JP2005285646A - Battery pack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery pack easily preventing overcharge of a lithium ion secondary battery. <P>SOLUTION: The battery pack 1 is equipped with the lithium ion secondary battery 5 having an electrolyte containing lithium ions, a positive active material, and a negative active material intercalating/de-intercalating lithium ions, a pair of plates 70, 72 between which the lithium ion secondary battery 5 is interposed, and a conducting path 46 electrically connected to the positive active material or the negative active material of the lithium ion secondary battery. The conducting path 46 is fixed to one plate 70 and the other plate 72 to connect them, and when prescribed tensile force is applied, conduction is shut off. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a battery pack, and more particularly to a battery pack provided with a lithium ion secondary battery.

  A battery pack including a lithium ion secondary battery that can be repeatedly charged and discharged is widely used as a power source for portable terminals and the like. When using this battery pack, if the lithium ion secondary battery is overcharged, various problems may occur, such as the lithium ion secondary battery generating intense heat or increasing the internal pressure. Therefore, it is important not to overcharge the lithium ion secondary battery.

Conventionally, a charger having an overcharge prevention protection circuit that controls a charging voltage according to a charging history, a battery characteristic, etc., charges the lithium ion secondary battery of the battery pack to prevent overcharging (for example, , See Patent Document 1).
JP-A-10-150730

  However, the method as described above is complicated because it is necessary to acquire a charge history, and a battery pack that can more easily prevent overcharge of a lithium ion secondary battery is required.

  This invention is made | formed in view of the said subject, and it aims at providing the battery pack which can prevent the overcharge of a lithium ion secondary battery easily.

  A battery pack according to the present invention includes a lithium ion secondary battery having an electrolyte containing lithium ions, a positive electrode active material, and a negative electrode active material that intercalates and deintercalates lithium ions, and a pair sandwiching the lithium ion secondary battery. And a conductive path electrically connected to the positive electrode active material or the negative electrode active material of the lithium ion secondary battery. The conductive path is fixed to one plate and the other plate to connect the one plate and the other plate, and when a predetermined tensile force is applied, the conduction is cut off.

  According to the battery pack of the present invention, lithium ions intercalate with the negative electrode active material during charging and the negative electrode active material expands, thereby expanding the volume of the lithium ion secondary battery. The volume expansion amount of the lithium ion secondary battery is correlated with the amount of lithium ions intercalated into the negative electrode active material, that is, the remaining capacity of the battery. Then, as the charging of the lithium ion secondary battery proceeds and the remaining capacity increases, and the volume of the lithium ion secondary battery increases accordingly, the distance between the pair of plates increases. As a result, a tensile force acts on the conductive path connecting the pair of plates. And when this tensile force exceeds a threshold value which is a predetermined tensile force, conduction of the conductive path is interrupted. Therefore, if the threshold value of the tensile force of the conductive path is set appropriately in advance and the lithium ion secondary battery of the battery pack is charged via this conductive path, overcharging to the lithium ion secondary battery can be prevented in advance. it can.

  Here, the lithium ion secondary battery has a laminated structure in which a positive electrode layer containing a positive electrode active material, a separator layer, and a negative electrode layer containing a negative electrode active material are laminated in this order, and the pair of plates is a lithium ion secondary battery. Is preferably sandwiched from both sides in the stacking direction of the stacked structure.

  According to this, since the expansion of the laminated structure caused by the expansion in the thickness direction of the negative electrode layer containing the negative electrode active material appears as an increase in the distance between the pair of plates, the accuracy depends on the state of charge of the lithium ion secondary battery. It is possible to cut off the conductive path well.

  Further, even when the negative electrode layer expands unevenly in the plane, for example, when the central portion of the negative electrode layer particularly expands, the expansion of the negative electrode layer is detected with high sensitivity by a pair of plates, and the conduction path is preferably cut off. Can be awakened.

  Here, it is preferable that the conductive path has a lead wire, and the lead wire is fixed to one plate and the other plate to connect the one plate and the other plate.

  According to this, when the lithium ion secondary battery is charged to increase the remaining capacity and the distance between the pair of plates is long, a tensile force is applied to the lead wires fixed to the pair of plates, respectively. When a tensile force, for example, the tensile strength of the lead wire is reached, the lead wire breaks. As a result, the conduction of the conductive path is interrupted, and overcharging can be prevented in advance.

  Further, when the lead wire is broken by the tensile force, discharge through the lead wire becomes impossible, and the thickness of the laminated structure is normally maintained. Thus, the spacing between the plates remains wide and the lead does not conduct again. Therefore, there is an effect of preventing the reuse of the battery pack that has been charged in such a manner as to exceed the predetermined threshold.

  Here, if the lead wire is cut, stress concentrates on the lead wire cut, and it is easy to accurately cut off the conduction of the conductive path at a desired tensile force threshold, that is, a desired remaining capacity. .

