JP2008047371A - Battery pack and charge and discharge method of battery pack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery pack and a charge and discharge method of the battery pack of long life and excellent energy density, capable of temperature control of batteries by charge and discharge, and hardly affected by surrounding environments. <P>SOLUTION: The battery pack 30 with a plurality of flat secondary batteries 10 stacked is provided with heat exchanger plates 7 each having a principal surface in contact with a principal surface of the secondary battery so as to exchange heat with the secondary battery and forming a battery/heat exchanging plate assembly in combination with the secondary battery, at least one thermoelectric conversion element 31 fitted at a side face of the battery/heat exchanging plate assemblies so as to exchange heat with a plurality of the stacked battery/heat exchanging plate assemblies, and an outer package member 38 with a heat insulating layer surrounding the battery/heat exchanging plate assemblies and the thermoelectric conversion element. The secondary battery has a combination of an anode active material and a cathode active material having an area in which an entropy variation ΔS of the total battery reaction under a normal temperature atmospheric pressure becomes endothermic. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an assembled battery obtained by stacking a plurality of flat secondary batteries and a method for charging and discharging the assembled battery.

  In recent years, the performance of secondary batteries has been improved, and application fields are diversified from portable electronic devices to hybrid vehicles, electric vehicles, power storage power supplies, and the like. From these backgrounds, the performance required for the secondary battery includes not only high input / output performance and high energy density, but also a long life and a wide operating temperature range. Furthermore, along with the increase in the output of the application power supply, the technical development of an assembled battery in which many single cells are stacked has become an urgent issue. In particular, in recent years, there has been a need for a method of use that can achieve stable performance regardless of the operating environment. Development is desired.

  On the other hand, nickel-metal hydride secondary batteries and lithium-ion secondary batteries are examples of secondary batteries used in various applications in recent years. These have the advantage of excellent rapid charge / discharge performance and high energy density, and are widely used from portable electronic devices to power storage.

  In recent years, in order to increase the energy density of assembled batteries, the unit cell outer tank has been improved from a conventional cylindrical one to a rectangular flat one. This is because the gap between the single cells can be eliminated when forming the assembled battery, and the dead space can be reduced. On the other hand, the assembled battery has a considerable problem in terms of equalizing the temperature of each square cell and heat dissipation treatment. In particular, high-power secondary batteries that carry large currents generate a large amount of heat during high-speed charging / discharging, and cooling and soaking of the constituent batteries are important issues for improving the battery life and maintaining battery capacity. It has become.

  When a conventional cylindrical battery is an assembled battery, a gap is always generated between the single cells. Therefore, as described in Patent Document 1, air is blown into the gap as a heat exchange medium. It is relatively easy to conduct heat transfer such as heat equalization, heat dissipation, and heat retention.

  On the other hand, when a flat rectangular cell is an assembled battery, there is no gap between the cells, so the heat exchange medium can be exchanged with the inside of the assembled battery only by exchanging heat with the surface of the assembled battery. Heat exchange is not possible. For this reason, reaction heat is accumulated inside the assembled battery, and a large temperature difference is generated between the inside and the surface of the assembled battery. Specifically, the unit cells closer to the both end surfaces of the stacked layers are more likely to be cooled, and heat is more likely to be accumulated closer to the center portion (core portion) of the assembled battery.

  As shown in FIG. 13, gaps 11 are formed between the rectangular flat batteries 10, and cooling air is allowed to flow through these gaps 11, so that the outer tub of the assembled battery is soaked and dissipated. This can be considered as well. However, the battery pack of this measure cannot take advantage of the rectangular flat battery having a high packing density, and there is a problem that it is difficult to improve the energy density of the battery pack.

  Patent Document 2 discloses a technique in which a cooling tab is arranged so that the cooling performance is the highest in the central portion in the thickness direction in an assembled battery in which rectangular flat batteries are stacked. According to this prior art, it is easy to equalize the temperature in the stacked flat battery surface, and the cooling tab also functions as a shared voltage detection tab. However, in the flat battery of Patent Document 2, the cooling tab protrudes in a direction perpendicular to the stacking direction of the assembled battery, and as a result, the projected area of the assembled battery increases, resulting in a decrease in energy density. There is a fear. Moreover, since the cooling tab is a voltage detection tab, the cooling tabs cannot be brought into contact with each other. The inability to contact the cooling tabs is considered to be disadvantageous in suppressing variation in the amount of heat between the batteries. Originally, in order to soak the constituent batteries, it is preferable that the batteries are in contact via a heat conducting medium.

