Battery module

Abstract

A battery module (15) comprises a plurality of battery cells (30) and a plurality of heat storage members (40). The heat storage members (40) absorb heat generated by the battery cells (30). The heat storage members (40) are, for example, a PCM (Phase Change Material) that changes phase between a solid and a liquid. The number of heat storage members (40) is less than the number of battery cells (30). The positive electrode of the battery cells (30), for example, may contain a first active material and a second active material. The first active material may have a crystal of a layered rock salt structure. The second active material may have crystals of an olivine structure.

Description

Battery module Cross-reference of related applications

[0001] This application is based on Japanese Patent Application No. 2024-174630, filed in Japan on October 3, 2024, and incorporates the contents of the basic application by reference in whole.

[0002] The disclosure in this specification relates to a battery module that cools battery cells with a heat storage member.

[0003] Patent Document 1 discloses a battery module comprising a battery cell and a PCM (Phase Change Material). The PCM is a heat storage member that can cool the battery cell in a latent heat region where it absorbs heat while undergoing a phase change. With this, since the PCM can cool the battery cell while maintaining a constant temperature (melting point), it is easy to control the temperature of the battery cell (cell temperature) so that it does not exceed an upper limit. If the cell temperature exceeds the upper limit, the battery cell deteriorates significantly, so the ease of temperature control through PCM cooling is useful.

[0004] U.S. Patent Application Publication No. 2021 / 0384567

[0005] In recent years, the need for lighter battery modules has been increasing.

[0006] One of the purposes of the disclosure is to provide a lightweight battery module.

[0007] One of the disclosed battery modules comprises multiple battery cells and multiple heat storage members that absorb the heat generated by the battery cells. The number of heat storage members is less than the number of battery cells.

[0008] According to the battery module disclosed above, since the number of heat storage elements is less than the number of battery cells, the weight of the battery module can be reduced compared to a case where the number of heat storage elements is equal to the number of battery cells.

[0009] The various embodiments disclosed in this specification employ different technical means to achieve their respective objectives. The claims and the reference numerals in parentheses in this section are illustrative in their correspondence with the embodiments described later and are not intended to limit the technical scope.

[0010] This is a diagram showing the schematic configuration of the eVTOL. This is a plan view showing the schematic configuration of the battery module according to the first embodiment. This is a diagram schematically showing the configuration of the battery cell according to the first embodiment. This is a cross-sectional view of the heat storage member according to the first embodiment. This is a cross-sectional view of the battery cell according to the first embodiment. This is a graph showing the PCM temperature changing over time. This is a diagram showing an example of the power profile and cell temperature change according to the first embodiment. This is a plan view schematically showing the battery module according to the second embodiment. This is a cross-sectional view schematically showing the battery module according to the third embodiment.

[0011] Several embodiments will be described below with reference to the drawings. In each embodiment, the same reference numerals are used for corresponding components, and redundant explanations may be omitted. If only a part of the configuration is described in each embodiment, the configuration of other embodiments described earlier can be applied to the other parts of that configuration. Furthermore, in addition to the combinations of configurations explicitly stated in the description of each embodiment, configurations from multiple embodiments can be partially combined even if not explicitly stated, as long as there are no particular problems with the combination.

[0012] (First Embodiment) The battery module of this embodiment is mounted on an electric vehicle. Electric vehicles include, for example, vehicles, aircraft, ships, construction machinery, agricultural machinery, etc. Electric vehicles include, for example, electric vehicles (BEVs), hybrid vehicles (HEVs), plug-in hybrid vehicles (PHEVs), etc. BEV is an abbreviation for Battery Electric Vehicle. HEV is an abbreviation for Hybrid Electric Vehicle. PHEV is an abbreviation for Plug-in Hybrid Electric Vehicle.

[0013] An electric aircraft is, for example, an electric vertical take-off and landing aircraft (eVTOL), an electric short take-off and landing aircraft (eSTOL), a drone, etc. eVTOL is an abbreviation of electronic Vertical Take-Off and Landing aircraft. eSTOL is an abbreviation of electronic Short distance Take-Off and Landing aircraft. Hereinafter, an example of being mounted on an eVTOL will be described.

[0014] <eVTOL> Figure 1 shows a schematic configuration of an eVTOL. As an example, the eVTOL 10 of the present embodiment includes a fuselage main body 11, a fixed wing 12, a rotary wing 13, a battery module 15, an EPU 16, a BMS 17, and a FCU 18.

[0015] The fuselage main body 11 is the fuselage part of the aircraft. The fuselage main body 11 has a shape extending in the front and rear directions. The fuselage main body 11 has a passenger cabin for passengers to ride in and / or a cargo compartment for loading luggage. The fixed wing 12 is a wing part of the aircraft and is connected to the fuselage main body 11. The fixed wing 12 provides lift for gliding.

[0016] A plurality of rotary wings 13 are provided on the aircraft. At least a part of the plurality of rotary wings 13 may be provided on the fixed wing 12. At least a part of the plurality of rotary wings 13 may be provided on the fuselage main body 11. The rotary wing 13 may be referred to as a rotor, a propeller, a fan, etc. The rotary wing 13 is rotationally driven by a motor of the EPU 16.

[0017] The rotary wing 13 generates thrust by rotation. The thrust mainly acts on the eVTOL 10 as rotational lift during take-off and landing of the eVTOL 10. The rotational lift is the lift generated by the rotation of the rotary wing 13. At the time of take-off and landing, the rotary wing 13 may provide only the rotational lift, or may provide a thrust for moving forward together with the rotational lift. The rotary wing 13 provides rotational lift during hovering of the eVTOL 10.

[0018] The propulsion force acts on the eVTOL 10 primarily as thrust during cruising. The rotor blades 13 primarily provide thrust during cruising. During cruising, the rotor blades 13 may provide only thrust, or they may provide both thrust and lift.