  On the other hand, the conductive path has a plug and a jack that can be connected to each other, the plug is fixed to one plate, the jack is fixed to the other plate, and the one plate and the other plate are connected by connecting the jack and the plug. And may be linked.

  According to this, when the lithium ion secondary battery is charged to increase the remaining capacity and the distance between the pair of plates is increased, the plug and the jack fixed to each plate are pulled in the opposite direction, and the coupling is established. Is released, the conduction of the conductive path is interrupted. Further, after the coupling between the plug and the jack is released by the pulling force, the thickness of the laminated structure is maintained without increasing the distance between the plates unless the discharge is performed, so that the conductive path does not conduct again. Therefore, there is also an effect of preventing reuse of a battery pack in a charged state that exceeds the threshold for blocking the conductive path.

  Further, in any of the battery packs described above, an outer case that houses the lithium ion secondary battery and a pair of plates that sandwich the lithium ion secondary battery, and a cushion provided between at least one of the pair of plates and the outer case; It is preferable to further have.

  In this case, since the lithium ion secondary battery and the pair of plates are accommodated in the outer case, the handleability of the battery pack is improved. In addition, since there is a cushion between the outer case and the plate, the lithium ion secondary battery can be sufficiently expanded in the outer case, and therefore the space between the plates is sufficiently widened, so that the overcharge prevention function can be sufficiently exerted. .

  Furthermore, it is preferable that the negative electrode active material of a lithium ion secondary battery contains Si. Thus, the negative electrode active material containing Si has a remarkably large volume expansion / contraction due to lithium ion intercalation and deintercalation. Therefore, the change in the volume of the lithium ion secondary battery according to the remaining capacity becomes large, and an extremely accurate overcharge prevention operation can be performed.

  ADVANTAGE OF THE INVENTION According to this invention, the overcharge of the battery pack provided with the lithium ion secondary battery can be prevented easily.

(First embodiment)
Next, a specific first embodiment of the present invention will be described with reference to FIGS. 1 is a partially broken perspective view of the battery pack, FIG. 2 is a view taken along the line II-II in FIG. 1, and FIG. 3 is a view taken along the line III-III in FIG.

  The battery pack 1 according to the present embodiment mainly electrically connects the lithium ion secondary battery 5, the pair of plates 70 and 72 that sandwich the lithium ion secondary battery 5, and the inside and outside of the lithium ion secondary battery 5. A positive electrode lead 41 and a negative electrode lead (conductive path) 46 for connection, a cushion 80, and a case 90 for housing them are provided.

(Lithium ion secondary battery)
As shown in FIGS. 1 and 2, the lithium ion secondary battery 5 mainly includes a laminated structure 50 and a pack (battery container) 55 that accommodates the laminated structure 50 in a sealed state.

(Laminated structure)
The laminated structure 50 includes, in order from the top, a positive electrode current collector 40, a secondary battery element 35, a negative electrode current collector 45, a secondary battery element 35, and a positive electrode current collector 40, each having a plate shape. ing.

  The secondary battery element 35 is formed by laminating a cathode layer (positive electrode layer) 10, a separator layer 30, and an anode layer (negative electrode layer) 20 in this order.

  Here, in each secondary battery element 35, the positive electrode current collector 40 and the negative electrode current collector are arranged so that the anode layer 20 is in contact with the surface of the negative electrode current collector 45 and the cathode layer 10 is in contact with the surface of the positive electrode current collector 40. It is arranged between the bodies 45. Here, the anode and the cathode are determined based on the polarity at the time of discharging of the lithium ion secondary battery 5 for convenience of explanation. When the lithium ion secondary battery 5 is charged, the direction of charge flow is opposite to that during discharge, so that the anode and the cathode are interchanged.

(Anode layer)
The anode layer 20 is a layer containing a negative electrode active material, a conductive aid, a binder and the like. Hereinafter, the anode layer 20 will be described.

The negative electrode active material is not particularly limited as long as it is a material capable of reversibly proceeding desorption (deintercalation) and insertion (intercalation) of lithium ions, and a known negative electrode active material can be used. . Examples of such active materials include carbon materials such as natural graphite, artificial graphite, non-graphitizable carbon, graphitizable carbon, and low-temperature calcined carbon, and metals that can be combined with lithium such as Al, Si, and Sn. Alternatively, an alloy thereof, an amorphous compound mainly composed of an oxide such as SiO ₂ or SnO _2, or lithium titanate (Li ₄ Ti ₅ O ₁₂ ) can be given. Among them, it is preferable to use Si or an alloy thereof in order to increase the expansion / contraction rate associated with intercalation or deintercalation. Examples of the Si alloy include LiSi.