  On the other hand, in addition to the problem of the battery structure, the active material and electrode structure constituting the battery also become a problem. In a high-speed charge / discharge type secondary battery, there is a large problem due to Joule heat generation due to internal resistance during charge / discharge. Further, the total entropy change in the electrode reaction (battery reaction) differs depending on the configuration of the active material, and these also contribute to the heat generation of the battery. When the thermal behavior of the battery due to a chemical reaction is simply described, the following equations (1) to (3) are obtained.

Positive electrode reaction; LiM → □ M + Li ⁺ + e ⁻ (1)
Negative electrode reaction; □ X + Li ⁺ + e ⁻ → LiX (2)
LiM + □ X → □ M + LiX (3)
The positive electrode active material was M, and the negative electrode active material was X. Here, the symbol □ represents a site that can accept lithium ions. These batteries react to generate heat or endotherm. The heat input and output in these batteries is expressed by the Gibbs-Helmholtz equation of the following equation (4) under the conditions of constant temperature and constant pressure.

ΔG = ΔH−TΔS (4)
Here, ΔG represents the Gibbs energy variation, ΔH represents the enthalpy variation, and ΔS represents the entropy variation. If Qs is the calorific value due to the total battery reaction, Qs is given by the following equation (5). Therefore, it is possible to determine whether the battery reaction is endothermic or exothermic based on the total entropy change ΔS of the battery reaction. it can.

Qs = Tcell · ΔS (5)
The entropy change amount ΔS varies depending on the charging depth (SOC) of the battery. Focusing on the LiCoO ₂ positive electrode and carbon-based negative electrode used in general-purpose lithium ion batteries, the positive electrode LiCoO ₂ exhibits an endothermic reaction in a wide range of charge depths during charging, but the negative electrode carbon-based material is being charged. There are many areas that exhibit an exothermic reaction. While there are areas where the endothermic reaction of the positive electrode and the exothermic reaction of the negative electrode cancel each other during charging, when viewed as a total reaction of both positive and negative electrodes, including the amount of heat generated by internal resistance and overvoltage, during charging and discharging As a result, the whole battery tends to generate heat. Therefore, since the structure of the conventional lithium ion assembled battery has a tendency that the battery generates heat during charging and discharging, some kind of cooling mechanism is required.

  By the way, by keeping the temperature of the assembled battery in an appropriate temperature range, a technique for exhibiting the performance of the battery without being affected by the environmental temperature is also required. The soaking and heat dissipation of the assembled battery is mainly due to the heat generated during charging and discharging of the secondary battery, but the influence of the environmental temperature must also be considered. For example, in order to demonstrate the performance of a secondary battery at an extremely low temperature, it is necessary to maintain the temperature of the battery itself within an appropriate temperature range.

  This is because the secondary battery is a power storage means using a chemical reaction and is therefore sensitive to the surrounding temperature environment. In particular, sufficient performance cannot be exhibited at low temperatures below the freezing point, and exposure to a high temperature of 40 ° C. or higher for a long time often leads to a decrease in life. Thus, in recent years, Patent Documents 1, 3, and 4 disclose techniques using an electrothermal element and a heat exchange element as means for actively keeping and cooling the battery.

In the prior art described in Patent Documents 1 and 3, the temperature of the assembled battery is controlled by flowing a heat medium (mainly fluid such as air) heated or cooled by the heat exchange element through the battery gap. These Patent Documents 1 and 3 describe an environment in which a fluid is unlikely to function as a heat medium for temperature control, such as in an environment where no heat medium exists (in a vacuum environment such as outer space) or in an environment such as extremely low temperature or extremely high temperature. Thus, the temperature of the assembled battery cannot be controlled efficiently. Even at room temperature, controlling the temperature via a medium with low heat transfer efficiency such as a fluid such as air is not preferable because energy may be lost as a result. Moreover, since the combination of the active materials disclosed in Patent Documents 1 and 3 has little or no endothermic region due to the charging reaction of the battery, it is difficult to control the temperature of the battery by charge / discharge control. .
JP 2003-109655 A Japanese Patent Laying-Open No. 2005-71784 JP 2003-142166 A Japanese Patent Laid-Open No. 11-176487

  In view of the above circumstances, the present invention provides an assembled battery of a rectangular flat battery and a charging / discharging method of the assembled battery, which has a long life and excellent energy density, can be temperature-controlled by charging and discharging, and is not easily affected by the surrounding environment. The purpose is to do.