[0019] The battery module 15 is a rechargeable secondary battery capable of storing DC power. The battery module 15 supplies power to the EPU 16 and FCU 18. The battery module 15 also supplies power to auxiliary equipment (not shown), such as air conditioning equipment. The eVTOL 10 may have one or more battery modules 15. If there are multiple battery modules 15, each battery module 15 may be connected to each other in series and / or in parallel, or they may be arranged independently without being connected to each other. Power may be distributed from one battery module 15 to multiple EPUs 16, or power may be supplied to one EPU 16 from multiple battery modules 15 for redundancy. The structure of the battery module 15 will be described in detail later.

[0020] The EPU 16 includes a motor and an inverter. The inverter converts the DC power supplied from the battery module 15 into AC power. The motor is rotated by the AC power converted by the inverter, thereby rotating the rotor blades 13. EPU is an abbreviation for Electric Propulsion Unit.

[0021] The BMS 17 monitors the status of the battery cells 30 in the battery module 15. BMS is an abbreviation for Battery Management System. For example, it may predict or detect abnormalities in the battery cells 30.

[0022] The FCU18 controls the flight state of the eVTOL10. FCU stands for Flight Control Unit. The FCU18 controls the flight of the eVTOL10 according to the flight state controlled by the pilot, the pilot remotely, or the control system. Based on the detection results of the BMS17 and various sensors, the FCU18 controls the motor drive of the EPU16. In this way, the FCU18 controls the flight of the eVTOL10.

[0023] <Battery Module> As shown in Figure 2, the battery module 15 comprises a plurality of battery cells 30, a heat storage member 40, a spacer 50, and a housing 60. The battery module 15 also includes busbars, connectors, fixing members, etc., which are not shown. The battery cells 30, the heat storage member 40, and the spacer 50 are housed within the housing 60. In this embodiment, the housing 60 is made of metal, but it may also be made of resin.

[0024] The battery cell 30 is a secondary battery that generates an electromotive force through a chemical reaction and can be discharged or charged. The battery cell 30 is, for example, a lithium-ion secondary battery, a nickel-metal hydride secondary battery, or an organic radical battery. The battery cell 30 may be a secondary battery with a liquid electrolyte, or a so-called all-solid-state battery with a solid electrolyte. Alternatively, the electrolyte may be a semi-solid electrolyte in which a gel polymer is mixed with a solid.

[0025] Multiple battery cells 30 have a common structure to each other. The number and arrangement of the multiple battery cells 30 are not particularly limited. Multiple battery cells 30 may be connected in series, or in parallel and series. As an example, the battery cells 30 in this embodiment are connected in series. Multiple battery cells 30 are arranged side by side in the X direction. Multiple battery cells 30 are stacked in the X direction via a heat storage member 40. The battery module 15 may comprise multiple stacks of battery cells 30.

[0026] As shown in Figure 3, the battery cell 30 has a positive electrode 31, a negative electrode 32, a separator 33, an electrolyte 34, a positive electrode terminal 35P, a negative electrode terminal 35N, and a laminate film 36.

[0027] The laminate film 36 houses the positive electrode 31, negative electrode 32, separator 33, and electrolyte 34 in a sealed state. The laminate film 36 has a rectangular plate shape when viewed in the X direction. In other words, the external shape of the battery cell 30 is a rectangular plate shape when viewed in the X direction. Multiple battery cells 30 are stacked so that the plate surface 36a of the laminate film 36 is oriented perpendicular to the X direction (stacking direction). In other words, multiple battery cells 30 are stacked with their plate surfaces 36a facing the same direction.

[0028] Furthermore, the laminate film 36 can also be said to be a battery case that provides the outer casing of the battery cell 30. The battery case may be formed using, for example, a metal material. The shape of the battery cell 30, that is, the battery case, is not particularly limited. For example, a cylindrical shape, a rectangular shape, etc., can be adopted. As an example, the battery cell 30 in this embodiment has a rectangular shape, and specifically has a flattened shape that is thin in the X direction.

[0029] The positive terminal 35P and the negative terminal 35N are also called current collectors. One end of the positive terminal 35P is connected to the positive electrode 31, and one end of the negative terminal 35N is connected to the negative electrode 32. The other ends of the positive terminal 35P and the negative terminal 35N are exposed from the laminate film 36 and connected to a busbar (not shown). Conductive materials such as metal foil or metal plates are used for the positive terminal 35P and the negative terminal 35N.

[0030] The separator 33 is positioned between the positive electrode 31 and the negative electrode 32, separating them. The separator 33 is permeable to lithium ions. The separator 33 is in sheet form and has a porous structure. The material of the separator 33 is, for example, made of polyolefin such as polyethylene or polypropylene.

[0031] The electrolyte 34 is an organic electrolyte solution impregnated into the positive electrode 31, the negative electrode 32, and the separator 33. The electrolyte 34 may, for example, contain 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, LiPF ６ LiBF ４ LiClO ４ These can be used, or mixtures thereof. Furthermore, the electrolyte 34 may also contain additives such as vinylene carbonate.

[0032] Furthermore, a solid electrolyte can be used as the electrolyte 34 of the battery cell 30. The solid electrolyte can be, for example, a polymer-based solid electrolyte such as polyethylene oxide, a sulfide-based solid electrolyte, or an oxide-based solid electrolyte. The electrolyte 34 can also be a mixture of two or more of the solid electrolytes exemplified above. Furthermore, the solid electrolytes exemplified above can also be contained in, for example, the positive electrode 31 and the negative electrode 32.

[0033] As shown in Figure 4, the battery cell 30 has a top surface 30a, a bottom surface 30b, and four sides. The bottom surface is the surface opposite to the top surface 30a in the Z direction. The four sides are surfaces that connect the top surface 30a and the bottom surface. Two sides 30c and 30d are in an opposite position relative to each other in the X direction. The other two sides are in an opposite position relative to each other in the Y direction. Side 30c corresponds to the board surface 36a of the laminate film 36.

[0034] The positive terminal 35P and the negative terminal 35N protrude from the upper surface 30a. The multiple battery cells 30 are arranged such that the positive terminal 35P and the negative terminal 35N are alternately positioned in the X direction. Furthermore, the multiple battery cells 30 are arranged such that the positions of the upper surface 30a in the Z direction are approximately equal to each other. The relative positions of the multiple battery cells 30 are fixed by a fixing member (not shown). The fixing member may be, for example, a case or a restraining member such as a band.