The conductive aid is not particularly limited as long as the conductivity of the anode layer 20 is improved, and a known conductive aid can be used. Examples thereof include carbon blacks, carbon materials, metal fine powders such as copper, nickel, stainless steel and iron, a mixture of carbon materials and metal fine powders, and conductive oxides such as ITO.

  The binder is not particularly limited as long as it can bind the negative electrode active material particles and the conductive additive particles to the negative electrode current collector 45, and a known binder can be used. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PEA), ethylene-tetrafluoro Fluorine resin such as ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), and styrene-butadiene rubber (SBR) Can be mentioned.

(Cathode layer)
The cathode layer 10 is a layer containing a positive electrode active material, a conductive aid, a binder and the like. Hereinafter, the cathode layer 10 will be described.

As the positive electrode active material, a known electrode active material can be used, and a material capable of reversibly progressing deintercalation and intercalation of lithium ions is preferable. For example, lithium cobalt oxide (LiCoO _2), lithium nickel oxide (LiNiO _2), lithium manganese spinel (LiMn ₂ O _4), and the general formula: represented by _{LiNi x Co y Mn z O 2} (x + y + z = 1) Composite metal oxide, lithium vanadium compound (LiV ₂ O ₅ ), olivine type LiMPO ₄ (where M represents Co, Ni, Mn or Fe), composite such as lithium titanate (Li ₄ Ti ₅ O ₁₂ ) A metal oxide is mentioned.

  As each component other than the positive electrode active material contained in the cathode layer 10, the same material as that constituting the anode layer 20 can be used. Also, the cathode layer 10 preferably contains the same electron conductive particles as the anode layer 20.

(Separator layer)
The separator layer 30 disposed between the anode layer 20 and the cathode layer 10 is formed from an electrically insulating porous body. The material of the separator layer 30 is not particularly limited, and a known separator material can be used. For example, as the electrically insulating porous body, at least one structure selected from the group consisting of a laminate of films made of polyethylene, polypropylene or polyolefin, a stretched film of a mixture of the above resins, or cellulose, polyester and polypropylene Examples thereof include a fiber nonwoven fabric made of a material.

  Here, as shown in FIG. 2, for each secondary battery element 35, the area of the separator layer 30, the anode layer 20, and the cathode layer 10 is reduced in order, and the end surface of the anode layer 20 is smaller than the end surface of the cathode layer 10. The end face of the separator layer 30 protrudes outward from the end faces of the anode layer 20 and the cathode layer 10.

  As a result, even if each layer is slightly displaced in the direction intersecting the stacking direction due to an error in manufacturing, the entire surface of the cathode layer 10 can be made to face the anode layer 20 in each secondary battery element 35. It becomes easy. Accordingly, lithium ions released from the cathode layer 10 are sufficiently taken into the anode layer 20 through the separator layer 30. Furthermore, since the separator layer 30 is larger than the cathode layer 10 and the anode layer 20 and protrudes from the end faces of the cathode layer 10 and the anode layer 20, short circuit due to contact between the cathode layer 10 and the anode layer 20 is also reduced. .

(Negative electrode current collector)
The material of the negative electrode current collector 45 to be bonded to the anode layer 20 is not particularly limited as long as it is a metal material usually used as an anode current collector of a lithium ion secondary battery, and examples thereof include copper and nickel. As shown in FIG. 2, the end of the negative electrode current collector 45 extends outward in a ribbon shape to form a tongue 45a.

(Positive electrode current collector)
The positive electrode current collector 40 bound to the cathode layer 10 is not particularly limited as long as it is a metal material usually used as a cathode current collector of a lithium ion secondary battery, and examples thereof include aluminum. As shown in FIG. 3, the end portions of the positive electrode current collector 40 extend outward in a ribbon shape to form a tongue-shaped portion 40 a.

(Electrolyte solution)
The electrolyte solution is contained in the pores of the anode layer 20, the cathode layer 10, and the separator layer 30. The electrolyte solution is not particularly limited, and an electrolyte solution containing a lithium salt (electrolyte aqueous solution, electrolyte solution using an organic solvent) used for a known lithium ion secondary battery element can be used. However, the electrolyte aqueous solution is preferably an electrolyte solution (non-aqueous electrolyte solution) using an organic solvent because the electrochemical decomposition voltage is low, and the withstand voltage during charging is limited to a low level. As the electrolyte solution for the secondary battery element, a lithium salt dissolved in a non-aqueous solvent (organic solvent) is preferably used. Examples of the lithium salt that is a source of lithium ions include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiCF ₃ , CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) _2, etc. are used. In addition, these salts may be used individually by 1 type, and may use 2 or more types together.

  Moreover, as an organic solvent, the solvent currently used for the known secondary battery element can be used. For example, propylene carbonate, ethylene carbonate, diethyl carbonate and the like are preferable. These may be used alone or in combination of two or more at any ratio.