  An assembled battery according to the present invention is an assembled battery in which a plurality of flat secondary batteries are stacked, and has a main surface in contact with the main surface of the secondary battery so as to be able to exchange heat with the secondary battery. A heat transfer plate that is combined with the secondary battery to form a battery / heat transfer plate assembly, and the battery / heat transfer plate is configured to be able to exchange heat with a plurality of the stacked battery / heat transfer plate assemblies. And at least one thermoelectric conversion element provided on a side surface of the assembly, and an exterior member having a heat insulating layer surrounding the battery / heat transfer plate assembly and the thermoelectric conversion element. It is characterized by having a combination of a negative electrode active material and a positive electrode active material having a region where the entropy change ΔS of all battery reactions under atmospheric pressure is endothermic.

The method for charging and discharging an assembled battery according to the present invention includes a combination of a negative electrode active material and a positive electrode active material having a region in which the entropy change ΔS of all battery reactions under normal temperature and atmospheric pressure is endothermic, and has a plurality of flat shapes. A secondary battery and a main surface that contacts the main surface of the secondary battery so that heat exchange with the secondary battery is possible, and is combined with the secondary battery to form a battery / heat transfer plate assembly. A heat plate, at least one thermoelectric conversion element provided on a side surface of the battery / heat transfer plate assembly so as to exchange heat with the plurality of stacked battery / heat transfer plate assemblies, and the battery / heat transfer plate In a method of charging or discharging an assembled battery comprising an assembly and an exterior member having a heat insulating layer surrounding the thermoelectric conversion element,
In order to control the assembled battery to an appropriate temperature range using the endothermic reaction during charging / discharging of the secondary battery, the current generated so that the amount of heat generated by the Joule heat of the secondary battery is less than the endothermic amount. It is characterized by controlling.

  According to the present invention, the endothermic reaction during charging is used to suppress the heat generation of the power generation unit from the inside of the assembled battery, and the power generation unit is cooled from the outside of the assembled battery via the heat transfer plate by the cooling means. The temperature difference between the core portion and the surface portion of the battery is reduced, and the temperature rise of the assembled battery is suppressed as a whole. For this reason, the assembled battery which is hard to be influenced by environmental temperature and has an excellent heat equalization characteristic (temperature uniformity) and cooling / heat retention characteristics is provided.

  Hereinafter, an assembled battery according to an embodiment of the present invention will be described with reference to the accompanying drawings. 1 to 4 show a unit cell as a component of the assembled battery, and FIG. 5 shows an outline of the entire assembled battery according to the embodiment of the present invention.

  FIG. 1A shows a square flat secondary battery 10, and FIG. 1B shows a substantially rectangular heat transfer plate 7. As shown in FIG. 2, the heat transfer plate 7 holds the secondary battery 10 so that the main surface 7a thereof is in contact with the main surface 10a of the secondary battery. Here, the “main surface” refers to the surface having the largest area. In the unit cell 10 and the heat transfer plate 7 shown in FIGS. 1A and 1B and FIG. 2, the surface parallel to the XY plane is referred to.

  The secondary battery 10 includes (i) an active material (positive and negative electrode active material) having a region where the entropy change ΔS of all battery reactions under normal temperature and atmospheric pressure is endothermic in each charged state (charging depth), ii) At the time of charging or discharging, the endothermic amount of the battery is maintained at 50% or more of the peak in a region of 50% or more of the total charge / discharge depth. In addition, as long as it is a square flat secondary battery that satisfies the above conditions (i) and (ii), a wide variety of secondary batteries can be applied to the present invention regardless of the type.

  In the case of a battery that exhibits endotherm in a region of less than 50% of the full charge / discharge depth, the SOC region where the endothermic reaction can be utilized is narrow, which makes it difficult to control the temperature of the battery. Even if the endotherm is shown at 50% or more of the full charge / discharge depth, if the endotherm is 50% or less at the peak, it is easily affected by heat generated by the Joule heat of the battery, and similarly temperature control by endotherm is difficult. This is not preferable.

  Next, each component of the square flat secondary battery 10 used in the assembled battery of the present invention will be described.

1) Negative electrode
The negative electrode is produced, for example, by applying a negative electrode material paste obtained by dispersing a negative electrode active material, a conductive agent, and a binder in a suitable solvent to one side or both sides of a current collector.

