material 42 is reduced to a nanometer size of less than 100 nm, it is easy for the particles of the second active material 42 to aggregate with each other, and it is easy to make it difficult to evenly mix the first active material 41 and the second active material 42. Therefore, the particle size of the second active material 42 is preferably set to 100 nm or more. As a result, manufacturability can be improved.

[0098] In the low SOC range, the resistance of the second active material 42 is lower than that of the first active material 41. Furthermore, the secondary battery 2 is configured to have a second high-utilization range in the low SOC range. Therefore, when the electric vehicle 100 is landed in the second high-utilization range within the low SOC range, the high output power of the secondary battery 2 can be further ensured. As a result, the output power during startup of the electric vehicle 10 can be further increased.

[0099] The electric flying object 100 includes the battery system 1. Therefore, when the electric flying object 100 is started, temporary deterioration of the secondary battery 2 is suppressed, thereby ensuring high output power.

[0100] The electric flying object 100 includes a secondary battery 2. Therefore, when the electric flying object 100 is started, high output power can be ensured by suppressing temporary degradation of the secondary battery 2.

[0101] As described above, according to this embodiment, it is possible to provide the battery system 1 , the secondary battery 2 , and the electric flying vehicle 100 that can improve the output power at the start-up of the electric vehicle 10 .

[0102] (Experimental Example 1)

[0103] In this example, while keeping the basic structure the same as that of the first embodiment, a plurality of secondary batteries having different compositions of the active materials of the positive electrodes were used to conduct discharge tests and cycle tests. As the active material of the positive electrode, LiNi 0.8 Co 0.1 Mn 0.1 O2 (hereinafter referred to as "NCM") and LiMn 0.6 Fe 0.4PO4 (hereinafter referred to as "LMFP"), graphite is used as the active material of the negative electrode. In addition, the electrolyte used is an electrolyte obtained by adding vinylene carbonate and 1M LiPF6 to a solvent. Vinylene carbonate is added so as to account for 1% of the entire electrolyte. In addition, as the solvent of the electrolyte, a solvent obtained by mixing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1 is used. In addition, Figure 9 This is a photograph of a cross section of the secondary battery of Example 1 shown in Table 1 described later, observed with a scanning electron microscope.

[0104] The test conditions for the discharge test are: an ambient temperature of 25°C, a SOC of the secondary battery at the start of discharge of 90%, a discharge rate of 10C, and a lower limit voltage of 2.8V. Furthermore, in the discharge test, the time from the start of discharge to the point where the discharge voltage reaches the lower limit and the discharge of the secondary battery stops, i.e., the power-on time, is investigated. Furthermore, the test conditions for the cycle test are: an ambient temperature of 25°C, a voltage of 2.8 to 4.2V during charge and discharge, and a discharge rate of 1C. Furthermore, in the cycle test, the capacity retention rate of the secondary battery after 300 cycles of charge and discharge is investigated. Here, the capacity retention rate refers to the ratio of the discharge capacity after the test to the discharge capacity before the test.

[0105] In this discharge test, a power-on time of 230 seconds or longer was used as a benchmark for improving the output power of an electric aircraft when using a secondary battery. Furthermore, in the discharge test, a power-on time of 240 seconds or longer was used as a benchmark for further improving the output power of an electric aircraft when starting. Therefore, based on the test results, the ratio of NCM to LMFP that meets this benchmark was determined. In Table 1 below, power-on times of 230 seconds or longer are indicated by "○," power-on times of 240 seconds or longer are indicated by "◎," and power-on times of less than 230 seconds are indicated by "×."

[0106] In this example's cycle test, a capacity retention rate of 80% or higher was used as the benchmark for sufficiently suppressing secondary battery degradation. Therefore, based on the test results, the ratio of NCM to LMFP that meets this benchmark was determined. In Table 1 below, a capacity retention rate of 80% or higher is indicated by an "O," while a capacity retention rate of less than 80% is indicated by an "X."

[0107] The results of the discharge test and cycle test are shown in Table 1 below. The active material ratio in Table 1 below indicates the weight ratio of the positive electrode NCM or LMFP to the total active material. In addition, the maximum temperature in Table 1 below indicates the temperature at which the secondary battery reached its highest temperature during the discharge test.