  In the present embodiment, the electrolyte solution may be a gel electrolyte obtained by adding a gelling agent in addition to liquid. Further, instead of the electrolyte solution, a solid electrolyte (a solid polymer electrolyte or an electrolyte made of an ion conductive inorganic material) may be contained.

(pack)
As shown in FIGS. 1 to 3, the pack 55 is formed by folding a rectangular flexible sheet into two at a substantially central portion in the longitudinal direction. ) Is sandwiched from both sides. Specifically, as shown in FIG. 1, among the end portions of the sheet 55s folded in half, the seal portions 55b on three sides excluding the folded portion 55a are adhered by heat sealing or an adhesive. And as shown in FIG. 3, the laminated structure 50 is sealed inside. The pack 55 prevents air and moisture from entering the pack 55 and prevents the electrolyte solution from leaking from the pack 55. In particular, it is preferable to use a pack 55 formed of a sheet 55s having a three-layer structure. Specifically, the innermost layer 55h of the sheet 55s is a resin layer formed of a synthetic resin such as unstretched polypropylene (CPP), the intermediate layer 55i is a metal layer formed of aluminum or the like, and the outermost layer 55j is unstretched polypropylene ( CPP) is a resin layer formed from a synthetic resin.

  Note that the pack 55 is not limited to such a three-layer structure, and packs such as one layer (resin layer) or two layers (resin layer + metal layer) used in known secondary battery elements are used. Can be used.

(plate)
As shown in FIGS. 1 to 3, the plates 70 and 72 are formed in a plate shape and are stacked on the top and bottom of the lithium ion secondary battery 5, and the lithium ion secondary battery 5 is stacked on the stacked structure 50. It is sandwiched from both sides of the direction.

  Specifically, the plate 70 is stacked between the pack 55 of the lithium ion secondary battery 5 and the upper plate 90a of the case 90, and the plate 72 is stacked with the pack 55 of the lithium ion secondary battery 5 and the cushion 80. It is piled up between. The plate 70 and the plate 72 are opposed to each other.

  Further, as shown in FIGS. 2 and 3, the areas of the plates 70 and 72 are equal to or larger than the area of the laminated structure 50, and these plates 70 and 72 are opposed to the entire surface of the laminated structure 50. .

  The material of the plate 70 is not particularly limited, and a resin material such as polypropylene or a metal material such as stainless steel or aluminum can be used. In particular, a hard material is preferably used so as not to absorb expansion and contraction of the lithium ion secondary battery 5, and a metal material, a hard resin, or the like is preferable.

(Negative lead and positive lead)
The negative electrode lead (conductive path) 46 is a strip-shaped lead wire extending in a ribbon shape, and one end of the negative electrode lead (conductive path) 46 is a tongue of the negative electrode current collector 45 in the pack 55 of the lithium ion secondary battery 5 as shown in FIG. It is connected to the shape part 45a. The material of the negative electrode lead 46 can be the same material as that of the negative electrode current collector 45. As shown in FIGS. 1 and 2, the other end of the negative electrode lead 46 protrudes outside the pack 55 through the seal portion 55 b of the pack 55.

  The positive electrode lead 41 is also a conductive path extending in a ribbon shape, and one end of the positive electrode lead 41 is connected to the tongue 40a of each positive electrode current collector 40 in the pack 55 of the lithium ion secondary battery 5 as shown in FIG. ing. The material of the positive electrode lead 41 can be the same as that of the positive electrode current collector 40. As shown in FIGS. 1 to 3, the other end of the positive electrode lead 41 protrudes outside the pack 55 through a seal portion 55 b of the pack 55.

  In the negative electrode lead 46 and the positive electrode lead 41, the portion sandwiched between the seal portions 55b of the pack 55 is covered with an insulator 14 such as a resin in order to improve the sealing performance as shown in FIGS. Although the material of the insulator 14 is not specifically limited, For example, it is preferable that each is formed from a synthetic resin.

  In the present embodiment, in particular, the negative electrode lead 46 coming out of the lithium ion secondary battery 5 has plates 70 and 72 in a state of sandwiching the lithium ion secondary battery 5 as shown in FIGS. 1 and 2. Are connected so that the plates 70 and 72 are connected.

  Specifically, as shown in FIGS. 1 and 2, the negative electrode lead 46, after exiting from the pack 55 of the lithium ion secondary battery 5, proceeds to the upper side in the stacking direction of the stacked structure 50 and ends 70 c of the plate 70. It reaches the top and then bends along the upper surface 70a of the plate 70. The negative electrode lead 46 proceeds along the upper surface 70 a toward the folded portion 55 a of the pack 55 and bends along the end surface 70 d on the opposite side of the plate 70. Subsequently, the negative electrode lead 46 is separated from the end surface 70 d of the plate 70, extends in the stacking direction of the stacked structure 50 along the folded portion 55 a of the pack 55, and reaches the end surface 72 d of the plate 72. Thereafter, the negative electrode lead 46 bends along the lower surface 72b of the plate 72, and again extends toward the side where the negative electrode lead 46 protrudes from the pack 55 in the lithium ion secondary battery 5 along the lower surface 72b of the plate 72. Further, it protrudes from the plate 72.

