In-vehicle battery module and in-vehicle battery device

Abstract

In this in-vehicle battery module, a plurality of secondary batteries are stacked in series. Each of the secondary batteries comprises: a positive electrode (13) provided with a positive electrode active material layer (17) containing an olivine-structure active material; a negative electrode (19) provided with a negative electrode active material layer (24); a separator (27); and a sealing body (40) that forms a sealed space (S) accommodating a liquid electrolyte between the positive electrode (13) and the negative electrode (19). The area of a negative electrode facing surface (24A) of the negative electrode active material layer (24) is larger than the area of a positive electrode facing surface (17A) of the positive electrode active material layer (17). The area of the positive electrode facing surface (17A) is 730 cm2 or more. The ratio (C1 / M1) of the volume (C1) of surplus space excluding the region occupied by the separator in the sealed space (S) to the area (M1) of the positive electrode facing surface (17A) is 0.02 cm or less.

Description

Automotive battery module and automotive battery device

[0001] This disclosure relates to an in-vehicle battery module and an in-vehicle battery device.

[0002] Patent Document 1 discloses a flat-type battery module constructed by stacking multiple secondary batteries in series. The secondary battery comprises a positive electrode, a negative electrode, and a separator positioned between the positive and negative electrodes. The positive electrode has a positive electrode active material layer formed on one side of a foil-shaped positive electrode current collector. The negative electrode has a negative electrode active material layer formed on one side of a foil-shaped negative electrode current collector, and the negative electrode active material layer is positioned to face the positive electrode active material layer of the positive electrode. The battery module disclosed in Patent Document 1 is formed by stacking multiple secondary batteries such that the positive electrode current collectors and negative electrode current collectors are in contact with each other.

[0003] Patent document 2 describes olivine-type lithium iron phosphate (LiFePO) ４ The present invention discloses a battery module having a positive electrode using olivine-type lithium iron phosphate as the positive electrode active material. Olivine-type structural active materials, such as olivine-type lithium iron phosphate, are positive electrode active materials with excellent thermal stability.

[0004] Japanese Patent Publication No. 2017-16825 Japanese Patent Publication No. 2019-185920

[0005] When charging a battery module containing multiple rechargeable batteries, all batteries are charged simultaneously while detecting the voltage of each individual battery. Charging stops when the voltage of any one of the batteries first reaches the upper limit voltage. The upper limit voltage is arbitrarily set as the voltage corresponding to a charge state lower than the fully charged state of the battery.

[0006] Furthermore, it is possible that, for some reason, charging may continue without stopping when the upper voltage limit is reached. If charging of the secondary battery continues after the upper voltage limit is reached, the temperature of the secondary battery will rise rapidly due to the increased resistance of the positive electrode when the secondary battery is fully charged. Therefore, in order to suppress an excessive temperature rise of the secondary battery, control is implemented to stop charging when the voltage of the battery module (corresponding to the total voltage of the secondary battery) reaches a predetermined overcharge detection voltage.

[0007] Setting the overcharge detection voltage to a high value may cause some secondary batteries to reach full charge before the overcharge detection voltage is reached, due to variations between individual batteries. On the other hand, setting the overcharge detection voltage to a low value may cause charging to stop unnecessarily if a momentary voltage surge occurs during normal charging before the upper limit voltage is reached. These problems are particularly pronounced in battery modules that use olivine-type structural active material as the positive electrode active material for secondary batteries.

[0008] The embodiments of the in-vehicle battery module and in-vehicle battery device of this disclosure are described below. [Embodiment 1] An in-vehicle battery module comprising multiple secondary batteries stacked in series, each of the secondary batteries comprising: a positive electrode having a positive electrode active material layer containing an olivine-type structural active material on the first surface of a positive electrode current collector; a negative electrode having a negative electrode active material layer on the first surface of a negative electrode current collector, with the negative electrode active material layer positioned to face the positive electrode active material layer of the positive electrode; a separator positioned between the positive electrode active material layer and the negative electrode active material layer; and a sealant positioned between the positive electrode and the negative electrode, surrounding the positive electrode active material layer and the negative electrode active material layer, and bonded to the first surfaces of the positive electrode current collector and the negative electrode current collector, thereby forming a sealed space for containing a liquid electrolyte between the positive electrode and the negative electrode, wherein the area of ​​the negative electrode facing surface of the negative electrode active material layer facing the positive electrode active material layer is larger than the area of ​​the positive electrode facing surface of the positive electrode active material layer facing the negative electrode active material layer, and the area of ​​the positive electrode facing surface is 730 cm². ２ The above-mentioned automotive battery module is characterized in that the ratio (C1 / M1) of the volume of the surplus space (C1) in the sealed space, excluding the area occupied by the separator, to the area (M1) of the positive electrode facing surface is 0.02 cm³ or less.

[0009] [Aspect 2] The automotive battery module according to aspect 1, wherein the density of the positive electrode active material layer is higher than the density of the negative electrode active material layer.

[0010] [Aspect 3] The density of the positive electrode active material layer is 1.7 g / cm³ ３ 2.3g / cm or more ３ The following conditions apply, and the density of the negative electrode active material layer is 1.1 g / cm³.３ 1.6g / cm or more ３ The vehicle-mounted battery module according to Embodiment 1 or Embodiment 2, which is as follows:

[0011] [Aspect 4] An in-vehicle battery module according to any one of aspects 1 to 3, wherein the positive electrode active material layer comprises first active material particles and second active material particles containing an olivine-type structured active material, the first active material particles having a particle diameter of 5 μm or more and 15 μm or less, the second active material particles having a particle diameter of 0.5 μm or more and 3 μm or less, and the ratio (A1 / A2) of the content of the first active material particles (A1) to the content of the second active material particles (A2) in the positive electrode active material layer is 2.4 or more and 9.0 or less.

[0012] [Aspect 5] An in-vehicle battery module according to any one of aspects 1 to 4, comprising a bipolar electrode in which the surface located opposite the first surface of the positive electrode current collector of the positive electrode constituting one of the adjacent secondary batteries is joined to the surface located opposite the first surface of the negative electrode current collector of the negative electrode constituting the other of the adjacent secondary batteries.

[0013] [Aspect 6] An in-vehicle battery device comprising an in-vehicle battery module according to any one of aspects 1 to 5 and a control device for controlling the in-vehicle battery module, wherein the control device stops charging the in-vehicle battery module based on the voltage of the in-vehicle battery module reaching an overcharge detection voltage during charging, and the overcharge detection voltage is set to a value greater than or equal to the product of the number of stacked secondary batteries and the side reaction start voltage at which a side reaction in which the liquid electrolyte decomposes starts at 60°C during charging of the secondary battery.

[0014] According to the present invention, with respect to an in-vehicle battery module and an in-vehicle battery device in which secondary batteries are stacked in series, overcharging can be detected more accurately based on voltage.

