JP2015125933A - Battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost battery pack with higher safety.SOLUTION: A battery pack 1 comprises at least a first secondary battery and a second secondary battery connected in parallel to the first secondary battery. The first secondary battery comprises a first electrode group 13A and a first current interruption unit 12A connected in series to the first electrode group. The second secondary battery comprises a second electrode group 13B. The battery pack further includes a second current interruption unit 12B connected in series to the second electrode group. The first secondary battery further includes an overcharge prevention mechanism which forms a first closed circuit including the first electrode group and the first current interruption unit and a second closed circuit including the second electrode group and the second current interruption unit in the first secondary battery when a switch 11 operates.

Description

  Embodiments described herein relate generally to an assembled battery.

  In recent years, automobiles using a secondary battery as an energy source have been put into practical use due to the reduction of carbon dioxide emissions and the fear of exhaustion of fossil fuels such as gasoline. The secondary battery is required to have high output, high energy density, small size, light weight, low price, etc., and improvement in safety and durability is indispensable.

  Lithium ion secondary batteries are known as high energy density secondary batteries for automobiles. This high energy density lithium ion secondary battery is typically one in which an electrode assembly in which a positive electrode and a negative electrode wound with a separator are wound is impregnated with an organic electrolyte and sealed in a battery can. In addition, an assembled battery in which a plurality of lithium ion secondary batteries are combined is generally used.

  Lithium ion secondary batteries use organic electrolytes, so when overcharged, not only does the battery voltage increase, but the pressure inside the battery rises due to the generation of gas, and the temperature inside the battery also increases. There is a possibility that it will rise, leading to a situation such as electrolyte leakage or can rupture. As a secondary battery for automobiles, charging and discharging are expected to be repeated frequently, and therefore, overcharge countermeasures for ensuring safety are taken.

  As a countermeasure against overcharge so far, an overcharge prevention mechanism including a current fuse has been installed inside the battery can, and if the voltage between the terminals exceeds the specified range, the current fuse blows and the charge current is cut off for safety. It is also known to secure.

  However, when all the secondary batteries in the assembled battery are provided with an overcharge prevention mechanism, there is a problem that the cost increases.

JP 2006-185708 A JP2013-020965A

  In order to solve the above problems, an assembled battery with higher safety is provided at a low cost.

  An assembled battery according to an embodiment is an assembled battery including at least a first secondary battery and a second secondary battery connected in parallel with the first secondary battery, wherein the first battery The secondary battery includes a first electrode group and a first current interrupting unit connected in series with the first electrode group, and the second secondary battery includes a second electrode. And the assembled battery includes a second current cut-off unit connected in series with the second electrode group, and the first secondary battery is disposed in the first secondary battery. Forming a first closed circuit including the first electrode group and the first current interrupting unit, and forming a second closed circuit including the second electrode group and the second current interrupting unit; An assembled battery further comprising an overcharge prevention mechanism.

FIG. 1 is a diagram for explaining an assembled battery according to an embodiment. FIG. 2 is a diagram for explaining an assembled battery according to an embodiment. FIG. 3 is a diagram for explaining an assembled battery according to an embodiment. FIG. 4 is a diagram for explaining an assembled battery according to an embodiment. FIG. 5 is a diagram for explaining an assembled battery according to an embodiment. FIG. 6 is a diagram for explaining an assembled battery according to an embodiment. FIG. 7 is a diagram for explaining a secondary battery according to an embodiment.

Hereinafter, description will be given with reference to the drawings.
FIG. 1 shows an example of a secondary battery 10 according to an embodiment.

  The secondary battery 10 of this example includes an outer can 19, a switch 11, an electrode group 13 housed in the outer can, a positive electrode terminal 14, a negative electrode terminal 15, a positive electrode short circuit lead 21, a negative electrode short circuit lead 22, a spacer 23, and a cap 24. A positive electrode lead 28, a negative electrode lead 29, a positive electrode current collecting tab 30, and a negative electrode current collecting tab 31. The positive electrode short-circuit lead 21 includes a current interrupting unit 12. The switch 11 includes a driving body 32, a fastening mechanism 33, a heating unit 34, and a voltage detection unit 35. The electrolyte is held in the electrode group 13. The electrolyte is a nonaqueous electrolyte, for example.

  The switch 11 is a switch provided between the positive terminal 14 and the negative terminal 15. The switch 11 shorts the positive electrode terminal 14 and the negative electrode terminal 15 when the voltage between the positive electrode terminal 14 and the negative electrode terminal 15 is equal to or greater than a preset value (threshold value). The switch 11 operates based on the detection result of the voltage detector 35 that measures the voltage between the positive terminal 14 and the negative terminal 15.