  Further, the negative electrode lead 46 routed in this way is fixed to the plate 70 and the plate 72 with an adhesive or the like, and connects the plate 70 and the plate 72.

  In addition, as shown in FIG. 1, a V-shaped notch is formed at the edge of the negative electrode lead 46 extending from the plate 70 to the plate 72, that is, at the edge of the portion facing the side surface of the laminated structure 50. 46c is formed. Specifically, a pair of cuts 46 c are provided at positions facing each other on both edges of the ribbon-like negative electrode lead 46.

(cushion)
The cushion 80 is a plate-like member as shown in FIGS. 1 to 3 and is formed of a material having elasticity such as rubber or foamed resin. The cushion 80 is disposed between the plate 72 and the lower plate 90b of the case 90. The cushion 80 fixes the lithium ion secondary battery 5 in the case 90 while allowing expansion and contraction in the stacking direction of the lithium ion secondary battery 5 in the case 90. The cushion 80 may be inserted not between the plate 72 and the case 90 but between the plate 70 and the case 90. The cushion 80 may be inserted between the plate 72 and the case 90 and between the plate 70 and the case 70. You may insert both between case 90.

(Case)
The case (outer case) 90 is a box-shaped container whose one side surface is opened. In order to maintain an interval between the upper plate 90a, the lower plate 90b facing the upper plate 90a, and the upper plate 90a and the lower plate 90b. There are three side plates 90c that connect the upper plate 90a and the lower plate 90b.

  Between the upper plate 90a and the lower plate 90b, the spacer 70, the lithium ion secondary battery 5, the plate 72, and the cushion 80 are stored in close contact with each other, and the upper plate 90a and the lower plate 90b are accommodated. The spacer 70, the lithium ion secondary battery 5, the plate 72, and the cushion 80 are sandwiched from both sides in the direction in which they are stacked (the vertical direction in the figure).

  The material of the case 90 is not particularly limited, but a resin material such as polypropylene or a metal material such as stainless steel or aluminum can be used.

(Production method)
Next, an example of a method for manufacturing the battery pack 1 described above will be briefly described with reference to FIGS.

  First, the lithium ion secondary battery 5 is created. First, as shown in FIG. 4, the cathode layer 10 is formed on one surface of the positive electrode current collector 40 provided with the tongue-like portion 40 a to obtain two two-layer laminates 120. The cathode layer 10 can be formed by coating the positive electrode current collector 40 with a solvent having the above-described positive electrode active material, conductive additive, binder, and the like.

  In addition, the anode layer 20 is formed on both surfaces of the negative electrode current collector 45 provided with the tongue 45a to obtain a three-layer laminate 140. The anode layer 20 can be formed by applying a solvent having the above-described negative electrode active material, conductive assistant, binder, etc. to the negative electrode current collector 45.

  Subsequently, two separator layers 30 made of an insulating porous material are prepared. And it laminates like 2 layer laminated body 120 / separator layer 30/3 layer laminated body 140 / separator layer 30/2 layer laminated body 120, and it heats across the in-plane center part of both sides of these lamination directions. The laminated structure 50 shown in FIGS. 2 and 3 is created. Further, a positive electrode lead 41 and a negative electrode lead 46 are prepared, and the negative electrode lead 46 is connected to the tongue 45a of the negative electrode current collector 45 as shown in FIG. 2, and the positive electrode current collector is shown in FIG. Each of the 40 tongues 40 a is connected to the positive electrode lead 41.

  Next, as shown in FIG. 5 (a), a rectangular sheet 55s obtained by laminating an aluminum foil with a heat-adhesive resin layer is folded and overlapped, and the two side seal portions 55b and 55b are formed by, for example, a sealing machine or the like. The bag-shaped pack 55 in which the opening part 55c for introducing the laminated structure 50 is formed is obtained by heat sealing.

  Then, the laminated structure 50 is inserted into the pack 55 having the opening 55c, and the electrolyte solution is injected into the pack 55 while reducing the pressure inside the pack 55 in the vacuum container, thereby forming the laminated structure 50. Immerse in the electrolyte solution. Thereafter, the end portions of the positive electrode lead 41 and the negative electrode lead 46 are protruded from the inside of the pack 55 to the outside, and the opening 55c of the pack 55 is sealed using a heat sealing machine. Thereby, the production of the lithium ion secondary battery 5 as shown in FIG. 1 is completed.