[0015] Figure 1 is a cross-sectional view of the battery module of the embodiment. Figure 2 is a detailed explanatory diagram of the secondary battery structure of the embodiment. Figure 3 is an explanatory diagram showing the battery device of the embodiment. Figure 4 is a schematic voltage curve and temperature curve showing the time change of voltage and temperature during charging of a conventional secondary battery. Figure 5 is a schematic voltage curve showing the time change of voltage during charging of the secondary battery provided in the battery module of the embodiment. Figure 6 is an explanatory diagram of a modified battery module.

[0016] An embodiment of the in-vehicle battery module of the present invention will be described below. <Battery Module> As shown in Figure 1, the in-vehicle battery module 10 (hereinafter referred to as battery module 10) comprises a laminate 11. The laminate 11 comprises a plurality of secondary batteries 12 connected in series. The plurality of secondary batteries 12 are stacked. The number of stacked secondary batteries 12 is, for example, 20 or more, or 25 or more. The number of stacked secondary batteries 12 is, for example, 70 or less. In the following description, the direction in which the secondary batteries 12 are stacked will be referred to as the stacking direction. In addition, viewing in the stacking direction may be referred to as a plan view.

[0017] Each of the secondary batteries 12 comprises a positive electrode 13, a negative electrode 19, and a separator 27. The positive electrode 13 comprises a positive electrode current collector 14 and a positive electrode active material layer 17. The positive electrode current collector 14 is in the form of a sheet. The positive electrode current collector 14 comprises a first surface 15 and a second surface 16. The first surface 15 and the second surface 16 are opposite to each other in the thickness direction of the positive electrode current collector 14. The thickness of the positive electrode current collector 14 is, for example, 5 μm or more, preferably 10 μm or more. The thickness of the foil-shaped positive electrode current collector 14 is, for example, 100 μm or less, preferably 60 μm or less.

[0018] An example of the positive electrode current collector 14 is an aluminum current collector in which the surface serving as the first surface 15 is made of aluminum. The aluminum current collector may be a single body entirely made of aluminum, or may be a composite body having a portion made of aluminum and a portion made of a material other than aluminum. Examples of the single body include an aluminum foil. Examples of the composite body include a multilayer structure in which the layer constituting the first surface 15 is an aluminum layer, and a base material whose surface including the first surface 15 is coated with an aluminum film.

[0019] The positive electrode current collector 14 may be formed of a material other than aluminum. Examples of the material other than aluminum include a metal material, a conductive resin material, and a conductive inorganic material. Examples of the metal material include copper, nickel, titanium, and stainless steel (e.g., SUS304, SUS316, SUS301, SUS304, etc. defined in JIS G 4305:2015). Examples of the conductive resin material include a conductive polymer material or a resin obtained by adding a conductive filler to a non-conductive polymer material as necessary.

[0020] The first surface 15 of the positive electrode current collector 14 may be coated with a known protective layer such as a carbon coating layer. The first surface 15 of the positive electrode current collector 14 may be treated by a known method such as plating.

[0021] The positive electrode active material layer 17 is provided on the first surface 15 of the positive electrode current collector 14. The positive electrode active material layer 17 contains a positive electrode active material capable of occluding and releasing lithium ions as charge carriers. The positive electrode active material includes an olivine-type structure active material. The olivine-type structure positive electrode active material is a polyanion-based compound having an olivine-type structure represented by the general formula LiM ｈ PO ４ and is a polyanion-based compound having an olivine-type structure represented by the general formula LiM ｈ PO ４In this case, M is at least one element selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, Te, and Mo, and h is a numerical value that satisfies 0 < h < 2. Examples of the olivine-type structure cathode active material include olivine-type lithium iron phosphate (LiFePO ４ ), and olivine-type lithium manganese iron phosphate (LiMnFePO ４ ). These olivine-type structure cathode active materials can be used alone or in combination of two or more. In order to improve the electric conductivity, the surface of the particles of the olivine-type structure cathode active material may be coated with a carbon-based material.

[0022] The cathode active material may be a combination of an olivine-type structure active material and another cathode active material other than the olivine-type structure active material. In this case, the mass ratio of the olivine-type structure active material in the entire cathode active material is, for example, 90% or more, preferably 95% or more, and more preferably 98% or more. The above mass ratio is, for example, 99% or less. The other cathode active materials are not particularly limited, and those that can be used as the cathode active material of a lithium-ion secondary battery are adopted. The other cathode active materials can be used alone or in combination of two or more. In the present embodiment, all of the cathode active materials are olivine-type lithium iron phosphate (LiFePO ４ ).

[0023] The cathode active material layer 17 can contain other components other than the cathode active material as needed. Examples of the other components include a binder, a dispersant, a conductive aid, an electrolyte (polymer matrix, ion-conductive polymer, electrolyte solution, etc.), and an electrolyte supporting salt (lithium salt) for enhancing the ion conductivity. The types and contents of the other components are not particularly limited, and the conventionally known knowledge about lithium-ion secondary batteries can be appropriately referred to. The content ratio of the cathode active material in the cathode active material layer 17 is, for example, 97.0% by mass or more and 99.0% by mass or less.

[0024] The negative electrode 19 comprises a negative electrode current collector 20 and a negative electrode active material layer 24. The negative electrode current collector 20 is in the form of a sheet. The negative electrode current collector 20 comprises a first surface 21 and a second surface 22. The first surface 21 and the second surface 22 are opposite to each other in the thickness direction of the negative electrode current collector 20. The thickness of the negative electrode current collector 20 is, for example, 4 μm or more, preferably 6 μm or more. The thickness of the negative electrode current collector 20 is, for example, 20 μm or less, preferably 10 μm or less.

[0025] An example of a negative electrode current collector 20 is a copper current collector in which the surface forming the first surface 21 is made of copper. The copper current collector may be a single object made entirely of copper, or it may be a composite having a part made of copper and a part made of a material other than copper. An example of the single object is copper foil. An example of the composite is a multilayer structure in which the layer forming the first surface 21 is a copper layer, or a substrate in which the surface including the first surface 21 is coated with a copper film.

[0026] The negative electrode current collector 20 may be made of a material other than copper. Examples of materials other than copper include metallic materials, conductive resin materials, and conductive inorganic materials. Examples of metallic materials include aluminum, nickel, titanium, and stainless steel (e.g., SUS304, SUS316, SUS301, SUS304, etc. as defined in JIS G 4305:2015). Examples of conductive resin materials include conductive polymer materials or resins to which conductive fillers are added as needed.

[0027] The negative electrode active material layer 24 is provided on the first surface 21 of the negative electrode current collector 20. The negative electrode active material layer 24 contains a negative electrode active material capable of intercepting and releasing charge carriers such as lithium ions. The negative electrode active material contains carbon. Examples of carbon include natural graphite, artificial graphite, hard carbon (carbon that is difficult to graphitize), and soft carbon (carbon that is easily graphitized). Examples of artificial graphite include highly oriented graphite and mesocarbon microbeads. These carbons can be used alone or in combination of two or more types.