  The current interrupting part 12 is melted by Joule heat when the current flowing through the current interrupting part 12 exceeds a predetermined threshold, and interrupts the passing current. The current interrupting unit 12 is provided between the positive terminal 14 and the electrode group 13. That is, the current interrupting unit 12 interrupts the current flowing through the electrode group 13. For example, the current interrupting unit 12 is a fuse or the like. Further, the current interrupting unit 12 may have a structure in which an area of a part of a cross section is smaller than that of another part. The current interrupting unit 12 may be replaceable.

  In the current interrupting unit 12, the current value when the switch 11 is turned on and the positive terminal 14 and the negative terminal 15 are electrically connected is set as a threshold value. That is, the current interrupting unit 12 interrupts the current that passes when the switch 11 is turned on and the positive terminal 14 and the negative terminal 15 are electrically connected.

  The electrode group 13 is formed by winding a positive electrode and a negative electrode in a flat shape with a separator between them. The positive electrode is a positive current collector excluding, for example, a strip-shaped positive current collector made of metal foil, a positive current collector tab 30 having one end parallel to the long side of the positive current collector, and at least the positive current collector tab 30 portion. A positive electrode material layer (positive electrode active material-containing layer) formed on the electric body. On the other hand, the negative electrode is, for example, a strip-shaped negative electrode current collector made of a metal foil, a negative electrode current collector tab 31 having one end parallel to the long side of the negative electrode current collector, and at least the negative electrode current collector tab 31 portion. A negative electrode material layer (negative electrode active material-containing layer) formed on the negative electrode current collector.

  Such a positive electrode, a separator, and a negative electrode are formed so that the positive electrode current collecting tab 30 protrudes from the separator in the winding axis direction of the electrode group 13 and the negative electrode current collecting tab 31 protrudes from the separator in the opposite direction. And it is wound by shifting the position of the negative electrode. By such winding, the electrode group 13 has a positive current collecting tab 30 wound in a spiral shape from one end face, and a negative current collecting tab 31 wound in a spiral form from the other end face. It becomes a state to do.

  The positive electrode terminal 14 is electrically connected to the positive electrode current collecting tab 30 via an internal positive electrode lead 28. The negative electrode terminal 15 is electrically connected to the negative electrode current collecting tab 31 through an internal negative electrode lead 29.

  The cap 24 is a plate that covers the upper surface of the outer can 19. The cap 24 includes a hole through which the positive electrode terminal 14 passes and a hole through which the negative electrode terminal 15 passes. The cap 24 fixes the positive electrode terminal 14 and the negative electrode terminal 15 via a spacer 23 that is an insulating member installed in the hole. Further, the cap 24 fixes the positive electrode short-circuit lead 21, the negative electrode short-circuit lead 22, the driving body 32, the fastening mechanism 33, and the like through an insulating material (not shown).

  The positive electrode lead 28 and the negative electrode lead 29 are each made of a strip-shaped conductive plate. The positive electrode lead 28 is electrically connected to the positive electrode current collecting tab 30, and the negative electrode lead 29 is electrically connected to the negative electrode current collecting tab 31. The positive electrode terminal 14 and the negative electrode terminal 15 are each fixed to the cap 24 via a spacer 23 that is an insulating member. The tip of the positive electrode lead 28 is electrically connected to the positive electrode terminal 14, and the tip of the negative electrode lead 29 is electrically connected to the negative electrode terminal 15.

  As described above, the switch 11 includes the driving body 32, the fastening mechanism 33, the heating unit 34, and the voltage detection unit 35. Further, the positive electrode short-circuit lead 21 and the negative electrode short-circuit lead 22 are provided in order of the positive electrode short-circuit lead 21, the space, and the negative electrode short-circuit lead 22 from the cap 24 side. A space of a predetermined interval is provided between the positive electrode short-circuit lead 21 and the negative electrode short-circuit lead 22 so as not to contact each other.

  The driving body 32 is an elastic body that generates a stress in accordance with an external pressure. When the driving body 32 is compressed, a stress is generated in a direction opposite to the direction in which the driving body 32 is compressed. The drive body 32 is a leaf | plate spring, a coil spring, etc., for example.

  The driving body 32 is installed between the positive electrode short-circuit lead 21 and the upper surface of the cap 24 in a compressed state. Therefore, the drive body 32 continues to apply upward stress to the positive electrode short-circuit lead 21. That is, the driving body 32 continues to apply stress to the positive electrode short-circuited lead 21 in a direction in which the negative electrode short-circuited lead 22 and the positive electrode short-circuited lead 21 are in contact with each other.

  The fastening mechanism 33 prevents the positive electrode short-circuit lead 21 from moving upward against the stress applied by the driving body 32. For example, the fastening mechanism 33 mechanically fastens the cap 24 and the positive electrode short-circuit lead 21. By the fastening mechanism 33, the positive electrode short-circuit lead 21 and the negative electrode short-circuit lead 22 can maintain a predetermined interval.