[0108] [Table 1]

[0109]

[0110] As shown in Table 1, Comparative Examples 1 and 2 did not meet the aforementioned criteria during the discharge test. In contrast, Examples 1 to 3 achieved a power-on time of 230 seconds or longer, meeting the aforementioned criteria. Examples 1 to 3 exhibited higher maximum temperatures than Comparative Example 1. These results suggest that, because Examples 1 to 3 contain LMFP as the positive electrode active material, they can reliably perform the heat generation step during high-rate discharge. This suggests that the internal resistance of the secondary battery can be reduced, allowing efficient high-rate discharge using NCM. Consequently, it is believed that the power-on time can be relatively long. Furthermore, Examples 1 to 3 exhibited a longer power-on time than Comparative Example 2. This suggests that, by containing LMFP at a ratio of 20% or less relative to the total positive electrode active material, Examples 1 to 3 prevent the heat generation step from becoming excessively prolonged even when the SOC at the start of discharge is relatively high, allowing for extended discharge while maintaining a sufficiently low internal resistance in the secondary battery. Furthermore, Examples 1 to 3 contain NCM, which has a high energy density, in their positive electrodes. Therefore, it is believed that Examples 1 to 3, by including NCM, can achieve a relatively long power-on time. Furthermore, in Example 2, the power-on time is over 240 seconds, which is longer than that of Examples 1 and 3. Here, in Example 2, LMFP is included at a ratio greater than 5% and less than 10% relative to the total active material of the positive electrode. Therefore, it is believed that the heat generation step can be performed during a more efficient period. That is, the temperature of the secondary battery can be sufficiently raised during the heat generation step, while the duration of the heat generation step can be shortened for discharge. As a result, it is believed that the high output power of secondary battery 2 can be maintained for a longer period of time, extending the power-on time. On the other hand, in Comparative Example 1, although NCM with a high energy density is used as the active material for the positive electrode, it does not contain LMPF. Therefore, it is believed that the secondary battery cannot generate sufficient heat and the internal resistance of the secondary battery cannot be sufficiently reduced. Therefore, it is believed that Comparative Example 1 does not meet the above criteria. Furthermore, Comparative Example 2 contains only LMPF as the active material for the positive electrode. Therefore, it is considered that the period during which the heating step is performed is too long in Comparative Example 2, and since NCM is not contained, the energization time is short. As a result, it is considered that the above-mentioned criteria cannot be satisfied.

[0111] In addition, as shown in Table 1 above, regarding the cycle test, in Examples 1 to 3 and Comparative Example 2, the capacity retention rate was 80% or more, and the results met the above-mentioned criteria. Here, LMPF is less likely to produce particle breakage and surface degradation caused by the implementation of charge and discharge compared to NCM. Therefore, it can be considered that Examples 1 to 3 and Comparative Example 2 containing LMPF as the active material for the positive electrode have high capacity retention rates. On the other hand, in Comparative Example 1 that does not contain LMPF as the active material for the positive electrode, the capacity retention rate is less than 80%, and the results do not meet the above-mentioned criteria.

[0112] The present disclosure is not limited to the above-described embodiments, but can be applied to various embodiments without departing from the spirit and scope of the present disclosure.

[0113] Although the present disclosure has been described based on the above embodiments, it should be understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also includes various modifications and variations within the scope of the equivalents. Moreover, various combinations or forms, as well as other combinations or forms containing only one element, more elements, or fewer elements, also fall within the scope or thought of the present disclosure.

[0114] <Other>

[0115] The features of the present disclosure are as follows.

[0116] [Item 1]

[0117] A battery system, characterized in that it is a battery system (1) mounted on an electric mobile body (10), the battery system comprising:

[0118] a secondary battery (2), and

[0119] a battery control unit (3) for controlling discharge of the secondary battery,

[0120] The battery control unit controls the secondary battery so that high-rate discharge is performed when the electric vehicle is started. The high-rate discharge is a discharge rate higher than the discharge rate of the secondary battery during normal operation of the electric vehicle.

[0121] The positive electrode (4) of the secondary battery has:

[0122] a first active substance (41), and

[0123] The second active material (42) has a high resistance region having a higher resistance than that of the first active material in a high rate discharge region, wherein the high rate discharge region is an SOC region of the secondary battery in which the high rate discharge is performed during the startup.