[0028] The negative electrode active material may be a combination of carbon and other negative electrode active materials. In this case, the mass percentage of carbon in the total negative electrode active material is, for example, 90% or more, preferably 95% or more, and more preferably 98% or more. The above mass percentage is, for example, 99% or less. The other negative electrode active materials are not particularly limited and any materials usable as negative electrode active materials for lithium-ion secondary batteries may be used. Examples of other negative electrode active materials include silicon and tin. The other negative electrode active materials can be used alone or in combination of two or more types. In this embodiment, all negative electrode active materials are graphite.

[0029] The negative electrode active material layer 24 may contain other components besides the negative electrode active material as needed. Examples of other components include binders, dispersants, conductive additives, electrolytes (polymer matrix, ion-conducting polymer, electrolyte solution, etc.), and electrolyte support salts (lithium salts) to enhance ion conductivity. The types and contents of other components are not particularly limited, and conventionally known knowledge regarding lithium-ion secondary batteries may be referenced as appropriate. The content ratio of the negative electrode active material in the negative electrode active material layer 24 is, for example, 95.0% by mass or more and 98.0% by mass or less.

[0030] The laminate 11 includes a bipolar electrode 25. The bipolar electrode 25 includes a current collector 26, a positive electrode active material layer 17 provided on one side of the current collector 26, and a negative electrode active material layer 24 provided on the other side of the current collector 26. The current collector 26 is formed by integrating a positive electrode current collector 14 and a negative electrode current collector 20 that are in contact with each other. For example, in the bipolar electrode 25, the current collector 26 is formed by joining the positive electrode current collector 14 and the negative electrode current collector 20 in a state where the second surface 16 of the positive electrode current collector 14 and the second surface 22 of the negative electrode current collector 20 are superimposed. The bipolar electrode 25 is formed by considering the positive electrode current collector 14 and the negative electrode current collector 20 that are in contact with each other as a single current collector 26.

[0031] The positive electrode 13 provided at one end of the laminate 11 is designated as the positive electrode terminal electrode 13A. The negative electrode 19 provided at the other end of the laminate 11 is designated as the negative electrode terminal electrode 19A. The positive electrode terminal electrode 13A and the negative electrode terminal electrode 19A sandwich a plurality of bipolar electrodes 25 from the stacking direction. The second surface 16 of the positive electrode current collector 14 of the positive electrode terminal electrode 13A constitutes the outer surface of the laminate 11. The second surface 22 of the negative electrode current collector 20 of the negative electrode terminal electrode 19A constitutes the outer surface of the laminate 11. The secondary battery 12 provided at one end of the laminate 11 comprises the positive electrode terminal electrode 13A and the negative electrode active material layer 24 of the bipolar electrode 25 adjacent to the positive electrode terminal electrode 13A. The secondary battery 12 provided at the other end of the laminate 11 comprises a negative terminal electrode 19A and a positive electrode active material layer 17 of a bipolar electrode 25 adjacent to the negative terminal electrode 19A. The secondary battery 12 provided between the secondary battery 12 at one end of the laminate 11 and the secondary battery 12 at the other end of the laminate 11 comprises a positive electrode active material layer 17 and a negative electrode active material layer 24 of a bipolar electrode 25 adjacent to each other.

[0032] The battery module 10 includes a positive electrode conductive plate 31 and a negative electrode conductive plate 32. The positive electrode conductive plate 31 and the negative electrode conductive plate 32 are made of a metal material such as aluminum, copper, or stainless steel.

[0033] The positive electrode current-carrying plate 31 is electrically connected to the second surface 16 of the positive electrode current collector 14 provided on the positive electrode terminal electrode 13A. The negative electrode current-carrying plate 32 is electrically connected to the second surface 22 of the negative electrode current collector 20 provided on the negative electrode terminal electrode 19A. The battery module 10 performs charging and discharging through the positive electrode terminal 31a provided on the positive electrode current-carrying plate 31 and the negative electrode terminal 32a provided on the negative electrode current-carrying plate 32.

[0034] The battery module 10 includes a encapsulant 40. The encapsulant 40 is rectangular in shape. The encapsulant 40 comprises a first portion 41 and a second portion 42. The first portion 41 is located between the current collectors 26, between the positive electrode current collector 14 of the positive terminal electrode 13A and the current collector 26 of the bipolar electrode 25 adjacent to the positive terminal electrode 13A, and between the negative electrode current collector 20 of the negative terminal electrode 19A and the current collector 26 of the bipolar electrode 25 adjacent to the negative terminal electrode 19A. The second portion 42 is located outside the peripheral edges of the current collectors 26, the positive electrode current collector 14 of the positive terminal electrode 13A, and the negative electrode current collector 20 of the negative terminal electrode 19A. The encapsulant 40 encapsulates the laminate 11.

[0035] Inside the secondary battery 12, a sealed space is formed surrounded by a seal 40, a positive electrode 13, and a negative electrode 19. In other words, the seal 40 is bonded to the first surfaces of the positive electrode current collector 14 and the negative electrode current collector 20, thereby forming a sealed space between the positive electrode 13 and the negative electrode 19 that houses the liquid electrolyte. This sealed space contains a separator 27 and a liquid electrolyte (electrolyte). The peripheral portion of the separator 27 is embedded in the seal 40.

[0036] The separator 27 is positioned between the positive electrode active material layer 17 and the negative electrode active material layer 24. The separator 27 prevents short circuits caused by contact between the two electrodes by isolating the positive electrode active material layer 17 and the negative electrode active material layer 24, while allowing charge carriers such as lithium ions to pass through.

[0037] Examples of liquid electrolytes include liquid electrolytes containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of electrolyte salts include LiPO4 ２ F ２、 LiClO ４ LiAsF ６ LiPF ６ LiBF ４ LiCF ３ SO ３ , LiN (FSO ２ ) ２ ,LiN(CF ３ SO ２ ) ２Known lithium salts such as those listed above can be used. Furthermore, known non-aqueous solvents such as cyclic carbonates, cyclic esters, linear carbonates, linear esters, and ethers can be used. Two or more of these known solvent materials may also be used in combination.

[0038] The electrolyte is not limited to a liquid electrolyte, but may also be a solid electrolyte such as a polymer gel electrolyte containing an electrolyte held in a polymer matrix. Furthermore, the separator 27 itself may be composed of an electrolyte such as a polymer electrolyte or an inorganic electrolyte.

[0039] Liquid electrolytes decompose when a voltage above a certain level is applied, releasing CO, CO2. ２ This generates gases such as [list of gases]. An example of a liquid electrolyte is a liquid electrolyte that decomposes and generates gas when a specific voltage is applied at 60°C. The specific voltage is, for example, 4.5V or less, preferably 4.1V or less. Alternatively, the specific voltage is, for example, 3.7V or more, preferably 3.9V or more.

[0040] The battery module 10 is equipped with voltage detection wires 51. The voltage detection wires 51 are, for example, long foil-like wires. One voltage detection wire 51 is provided on each of the current collectors 26 of the bipolar electrode 25, the positive electrode current collector 14 of the positive electrode terminal electrode 13A, and the negative electrode current collector 20 of the negative electrode terminal electrode 19A. For example, the voltage detection wires 51 are joined to each of the current collectors 26 of the bipolar electrode 25, the positive electrode current collector 14 of the positive electrode terminal electrode 13A, and the negative electrode current collector 20 of the negative electrode terminal electrode 19A by ultrasonic welding. This makes it possible to detect the voltage of the secondary battery 12 by two voltage detection wires 51 that are adjacent to each other in the stacking direction.