  Subsequently, as shown in FIG. 5B, the plate 70 and the plate 72 having a predetermined thickness are used, the lithium ion secondary battery 5 is sandwiched between the plates 70 and 72, and the negative electrode lead 46 is connected to the plate 70 / The positive electrode lead 46 is bonded and fixed to the plates 70 and 72 while being wound around the outer periphery of the laminate L composed of the lithium ion secondary battery 5 / plate 72. Then, after the cushion 80 is overlaid on the lower surface of the plate 72, the laminate M composed of the plate 70 / lithium ion secondary battery 5 / plate 72 is stored in a case 90 having a predetermined size. Here, the total sum of the thicknesses of the stacked body M is substantially the same as or less than the distance between the upper plate 90a and the lower plate 90b of the case 90. Thereby, the battery pack 1 of this embodiment as shown in FIG. 1 is completed.

  According to the battery pack 1 of the present embodiment, when the battery pack 1 is charged via the positive electrode lead 41 and the negative electrode lead 46, lithium ions are intercalated into the negative electrode active material of the anode layer 20, and the negative electrode active material, That is, the anode layer 20 expands, and thereby the volume of the laminated structure 50 of the lithium ion secondary battery 5 expands. The volume expansion amount of the laminated structure 50 has a correlation with the amount of lithium ions intercalated into the negative electrode active material, that is, the remaining capacity of the battery. Then, as the charging of the lithium ion secondary battery 5 proceeds and the remaining capacity increases, the volume of the laminated structure 5 increases accordingly, the distance between the pair of plates 70 and 72 becomes longer, and the negative electrode lead 46 Tensile force works. Further, when the battery is further charged to increase the remaining capacity and the volume of the laminated structure 50 is increased to a predetermined value, the negative electrode lead 46 fixed to the pair of plates 70 and 72 and connecting them is more than the tensile strength. A large tensile force is applied to break the negative electrode lead 46 along the cut 46c. As a result, the conduction of the negative electrode lead 46 is interrupted, and further overcharge of the lithium ion secondary battery 5 can be prevented beforehand.

  Here, the thickness of the laminated structure 50 corresponding to a predetermined maximum overcharge rate (for example, 5% overcharge rate) is obtained in advance, and the force applied to the negative electrode lead 46 when the laminated structure 50 expands to this thickness. The shape of the negative electrode lead 46 may be set so that the tensile strength of the negative electrode lead 46 is equal. Specifically, for example, the tensile strength can be arbitrarily set by adjusting the thickness and width of the negative electrode lead 46 and the depth, position, width, number, and the like of the cuts 46c.

  Further, in the present embodiment, when the negative electrode lead 46 breaks once due to a tensile force exceeding the threshold value, discharge through the negative electrode lead 46 becomes impossible, and the thickness of the laminated structure 50 is normally maintained. Therefore, the distance between the plates 70 and 72 remains wide, and the negative electrode lead 46 does not conduct again. Therefore, there is an effect of preventing reuse of the battery pack 1 that has been charged in such a manner as to exceed a predetermined threshold.

  Further, since the laminated structure 50 is sandwiched by the pair of plates 70 and 72 from both sides in the laminating direction, the anode layer 20 in the laminated structure 50 is uneven in the plane, for example, even when the central portion is particularly expanded. Since the space between the plates 70 and 72 is efficiently opened, the breakage of the negative electrode lead 46 can be efficiently caused.

  In addition, a cut 46 c is formed in a portion of the negative electrode lead 46 that connects the plate 70 and the plate 72. Accordingly, when the gap between the pair of plates 70 and 72 is widened and a tensile force is applied to the negative electrode lead 46, the negative electrode lead 46 is more reliably broken due to the stress concentration on the notch 36c. Therefore, the conduction of the negative electrode lead 46 can be accurately interrupted when a desired tensile force threshold, that is, a desired remaining capacity or overcharge rate is reached.

  Further, a case 90 that houses the lithium ion secondary battery 5 and a pair of plates 70 and 72 that sandwich the lithium ion secondary battery 5, and a cushion 80 is provided between at least one of the pair of plates 70 and 72 and the case 90. .

  Thereby, since the lithium ion secondary battery 5 and a pair of plates 70 and 72 are accommodated in the case 90, the handleability of the battery pack 1 is improved. In addition, since the cushion 80 is provided between the case 90 and the plates 70 and 72, the laminated structure 50 of the lithium ion secondary battery 5 can be sufficiently expanded in the case 90. Therefore, the space between the plates 70 and 72 is sufficient. Since it becomes wider, the overcharge prevention function can be fully demonstrated.

  Furthermore, when the negative electrode active material of the lithium ion secondary battery contains Si, the expansion and contraction of the volume of the negative electrode active material, that is, the anode layer 20 accompanying the intercalation and deintercalation of lithium ions is remarkably large. Therefore, the change in the volume of the lithium ion secondary battery 5 according to the remaining capacity becomes large, and an extremely accurate conduction interruption operation for preventing overcharge becomes possible.