[0035] In the above-described arrangement, adjacent positive terminals 35P and negative terminals 35N are electrically connected by busbars (external conductors) (not shown). In other words, multiple battery cells 30 are connected in series by busbars.

[0036] <Heat Storage Member> As shown in Figure 4, the heat storage member 40 has a support 41, a heat storage material 42, and a beam 43. When the thickness of the heat storage member 40 is relatively thin compared to the battery cell 30, the heat storage member 40 may be called a cold storage sheet.

[0037] The support 41 supports the heat storage material 42. The support 41 has walls and voids defined by the walls. The support 41 holds the heat storage material 42 in its voids (storage space). The support 41 is formed using a material with better thermal conductivity than the heat storage material 42. The support 41 can be formed using, for example, metal, ceramic, or resin with added fillers.

[0038] As an example, the support 41 in this embodiment is formed from a metal, specifically an aluminum-based material. The support 41 is a thin box shape in the X direction. The support 41 has opposing walls 411a, 411b and a side wall 411c. The opposing walls 411a, 411b face each other in the X direction. The side wall 411c connects the ends of the opposing walls 411a, 411b and closes the housing space.

[0039] The heat storage material 42 cools the battery cell 30 by absorbing the heat generated in the battery cell 30. The heat storage material 42 is, for example, a latent heat storage material. Latent heat storage materials are sometimes called PCMs. PCM is an abbreviation for Phase change material. PCMs undergo a phase change between solid and liquid. As a PCM, for example, a nonhydrate-type carbon compound, specifically a paraffin-type compound, may be used. Alternatively, a hydrate-type compound may be used. Hydrate-type compounds include, for example, hydrates of sodium acetate, sodium sulfate, and sodium nitrate.

[0040] As an example, the heat storage material 42 in this embodiment is a nonhydrate-type carbon compound, that is, a paraffin-type cold storage material. Furthermore, the phase transition temperature between the solid phase and the liquid phase of the heat storage material 42 is set within the range of 30°C to 60°C. The density of the heat storage material 42 (for example, paraffin-type) is higher in the solid state than in the liquid state. Therefore, when it changes from the solid phase to the liquid phase, its volume expands by about 10%. Accordingly, it is preferable to adjust the packing rate in the solid state so that the packing rate to the voids is 100% or less, preferably close to 100%, in the liquid state.

[0041] The beam 43 bridges the opposing walls 411a and 411b of the support 41. The beam 43 is in contact with the heat storage material 42. The beam 43 is sometimes referred to as a bridging member. Multiple beams 43 are provided at a predetermined pitch in the Z direction. Multiple beams 43 divide the heat storage material 42, which is placed in the void, into multiple sections. Like the support 41, the beam 43 is formed using a material that has better thermal conductivity than the heat storage material 42. The beam 43 can be formed using, for example, metal, ceramic, or resin with fillers added. The beam 43 may be formed using the same material as the support 41, or it may be formed using a different material. For example, the beam 43 and the support 41 are integrally molded by extrusion tube processing using an aluminum-based material.

[0042] As shown in Figure 4, the opposing wall 411a of the support 41 is in direct contact with one side surface 30c of the battery cell 30. The opposing wall 411b of the support 41 is in direct contact with the other side surface 30c of the battery cell 30. The heat storage member 40 is sandwiched by the battery cell 30 in the X direction. The opposing walls 411a and 411b may also be indirectly in contact with the battery cell 30 via a heat conductive member.

[0043] In Figure 2, an example is shown in which the heat storage members 40 are placed only on one side, specifically only on the inner side in the stacking direction, for the battery cells 30 located at both ends in the stacking direction. Alternatively, the heat storage members 40 may also be placed on the outer side in the stacking direction. In this case, only one of the opposing walls 411a, 411b of the heat storage members 40 located at both ends in the stacking direction will be in contact with the side surface 30c of the battery cell 30.

[0044] Multiple battery cells 30 are arranged spaced apart from each other in the stacking direction. The region between two adjacent battery cells 30 is called the inter-cell region. As shown in Figure 2, the multiple inter-cell regions include a first inter-cell region A1 and a second inter-cell region A2. The first inter-cell region A1 is the region where the heat storage member 40 is arranged. The second inter-cell region A2 is the region where the spacer 50 is arranged while the heat storage member 40 is excluded. The first inter-cell region A1 and the second inter-cell region A2 are arranged alternately in the X direction. In other words, the heat storage member 40 and the spacer 50 are arranged alternately in the X direction. As a result, when the heat storage member 40 is arranged only on the inside in the stacking direction for battery cells 30 located at both ends of the stacking direction, the number of heat storage members 40 is less than the number of battery cells 30. In other words, the number of heat storage members 40 housed in one housing 60 is less than the number of battery cells 30. One heat storage member 40 is provided for every two battery cells 30.

[0045] The spacer 50 is elastically deformable in the X direction. When the battery cell 30 is subjected to a force in the X direction, the spacer 50 is elastically deformed by that force. In other words, the spacer 50 also functions as a buffer for the battery cell 30. Furthermore, the spacer 50 also has the function of absorbing the dimensional tolerances of the battery cell 30 in the X direction. When the spacer 50 is not elastically deformed, its shape and size are the same as those of the heat storage member 40.

[0046] <Positive and Negative Electrodes> Next, the positive electrode 31 and negative electrode 32 of the battery cell 30 will be described in detail. As shown in Figure 5, the positive electrode 31 is provided on the surface of the positive electrode terminal 35P, and the negative electrode 32 is provided on the surface of the negative electrode terminal 35N. The positive electrode 31 has an active material layer 310, and the negative electrode 32 has an active material layer 320. The active material layer 310 has a first active material 311 and a second active material 312, and the active material layer 320 has an active material 321. These active material layers 310 and 320 may contain, in addition to the active material, a conductive material, a binder, etc.

[0047] As the active material 321 contained in the active material layer 320 of the negative electrode 32, for example, graphite, silicon, lithium metal, or LTO (lithium titanate) based active materials can be used.