[0041] A portion of the voltage detection wire 51 is covered by the encapsulant 40. The voltage detection wire 51 extends outward from the encapsulant 40. A portion of the voltage detection wire 51 is exposed to the outside of the encapsulant 40. In other words, the voltage detection wire 51 is led outward from the encapsulant 40 so that the voltage of the secondary battery 12 can be detected outside the encapsulant 40.

[0042] [Details of the secondary battery] Figure 2 is a schematic cross-sectional view showing each component of a secondary battery 12. The positive electrode 13 and negative electrode 19 constituting the secondary battery 12 are arranged such that the positive electrode active material layer 17 and the negative electrode active material layer 24 face each other in the stacking direction. The opposing directions of the positive electrode 13 and the negative electrode 19 coincide with the stacking direction. The positive electrode active material layer 17 has a positive electrode opposing surface 17A which is the surface facing the negative electrode active material layer 24. The negative electrode active material layer 24 has a negative electrode opposing surface 24A which is the surface facing the positive electrode active material layer 17.

[0043] The planar shape of the positive electrode active material layer 17 in a plan view from the stacking direction is, for example, rectangular. The planar shape of the positive electrode active material layer 17 may also be a polygon, a circle, or other shape. The planar shape of the negative electrode active material layer 24 in the above planar view is, for example, rectangular. The planar shape of the negative electrode active material layer 24 may also be a polygon, a circle, or other shape.

[0044] The thickness of the positive electrode active material layer 17 is, for example, 200 μm or more, preferably 240 μm or more. The thickness of the positive electrode active material layer 17 is, for example, 600 μm or less, preferably 530 μm or less.

[0045] The area (M1) of the positive electrode opposing surface 17A of the positive electrode active material layer 17 is, for example, 730 cm². ２ The above, preferably 800 cm ２ That is all, more 1000 cm ２ That concludes the explanation. The area (M1) of the positive electrode opposing surface 17A is, for example, 20,000 cm². ２ The following, preferably 18,000 cm² ２ The following applies: The area (M1) of the positive electrode active material layer 17 facing the positive electrode surface 17A may be the same as the area of ​​the region on the first surface 15 of the positive electrode current collector 14 where the positive electrode active material layer 17 is formed (the coating area of ​​the positive electrode active material layer 17).

[0046] The porosity of the positive electrode active material layer 17 is, for example, 39.5% or more, preferably 40% or more. The porosity of the positive electrode active material layer 17 is, for example, 45% or less, preferably 43% or less.

[0047] The density of the positive electrode active material layer 17 is higher than the density of the negative electrode active material layer 24, which will be described later. The density of the positive electrode active material layer 17 is, for example, 1.7 g / cm³. ３ The above is preferable, and preferably 1.8 g / cm³. ３ That concludes the explanation. The density of the positive electrode active material layer 17 is, for example, 2.3 g / cm³. ３ The following, preferably 2.2 g / cm³ ３ The following applies:

[0048] The positive electrode active material contained in the positive electrode active material layer 17 includes first active material particles and second active material particles with different particle sizes. The first active material particles and second active material particles are particles containing an olivine-type structured active material. Preferably, the first active material particles and second active material particles are particles with the same main component. Having the same main component means that the components constituting 95% or more by mass are the same. The first active material particles and second active material particles may be particles with different main components.

[0049] Within the positive electrode active material layer 17, first active material particles and second active material particles are stacked in the thickness direction. The mixture of relatively large first active material particles and relatively small second active material particles results in a dense packing of first and second active material particles. In this case, it is easy to lower the porosity and increase the density of the positive electrode active material layer 17 compared to the negative electrode active material layer 24.

[0050] The first active material particles have a particle diameter of 5 μm or more and 15 μm or less, and are larger in size than the second active material particles. The second active material particles have a particle diameter of 0.5 μm or more and 3 μm or less, and are smaller in size than the first active material particles. The particle diameters of the first and second active material particles can be measured, for example, by observing the cross-section of the positive electrode active material layer 17 using an electron microscope such as a scanning electron microscope (SEM). As an example, the cross-section of the active material layer obtained by cutting the positive electrode active material layer 17 is observed using an electron microscope, and the major axis of the particle cross-section is estimated to be the particle diameter of each individual active material particle appearing in the cross-section of the active material layer. The orientation of the cross-section of the active material layer is not particularly limited.

[0051] The ratio (A1 / A2) of the content of first active material particles (A1) to the content of second active material particles (A2) in the positive electrode active material layer 17 is, for example, 2.4 or more and 9.0 or less, preferably 3.0 or more and 5.7 or less.

[0052] The content of first active material particles (A1) in the positive electrode active material layer 17 is, for example, 68.5% by mass or more and 89.1% by mass or less, preferably 72.8% by mass or more and 84.2% by mass or less. The content of second active material particles (A2) in the positive electrode active material layer 17 is, for example, 9.7% by mass or more and 29.1% by mass or less, preferably 14.5% by mass or more and 24.8% by mass or less. The content of first active material particles and second active material particles can be measured, for example, by observing a cross-section of the positive electrode active material layer 17 using an electron microscope such as a scanning electron microscope (SEM). As an example, the ratio of first active material particles and second active material particles to the total positive electrode active material particles is calculated from a micrograph of the cross-section of the positive electrode active material layer 17. Then, the content of first active material particles and second active material particles is determined from that ratio and the content of positive electrode active material in the positive electrode active material layer 17.

[0053] The thickness of the negative electrode active material layer 24 is, for example, 120 μm or more, preferably 140 μm or more. The thickness of the negative electrode active material layer 24 is, for example, 450 μm or less, preferably 360 μm or less.

[0054] The area (M2) of the negative electrode facing surface 24A of the negative electrode active material layer 24 is, for example, 770 m². ２ The above is preferable, and preferably 840m ２ That concludes the explanation. The area (M2) of the negative electrode opposing surface 24A is, for example, 26,000 m². ２ The following, preferably 23,000 m ２ The following applies: The area (M2) of the negative electrode active material layer 24 facing the negative electrode surface 24A may be the same as the area of ​​the region on the first surface 21 of the negative electrode current collector 20 where the negative electrode active material layer 24 is formed (coating area of ​​the negative electrode active material layer 24).

[0055] Preferably, the area (M2) of the negative electrode facing surface 24A of the negative electrode active material layer 24 is larger than the area (M1) of the positive electrode facing surface 17A of the positive electrode active material layer 17. For example, the ratio (M2 / M1) of the area of ​​the negative electrode facing surface 24A (M2) to the area of ​​the positive electrode facing surface 17A (M1) is 1.05 or more and 1.34 or less. When the area (M2) of the negative electrode facing surface 24A is larger than the area (M1) of the positive electrode facing surface 17A, a protruding portion 24A1 is formed on the outer periphery of the negative electrode facing surface 24A of the negative electrode active material layer 24, which protrudes outward from the outer edge of the positive electrode facing surface 17A of the positive electrode active material layer 17 in the plan view described above.