  Examples of the negative electrode active material include carbonaceous materials, metal oxides, metal sulfides, metal nitrides, alloys, and light metals that occlude and release lithium ions. In combination with the positive electrode described later, the entropy in the overall battery reaction If the change is in the region of 50% or more of the total charge / discharge depth and the endothermic amount of the battery shows 50% or more of the peak, it can be applied as the negative electrode of the present invention.

  In addition, the measurement method of the entropy change resulting from the heat generation and endotherm of the battery is as follows: a battery having an arbitrary SOC is kept in a constant temperature bath for 24 hours or more, and then kept at 10 to 40 ° C. for 6 hours. Then, dVo / dT is measured from the temperature change of the open circuit voltage Vo of the battery. The following formula (6) is derived from the relationship of the above formula (5) and ΔG = n · F · E, and the electromotive force E is approximated to the measured open-circuit voltage Vo, whereby the total entropy change from the following formula (6). The amount ΔS can be calculated. Where n is the number of charges involved in the reaction, F is the Faraday constant, and E is the electromotive force.

ΔS = − (∂ΔG / ∂T) = n · F · (∂E / ∂T) (6)
As the negative electrode active material, it is desirable to use lithium titanate having a spinel structure because it does not have an exothermic peak during charging at a wide charge / discharge depth. In this case, it is desirable to use any one of a lithium cobalt composite oxide, a lithium nickel cobalt composite oxide, and a lithium nickel cobalt manganese composite oxide having a strong endothermic peak during charging as the positive electrode active material. A non-aqueous electrolyte secondary battery using such a positive electrode active material and a negative electrode active material maintains an endothermic amount of 50% or more of the peak value at 50% or more of the total charge / discharge depth. It is preferable because it can be cooled.

  The average particle size of the negative electrode active material is desirably 1 μm or less. By using a negative electrode active material having an average particle diameter of 1 μm or less, the cycle performance of the nonaqueous electrolyte secondary battery exhibiting the above charge curve can be improved. In particular, this effect becomes significant during rapid charging and high-power discharging. Moreover, the overvoltage at the time of charging / discharging can be reduced, and as a result, endothermic reaction can be utilized efficiently. However, if the average particle size is too small, the distribution of the non-aqueous electrolyte is biased toward the negative electrode, which may lead to depletion of the electrolyte at the positive electrode, so the lower limit is preferably set to 0.001 μm.

  The particle size of the negative electrode active material is measured using, for example, a laser diffraction distribution measuring device (Shimadzu SALD-300). First, about 0.1 g of a sample, a surfactant, and 1 to 2 mL of distilled water are placed in a beaker. After adding and stirring sufficiently, it can inject | pour into a stirring water tank, and can measure by the method of measuring a luminous intensity distribution 64 times at intervals of 2 second, and analyzing a particle size distribution data.

  Examples of the carbonaceous material that occludes / releases lithium ions include coke, carbon fiber, pyrolytic vapor phase carbon material, graphite, resin fired body, mesophase pitch carbon fiber, and mesophase spherical carbon fired body. Among these, it is preferable to use mesophase pitch-based carbon fiber or mesophase spherical carbon graphitized at 2500 ° C. or higher because the electrode capacity is increased.

Examples of the metal oxide include titanium-containing metal composite oxides, for example, tin-based oxides such as SnB _0.4 P _0.6 O _3.1 and SnSiO ₃ , silicon-based oxides such as SiO, and tungsten-based oxides such as WO ₃ Etc. Among these metal oxides, when a negative electrode active material having a potential higher than 0.5 V with respect to metal lithium, for example, a titanium-containing metal composite oxide such as lithium titanate is used, the battery is rapidly charged However, lithium dendrite does not occur on the negative electrode, which is preferable because deterioration is reduced.

Examples of titanium-containing metal composite oxides include lithium-titanium composite oxides in which some of the constituent elements of lithium-containing titanium-based oxides, lithium-titanium oxides, and lithium-titanium oxides are replaced with different elements during oxide synthesis. Things can be mentioned. Examples of the lithium titanium oxide include lithium titanate having a spinel structure (for example, Li _{4 + x} Ti ₅ O ₁₂ (x is a value that varies depending on charge / discharge, 0 ≦ x ≦ 3)), ramsteride type titanium. Lithium acid (for example, Li _{2 + y} Ti ₃ O ₇ (y is a value that varies depending on charge / discharge, 0 ≦ y ≦ 3)), etc. These are at 90% or more of the total charge / discharge depth during charging. Since there is no conspicuous peak of heat generation, the battery of the present invention can be easily configured in combination with a positive electrode having a wide endothermic region to be described later, which is preferable.