[0048] The first active material 311 contained in the active material layer 310 of the positive electrode 31 is lithium nickel cobalt manganese oxide (NMC) having a layered rock salt structure. The second active material 312 is lithium manganese iron phosphate (LMFP) having an olivine structure. The lithium nickel cobalt manganese oxide, which is the first active material 311, has a higher energy density than the lithium manganese iron phosphate, which is the second active material 312. Note that the active material layer 310 of the positive electrode 31 may contain, for example, active materials other than the first active material 311 and the second active material 312.

[0049] The resistance of the first active material 311 decreases as the state of charge (SOC) of the battery cell 30 increases. SOC is an abbreviation for State of Charge. Further, NMC, which is the first active material 311, can be represented by the following formula (1), where x + y + z = 1, 0.6 ≤ x < 1, 0.02 ≤ y ≤ 0.2, and 0.02 ≤ z ≤ 0.2. Further, as a specific example of the formula (1), the formula (2) is given. LiNi ｘ Co ｙ Mn ｚ O ２ ...(1) LiNi ０．８ Co ０．１ Mn ０．１ O ２ ...(2)

[0050] When the value of the SOC of the battery cell 30 is a predetermined value, the resistance of the second active material 312 becomes higher than that of the first active material 311. That is, the second active material 312 has a high-resistance region where the resistance is higher than that of the first active material 311 in the high-rate discharge region described later. LMFP, which is the second active material 312, can be represented by the following formula (3), where x > 0.5. Further, as a specific example of the formula (3), the formula (4) is given. LiMn ｘ Fe １－ｘ PO ４ ...(3) LiMn ０．６ Fe ０．４ PO ４ ...(4)

[0051] The ratio of the first active material 311 to the total active material of the positive electrode 31 is 50 to 95% by weight, and the ratio of the second active material 312 to the total active material of the positive electrode 31 is 5 to 50% by weight. Furthermore, when the initial SOC value, described later, is set to a relatively high 90%, the ratio of the second active material 312 to the total active material of the positive electrode 31 is preferably 5 to 20% by weight, and the ratio of the first active material 311 to the total active material of the positive electrode 31 is preferably 80 to 95% by weight. Moreover, the ratio of the first active material 311 to the total active material of the positive electrode 31 is more preferably 90% by weight or more, and the ratio of the second active material 312 to the total active material of the positive electrode 31 is more preferably 10% by weight or less. Furthermore, the ratio of the second active material 312 to the total active material of the positive electrode 31 is even more preferably 9% by weight or less. Furthermore, when the starting SOC value is set to a relatively low 60%, the ratio of the second active material 312 to the total active material of the positive electrode 31 is preferably 40 to 50% by weight, and the ratio of the first active material 311 to the total active material of the positive electrode 31 is preferably 50 to 60% by weight.

[0052] The average particle diameter of the first active material 311 is larger than the average particle diameter of the second active material 312. In other words, the average particle diameter of the second active material 312 is smaller than the average particle diameter of the first active material 311. However, the average particle diameter of the first active material 311 may be smaller than the average particle diameter of the second active material 312. In any of these relative sizes, the output at startup of the eVTOL 10 can be improved. The average particle diameter of the first active material 311 can be, for example, 5 to 15 μm, and the average particle diameter of the second active material 312 can be, for example, 0.1 to 20.0 μm.

[0053] <Characteristics of the battery cell> Here, the positive electrode 31 is LiFePO ４In the case of lithium iron phosphate (LFP), such as those mentioned above, thermal stability is high, and the risk of thermal damage due to overheating or overcharging is low. However, the energy density is low. In contrast, LMFP, which is used as the second active material 312, has high thermal stability and a higher energy density compared to LFP. Furthermore, the crystal lattice of LMFP is an olivine structure. The olivine structure is generally classified as orthorhombic, and its crystal lattice is relatively simple and structurally stable. Thus, the second active material 312, with its olivine structure, has high thermal and chemical stability due to its stable crystal structure. This reduces the risk of thermal damage due to overheating or overcharging.

[0054] The crystal lattice of NMC used as the first active material 311 is a layered rock salt structure. Layered rock salt structures are generally classified as hexagonal crystal systems, and their crystal lattice consists of alternating lithium layers and metal oxide layers. Lithium ions are contained in the metal oxide layers (for example, CoO ２ Layers and NiMnCoO ２ It is inserted between the layers. Due to this layered structure, lithium ions can move relatively freely. Therefore, the first active material 311, which has a layered rock salt structure, is less stable than the olivine structure and is inferior in terms of thermal stability and chemical stability. On the other hand, the layered rock salt structure has a higher energy density than the olivine structure, making it superior for increasing the output of the battery cell 30.

[0055] In short, the positive electrode 31 according to this embodiment includes both a first active material 311 that is high-power and low-stability, and a second active material 312 that is low-power and highly stable. This enables the realization of a battery cell 30 that is both high-power and highly stable. This means that a battery cell 30 that is both high-power and heat-resistant can be realized. In other words, the upper limit temperature at which the battery cell 30 deteriorates can be raised.

[0056] The second active material 312 primarily performs reactions during charging and discharging in the potential ranges of approximately 3.4V and 4.0V. Therefore, when the voltage of the battery cell 30 is approximately 3.4V and 4.0V, there is a second high utilization region where the utilization rate of the second active material 312 is higher than that of the first active material 311. Furthermore, the second high utilization region exists when the SOC value of the battery cell 30 is approximately 10% and approximately 80-90%. In these second high utilization regions, the second active material 312 is mainly involved in the reactions during charging and discharging. In other words, the battery cell 30 is configured to have a second high utilization region in the low SOC region where the SOC value of the battery cell 30 is lower than a predetermined value. The low SOC region can be, for example, a region where the SOC value is 30% or less. Note that an SOC of 0% means that the battery cell 30 is completely discharged, and an SOC of 100% means that the battery cell 30 is fully charged.

[0057] Furthermore, apart from the two second high utilization regions, the first high utilization region exists where the utilization rate of the first active material 311 is higher than the utilization rate of the second active material 312. In the first high utilization region, the first active material 311 is mainly used in the reaction during charging and discharging.