  The fastening mechanism 33 is formed of a material that has a strength necessary for fixing the positive electrode short-circuit lead 21 and is melted and cut by the heat of the heating unit 34 that is heated by the electric power generated by the secondary battery 10. . The substance constituting the fastening mechanism 33 is, for example, polyphenyl sulfide (PPS).

  The heating unit 34 converts the electric power generated by the secondary battery 10 into Joule heat. The heating unit 34 applies the generated Joule heat to the fastening mechanism 33. In the embodiment, the heating unit 34 applies Joule heat to the region 33 a of the fastening mechanism 33 between the upper surface of the cap 24 and the positive electrode short-circuit lead 21. For example, the heating unit 34 is a nichrome wire or the like. For example, the heating unit 34 is wound around the region 33 a of the fastening mechanism 33.

  The voltage detection unit 35 applies a voltage to the heating unit 34 when determining that the voltage between the positive electrode short-circuit lead 21 and the negative electrode short-circuit lead 22 has exceeded a predetermined threshold value. When a voltage is applied, the heating unit 34 applies Joule heat to the region 33 a of the fastening mechanism 33. As a result, the heating unit 34 can melt the region 33 a of the fastening mechanism 33.

  When the heating unit 34 melts the region 33a of the fastening mechanism 33, the fastening mechanism 33 is cut in the region 33a. When the fastening mechanism 33 is cut, the driving body 32 pushes the positive electrode short-circuit lead 21 upward by its own stress. When the driving body 32 pushes up the positive electrode short-circuit lead 21, the positive electrode short-circuit lead 21 comes into contact with the negative electrode short-circuit lead 22 and is electrically connected to the negative electrode short-circuit lead 22. Thereby, the switch 11 is turned on.

  When the negative electrode short-circuit lead 22 and the positive electrode short-circuit lead 21 are electrically connected, the positive electrode short-circuit lead 21, the positive electrode terminal 14, the positive electrode lead 28, the positive electrode current collecting tab 30, the electrode group 13, the negative electrode current collecting tab 31, and the negative electrode lead 29, a closed circuit composed of the negative electrode terminal 15 and the negative electrode short-circuit lead 22 is formed. If the said closed circuit is formed, the electric current which flows into the electric current interruption part 12 will exceed the threshold value of the electric current which the electric current interruption part 12 cut | disconnects. Therefore, the current interrupting unit 12 interrupts the electrical connection between the positive electrode current collecting tab 30 and the positive electrode terminal 14.

  Hereinafter, the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte of the secondary battery will be described.

(1) Positive Electrode The positive electrode includes a positive electrode current collector and a positive electrode material layer that is supported on one or both surfaces of the current collector and includes a positive electrode active material.

Examples of the positive electrode active material include lithium-containing composite compounds, manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, conductive polymer materials such as polyaniline and polypyrrole, disulfide polymer materials, sulfur (S), fluorine. And carbonized iron, iron sulfate (Fe ₂ (SO ₄ ) ₃ ), and vanadium oxide (for example, V ₂ O ₅ ). Among these, lithium-containing composite compounds are preferable. Examples of the lithium-containing composite compound include Li _a MnO ₂ (0 <a ≦ 1.2), lithium cobalt composite oxide (Li _a CoM _h O ₂ , where M is a group consisting of Al, Cr, Mg, and Fe. At least one or two or more elements selected from: 0 <a ≦ 1.2, 0 ≦ h ≦ 0.1, lithium manganese cobalt composite oxide (for example, LiMn _1- gh Co _g M _h O ₂ , where M is at least one element selected from the group consisting of Al, Cr, Mg and Fe, 0 ≦ g ≦ 0.5, 0 ≦ h ≦ 0.1), lithium manganese nickel Composite oxide {for example, LiMn _j Ni _j M _1-2j O ₂ (M is at least one element selected from the group consisting of Co, Cr, Al, Mg and Fe, 1/3 ≦ j ≦ 1/2), _{iMn 1/3 Ni 1/3 Co 1/3 O 2} , LiMn 1/2 Ni 1/2 O 2}, spinel type lithium-manganese composite oxide (e.g., _{Li a Mn 2-b M b} O 4, wherein M Is at least one element selected from the group consisting of Al, Cr, Ni and Fe, 0 <a ≦ 1.2, 0 ≦ b ≦ 1), spinel type lithium manganese nickel composite oxide (for example, Li _a Mn _2-b Ni _b O ₄ , 0 <a ≦ 1.2, 0 ≦ b ≦ 1), lithium phosphate having an olivine structure {for example, Li _a FePO ₄ (0 <a ≦ 1.2) , Li _a Fe _1-b Mn _b PO ₄ (0 <a ≦ 1.2, 0 ≦ b ≦ 1), Li _a CoPO ₄ (0 <a ≦ 1.2), etc.}.