Examples of the titanium-based oxide include metal composite oxides containing at least one element selected from the group consisting of TiO ₂ , Ti and P, V, Sn, Cu, Ni, Co, and Fe. TiO ₂ is preferably anatase type and low crystalline having a heat treatment temperature of 300 to 500 ° C. Examples of the metal composite oxide containing at least one element selected from the group consisting of Ti and P, V, Sn, Cu, Ni, Co, and Fe include TiO ₂ —P ₂ O ₅ , 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, Co and Fe). Can be mentioned. This metal complex oxide preferably has a microstructure in which a crystal phase and an amorphous phase coexist or exist alone. With such a microstructure, the cycle performance can be greatly improved. Among these, a lithium titanium oxide, a metal composite oxide containing at least one element selected from the group consisting of Ti and P, V, Sn, Cu, Ni, Co, and Fe is preferable.

Examples of the metal sulfide include lithium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), and iron sulfide (FeS, FeS ₂ , Li _x FeS ₂ ). Examples of the metal nitride include lithium cobalt nitride (Li _x Co _y N, 0 <x <4, 0 <y <0.5).

  As the conductive agent, for example, a carbon material such as acetylene black, carbon black, coke, carbon fiber, and graphite can be used.

  As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), or the like is used. Can do.

  As the current collector, various metal foils and the like can be used depending on the potential of the negative electrode, and examples include aluminum foil, aluminum alloy foil, stainless steel foil, titanium foil, copper foil, nickel foil, and the like. In this case, the thickness of the foil is preferably 8 μm or more and 25 μm or less. When the thickness of the current collector is less than 8 μm, not only the electric resistance increases and Joule heat increases, but also the mechanical strength is insufficient and the glass tends to break. On the other hand, when the thickness of the current collector exceeds 25 μm, the weight of the current collector with respect to the electrode active material increases, which causes a problem that the energy density per weight of the battery decreases. When the negative electrode potential is nobler than 0.3 V with respect to metallic lithium, for example, when lithium titanium oxide is used as the negative electrode active material, an aluminum foil or an aluminum alloy foil can suppress the battery weight. Therefore, it is preferable.

  The average crystal grain size of the aluminum foil and the aluminum alloy foil is preferably 50 μm or less. This is because an aluminum foil having an average crystal grain size larger than 50 μm lacks mechanical strength. Thereby, since the intensity | strength of an electrical power collector can be increased greatly, it becomes possible to make a negative electrode high density with a high press pressure, and can increase battery capacity. Moreover, since the dissolution / corrosion deterioration of the negative electrode current collector in the overdischarge cycle under a high temperature environment (40 ° C. or higher) can be prevented, an increase in the negative electrode impedance can be suppressed. Furthermore, output characteristics, quick charge, and charge / discharge cycle characteristics can also be improved. Further, the endothermic reaction can be efficiently utilized by reducing the internal resistance. A more preferable range of the average crystal grain size is 30 μm or less, and a further preferable range is 5 μm or less.

The average crystal grain size is determined as follows. The structure of the current collector surface is observed with an optical microscope, and the number n of crystal grains existing within 1 mm × 1 mm is determined. Using this n, the average crystal grain area S is determined from S = 1 × 10 ⁶ / n (μm ² ). The average crystal particle diameter d (μm) is calculated from the obtained area S value and the following equation (7).

d = 2 (S / π) ^1/2 (7)
The aluminum foil or aluminum alloy foil having a range of the average crystal particle diameter of 50 μm or less is complicatedly affected by many factors such as material composition, impurities, processing conditions, heat treatment history and annealing conditions, The crystal particle diameter (diameter) is adjusted by combining the above factors in the production process.

  The thickness of the aluminum foil and the aluminum alloy foil is 20 μm or less, more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% 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% or less. In the case of in-vehicle use, an aluminum alloy foil is particularly preferable.

  The compounding ratio of the negative electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by mass of the negative electrode active material, 3 to 20% by mass of the conductive agent, and 1.5 to 7% by mass of the binder. . When the blending ratio is out of these ranges, problems such as output reduction and cycle characteristic deterioration due to electrode peeling and conductivity decrease occur.

  Moreover, as thickness of the electrode apply | coated to aluminum foil, it is preferable to set it as 10-50 micrometers by the thickness at the time of completion of an electrode, More preferably, it is 20-30 micrometers. This is not preferable if the coating amount of the electrode is thicker than 50 μm, because the diffusion distance of the reacting lithium ions is extended, and loss due to overvoltage is likely to occur, leading to heat generation of the battery and deterioration of charge / discharge rate characteristics. On the other hand, if the thickness is less than 15 μm, the weight of the current collector with respect to the amount of the active material increases, so that the capacity energy density per weight is extremely deteriorated.