[0058] The first active material 311 and the second active material 312 have different resistances. Furthermore, the internal resistance of the battery cell 30 and the resistance of the active materials change depending on the charge state of the battery cell 30, i.e., the SOC value. In this embodiment, in the low SOC region, the second active material 312 has lower resistance than the first active material 311. Also, in the low SOC region, the first active material 311 has higher resistance than other SOC regions. The second active material 312 has a high-resistance region where its resistance is higher than that of the first active material 311 in the high-rate discharge region where the SOC value is in the range of 70 to 90%.

[0059] Figure 6 shows the time change in the temperature (PCM temperature) of the heat storage material 42 when the heat storage material 40 cools the battery cell 30 during flight. Figure 7 shows an example of the power profile related to charging and discharging of the battery cell 30 and the cell temperature change. The solid line in Figure 7 shows the power profile with power input / output to the battery cell 30 on the vertical axis. The dashed line in Figure 7 shows the cell temperature change.

[0060] Furthermore, the eVTOL 10's takeoff and landing area is equipped with a charging device and a cooling device (not shown). The charging device charges the battery cells 30, which have become low SOC (State of Cooling) due to flight. The cooling device cools the heat storage member 40 and the battery cells 30, which have become hot due to heat accumulation during flight. The cooling device performs boiling cooling using a refrigerant. Boiling cooling is a cooling technique that utilizes the phenomenon of a liquid boiling to remove heat. When a liquid refrigerant is heated, boiling begins when it reaches a certain temperature, and it undergoes a phase change from liquid to gas. In this process, heat is removed from the battery cells 30 by utilizing the latent heat of the liquid (latent heat of vaporization).

[0061] As shown in Figure 7, eVTOL 10 takes off at time t1 and lands at time t4. During the takeoff period from time t1 to t2, eVTOL 100 ascends vertically from its landing position to its cruising altitude. Then, from time t2 to t3, it cruises while maintaining its cruising altitude. Subsequently, during the landing period from time t3 to t4, eVTOL 100 descends vertically from above the destination until it lands on the ground.

[0062] During the takeoff and landing periods, the output of the battery cell 30 is at a higher rate compared to the cruising period from time t2 to time t3, corresponding to the high-rate discharge described above. Furthermore, the SOC region in which discharge occurs during the takeoff period corresponds to the high-rate discharge region described above. In this high-rate discharge region, the electrical resistance of the second active material 312 is higher than that of the first active material 311. Also, the SOC value at the start of high-rate discharge corresponds to the initial SOC value described above.

[0063] During the waiting period up to time t1, the battery cell 30 is sufficiently cooled, and the heat storage material 42 is in a supercooled state. Therefore, the cell temperature at time t1 is lower than the melting point of the heat storage material 42 (target temperature Tc3). The battery output during the takeoff and landing periods is extremely large compared to the cruising period, and the amount of heat generated by the battery cell 30 is large. Therefore, during the takeoff period, as the power output increases, the cell temperature rises towards the melting point of the heat storage material 42. During the cruising period, the cell temperature is maintained at the melting point of the heat storage material 42. During the landing period, the amount of heat generated by the battery cell 30 is large, and as the heat storage material 42 completely melts, the cell temperature continues to rise from the melting point.

[0064] At landing time t4, the entire heat storage material 42 is melted, and the cell temperature is higher than the melting point of the heat storage material 42. During the preparation period from t4 to t5, preparations are made to cool the heat storage member 40 and the battery cell 30 with a cooling device, and preparations are made to charge the battery cell 30 with a charging device. During the charging period from t5 to t7, when the preparations are complete, the SOC rises to the target SOC, and charging is completed at t7. If the cell temperature drops to the boiling point of the refrigerant at t6, the cell temperature is maintained at the boiling point of the refrigerant during the period from t6 to t7. In the example shown in Figure 7, the target charging temperature Tc1 is set to the melting point of the heat storage material 42.

[0065] After charging is complete at time t7, the battery cell 30 is further cooled, and the cell temperature drops to the refrigerant boiling point (target temperature Tc3) at time t8. Even after the cell temperature has dropped to the refrigerant boiling point, cooling may be continued to sufficiently supercool the heat storage material 42. After cooling is complete at time t8, flight preparations are made, such as removing the charging and cooling devices from the battery module 15. After that, the eVTOL 10 waits at the takeoff and landing area for the next flight.

[0066] <Summary of the First Embodiment> Comparing the characteristics of the first active material 311 and the second active material 312 contained in the positive electrode 31, the first active material 311 has high output but poor stability, while the second active material 312 has excellent stability but low output. The inventors have found that by including both the first active material 311 and the second active material 312, the advantages of each are realized. In other words, stability can be improved by the second active material 312, while high output can be achieved by the first active material 311. In view of this, the battery module 15 according to this embodiment comprises a battery cell 30 having a positive electrode 31 and a negative electrode 32, and a heat storage member 40 that absorbs heat generated in the battery cell 30. The positive electrode 31 contains a first active material 311 having a layered rock salt structure crystal and a second active material 312 having an olivine structure crystal.

[0067] This enables the realization of a battery cell 30 that is highly powerful and stable. This means that a battery cell 30 that is highly heat resistant while maintaining high output can be realized. In other words, the maximum temperature at which the battery cell 30 does not degrade (upper temperature limit) can be raised. Therefore, even if the amount of heat generated by the battery cell 30 increases with higher output and exceeds the latent heat capacity of the heat storage member 40, reaching the sensible heat region, concerns about battery cell degradation due to temperature rise in the sensible heat region can be reduced. In other words, it is possible to achieve both maximizing the cooling capacity by utilizing the sensible heat region of the heat storage member 40 to cool the battery cell 30, and reducing concerns about battery cell degradation.