[0056] The protruding portion 24A1 is preferably formed over the entire circumferential surface 24A of the negative electrode active material layer 24. In other words, the negative electrode active material layer 24 is preferably formed to be slightly larger than the positive electrode active material layer 17, and in a plan view, it is preferable that the entire formation area of ​​the positive electrode active material layer 17 is located within the formation area of ​​the negative electrode active material layer 24. The formation range of the protruding portion 24A1 over the entire circumference of the negative electrode opposing surface 24A is, for example, 50% or more, preferably 80% or more, and more preferably 90% or more.

[0057] The protruding length of the protruding portion 24A1 is, for example, 1 mm or more, preferably 5 mm or more. The protruding length is, for example, 20 mm or less. The porosity of the negative electrode active material layer 24 is, for example, 40% or more, preferably 42% or more. The porosity of the negative electrode active material layer 24 is, for example, 50% or less, preferably 48% or less.

[0058] The density of the negative electrode active material layer 24 is, for example, 1.1 g / cm³. ３ The above is preferable, and preferably 1.2 g / cm³. ３ That concludes the explanation. The density of the negative electrode active material layer 24 is, for example, 1.6 g / cm³. ３ The following, preferably 1.4 g / cm³ ３ The following applies:

[0059] The negative electrode active material layer 24 contains particles of the negative electrode active material having a particle diameter of 10 μm or more and 20 μm or less. The particle diameter of the negative electrode active material particles can be measured, for example, using an electron microscope such as a scanning electron microscope (SEM).

[0060] Inside the secondary battery 12, a sealed space S is formed, surrounded by the sealant 40, the positive electrode 13, and the negative electrode 19. A portion of the separator 27 is located within the sealed space S. The volume of the surplus space C1 is the volume of the surplus space remaining after removing the area occupied by the separator 27 in the sealed space S. In Figure 2, the area indicated by the dots is the surplus space. The surplus space can also be defined as the area in the secondary battery 12 where the liquid electrolyte may exist, excluding the void portion inside the positive electrode active material layer 17, the void portion inside the negative electrode active material layer 24, and the void portion inside the separator 27.

[0061] The secondary battery 12 of this embodiment is configured to have a small excess space volume C1. More specifically, the excess space volume C1 is set such that the ratio (C1 / M1) of the area (M1) of the positive electrode active material layer 17 to the positive electrode facing surface 17A is less than or equal to a specific value. The ratio (C1 / M1) is 0.02 cm or less, preferably 0.015 cm or less, and more preferably 0.01 cm or less. For example, the ratio (C1 / M1) is 0.002 cm or more, and more preferably 0.004 cm or more.

[0062] The excess space volume C1 can be adjusted, for example, by changing the shape of the sealant 40. As an example, to reduce the excess space volume C1, the inner circumference of the frame-shaped sealant 40 is moved closer to the positive electrode active material layer 17 or the negative electrode active material layer 24.

[0063] [Battery Device] As shown in Figure 3, the battery device 100 comprises a battery module 10 and a control device 60. The control device 60 comprises a voltage detection unit 61 and a charge control unit 63. The voltage detection unit 61 comprises a first voltage detection unit 62a and a second voltage detection unit 62b.

[0064] The first voltage detection unit 62a detects the voltage of each secondary battery 12 from the potential input from the voltage detection line 51. The second voltage detection unit 62b detects the voltage of the battery module 10. The voltage of the battery module 10 is the sum of the voltages of the secondary batteries 12 that make up the battery module 10.

[0065] The charging control unit 63 charges each secondary battery 12 in the battery module 10 by applying a DC voltage to the battery module 10 from a power supply device (not shown). The charging control unit 63 also stops charging based on the detected voltage values ​​of each secondary battery 12 and the detected voltage value of the battery module 10.

[0066] The charging control unit 63 includes, for example, a processor 64 and a storage unit 65. The processor 64 is, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or a DSP (Digital Signal Processor). The storage unit 65 includes RAM (Random Access Memory) and ROM (Read Only Memory). The storage unit 65 stores a program and information for performing charging.

[0067] The above information includes the upper voltage limit and the overcharge detection voltage. The upper voltage limit is a value arbitrarily set based on the design value of the secondary battery 12, etc. Since all of the secondary batteries 12 in the battery module 10 have the same design, the upper voltage limit is set as a common value for all secondary batteries 12. The upper voltage limit is, for example, the voltage of the secondary battery 12 when the cumulative charge capacity is set to 100% SOC (State of Charge).

[0068] The overcharge detection voltage is a value arbitrarily set based on the design value of the secondary battery 12, and is a voltage higher than the product of the upper limit voltage and the number of stacked secondary batteries 12. For example, the overcharge detection voltage is set to a value greater than or equal to the product of the side reaction initiation voltage at which a side reaction in which the liquid electrolyte decomposes starts at 60°C during charging of the secondary battery 12, and the number of stacked secondary batteries 12 constituting the battery module 10 (hereinafter referred to as the specific voltage integrated value). As an example, if the side reaction initiation voltage is 3.9V and the number of stacked secondary batteries 12 is 30, the specific voltage integrated value will be 117V (= 3.9V × 30). The overcharge detection voltage is 1 or more times the specific voltage integrated value, preferably 1.1 or more times, and more preferably 1.15 or more times.

[0069] The overcharge detection voltage is less than the product of the voltage when the secondary battery 12 is fully charged (hereinafter referred to as the full charge voltage) and the number of stacked secondary batteries 12, preferably 0.98 times or less the product of the full charge voltage and the number of stacked secondary batteries 12, and more preferably 0.95 times or less the product of the full charge voltage and the number of stacked secondary batteries 12. The full charge state means a state in which charge carriers such as lithium ions have been completely detached from the positive electrode active material contained in the positive electrode active material layer 17 of the secondary battery 12.

[0070] When charging the battery module 10, the charging control unit 63 simultaneously charges the multiple secondary batteries 12 of the battery module 10. While charging is in progress, the first voltage detection unit 62a individually detects the voltage of the secondary batteries 12, and the second voltage detection unit 62b detects the voltage of the battery module 10. During charging, the charging control unit 63 continuously or intermittently acquires the voltage of each of the multiple secondary batteries 12 using the first voltage detection unit 62a. The charging control unit 63 then performs a first stop process to stop charging, triggered by the detection that the voltage of any one of the secondary batteries 12 has reached its upper limit voltage.

[0071] Furthermore, the charging control unit 63 acquires the voltage of the battery module 10 continuously or intermittently using the second voltage detection unit 62b. The charging control unit 63 then performs a second stop process to stop charging, triggered by the detection that the voltage of the battery module 10 has reached the overcharge detection voltage. The second stop process is provided in anticipation of a case where charging continues without being stopped by the first stop process due to some reason such as a malfunction of the first voltage detection unit 62a.