2) Positive electrode
The positive electrode is produced, for example, by applying a positive electrode material paste obtained by dispersing a positive electrode active material, a conductive agent and a binder in a suitable solvent to one side or both sides of a current collector.

Examples of the active material of the positive electrode include various oxides and sulfides. For example, manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (for example, Li _x Mn ₂ O ₄ or Li _x MnO ₂ ), lithium nickel composite oxide (for example, Li _x NiO ₂ ) Lithium cobalt composite oxide (e.g. Li _x CoO ₂ ), lithium nickel cobalt composite oxide (e.g. LiNi _1-y Co _y O ₂ ), lithium manganese cobalt composite oxide (e.g. LiMn _y Co _1-y O ₂ ), spinel-type lithium-manganese-nickel composite oxide _{(Li x Mn 2-y Ni} y O 4), lithium phosphates having an olivine structure _{(Li x FePO 4, Li x} Fe 1-y Mn y PO 4, Li x CoPO 4 Etc.), iron sulfate (Fe ₂ (SO ₄ ) ₃ ), vanadium oxide (for example, V ₂ O ₅ ) and the like. In addition, conductive polymer materials such as polyaniline and polypyrrole, disulfide-based polymer materials, organic materials such as sulfur (S) and carbon fluoride, and inorganic materials are also included. The entropy change in the total battery reaction in which these positive electrodes and the above-described negative electrodes are combined can be used by combining them so as to maintain 50% or more of the peak heat absorption in the region of 50% or more of the total charge / discharge depth. .

More preferable positive electrodes for secondary batteries include lithium manganese composite oxide (Li _x Mn ₂ O ₄ ), lithium nickel composite oxide (Li _x NiO ₂ ), and lithium cobalt composite oxide (Li _x CoO ₂ ) having a high battery voltage. ), Lithium nickel cobalt composite oxide (Li _x Ni _1-y Co _y O ₂ ), spinel type lithium manganese nickel composite oxide (Li _x Mn _2-y Ni _y O ₄ ), lithium manganese cobalt composite oxide (Li _{x Mn y Co 1-y O} 2), lithium iron phosphate (Li _x FePO _4), and the like. X and y are preferably in the range of 0 to 1. More preferably, lithium cobalt composite oxide (Li _x CoO ₂ ) having a strong endothermic peak in a wide charge / discharge depth region can be used.

Further, the positive electrode active material has a composition of Li _a Ni _b Co _c Mn _d O ₂ (however, the molar ratios a, b, c and d are 0 ≦ a ≦ 1.1, 0.1 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.9). , 0.1 ≦ d ≦ 0.5), a lithium nickel cobalt manganese composite oxide can be used.

  As the conductive agent, for example, acetylene black, carbon black, artificial graphite, natural graphite, conductive polymer, or the like can be used.

  As a binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), modified PVdF in which at least one of hydrogen or fluorine of PVdF is substituted with another substituent, vinylidene fluoride-6fluoride A copolymer of propylene, a terpolymer of polyvinylidene fluoride-tetrafluoroethylene-6propylene fluoride, or the like can be used.

  As an organic solvent for dispersing the binder, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF) or the like is used.

  Examples of the current collector include aluminum foil, aluminum alloy foil, stainless steel foil, and titanium foil having a thickness of 8 to 25 μm.

  The positive electrode current collector is preferably an aluminum foil or an aluminum alloy foil, and the average crystal grain size is preferably 50 μm or less, like the negative electrode current collector. More preferably, it is 30 μm or less. More preferably, it is 5 μm or less. When the average crystal grain size is 50 μm or less, the strength of the aluminum foil or the aluminum alloy foil can be dramatically increased, the positive electrode can be densified with a high press pressure, and the battery capacity can be increased. Can be increased.

  Aluminum foil or aluminum alloy foil with an average grain size range of 50 μm or less is affected by multiple factors such as material structure, impurities, processing conditions, heat treatment history, and annealing conditions, and the grain size is manufactured. In the process, the above factors are adjusted in combination.

  The thickness of the aluminum foil and the aluminum alloy foil is 20 μm or less, more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% 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% or less.