[0068] In this embodiment, the positive electrode 31 contains NMC (first active material) and LMFP (second active material). In the comparative example, the positive electrode 31 contains NMC (first active material), but does not contain LMFP (second active material). In the case of the battery module according to this comparative example, as shown in Figure 6, the capacity of the heat storage member 40 must be set so that the cooling of the battery cell 30 during the flight period is completed in the latent heat region. This is because the cell temperature rises rapidly in the sensible heat region when all of the heat storage material 42 becomes liquid, making it difficult to manage the cell temperature so as not to exceed the upper limit temperature. In contrast, in this embodiment, the battery cell 30 has excellent heat resistance, so the upper limit temperature of the battery cell 30 is high. Therefore, even if the cell temperature rises rapidly in the sensible heat region, it does not easily exceed the upper limit temperature. In other words, it is easy to manage the cell temperature so as not to exceed the upper limit temperature.

[0069] Furthermore, in this embodiment, the first active material 311 contains lithium nickel cobalt manganese oxide, and the second active material 312 contains manganese iron lithium phosphate. The proportion of the first active material 311 contained in the positive electrode 31 is less than the proportion of the second active material 312. This allows for a good balance between the effect of the first active material 311 (high power output) and the effect of the second active material 312 (degradation suppression).

[0070] Furthermore, in this embodiment, when the battery cell 30 performs high-rate discharge during startup, it is configured such that the utilization rate of the second active material 312 is initially higher than that of the first active material 311. Subsequently, it is configured such that the utilization rate of the first active material 311 is higher than that of the second active material 312. Therefore, by raising the cell temperature during startup, the internal resistance of the battery cell 30 is reduced, and high-rate discharge of the battery cell 30 can be performed. In other words, by suppressing the temporary degradation of the battery cell 30, a high output of the battery cell 30 can be ensured. As a result, the output of the eVTOL 10 during startup can be improved.

[0071] Furthermore, in this embodiment, the battery cell 30 has a first active material 311 and a second active material 312. The second active material 312 has a higher resistance than the first active material 311 when the SOC value is a predetermined value. The first active material 311 is lithium nickel cobalt manganese oxide having a layered rock salt type structure, and the second active material is lithium iron manganese phosphate having an olivine type structure. Therefore, by suppressing the temporary degradation of the battery cell 30 during startup, a high output of the battery cell 30 can be ensured. As a result, the output of the eVTOL 10 during startup can be improved.

[0072] The battery module 15 according to this embodiment comprises a plurality of battery cells 30 and a plurality of heat storage members 40 that absorb heat generated by the battery cells 30. The number of heat storage members 40 is less than the number of battery cells 30. Therefore, the number of heat storage members 40 can be reduced, and the battery module 15 can be made lighter. In particular, according to this embodiment, which includes a first active material 311 with a layered rock salt structure and a second active material 312 with an olivine structure, the cooling capacity of the heat storage members 40 can be utilized to the maximum extent, so it is easy to reduce the number of heat storage members 40 to less than the number of battery cells 30.

[0073] Furthermore, in this embodiment, the battery cell 30 is plate-shaped, and multiple battery cells 30 are stacked with their plate surfaces 36a facing the same direction. The heat storage member 40 is positioned opposite the plate surface 36a. In addition, in the stacking direction in which the multiple battery cells 30 are stacked, at least a portion of the terminals 35P and 35N face the heat storage member 40. This allows for preferential cooling of the terminals 35P and 35N, which are prone to temperature rise, thereby reducing temperature distribution unevenness in the battery cell 30.

[0074] Furthermore, in this embodiment, the multiple battery cells 30 are arranged spaced apart from each other in the stacking direction. The inter-cell region between two adjacent battery cells 30 includes a first inter-cell region A1 where a heat storage member 40 is placed, and a second inter-cell region A2 where a spacer 50 is placed. This makes it possible to reduce the number of heat storage members 40 to less than the number of battery cells 30, thereby suppressing the variation in the spacing between adjacent battery cells 30 depending on the stacking position.

[0075] Furthermore, the battery module 15 according to this embodiment is mounted on an electric aircraft having a passenger cabin (for example, an eVTOL 10). Unlike unmanned electric aircraft such as drones, electric aircraft with a passenger cabin generally plan their flight path in detail before flying. Therefore, according to this embodiment mounted on such an eVTOL 10, it is easier to manage the temperature rising in the sensible heat region of the heat storage member 40 so that it does not exceed the upper limit temperature, making it suitable for a battery module 15 that utilizes the sensible heat region.

[0076] Furthermore, in this embodiment, a solid-state battery having a solid electrolyte, or a semi-solid-state battery having a semi-solid electrolyte, may be applied to the battery cell 30. When applied to a solid-state battery, it is suitable for a battery module 15 that utilizes the sensible heat region because solid-state batteries have a higher heat resistance temperature than batteries with liquid electrolytes. Also, when applied to a semi-solid-state electrolyte, it has a lower heat resistance temperature than solid-state batteries, so the effect of improving heat resistance by including the second active material 312 is suitably exhibited.

[0077] (Second Embodiment) As shown in Figure 8, the battery module 15 according to this embodiment includes a relay unit 70 and a control unit 80. The relay unit 70 has at least one of a relay, a fuse, a resistor, and a current sensor. The relay switches between supplying and interrupting the output current from the battery cell 30. The fuse interrupts the output current. The resistor provides the electrical resistance of the output current. The current sensor detects the magnitude of the output current.

[0078] The control unit 80 has a computer with memory and a processor, and controls the charging and discharging of the battery cells 30. The control unit 80 also controls the operation of the relays in the relay unit 70. Furthermore, the control unit 80 has a function to monitor the status of the battery cells 30 in the same manner as the BMS 17.

[0079] The battery cells 30, heat storage member 40, and spacer 50 are modularized in a stacked state, similar to the first embodiment, to form one cell module 30M. In the example shown in Figure 8, four cell modules 30M are provided. The four cell modules 30M, relay unit 70, and control unit 80 are housed in a common housing 60. In other words, in the first embodiment, the relay unit 70 and control unit 80 are located outside the housing 60 shown in Figure 2. In contrast, in this embodiment, the relay unit 70 and control unit 80 are located inside the housing 60.

[0080] The cell module 30M may have a case that houses the battery cell 30, the heat storage member 40, and the spacer 50, and this case may be housed in the housing 60. The relay unit 70 may have a case that houses components such as relays, and this case may be housed in the housing 60. The control unit 80 may have a case that houses components such as a computer, and this case may be housed in the housing 60.