[0072] <Operation> The secondary battery 12 provided in the battery module 10 of this embodiment has an area (M1) of the positive electrode facing surface 17A of the positive electrode active material layer 17 of 730 cm². ２ As described above, the ratio of the excess space volume (C1) to the area (M1) of the positive electrode opposing surface 17A of the positive electrode active material layer 17 (C1 / M1) is 0.02 cm or less. In other words, the secondary battery 12 employs a structure in which the positive electrode active material layer 17 is wide in the planar direction and has a small excess space volume (C1) (hereinafter referred to as the specific structure).

[0073] The graph in Figure 4 schematically shows the voltage curve representing the voltage change over time and the temperature curve representing the temperature change over time during charging of a conventional secondary battery without a specific structure. In the case of a secondary battery without a specific structure, at the end of charging, the voltage of the secondary battery increases with time and reaches the upper limit voltage V1 at the first timing t1. If charging continues after the first timing t1, the voltage of the secondary battery increases at a similar gradient until the second timing t2, and after the predetermined second timing t2, the voltage of the secondary battery 12 increases at a gentler gradient than before. The second timing t2 is the timing when the voltage of the secondary battery 12 reaches the side reaction start voltage V2, at which the side reaction in which the liquid electrolyte decomposes begins. After the second timing t2, electrons are consumed in the above side reaction, so the gradient of the voltage increase becomes gentler. Note that the above trend is particularly pronounced in secondary batteries that use an olivine-type structural active material as the positive electrode active material. The reason for this is thought to be that, in secondary batteries using olivine-type structural active materials as the positive electrode active material, there is a flat region at the end of the charging phase in which charging progresses but the voltage hardly rises.

[0074] Subsequently, if charging continues, the secondary battery will reach a fully charged state at the third timing t3. When the secondary battery reaches a fully charged state, further charging reactions are no longer possible, causing the resistance to rise sharply. Along with the rapid rise in resistance, the voltage also rises sharply. Furthermore, a rapid increase in the resistance of the secondary battery increases the amount of heat generated by Joule heating. Therefore, as shown in the temperature curve in Figure 4, the temperature of the secondary battery also rises sharply at the third timing t3. This temperature rise at the third timing t3 is a factor that degrades the secondary battery. For example, if the temperature of the secondary battery rises to the temperature at which the separator melts, there is a risk of a short circuit occurring due to the melting of the separator.

[0075] The graph in Figure 5 schematically shows a voltage curve representing the voltage change over time during charging of the secondary battery 12 in the battery module 10 of this embodiment, which has a specific structure. In addition, in Figure 5, the voltage curve shown in Figure 4 is superimposed with a dashed line.

[0076] In this case, the voltage of the secondary battery 12 rises in the same manner as the voltage curve in Figure 4 until the second timing t2, when it reaches the side reaction initiation voltage V2. Then, at the second timing t2, the voltage of the secondary battery 12 rises. This voltage rise is caused by the widening of the electrode distance D of the secondary battery 12 based on a specific structure.

[0077] As shown in Figure 2, the electrode distance D of the secondary battery 12 refers to the distance between the positive electrode facing surface 17A of the positive electrode active material layer 17 and the negative electrode facing surface 24A of the negative electrode active material layer 24 of the secondary battery 12. Under normal conditions, the positive electrode facing surface 17A of the positive electrode active material layer 17 and the negative electrode facing surface 24A of the negative electrode active material layer 24 of the secondary battery 12 are in contact with the separator 27. Therefore, the electrode distance D under normal conditions is approximately equal to the thickness of the separator 27.

[0078] At the second timing t2, when the liquid electrolyte decomposes due to the above side reaction, decomposition gas is generated in the sealed space S of the secondary battery 12. The decomposition gas is mainly generated on the positive electrode facing surface 17A of the positive electrode active material layer 17. Here, when a specific structure is adopted, the positive electrode facing surface 17A is wide, so the decomposition gas is generated over a wide area. As a result, more decomposition gas is generated between the positive electrode facing surface 17A of the positive electrode active material layer 17 and the separator 27. In addition, when a specific structure is adopted, the excess space volume (C1) is small, so the degree of increase in the internal pressure of the sealed space S is large. When the internal pressure of the sealed space S increases, the positive electrode 13 and the negative electrode 19 bend, and the distance D between the electrodes widens. When the distance D between the electrodes of the secondary battery 12 widens, the resistance of the secondary battery 12 increases, and as a result, the voltage of the secondary battery 12 increases.

[0079] As shown in Figure 5, the voltage of the secondary battery from the second timing t2 onward rises gradually, similar to the voltage curve of a conventional structure, and then, as charging continues, it rises sharply at the third timing t3 when it reaches a fully charged state.

[0080] Here, we consider the timing t4 at which the voltage of the secondary battery reaches a specific detection voltage Vth, after the first timing t1 at which the upper limit voltage V1 is reached. The detection voltage Vth is set to a value between the side reaction start voltage V2 at which the side reaction begins and the voltage V3 at the third timing t3. When a specific structure is adopted, the voltage of the secondary battery 12 increases at the second timing t2, so that the timing t4 at which the detection voltage Vth is reached is earlier compared to a conventional structure that does not adopt a specific structure. Therefore, in the secondary battery 12, it is possible to set the detection voltage Vth to a high value and to reach the detection voltage Vth earlier.

[0081] The voltage curve of a battery module 10, which consists of stacked secondary batteries 12 employing a specific structure, is the sum of the voltage curves of the individual secondary batteries 12, and therefore changes in a similar manner to the voltage curve shown in Figure 5. Consequently, even when detecting overcharge based on the voltage of the battery module 10, it is possible to set the overcharge detection voltage to a high value and to bring the voltage of the battery module 10 to the overcharge detection voltage early.

[0082] <Effects> According to this embodiment, the following effects can be obtained. (1) The in-vehicle battery module 10 has a plurality of secondary batteries 12 stacked in series. Each of the secondary batteries 12 includes a positive electrode 13 provided with a positive electrode active material layer 17 containing an olivine-type structural active material, a negative electrode 19 provided with a negative electrode active material layer 24, a separator 27, and a sealing body 40 that forms a sealed space S containing a liquid electrolyte between the positive electrode 13 and the negative electrode 19. The area of ​​the negative electrode facing surface 24A of the negative electrode active material layer 24 is larger than the area of ​​the positive electrode facing surface 17A of the positive electrode active material layer 17. The area of ​​the positive electrode facing surface 17A is 730 cm². ２ That concludes the findings. The ratio (C1 / M1) of the volume of the surplus space (C1) in the sealed space S, excluding the area occupied by the separator, to the area (M1) of the positive electrode opposing surface 17A is 0.02 cm² or less.

[0083] With the above configuration, it is possible to set the overcharge detection voltage, which is the detection voltage used to detect overcharge based on the voltage of the battery module 10, to a high value, and to reach the overcharge detection voltage of the battery module 10 early. By setting the overcharge detection voltage to a high value, it is possible to suppress unnecessary charging stoppages caused by reaching the overcharge detection voltage due to a momentary voltage rise during normal charging. In addition, by having the voltage of the battery module 10 reach the overcharge detection voltage early, it is possible to prevent the secondary battery 12, which is charging ahead due to individual differences, from becoming fully charged.