  When the positive electrode material layer contains a binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or fluorine-based rubber can be used as the binder.

  The positive electrode material layer may contain a conductive agent. Examples of the conductive agent include carbonaceous materials such as acetylene black, carbon black, and graphite.

  The mixing ratio of the positive electrode active material, the conductive agent, and the binder is preferably 73 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder.

  The positive electrode current collector is preferably formed from an aluminum foil or an aluminum alloy foil. The thickness of the aluminum foil and the aluminum alloy foil can be 20 μm or less, and more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. As the aluminum alloy, an alloy containing elements such as magnesium, zinc and silicon is preferable. On the other hand, the content of transition metals such as iron, copper, nickel and chromium is preferably 1% by mass or less.

  For the positive electrode, for example, a conductive agent and a binder are added to the positive electrode active material, these are suspended in an appropriate solvent, and this suspension (slurry) is applied to a current collector, dried and pressed to form a strip electrode It is produced by making.

(2) Negative Electrode The negative electrode includes a negative electrode current collector and a negative electrode material layer that is supported on one or both surfaces of the negative electrode current collector and includes a negative electrode active material.

Examples of the negative electrode active material include metal lithium and a material that can occlude and release lithium ions. As a substance capable of inserting and extracting lithium ions, for example, lithium titanium composite oxide can be given. The lithium titanium composite oxide is, for example, a spinel type lithium titanate represented by Li _{4 + x} Ti ₅ O ₁₂ (x varies in the range of −1 ≦ x ≦ 3 by charge / discharge reaction), ramsteride type Li _{2 + x} Ti ₃ O ₇ (x varies in the range of −1 ≦ x ≦ 3 by charge / discharge reaction), at least one element selected from the group consisting of Ti and P, V, Sn, Cu, Ni and Fe And metal composite oxides containing. Examples of the metal composite oxide containing at least one element selected from the group consisting of Ti and P, V, Sn, Cu, Ni and Fe include TiO ₂ —P ₂ O ₅ and TiO ₂ —V _2. O ₅ , TiO ₂ —P ₂ O ₅ —SnO ₂ , TiO ₂ —P ₂ O ₅ —MeO (Me is at least one element selected from the group consisting of Cu, Ni and Fe). These metal composite oxides change to lithium titanium composite oxides when lithium is inserted by charging. Among lithium titanium composite oxides, spinel type lithium titanate is preferable because of its excellent cycle characteristics.

  Examples of other substances that can occlude and release lithium ions include carbonaceous materials and metal compounds.

Examples of the carbonaceous material include natural graphite, artificial graphite, coke, vapor grown carbon fiber, mesophase pitch carbon fiber, spherical carbon, and resin-fired carbon. More preferable carbonaceous materials include vapor grown carbon fiber, mesophase pitch carbon fiber, and spherical carbon. The carbonaceous material preferably has a (002) plane spacing d ₀₀₂ of 0.34 nm or less by X-ray diffraction.

As the metal compound, metal sulfide or metal nitride can be used. As the metal sulfide, titanium sulfide such as TiS ₂ , molybdenum sulfide such as MoS ₂ , and iron sulfide such as FeS, FeS ₂ , and Li _x FeS ₂ can be used. As the metal nitride, for example, lithium cobalt nitride (for example, Li _s Co _t N, 0 <s <4, 0 <t <0.5) can be used.

  As the current collector, for example, a copper foil, an aluminum foil, or an aluminum alloy foil can be used. The thickness of the aluminum foil or aluminum alloy foil is desirably 20 μm or less, more preferably 15 μm or less. The aluminum foil preferably has a purity of 99% by mass or more. The aluminum alloy is preferably an alloy containing elements such as magnesium, zinc, and silicon. Transition metals such as iron, copper, nickel and chromium contained as alloy components are preferably 1% by mass or less.

  The negative electrode material layer can contain a binder. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, and styrene butadiene rubber.

  The negative electrode material layer can contain a conductive agent. Examples of the conductive agent include carbonaceous materials such as acetylene black, carbon black, and graphite.

  The blending ratio of the negative electrode active material, the conductive agent and the binder is preferably in the range of 73 to 96% by weight of the negative electrode active material, 2 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder.

  For example, the negative electrode is prepared by adding a conductive agent and a binder to a powdered negative electrode active material, suspending them in a suitable solvent, applying the suspension (slurry) to a current collector, drying, and pressing. It is produced by forming a strip electrode.