[0081] Multiple cell modules 30M are arranged in a line in the Y direction, perpendicular to the X direction (stacking direction). The relay unit 70, cell modules 30M, and control unit 80 are arranged in a line in the X direction, and the cell modules 30M are positioned between the control unit 80 and the relay unit 70. In other words, the cell modules 30M are located in the central part of the housing 60.

[0082] <Summary of the Second Embodiment> Here, the cell module 30M is extremely heavy compared to the control unit 80 and the relay unit 70. Therefore, contrary to this embodiment, if the cell module 30M is positioned away from the central part of the housing 60, the center of gravity of the entire battery module 15 will be significantly shifted from the central part of the housing 60. As a result, when mounting the battery module 15 onto the main body 11, etc., it will be mounted in an unstable state.

[0083] In light of this, in this embodiment, the cell module 30M is positioned between the control unit 80 and the relay unit 70. Therefore, it is possible to avoid the center of gravity of the battery module 15 being significantly off-center from the central part of the housing 60. Thus, the mounting stability of the battery module 15 can be improved. Furthermore, in this embodiment, even if the battery cell 30 overheats abnormally, the starting point of the abnormal heat generation will be in the central part of the housing 60. Therefore, the spread of fire to the outside of the housing 60 can be suppressed.

[0084] (Third Embodiment) As shown in Figure 9, the heat storage member 40 according to this embodiment forms a refrigerant passage 40a between itself and the battery cell 30. The refrigerant passage 40a is a passage for circulating refrigerant R and has an inlet and an outlet. The housing 60 is provided with a supply port 61 for supplying refrigerant R. The refrigerant R is supplied into the housing 60 from the supply port 61 by a refrigerant supply device, which is a ground-based facility. When the battery cell 30 is being charged, the refrigerant R is supplied to the housing 60 and cools the battery cell 30 and the heat storage member 40. During flight, the refrigerant R is discharged from the housing 60.

[0085] A liquid-phase refrigerant R is supplied into the housing 60. A portion of the refrigerant R boils as heat is removed, becoming a gaseous refrigerant Rg. In other words, the refrigerant R boils and cools the battery cell 30 and the heat storage member 40, utilizing the latent heat of the liquid (latent heat of vaporization).

[0086] In short, in each of the above embodiments, the battery cell 30 and the heat storage member 40 are in close contact without any gaps. In contrast, in this embodiment, the heat storage member 40 has a structure that forms a refrigerant passage 40a between itself and the battery cell 30. Although the spacer 50 is omitted in the example shown in Figure 9, this embodiment may also be applied to a battery module 15 equipped with a spacer 50, as shown in Figures 2 and 8.

[0087] (Other Embodiments) The disclosures in this specification and drawings are not limited to the exemplary embodiments. The disclosures include the exemplary embodiments and variations thereof by those skilled in the art. For example, the disclosures are not limited to combinations of parts and / or elements shown in the embodiments. The disclosures are implementable in a variety of combinations. The disclosures may have additional parts that can be added to the embodiments. The disclosures include those in which parts and / or elements of an embodiment have been omitted. The disclosures include substitutions or combinations of parts and / or elements between one embodiment and another. The scope of the disclosed technical areas is not limited to the descriptions of the embodiments. Some of the scope of the disclosed technical areas are indicated by the descriptions of the claims and should be understood to include all modifications within the meaning and scope equivalent to the descriptions of the claims.

[0088] In the first embodiment described above, the first active material 311 is represented by the aforementioned formulas (1) and (2), but the first active material 311 may also be represented by the following formula (5). Li α M β XO ４－γ ... (5)

[0089] In equation (5), the values ​​of α, β, and γ are 0 ≤ α ≤ 2, 0 ≤ β ≤ 1, and 0 ≤ γ ≤ 1. M is preferably one or more selected from Mg, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Zr, Nb, and Mo. X is preferably one or more selected from P, Si, and B. More preferably, LiFePO ４ , LiMnFePO ４ LiCoPO ４ LiMnCoPO ４ LiNiPO ４ LiMnNiPO ４ Li ３ V ２ (PO ４ ) ３ Li ３ Fe ２ (PO ４ ) ３ , LiMnSi ２ O ６ LiFeSi ２ O６ LiCoSi ２ O ６ Li ２ MnSiO ４ Li ２ FeSiO ４ Li ２ CoSiO ４ Li ２ NiSiO ４ These include materials having an olivine structure containing Mn, which is more preferable.

[0090] In the first embodiment described above, the first active material 311 contained in the positive electrode 31 is Li(NiMnCo)O ２ These are lithium nickel cobalt manganese oxides (NMCs). The second active material 312 is LiMnFePO ４ These are lithium manganese iron phosphates (LMFPs). In addition to these active materials, the following are specific examples of active materials included in the positive electrode 31: LiCoO ２ Lithium cobalt oxide (LCO), LiMn, etc. ２ O ４ Lithium manganese oxide (LMO), LiFePO, etc. ４ Lithium iron phosphate (LFP), Li(NiMnCo)O, etc. ２ Lithium nickel cobalt manganese oxide (NMC), Li(NiCoAl)O, etc. ２ Lithium nickel cobalt aluminum oxide (NCA), Li ４ Ti ５ O １２ Lithium titanate (LTO), etc.

[0091] In the first embodiment described above, the proportion of the first active material 311 contained in the positive electrode 31 is less than the proportion of the second active material 312 contained in the positive electrode 31. Conversely, the proportion of the first active material 311 may be greater than the proportion of the second active material 312.

[0092] In the first embodiment described above, the shape of the battery cell 30 is plate-shaped, but it may also be cylindrical. In the first embodiment described above, the heat storage member 40 is positioned opposite the plate surface 36a of the battery cell 30. In contrast, it may be positioned opposite the top surface 30a, the bottom surface 30b, or any of the four sides of the battery cell 30. Alternatively, the heat storage material 42 may be injected into the housing 60, and the entire battery cell 30 may be immersed in the heat storage material 42.