[0084] (2) The porosity of the positive electrode active material layer 17 is 39.5% or more and 45% or less, and the porosity of the negative electrode active material layer is 40% or more and 50% or less. By increasing the porosity of the positive electrode active material layer 17 and the porosity of the negative electrode active material layer 24, the surface area of ​​the positive electrode facing surface 17A and the surface area of ​​the negative electrode facing surface 24A are increased. In this case, the amount of liquid electrolyte in contact with the surface area of ​​the positive electrode facing surface 17A and the negative electrode facing surface 24A increases, so that the amount of gas generated by the side reaction at the second timing t2 increases. As a result, the increase in the resistance of the secondary battery 12 due to the widening of the distance D between electrodes becomes more pronounced.

[0085] (3) The density of the positive electrode active material layer 17 is 1.7 g / cm³ ３ 2.3g / cm or more ３ The following is true, and the density of the negative electrode active material layer 24 is 1.1 g / cm³. ３ 1.6g / cm or more ３ The following is the explanation: By increasing the density of the positive electrode active material layer 17 and the negative electrode active material layer 24, the resistance to ion movement within the positive electrode active material layer 17 and the negative electrode active material layer 24 increases. As a result, at the second timing t2, the increase in the resistance of the secondary battery 12 due to the widening of the distance D between the electrodes becomes more pronounced. Consequently, the voltage increase of the secondary battery 12 at the second timing t2 becomes more pronounced. Furthermore, this effect is particularly pronounced when the density of the positive electrode active material layer 17 is increased.

[0086] (4) The positive electrode active material layer 17 contains first active material particles and second active material particles, each containing an olivine-type structured active material. The first active material particles have a particle diameter of 5 μm or more and 15 μm or less. The second active material particles have a particle diameter of 0.5 μm or more and 3 μm or less. The ratio (A1 / A2) of the content of first active material particles (A1) to the content of second active material particles (A2) in the positive electrode active material layer 17 is 2.4 or more and 9.0 or less.

[0087] In the positive electrode active material layer 17, the first active material particles, which are relatively larger in size, and the second active material particles, which are relatively smaller in size, are mixed together, resulting in a dense packing of the first and second active material particles. This allows for a high density of the positive electrode active material layer 17.

[0088] <Examples of Modifications> This embodiment can be implemented with the following modifications. This embodiment and the following examples of modifications can be combined with each other to the extent that they do not contradict each other technically.

[0089] ○The battery module 10 may be equipped with a restraining member that applies a predetermined restraining pressure to a plurality of stacked secondary batteries 12 in the stacking direction. The restraining pressure applied by the restraining member is set to a strength such that, during charging, the distance D between the electrodes of the secondary batteries 12 widens due to the increase in internal pressure of the sealed space S based on the gas generated by the side reaction. An example of a battery module 10 equipped with a restraining member is shown in Figure 6.

[0090] The battery module 200 shown in Figure 6 comprises a module body 101 and an outer film 110 as a restraining member. The module body 101 is the battery module 10 of the above embodiment.

[0091] The outer film 110 surrounds and houses the module body 101. The outer film 110 is, for example, a laminate film including a metal layer. An example of the outer film 110 is a sheet-like member in which at least a portion of a metal layer, such as aluminum, is covered with a resin layer. The outer film 110 surrounds and houses the entire module body 101. The outer film 110 is depressurized to a pressure below atmospheric pressure. As a result, the outer film 110, pressed by atmospheric pressure, adheres tightly to the module body 101, applying restraining pressure to the module body 101.

[0092] ○The battery module 10 may have an exhaust structure for discharging gas generated in the sealed space S during normal use. The exhaust structure is configured to gradually discharge gas generated in the sealed space S during normal use and does not prevent a rapid increase in the internal pressure of the sealed space S due to decomposition gas generated by a side reaction at the second timing t2. An example of the exhaust structure is shown in Figure 6.

[0093] As shown in Figure 6, the battery module 200 includes a cover member 111. The cover member 111 is housed in the outer film 110 so as to be interposed between the module body 101 and the outer film 110. The cover member 111 is attached to the side surface of the module body 101 that intersects the stacking direction of the secondary batteries 12.

[0094] The cover member 111 comprises a first wall portion 111A and a second wall portion 111B facing each other in the stacking direction, and a third wall portion 111C facing the side surface of the module body 101 and connecting the first wall portion 111A and the second wall portion 111B. Inside the cover member 111 attached to the module body 101, an internal space S2 is formed, partitioned by each wall portion of the cover member 111 and the side surface of the module body 101. The side surface of the module body 101 is formed by a sealant 40. The sealant 40 is made of a gas-permeable material. Examples of gas-permeable materials include polyolefins such as polyethylene and polypropylene.

[0095] According to the above configuration, gas generated in the sealed space S during normal use is slowly discharged from the sealed space S to the internal space S2 through the sealant 40, which is made of a gas-permeable material. This suppresses the rise in internal pressure of the sealed space S caused by gas generated in the sealed space S during normal use. Furthermore, with the above configuration, there is no need to change the size of the sealed space S, that is, there is no need to change the excess space volume, so it can be suitably combined with the configuration of the above embodiment which reduces the excess space volume.

[0096] ○A battery module may be formed by stacking multiple module bodies 101 (battery module 10 in the above embodiment). In this case, current collectors may be placed between adjacent module bodies 101 in the stacking direction to electrically connect them to each other. For example, the current collectors electrically connect the positive electrode current-carrying plate 31 of one of the adjacent module bodies 101 to the negative electrode current-carrying plate 32 of the other module body 101. The current collectors may also serve as cooling plates that have the function of cooling the module bodies 101.

[0097] The following describes an embodiment that further elaborates on the above embodiment. <Embodiment 1> As a current collector, a 50 μm thick aluminum foil was prepared with an 8 μm thick copper foil laminated to one side of its surface.

[0098] A negative electrode mixture was applied in a film-like manner to the copper foil surface of the current collector using the doctor blade method. The negative electrode mixture consisted of graphite (negative electrode active material), carbon nanotubes (conductive additive), carboxymethylcellulose (binding agent), and styrene-butadiene rubber (binding agent) in a solid content mass ratio of 97.25:0.05:0.4:2.3, with water as the solvent. The applied negative electrode mixture was heat-treated at 50°C to dry and solidify the negative electrode mixture, thereby forming a negative electrode active material layer.

[0099] Subsequently, the positive electrode composite material was applied in a film-like manner to the aluminum foil side surface of the current collector using the doctor blade method. The positive electrode composite material used was LiFePO ４A slurry containing (positive electrode active material), carbon nanotubes (conductive additive), carboxymethylcellulose (binding agent), and styrene-butadiene rubber (binding agent) in a solid content mass ratio of 98.55:0.05:0.4:1.0, with water as the solvent, was used. ４ Particles with an average particle size (D50) of 7 μm were used. The coated positive electrode mixture was heat-treated at 50°C to dry and solidify the positive electrode mixture, thereby forming a positive electrode active material layer.