(3) Separator The separator is not particularly limited as long as it has insulating properties, but a porous film or a nonwoven fabric made of a polymer such as polyolefin, cellulose, polyethylene terephthalate, and vinylon can be used. One type of separator material may be used, or two or more types may be used in combination.

(4) Nonaqueous electrolyte The nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. The non-aqueous solvent may contain a polymer.

Examples of the electrolyte salt include LiPF ₆ , LiBF ₄ , Li (CF ₃ SO ₂ ) ₂ N (bistrifluoromethanesulfonylamidolithium; commonly known as LiTFSI), LiCF ₃ SO ₃ (commonly known as LiTFS), and Li (C ₂ F ₅ SO ₂ ). ₂ N (bis pentafluoroethanesulfonyl amide lithium; called _{LiBETI), LiClO 4, LiAsF 6} , LiSbF 6, bisoxalato Lato lithium borate _{{LiB (C 2 O 4)} 2, commonly known; LiBOB}, difluoro (tri-fluoro-2 Use of a lithium salt such as -oxide-2-trifluoro-methylpropionate (2-)-0,0) lithium borate {LiBF ₂ OCOOC (CF ₃ ) ₂ , commonly known; LiBF ₂ (HHIB)} it can. These electrolyte salts may be used alone or in combination of two or more. In particular, LiPF ₆ and LiBF ₄ are preferable.

  The electrolyte salt concentration is preferably 1 to 3 mol / L. Such regulation of the electrolyte concentration makes it possible to further improve the performance when a high load current is passed while suppressing the influence of an increase in viscosity due to an increase in the electrolyte salt concentration.

  The non-aqueous solvent is not particularly limited, and examples thereof include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC). Alternatively, linear carbonate such as dipropyl carbonate (DPC), 1,2-dimethoxyethane (DME), γ-butyrolactone (GBL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeHF), 1,3-dioxolane , Sulfolane, acetonitrile (AN) can be used. These solvents may be used alone or in combination of two or more. Nonaqueous solvents containing cyclic carbonates and / or chain carbonates are preferred.

  An additive may be added to the non-aqueous electrolyte. Although it does not specifically limit as an additive, Vinylene carbonate (VC), vinylene acetate (VA), vinylene butyrate, vinylene hexanate, vinylene crotonate, catechol carbonate, etc. are mentioned. The concentration of the additive is preferably in the range of 0.1% by weight to 3% by weight with respect to 100% by weight of the nonaqueous electrolyte. A more preferable range is 0.5% by weight or more and 1% by weight or less.

  2 thru | or FIG. 4 shows the example of the assembled battery 1 which concerns on one Embodiment.

  The assembled battery 1 includes a plurality of secondary batteries 10. For example, the assembled battery 1 includes a first secondary battery 10A and a second secondary battery 10B connected in parallel to the first secondary battery 10A as shown in FIG. Secondary battery 10A and secondary battery 10B are electrically connected via a bus bar. That is, the bus bar is a wiring for connecting the secondary battery 10B to the secondary battery 10A in parallel.

  The first secondary battery 10A has the same configuration as the secondary battery 10 of FIG. That is, the first secondary battery 10 </ b> A includes at least an outer can 19, a current blocking unit 12 </ b> A, an electrode group 13 </ b> A housed in the outer can 19, a positive terminal 14 </ b> A, and a negative terminal 15 </ b> A. Further, the electrolyte is held in the electrode group 13A. The electrolyte is a nonaqueous electrolyte, for example.

  The second secondary battery 10 </ b> B is different in that the secondary battery 10 and the current interrupting unit 12 in FIG. 1 are not provided with the switch 11, the positive electrode short-circuit lead 21, and the negative electrode short-circuit lead 22. The second secondary battery 10B includes at least an outer can 19, a current blocking unit 12B, an electrode group 13B accommodated in the outer can 19, a positive terminal 14B, and a negative terminal 15B. The electrolyte is held in the electrode group 13B. The electrolyte is a nonaqueous electrolyte, for example. Furthermore, the current interrupting part 12B of the second secondary battery 10B is provided between the negative electrode terminal 15B and the electrode group 13B.

  The outer can 19 of the second secondary battery 10B, the current blocking part 12B, the electrode group 13B, the positive terminal 14B, and the negative terminal 15B housed in the outer can 19 are the outer can 19 of the first secondary battery 10A. The current blocking unit 12A, the electrode group 13A housed in the outer can 19, the positive electrode terminal 14A, and the negative electrode terminal 15A have the same configuration. The second secondary battery 10B has a configuration in which a positive electrode terminal 14B, a current interrupting unit 12B, an electrode group 13B, and a negative electrode terminal 15B are connected in series.

  Next, the current flowing through the assembled battery 1 will be described.