[0093] In the first embodiment described above, the positive electrode 31 contains two types of active materials: NMC and LMFP. However, the positive electrode 31 may contain three or more types of active materials, or it may contain just one type. If there is only one type, NMC is preferred. Furthermore, if the number of heat storage members 40 is less than the number of battery cells 30, either the first active material 311 or the second active material 312 may be omitted. Moreover, it is not essential that the positive electrode 31 contains a layered rock salt structure or an olivine structure. Alternatively, if the positive electrode 31 contains a layered rock salt structure or an olivine structure, it is not essential that the number of heat storage members 40 is less than the number of battery cells 30.

[0094] In the first embodiment described above, the battery module 15 is applied to an eVTOL 10 (electric aircraft) having a passenger cabin, but it may also be applied to an eVTOL 10 that has a cockpit but no passenger cabin. Alternatively, it may be applied to an unmanned eVTOL 10 that does not have a cockpit. Alternatively, it may be applied to an unmanned drone.

[0095] (Disclosure of Technical Ideas) This specification discloses several technical ideas as described in the following paragraphs. Some paragraphs may be written in a multiple dependent form, where subsequent paragraphs optionally refer to preceding paragraphs. Furthermore, some paragraphs may be written in a multiple dependent form, where they refer to other multiple dependent forms. These paragraphs written in multiple dependent forms define several technical ideas.

[0096] (Technical Concept 1) A battery module comprising a plurality of battery cells (30) and a plurality of heat storage members (40) that absorb heat generated by the battery cells, wherein the number of heat storage members is less than the number of battery cells.

[0097] (Technical Concept 2) The battery module according to Technical Concept 1, wherein the battery cells are plate-shaped, and a plurality of the battery cells are stacked with their plate surfaces (36a) facing the same direction.

[0098] (Technical Concept 3) The heat storage member is arranged opposite the plate surface, and is a battery module as described in Technical Concept 2.

[0099] (Technical Concept 4) The battery module according to Technical Concept 3, wherein a plurality of the battery cells are arranged spaced apart from each other in the stacking direction, and the inter-cell region between two adjacent battery cells includes a first inter-cell region (A1) in which the heat storage member is arranged and a second inter-cell region (A2) in which the heat storage member is excluded and a spacer (50) is arranged.

[0100] (Technical Idea 5) The battery module according to any one of Technical Ideas 2 to 4, wherein the battery cell has terminals (35P, 35N) that are electrically connected to an external conductor, and in the stacking direction of the plurality of battery cells, at least a portion of the terminals faces the heat storage member.

[0101] (Technical Concept 6) A battery module according to any one of Technical Concepts 1 to 5, comprising: a relay unit (70) that switches between supplying and interrupting the output current from the battery cell; a control unit (80) that controls the charging and discharging of the battery cell; and a housing (60) that houses the battery cell, the heat storage member, and the relay unit inside, wherein the battery cell and the heat storage member are arranged between the control unit and the relay unit.

[0102] (Technical Idea 7) The battery module according to any one of Technical Ideas 1 to 6, wherein the battery cell has a positive electrode (31) and a negative electrode (32), and the positive electrode contains a first active material (311) having a layered rock salt structure crystal and a second active material (312) having an olivine structure crystal.

[0103] (Technical Idea 8) The battery module according to Technical Idea 7, wherein the first active material contains lithium nickel cobalt manganese oxide and the second active material contains manganese iron lithium phosphate.

[0104] (Technical idea 9) The battery module according to technical idea 8, wherein the proportion of the first active material contained in the positive electrode is less than the proportion of the second active material contained in the positive electrode.

[0105] (Technical Concept 10) A battery module described in any one of Technical Concepts 1 to 9, which is mounted on an electric aircraft (10) having a passenger cabin.

[0106] (Technical Concept 11) The battery module according to any one of Technical Concepts 1 to 10, wherein the battery cell is a solid battery having a solid electrolyte, or a semi-solid battery having a semi-solid electrolyte.

Claims

1. A battery module comprising a plurality of battery cells (30) and a plurality of heat storage members (40) that absorb heat generated by the battery cells, wherein the number of heat storage members is less than the number of battery cells.

2. The battery module according to claim 1, wherein the battery cells are plate-shaped, and a plurality of the battery cells are stacked with their plate surfaces (36a) facing the same direction.

3. The battery module according to claim 2, wherein the heat storage member is arranged opposite to the plate surface.

4. The battery module according to claim 3, wherein the plurality of battery cells are arranged spaced apart from each other in the stacking direction, and the inter-cell region between two adjacent battery cells includes a first inter-cell region (A1) in which the heat storage member is arranged and a second inter-cell region (A2) in which the heat storage member is excluded and a spacer (50) is arranged.

5. The battery module according to any one of claims 2 to 4, wherein the battery cell has terminals (35P, 35N) that are electrically connected to an external conductor, and at least a portion of the terminals face the heat storage member in the stacking direction of the plurality of battery cells.

6. A battery module according to any one of claims 1 to 4, comprising: a relay unit (70) for switching the supply and interruption of output current from the battery cell; a control unit (80) for controlling the charging and discharging of the battery cell; and a housing (60) for housing the battery cell, the heat storage member, and the relay unit inside, wherein the battery cell and the heat storage member are arranged between the control unit and the relay unit.

7. The battery module according to any one of claims 1 to 4, wherein the battery cell has a positive electrode (31) and a negative electrode (32), and the positive electrode contains a first active material (311) having a layered rock salt structure crystal and a second active material (312) having an olivine structure crystal.

8. The battery module according to claim 7, wherein the first active material comprises lithium nickel cobalt manganese oxide, and the second active material comprises manganese iron lithium phosphate.

9. The battery module according to claim 8, wherein the proportion of the first active material contained in the positive electrode is less than the proportion of the second active material contained in the positive electrode.

10. A battery module according to any one of claims 1 to 4, which is mounted on an electric aircraft (10) having a passenger cabin.

11. The battery module according to any one of claims 1 to 4, wherein the battery cell is a solid battery having a solid electrolyte, or a semi-solid battery having a semi-solid electrolyte.

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