[0124] The secondary battery is configured such that, after the utilization rate of the second active material becomes higher than that of the first active material during the high-rate discharge at the start-up, the utilization rate of the first active material becomes higher than that of the second active material.

[0125] [Item 2]

[0126] The battery system according to item 1, wherein the resistance of the first active material decreases as the SOC of the secondary battery increases.

[0127] [Item 3]

[0128] The battery system according to item 1 or 2, wherein the ratio of the first active material to the total active material of the positive electrode is 50 to 95% by weight, and the ratio of the second active material to the total active material of the positive electrode is 5 to 50% by weight.

[0129] [Item 4]

[0130] The battery system according to any one of items 1 to 3, wherein the first active material is lithium nickel cobalt manganese oxide having a layered rock salt structure, and the second active material is lithium manganese iron phosphate having an olivine structure.

[0131] [Item 5]

[0132] A secondary battery, characterized in that it is a secondary battery (2) mounted on an electric flying object (100) and having a positive electrode (4) and a negative electrode (5),

[0133] The positive electrode has:

[0134] a first active substance (41), and

[0135] a second active material (42) having a resistance higher than that of the first active material when the SOC value of the secondary battery is a predetermined value;

[0136] The first active material is lithium nickel cobalt manganese oxide having a layered rock salt structure, and the second active material is lithium manganese iron phosphate having an olivine structure.

[0137] [Item 6]

[0138] A secondary battery according to item 5, wherein, in a low SOC region where the SOC value of the secondary battery is lower than a specified value, the resistance of the second active material is smaller than the resistance of the first active material, and the secondary battery is configured to have a second high utilization region in the low SOC region, and the second high utilization region is a region where the utilization rate of the second active material is higher than the utilization rate of the first active material.

[0139] [Item 7]

[0140] An electric flying object (100) comprising the battery system according to any one of items 1 to 4.

[0141] [Item 8]

[0142] An electric flying object comprising the secondary battery according to item 5 or 6.

Claims

1. A battery system, characterized in that: A battery system 1 mounted on an electric vehicle 10 includes: secondary battery 2, and The battery control unit 3 controls the discharge of the secondary battery. The battery control unit controls the secondary battery so that high-rate discharge is performed when the electric vehicle is started, wherein the high-rate discharge is a discharge rate higher than a discharge rate of the secondary battery during normal operation of the electric vehicle. The positive electrode 4 of the secondary battery has: a first active material 41, and The second active material 42 has a high-resistance region having a higher resistance than that of the first active material in a high-rate discharge region, wherein the high-rate discharge region is an SOC region of the secondary battery in which the high-rate discharge is performed during the startup. The secondary battery is configured such that, after the utilization rate of the second active material becomes higher than the utilization rate of the first active material during the high-rate discharge at the start-up, the utilization rate of the first active material becomes higher than the utilization rate of the second active material.

2. The battery system according to claim 1, wherein: The higher the SOC of the secondary battery, the smaller the resistance of the first active material.

3. The battery system according to claim 1 or 2, wherein: The ratio of the first active material to the total active material of the positive electrode is 50 to 95% by weight, and the ratio of the second active material to the total active material of the positive electrode is 5 to 50% by weight.

4. The battery system according to claim 1 or 2, wherein: The first active material is lithium nickel cobalt manganese oxide having a layered rock salt structure, and the second active material is lithium manganese iron phosphate having an olivine structure.

5. A secondary battery, characterized in that: The secondary battery 2 is mounted on the electric flying vehicle 100 and includes a positive electrode 4 and a negative electrode 5. The positive electrode has: a first active material 41, and The second active material 42 has a resistance higher than that of the first active material when the SOC value of the secondary battery is a predetermined value. The first active material is lithium nickel cobalt manganese oxide having a layered rock salt structure, and the second active material is lithium manganese iron phosphate having an olivine structure.

6. The secondary battery according to claim 5, wherein In a low SOC region where the SOC value of the secondary battery is lower than a specified value, the resistance of the second active material is smaller than the resistance of the first active material, and the secondary battery is configured to have a second high utilization region in the low SOC region, and the second high utilization region is a region where the utilization rate of the second active material is higher than the utilization rate of the first active material. 7 . An electric flying object 100 comprising the battery system according to claim 1 . 8 . An electric flying vehicle comprising the secondary battery according to claim 5 .

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