  FIG. 2 is a circuit diagram illustrating an example of a current flowing through the assembled battery 1 in a normal charge state (that is, not an overcharge state).

  The assembled battery 1 is charged by the charging device 20. As shown in FIG. 2, when the switch 11 is open (OFF state), a current flows from the charging device 20 to the assembled battery 1.

  The current has two paths, a path through the secondary battery 10A and a path through the secondary battery 10B.

  The current in the first path passes from the positive terminal of the charging device 20 through the wiring 27a through the positive terminal 14A and the current blocking unit 12A, and charges the electrode group 13A. When passing through the electrode group 13A, the current flows to the negative terminal of the charging device 20 through the negative terminal 15A and the wiring 27b.

  The current in the second path passes from the positive terminal of the charging device 20 through the wiring 27a through the positive terminal 14B and the current interrupting part 12B, and charges the electrode group 13B. When passing through the electrode group 13B, the current flows to the negative terminal of the charging device 20 through the negative terminal 15B and the wiring 27b.

  Here, since secondary battery 10A and secondary battery 10B are connected in parallel, the currents flowing through secondary battery 10A and secondary battery 10B are equal, and the voltages applied to secondary battery 10A and secondary battery 10B are also equal. That is, the current A flows through the first secondary battery 10A, and the current B equal to the current A flows through the second secondary battery 10B.

  Here, the current flowing through the current interrupters 12A and 12B is smaller than the current that melts the current interrupters 12A and 12B. Therefore, the current interrupting unit 12A electrically connects the positive terminal 14A and the electrode group 13A without melting. Further, the current interrupting part 12B electrically connects the positive electrode terminal 14B and the electrode group 13B.

Next, the current flowing through the assembled battery 1 when an overcharge state occurs will be described.
When the secondary battery 10A or the secondary battery 10B is overcharged, the secondary battery 10A or the secondary battery 10B generates a voltage higher than normal (that is, a voltage higher than a set threshold value).

  When the voltage between the positive terminal 14A and the negative terminal 15A is equal to or higher than the above threshold, the switch 11 is turned on. When the switch 11 is turned on, a closed circuit is simultaneously formed in the secondary battery 10A and in the switch 11 and the second secondary battery 10B. As a result, as shown by FIG. 3, the short circuit current C and the short circuit current D begin to flow simultaneously in the respective closed circuits.

  When a closed circuit is formed in the secondary battery 10A, the short circuit current C flows from the positive electrode side of the electrode group 13A. When the short-circuit current C flows through the current interrupting unit 12, it passes through the positive terminal 14A, the switch 11, and the negative terminal 15A, and flows to the negative side of the electrode group 13A.

  Here, the short circuit current C flowing through the current interrupting unit 12A exceeds the threshold value of the current that the current interrupting unit 12A cuts. Therefore, after the state shown in FIG. 3 occurs, the current interrupting unit 12A disconnects and disconnects the electrical connection between the positive terminal 14A and the electrode group 13A.

  When a closed circuit is formed in the switch 11 and the second secondary battery 10B, the short-circuit current D flows from the positive electrode side of the electrode group 13B. The short-circuit current D passes through the positive electrode terminal 14B, the switch 11, the negative electrode terminal 15B, and the current interrupting unit 12B, and flows to the negative electrode side of the electrode group 13B.

  Here, the short circuit current D flowing through the current interrupting unit 12B exceeds the threshold value of the current that the current interrupting unit 12B cuts. Therefore, after the state shown in FIG. 3 occurs, the current interrupting part 12B is cut off and the electrical connection between the positive terminal 14B and the electrode group 13B is interrupted.

  As a result, as shown in FIG. 4, the current interrupting unit 12A and the current interrupting unit 12B are melted, and the current from the charging device 20 is not supplied to the first secondary battery 10A and the second secondary battery 10B. It becomes a state. As a result, a current E by the charging device 20 flows in a closed circuit including the charging device 20 and the switch 11.

  With the above operation, the secondary battery 10 converges the overcharged state of the secondary battery 10 without being further charged with power from the charging device 20.

  The driver 32, the fastening mechanism 33, and the heating unit 34 may be installed on the negative electrode short-circuit lead 22 side.

  As described above, the assembled battery 1 includes a plurality of secondary batteries connected in parallel. Furthermore, at least one of the plurality of secondary batteries includes a switch as an overcharge prevention mechanism. Further, each secondary battery includes a fusible fuse on a series circuit of a positive electrode terminal and a negative electrode terminal.

  According to such a configuration, the assembled battery 1 operates the switch in the ON state when the voltage of the secondary battery becomes equal to or higher than a predetermined value. Thereby, the assembled battery 1 short-circuits the positive electrode terminal and negative electrode terminal of a some secondary battery with one switch. Thereby, the assembled battery 1 can form a closed circuit including a plurality of secondary battery electrode groups and fuses. As a result, the fuse can be blown by the energy stored in the secondary battery. That is, a switch of one overcharge prevention mechanism can function as a switch for forming a closed circuit of another secondary battery connected in parallel.