  The compounding ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by mass of the positive electrode active material, 3 to 20% by mass of the conductive agent, and 1.5 to 7% by mass of the binder. . Moreover, as thickness of the electrode apply | coated to aluminum foil, it is preferable to set it as 10-50 micrometers by the thickness at the time of completion of an electrode, More preferably, it is 20-30 micrometers. This is because if the coating amount of the electrode is thicker than 50 μm, the diffusion distance of the reacting lithium ions is increased, so that loss due to overvoltage is liable to occur, which leads to heat generation of the battery and deterioration of charge / discharge rate characteristics. . On the other hand, if the thickness is less than 15 μm, the weight of the current collector with respect to the amount of the active material increases, so that the capacity energy density per weight is extremely deteriorated.

3) Separator
A porous separator is used as the separator.

  Examples of the porous separator include a porous film containing polyethylene, polypropylene, cellulose, or polyvinylidene fluoride (PVdF), and a synthetic resin nonwoven fabric. Among these, porous films made of polyethylene or polypropylene, or both, are easy to add a shutdown function that closes the pores and significantly attenuates the charge / discharge current when the battery temperature rises. This is preferable because the property can be improved.

4) Non-aqueous electrolyte
As the non-aqueous _{electrolyte, LiBF 4, LiPF 6, LiAsF} 6, LiClO 4, LiCF 3 SO 3, LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, Li (CF 3 SO 2) 3 Examples thereof include an organic electrolyte obtained by dissolving one or more lithium salts selected from C, LiB [(OCO) ₂ ] _{2 and the} like in an organic solvent at a concentration of 0.5 to 2 mol / L.

  Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC), and dimethoxyethane. (DME), chain ethers such as dietoethane (DEE), cyclic ethers such as tetrahydrofuran (THF) and dioxolane (DOX), γ-butyrolactone (GBL), acetonitrile (AN), sulfolane (SL) alone or It is preferable to use a mixed solvent.

  Moreover, a room temperature molten salt (ionic melt) containing lithium ions can be used as the non-aqueous electrolyte. A secondary battery having a wide operating temperature can be obtained by selecting an ionic melt composed of lithium ions, an organic cation and an anion, which is liquid at 100 ° C. or lower, preferably at room temperature (23 ° C.) or lower. it can.

5) Laminate exterior material
In the laminate type lithium ion battery, it is desirable that the thickness of the laminate film used for the exterior material is 0.2 mm or less.

  As shown in FIG. 4, the laminate film includes, for example, an innermost heat-fusible resin film 10 b (thermoplastic resin film) covering the battery body 10 a, a metal foil 10 c such as an aluminum foil, and a rigid organic resin film. A composite film material in which 10d are laminated in this order can be used.

  Although not shown in FIGS. 1 and 4, the peripheral portion of the laminate exterior material on the main surface of the secondary battery may have a seal portion in which the innermost layers 10 b are heat-sealed.

  As the heat-fusible resin film, for example, a polyethylene (PE) film, a polypropylene (PP) film, a polypropylene-polyethylene copolymer film, an ionomer film, an ethylene vinyl acetate (EVA) film, or the like can be used. Moreover, as an organic resin film which has the said rigidity, a polyethylene terephthalate (PET) film, a nylon film, etc. can be used, for example.

6) Positive terminal and negative terminal
For the positive electrode terminal, aluminum, titanium, alloys based on them, stainless steel, or the like can be used. For the negative electrode terminal, nickel, copper, an alloy based on them, or the like can be used. When the negative electrode potential is nobler than 1 V with respect to metallic lithium, for example, when lithium titanium oxide is used as the negative electrode active material, aluminum or an aluminum alloy can be used as the negative electrode terminal. In this case, it is preferable to use aluminum or an aluminum alloy for both the positive electrode terminal and the negative electrode terminal because the light weight and the electric resistance can be kept small, and the endothermic reaction can be efficiently used.

7) Heat transfer plate for battery pack
The material of the heat transfer plate 7 shown in FIG. 1B is a metal having a thermal conductivity of 150 W · m ⁻¹ · K ⁻¹ or more, such as aluminum, gold, silver, copper, or silicon, at room temperature. desirable. If the thermal conductivity is lower than 150 W · m ⁻¹ · K ⁻¹ , the soaking performance between the constituent batteries and the heat transfer efficiency of the electrothermal transducer are deteriorated. Among these metals, the specific gravity is preferably a light metal because it affects the energy density of the assembled battery, and aluminum and copper are preferable in consideration of cost and the like. More preferably, aluminum which forms a surface oxide film and is stable as a metal can be said to be the most suitable material. In addition to these metals, composite metal materials such as stainless steel and brass may be used. Further, a sputter material, a clad material, etc., in which a metal is coated on the surface of the heat transfer plate, can also be used.