[0100] Subsequently, a bipolar electrode having a positive electrode active material layer and a negative electrode active material layer was fabricated by simultaneously pressing the formed negative electrode active material layer and positive electrode active material layer from both sides. Table 1 shows the opposing area, porosity, and density of the positive electrode active material layer and negative electrode active material layer of the fabricated bipolar electrode. Table 1 also shows the ratio (M2 / M1) of the opposing area (M1) of the positive electrode active material layer to the opposing area (M2) of the negative electrode active material layer.

[0101] Using the fabricated bipolar electrodes and polyethylene separator, a battery module with the structure shown in Figure 1 was constructed, and this was designated as Example 1. The battery module of Example 1 comprises 30 secondary batteries connected in series. The liquid electrolyte was prepared by dissolving vinylene carbonate, 1,3-propensultone, and lithium difluorophosphate in a mixed solvent of ethylene carbonate and methyl propionate in a volume ratio of 15:85, at concentrations of 1.5% by mass, 1.3% by mass, and 1.5% by mass, respectively. A polyethylene resin was used as the encapsulant.

[0102] Table 1 shows the excess space volume (C1) of the fabricated battery module and the ratio (C1 / M1) of the excess space volume (C1) to the opposing area of ​​the positive electrode active material layer (M1). <Example 2> A battery module of Example 2 was fabricated in the same manner as in Example 1. The battery module of Example 2 is equipped with 30 secondary batteries connected in series. As shown in Table 1, the battery module of Example 2 differs from that of Example 1 in terms of the opposing area of ​​the positive electrode active material layer (M1), the opposing area of ​​the negative electrode active material layer (M2), and the excess space volume (C1).

[0103] <Comparative Example 1> A battery module of Comparative Example 1 was manufactured in the same manner as in Example 1. The battery module of Comparative Example 1 is equipped with one secondary battery. As shown in Table 1, the battery module of Comparative Example 1 differs from that of Example 1 in the opposing area of ​​the positive electrode active material layer (M1), the opposing area of ​​the negative electrode active material layer (M2), and the excess space volume (C1).

[0104] <Charging Test> For each of Example 1 and Example 2, all secondary batteries constituting the battery module were charged simultaneously. Charging was performed at 60°C and a constant current of 2.4C until the voltage reached 4.64V. During charging, the voltage of any one secondary battery composed of two bipolar electrodes was measured at predetermined intervals.

[0105] The secondary battery of Comparative Example 1 was charged. Charging was performed at 60°C and a constant current of 2.4C until the voltage reached 4.64V. During charging, the voltage of the secondary battery was measured at predetermined intervals. From the voltage measurement results obtained during the above charging for Example 1, Example 2, and Comparative Example 1, voltage curves showing the time change of voltage, as shown in Figure 4, were created for each. Then, for each of Example 1, Example 2, and Comparative Example 1, it was confirmed whether a voltage increase occurred at the second timing t2 when the voltage reached 3.9V. The results are shown in Table 1. Note that the liquid electrolyte used in this test decomposes and generates gas when a voltage of 3.9V or higher is applied at 60°C. Furthermore, a voltage increase at the second timing t2 was determined to have occurred if the voltage increase between 3.9V and 4.05V was greater than the voltage increase between 3.75V and 3.9V.

[0106]

[0107] As shown in Table 1, in Examples 1 and 2, where the ratio (C1 / M1) was 0.02 cm or less, a voltage increase at the second timing t2 was confirmed. On the other hand, in Comparative Example 1, where the ratio (C1 / M1) exceeded 0.02 cm, no voltage increase at the second timing t2 was confirmed.

[0108] S...Sealed space 10...Automotive battery module 12...Secondary battery 13...Positive electrode 14...Positive electrode current collector 17...Positive electrode active material layer 17A...Positive electrode opposing surface 19...Negative electrode 20...Negative electrode current collector 24...Negative electrode active material layer 24A...Negative electrode opposing surface 25...Bipolar electrode 27...Separator 40...Sealing body

Claims

1. An in-vehicle battery module in which multiple secondary batteries are stacked in series, wherein each secondary battery comprises: a positive electrode having a positive electrode active material layer containing an olivine-type structural active material on the first surface of a positive electrode current collector; a negative electrode having a negative electrode active material layer on the first surface of a negative electrode current collector, the negative electrode active material layer being arranged to face the positive electrode active material layer of the positive electrode; a separator disposed between the positive electrode active material layer and the negative electrode active material layer; and a sealant disposed between the positive electrode and the negative electrode so as to surround the positive electrode active material layer and the negative electrode active material layer, and being bonded to the first surfaces of the positive electrode current collector and the negative electrode current collector, thereby forming a sealed space for containing a liquid electrolyte between the positive electrode and the negative electrode, wherein the area of ​​the negative electrode facing surface of the negative electrode active material layer facing the positive electrode active material layer is larger than the area of ​​the positive electrode facing surface of the positive electrode active material layer facing the negative electrode active material layer. The area of ​​the positive electrode opposing surface is 730 cm². ２ The above is true, and the ratio (C1 / M1) of the volume of the surplus space (C1) in the sealed space, excluding the area occupied by the separator, to the area (M1) of the positive electrode facing surface is 0.02 cm or less.

2. The automotive battery module according to claim 1, wherein the density of the positive electrode active material layer is higher than the density of the negative electrode active material layer.

3. The density of the positive electrode active material layer is 1.7 g / cm³. ３ 2.3g / cm or more ３ The following conditions apply, and the density of the negative electrode active material layer is 1.1 g / cm³. ３ 1.6g / cm or more ３ The vehicle battery module according to claim 1 or claim 2, which is as follows:

4. The automotive battery module according to any one of claims 1 to 3, wherein the positive electrode active material layer comprises first active material particles and second active material particles containing an olivine-type structured active material, the first active material particles having a particle diameter of 5 μm or more and 15 μm or less, the second active material particles having a particle diameter of 0.5 μm or more and 3 μm or less, and the ratio (A1 / A2) of the content of the first active material particles (A1) to the content of the second active material particles (A2) in the positive electrode active material layer is 2.4 or more and 9.0 or less.

5. An in-vehicle battery module according to any one of claims 1 to 4, comprising a bipolar electrode in which the surface of the positive electrode current collector of the positive electrode constituting one of the adjacent secondary batteries, located opposite the first surface, and the surface of the negative electrode current collector of the negative electrode constituting the other of the adjacent secondary batteries, located opposite the first surface, are joined together.

6. An in-vehicle battery device comprising an in-vehicle battery module according to any one of claims 1 to 5 and a control device for controlling the in-vehicle battery module, wherein the control device stops charging the in-vehicle battery module based on the voltage of the in-vehicle battery module reaching an overcharge detection voltage during charging, and the overcharge detection voltage is set to a value greater than or equal to the product of the number of stacked secondary batteries and the side reaction start voltage at 60°C during charging of the secondary battery at which a side reaction in which the liquid electrolyte decomposes begins.

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