  Accordingly, it is sufficient that one secondary battery in the assembled battery 1 has an overcharge prevention mechanism, and it becomes unnecessary for each of the plurality of secondary batteries to have an overcharge prevention mechanism. As a result, an assembled battery with higher safety can be provided at a low cost.

  In the above-described embodiment, the example in which the current interrupting part 12B is provided in the secondary battery 10B has been described, but the present invention is not limited to this configuration. The current interrupting unit may be provided outside the secondary battery.

  5 to 7 show an example of the assembled battery 1 according to an embodiment.

  The assembled battery 1 includes a plurality of secondary batteries. For example, as shown in FIG. 5, the assembled battery 1 includes a first secondary battery 10A, a second secondary battery 10C connected in parallel to the first secondary battery 10A, and a second secondary battery. 10C and a current interrupting unit 12C connected in series. Secondary battery 10A and secondary battery 10C are electrically connected via a bus bar. That is, the bus bar is a wiring for connecting the secondary battery 10C to the secondary battery 10A in parallel. Since the first secondary battery 10A has the same configuration as the first secondary battery 10A of the above embodiment, detailed description thereof is omitted.

  The second secondary battery 10 </ b> C is different from the secondary battery 10 of FIG. 1 described above in that the switch 11, the current interrupting unit 12, the positive electrode short-circuit lead 21, and the negative electrode short-circuit lead 22 are not provided. The second secondary battery 10C includes at least an outer can 19, an electrode group 13C housed in the outer can 19, a positive terminal 14C, and a negative terminal 15C. Further, the electrolyte is held in the electrode group 13C. The electrolyte is a nonaqueous electrolyte, for example. The second secondary battery 10C has a configuration in which a positive electrode terminal 14C, an electrode group 13C, and a negative electrode terminal 15C are connected in series. Next, the current flowing through the assembled battery 1 will be described.

  FIG. 5 is a circuit diagram illustrating an example of a current flowing through the assembled battery 1 in a normal charge state (that is, not an overcharge state).

  The assembled battery 1 is charged by the charging device 20. As shown in FIG. 5, when the switch 11 is open (OFF state), a current flows from the charging device 20 to the assembled battery 1.

  The current has two paths, a path through the secondary battery 10A and a path through the secondary battery 10C.

  The current in the first path passes from the positive terminal of the charging device 20 through the wiring 27a through the positive terminal 14A and the current blocking unit 12A, and charges the electrode group 13A. When passing through the electrode group 13A, the current flows to the negative terminal of the charging device 20 through the negative terminal 15A and the wiring 27b.

  The current of the second path passes from the positive terminal of the charging device 20 through the wiring 27a through the current interrupting unit 12C and the positive terminal 14C, and charges the electrode group 13C. When passing through the electrode group 13C, the current flows to the negative terminal of the charging device 20 through the negative terminal 15C and the wiring 27b.

  Here, since secondary battery 10A and secondary battery 10C are connected in parallel, the currents flowing through secondary battery 10A and secondary battery 10C are equal, and the voltages applied to secondary battery 10A and secondary battery 10C are also equal. That is, the current F flows through the first secondary battery 10A, and the current G equal to the current F flows through the second secondary battery 10C.

  Here, the current flowing through the current interrupters 12A and 12C is smaller than the current that melts the current interrupters 12A and 12C. Therefore, the current interrupting unit 12A electrically connects the positive terminal 14A and the electrode group 13A without melting. The current interrupting unit 12C electrically connects the charging device 20 and the positive terminal 14C.

Next, the current flowing through the assembled battery 1 when an overcharge state occurs will be described.
When the secondary battery 10A or the secondary battery 10C enters an overcharged state, the secondary battery 10A or the secondary battery 10C generates a voltage higher than usual (that is, a voltage higher than a set threshold value).

  When the voltage between the positive terminal 14A and the negative terminal 15A is equal to or higher than the above threshold, the switch 11 is turned on. When the switch 11 is turned on, a closed circuit is simultaneously formed in the secondary battery 10A and in the switch 11 and the second secondary battery 10C. As a result, as shown by FIG. 6, the short-circuit current H and the short-circuit current I begin to flow simultaneously in each closed circuit.

  When a closed circuit is formed in the secondary battery 10A, the short circuit current H flows from the positive electrode side of the electrode group 13A. When the short-circuit current H flows through the current interrupting unit 12, it passes through the positive terminal 14A, the switch 11, and the negative terminal 15A and flows to the negative side of the electrode group 13A.