  In addition, since the lithium ion secondary battery 5 further includes a pack 55 that seals the electrolyte solution containing lithium ions, the cathode layer 10 containing the positive electrode active material, and the anode layer 20 containing the negative electrode active material, the electrolyte solution However, the lithium ion secondary battery 5 is less likely to leak out, which is preferable.

(Second embodiment)
Next, the battery pack 2 according to the second embodiment will be described with reference to FIG. The battery pack 2 according to this embodiment is different from the battery pack 1 according to the first embodiment in that a plug 47 and a jack 48 that can be coupled to each other are connected to the middle of the negative electrode lead 46. The plug 47 is fixed to one plate 70, and the jack 48 is fixed to the other plate 72. In addition, the plate 70 and the plate 72 are connected by connecting the plug 47 and the jack 48.

  The form of the plug 47 and the jack 48 is not particularly limited as long as the plug 47 and the jack 48 are inserted into the jack 48 so that they become conductive, and when the jack 48 is pulled out of the plug 47, the conduction is cut off. Good.

  According to this, when the lithium ion secondary battery 5 is charged in the same manner as in the first embodiment and the remaining capacity of the lithium ion secondary battery 5 increases, the laminated structure 50 of the lithium ion secondary battery 5 expands. The interval between the pair of plates 70 and 72 becomes longer. As a result, the plug 47 and the jack 48 fixed to the plates 70 and 72 are pulled in opposite directions to release the coupling therebetween, so that the conduction of the negative electrode lead 46 is interrupted. Therefore, the overcharge of the lithium ion secondary battery 5 can be prevented in advance as in the first embodiment. Other functions and effects are the same as in the first embodiment.

  In addition, this invention is not limited to the said embodiment, It can take various deformation | transformation aspects.

  For example, in the above-described embodiment, the pair of plates 70 and 72 are connected by the negative electrode lead 46, the plug 47, and the jack 48. However, any material can be used as long as conduction is interrupted by a predetermined tensile force.

  In the above embodiment, the plates 70 and 72 are connected by the negative electrode lead 46 and the conduction of the negative electrode lead 46 is cut off. However, the plates 70 and 72 are connected by the positive electrode lead 41 and this positive electrode is connected. You may comprise so that conduction | electrical_connection of the lead 41 may be interrupted | blocked.

  In the first embodiment, the plate 70 and the plate 72 are connected by the single negative electrode lead 46, but may be connected by a plurality of negative electrode leads, or both of the positive electrode lead and the negative electrode lead. . In this case, one end of the plate 70 and the plate 72 may be connected by a plurality of leads, but one end and the other end of the plate 70 and the plate 72 are connected by leads. Further, the four sides of the plate 70 and the plate 72 may be connected by leads.

  Moreover, in the said embodiment, although the laminated structure 50 had two secondary battery elements 35 as a single cell, it may have more than two secondary battery elements, One may be sufficient.

  Hereinafter, the present invention will be described in more detail with reference to examples of the battery pack according to the present embodiment, but the present invention is not limited to these examples.

First, a cathode laminate was produced by the following procedure. First, LiCoO ₂ as a positive electrode active material, carbon black and graphite as a conductive aid, polyvinylidene fluoride as a binder (PVdF; PVdF homopolymer particles manufactured by Atofina Kynar 741, weight average molecular weight Mw 5.5 × 10 ⁵ , average particle diameter 0.2 μm, soluble in NMP), and after mixing and dispersing with a planetary mixer such that the weight ratio thereof is positive electrode active material: carbon black: graphite: binder = 90: 3: 3: 4 To this, NMP as a solvent was mixed at room temperature so that the weight ratio of NMP: binder was 94: 6 to prepare a slurry cathode coating solution (slurry). Subsequently, a cathode coating solution is applied to one side of a 60 μm thick aluminum foil by a doctor blade method and dried to form a cathode laminate for both ends, and the cathode coating solution is applied to both sides of a 20 μm thick aluminum foil. It was applied using a doctor blade and dried to obtain a cathode laminate for an intermediate layer.

  Subsequently, an anode laminate was produced by the following procedure. First, silicon powder is used as the negative electrode active material, carbon black and graphite are used as the conductive additive, and the same PVdF is used as the binder as the cathode, and the weight ratio thereof is negative electrode active material: carbon black: graphite: binding. Agent = 75: 3: 12: 10 After mixing and dispersing with a planetary mixer, NMP as a solvent is added to this at room temperature so that the weight ratio of NMP: binder is 93: 7. A slurry-like coating solution for anode was prepared by mixing below. Next, a copper foil (thickness: 10 μm) as a current collector was prepared, and an anode coating solution was applied to both sides of the copper foil by a doctor blade method and dried to obtain an anode laminate.