  Here, the short-circuit current H flowing through the current interrupting unit 12A exceeds the threshold value of the current that the current interrupting unit 12A cuts. Therefore, after the state shown in FIG. 6 occurs, the current interrupting unit 12A disconnects and disconnects the electrical connection between the positive terminal 14A and the electrode group 13A.

  When a closed circuit is formed in the switch 11 and the second secondary battery 10C, the short circuit current I flows from the positive electrode side of the electrode group 13C. The short-circuit current I passes through the positive terminal 14C, the current interrupting part 12C, the switch 11, and the negative terminal 15C, and flows to the negative side of the electrode group 13C.

  Here, the short-circuit current I flowing through the current interrupting unit 12C exceeds the threshold value of the current that the current interrupting unit 12C cuts. Therefore, after the state illustrated in FIG. 6 occurs, the current interrupting unit 12C disconnects and disconnects the electrical connection between the charging device 20 and the positive electrode terminal 14C.

  As a result, as shown in FIG. 7, the current interrupting unit 12A and the current interrupting unit 12C are melted, and the current from the charging device 20 is not supplied to the first secondary battery 10A and the second secondary battery 10C. It becomes a state. As a result, a current J from the charging device 20 flows in a closed circuit including the charging device 20 and the switch 11.

  With the above operation, the secondary battery 10 converges the overcharged state of the secondary battery 10 without being further charged with power from the charging device 20. Even with the configuration as described above, the assembled battery 1 can form a closed circuit of a plurality of secondary batteries connected in parallel with a switch of one overcharge prevention mechanism. Furthermore, according to this configuration, in the assembled battery 1, one of the plurality of secondary batteries may include the current interrupting unit. For this reason, a secondary battery without a fuse or the like can be used for the assembled battery 1. Furthermore, since the circuit in the secondary battery is not interrupted, the electrical energy charged in the secondary battery can be safely released. As a result, an assembled battery with higher safety can be provided at a low cost.

  In the above-described embodiment, the secondary battery has been described as having a configuration in which the switch 11 is turned on when the voltage between the positive electrode terminal 14 and the negative electrode terminal 15 exceeds a predetermined value. It is not limited. The secondary battery may be configured to turn on the switch 11 according to the pressure in the outer can in which the electrode group 13 is accommodated.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Assembly battery, 10 ... Secondary battery, 11 ... Switch, 12 ... Current interruption | blocking part, 13 ... Electrode group, 14 ... Positive electrode terminal, 15 ... Negative electrode terminal, 19 ... Outer can, 20 ... Charger, 21 ... Positive electrode short circuit Lead, 22 ... Negative electrode short-circuit lead, 23 ... Spacer, 24 ... Cap, 27a ... Wiring, 27b ... Wiring, 28 ... Positive electrode lead, 29 ... Negative electrode lead, 30 ... Positive electrode current collecting tab, 31 ... Negative electrode current collecting tab, 32 ... Drive unit 33 ... fastening mechanism 33a ... region 34 ... heating unit 35 ... voltage detection unit

Claims (7)

An assembled battery comprising at least a first secondary battery and a second secondary battery connected in parallel with the first secondary battery,
The first secondary battery is
A first electrode group;
A first current interrupting unit connected in series with the first electrode group;
Comprising
The second secondary battery includes a second electrode group,
The assembled battery includes a second current interrupting unit connected in series with the second electrode group,
The first secondary battery forms a first closed circuit including the first electrode group and the first current interrupter in the first secondary battery, and the second electrode group And an overcharge prevention mechanism for forming a second closed circuit including the second current interrupting unit.   2. The assembled battery according to claim 1, wherein the second current interrupting unit is provided in series with the second electrode group in the second secondary battery. The assembled battery further includes a bus bar that electrically connects the first secondary battery and the second secondary battery,
2. The assembled battery according to claim 1, wherein the second current interrupting unit is provided in the bus bar so as to be connected in series with the second electrode group.   The overcharge prevention mechanism forms the first closed circuit and the second closed circuit by short-circuiting a positive electrode and a negative electrode included in the first secondary battery. Battery pack.   The overcharge prevention mechanism short-circuits the positive electrode and the negative electrode of the first secondary battery when the voltage between the positive electrode and the negative electrode of the first secondary battery becomes equal to or higher than a threshold value. The assembled battery as described.   The assembled battery according to any one of claims 1 to 5, wherein negative electrodes of the first secondary battery and the second secondary battery are formed of a lithium titanium composite oxide.   In the first secondary battery and the second secondary battery, an overcharge prevention agent is provided in an outer can in which the first electrode group is accommodated and an outer can in which the second electrode group is accommodated. The assembled battery according to any one of claims 1 to 6, each comprising an added electrolytic solution.

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