  Next, a polyolefin porous membrane is prepared as a separator, and a cathode laminated body for both ends / separator / anode laminated body / separator / cathode laminated body for intermediate layer /.../ separator / anode laminated body / separator / The laminated structure was laminated like a cathode laminated body for both ends, and fixed by thermocompression bonding from both end faces. Here, lamination was performed such that a cathode laminate having a cathode supported on one side was disposed on the outermost layer of the laminate structure.

Next, LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed so as to have a concentration of 1 mol / dm ³ to obtain a nonaqueous electrolyte solution.

  Next, a pack in which an aluminum laminate film was formed in a bag shape was prepared, a laminated structure was inserted, and a nonaqueous electrolyte solution was injected in a vacuum chamber to impregnate the laminated structure in the nonaqueous electrolyte solution. Thereafter, in the reduced pressure state, the entrance of the pack was sealed such that a part of the lead protruded from the outer package, and initial charge / discharge was performed to obtain a stacked lithium ion secondary battery.

  When the charge / discharge cycle was repeated for such a lithium ion secondary battery, the thickness of the lithium ion secondary battery expanded greatly when discharged as shown in line A of FIG. 7, and contracted greatly when discharged. It was confirmed. Although a lithium ion secondary battery using graphite as a negative electrode active material was also produced, even in this case, as shown by a line B in FIG.

  Subsequently, a pair of stainless steel plates with a predetermined thickness, a cushion, and a squeezed aluminum box-shaped case with a predetermined opening width are prepared, the lithium ion secondary battery is sandwiched between the pair of plates, and the negative electrode lead is A pair of plates were connected by winding around these laminates, and a cushion was stacked on the lower side and inserted into the case to complete the battery pack. The thickness of the cushion was set so that there was no gap in the thickness direction within the case. Further, the negative electrode lead was set to break when the overcharge rate corresponded to 5%.

  FIG. 8 shows changes in the thickness and current value of the lithium ion secondary battery over time when constant current charging is performed on such a battery pack via the positive electrode lead and the negative electrode lead. As charging progressed, the thickness of the lithium ion secondary battery increased, but when the overcharge rate reached 5%, the negative electrode lead broke and no further charging was performed.

It is a partially broken perspective view of the battery pack according to the first embodiment. It is an II-II arrow line view of the battery pack of FIG. It is an III-III arrow line view of the battery pack of FIG. It is sectional drawing explaining the method of manufacturing a battery pack. FIG. 4A and FIG. 4B are perspective views following FIG. 3 for explaining a method of manufacturing a battery pack. It is a partially broken perspective view of the battery pack which concerns on 2nd embodiment. It is a graph which shows the change of the thickness accompanying charging / discharging of the lithium ion secondary battery used for the battery pack which concerns on an Example. It is a graph which shows the time-dependent change of thickness and an electric current when carrying out constant current charge to the battery pack which concerns on an Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Battery pack, 5 ... Lithium ion secondary battery, 10 ... Cathode layer (positive electrode layer), 20 ... Anode layer (negative electrode layer), 30 ... Separator layer, 46 ... Negative electrode lead (conductive path, lead wire), 47 ... Plug, 48 ... Jack, 46c ... Cut, 50 ... Laminated structure, 55 ... Pack (battery container), 70, 72 ... Plate, 80 ... Cushion, 90 ... Case (outer case).

Claims (7)

A lithium ion secondary battery having an electrolyte containing lithium ions, a positive electrode active material, and a negative electrode active material that intercalates and deintercalates the lithium ions;
A pair of plates sandwiching the lithium ion secondary battery;
A conductive path electrically connected to the positive electrode active material or the negative electrode active material of the lithium ion secondary battery,
The battery path is fixed to one of the plates and the other plate, connects the one plate and the other plate, and cuts off the conductivity when a predetermined tensile force is applied. The lithium ion secondary battery has a laminated structure in which a positive electrode layer containing the positive electrode active material, a separator layer, and a negative electrode layer containing the negative electrode active material are laminated in this order,
The battery pack according to claim 1, wherein the pair of plates sandwich the lithium ion secondary battery from both sides in the stacking direction of the stacked structure.   The battery according to claim 1, wherein the conductive path has a lead wire, and the lead wire is fixed to one plate and the other plate to connect the one plate and the other plate. pack.   The battery pack according to claim 3, wherein the lead wire has a cut. The conductive path has a plug and a jack that can be coupled to each other,
The plug is fixed to one of the plates, the jack is fixed to the other of the plates, and the one plate and the other plate are connected to each other by coupling the jack and the plug. 2. The battery pack according to 2.   The outer case for housing the lithium ion secondary battery and the pair of plates, and a cushion provided between at least one plate of the pair of plates and the outer case. The battery pack according to any one of the above.   The battery pack according to claim 1, wherein the negative electrode active material of the lithium ion secondary battery contains Si.

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