  As shown in FIG. 1 (b), the heat transfer plate 7 includes a main surface 7a, a pair of side projection covers 9 arranged at intervals on the edge of one long side, and One side protrusion cover 9 disposed in the center, one recess 8 provided between the pair of side protrusion covers 9, and a pair of protrusions provided between the one side protrusion cover 9 And a recess 8. The heat transfer plate 7 is configured to be in contact with the widest surface of the flat battery 10. In particular, when the flat battery 10 is a battery covered with the laminate exterior materials 10b, 10c, and 10d shown in FIG. 4 (hereinafter referred to as a laminate exterior battery), the temperature within the battery surface is brought into contact with the heat transfer plate 7. Distribution can be relaxed and soaking. The first layer (innermost layer) laminate sheathing material 10b is a resin, the second layer (intermediate layer) laminate sheathing material 10c is an aluminum foil, and the third layer (outermost layer) laminate sheathing material 10d is a resin.

  Further, the heat transfer plate 7 has three side protrusion covers 9 that extend in a direction substantially orthogonal to the joining surface of the battery. By providing these three side projection covers 9 asymmetrically with respect to the heat transfer plate 7, when stacking as an assembled battery, as shown in FIG. It fits into the recess 8 between the pair of side projection covers 9 of the upper battery, and the side projection cover 9 at the center of the upper battery fits into the recess 8 between the pair of side projection covers 9 of the lower battery. Fit. In this way, the side protrusion covers 9 of the upper and lower batteries stacked together complement each other, so that the side surfaces of the heat transfer plate 7 can be configured, and the side protrusion cover 9 functions as a guide when creating the assembled battery. Therefore, it greatly contributes to productivity improvement.

  Moreover, when connecting assembled batteries in series, the direction of the positive electrode tab 12a and the negative electrode tab 12b is uniquely decided by the direction of the side protrusion cover 9 by setting the cell 10 to the heat exchanger plate 7. As a result, by alternately laminating the irregularities formed by the side protrusion covers 9, the battery polarity direction is uniquely determined as a series connection, so that an assembled battery can be created without erroneous connection of the batteries. It becomes.

8) Method for Laminating Single Cells FIG. 3 is a schematic cross-sectional view showing a laminated body in which the flat battery 10 and the heat transfer plate 7 are stacked. Here, it is preferable that the flat battery 10 and the heat transfer plate 7 are fixed with a double-sided pressure-sensitive adhesive tape or an adhesive indicated by reference numeral 20. By using these materials, the gap between the heat transfer plate 7 and the flat battery 10 can be eliminated, and the heat transfer efficiency can be increased. These adhesive tapes and adhesives preferably have high thermal conductivity, and commercially available thermal conductive double-sided tapes and thermal conductive adhesives can be used.

  The battery stacked as described above is an assembled battery 30 as shown in FIG. A thermoelectric conversion element (Peltier element) 31 is attached to the side surface of the heat transfer plate 7 formed by the side protrusion cover 9. For the attachment of the Peltier element 31 and the side surface, the heat conductive adhesive tape 20 or the adhesive as described above can be used. Furthermore, it is desirable to promote soaking between the assembled batteries by sticking a thin aluminum foil sheet between the thermoelectric conversion element 31 and the side surface portion of the assembled battery 30. This is because heat transfer between the single cells can be further promoted by bringing the side projection covers 9 of the stacked upper and lower single cells into surface contact with each other.

9) Control circuit and control method for battery pack The control circuit board 32 includes a protection circuit (not shown), an arithmetic circuit 32a, a storage device 32b, and a temperature control circuit 33. The protection circuit controls the temperature of the battery and adjusts / cuts off the current. The arithmetic circuit 32a receives a temperature detection signal from the temperature detection means 34, calls a desired formula or data from the storage device 32b, and performs an operation. Further, the arithmetic circuit 32a receives an SOC detection signal from the SOC detection means 42 of the HEV drive system 4, calls a desired formula or data from the storage device 32b, and performs an operation. The storage device 32b serves as a database for storing and storing various arithmetic expressions and data. The temperature control circuit 33 receives the control command signal from the arithmetic circuit 32a and controls the thermoelectric conversion element 31 based on the control command signal.

  In addition, when the flat battery 10 is a lithium ion secondary battery, it is preferable to give the control circuit board 32 a protective circuit function. The positive electrode tab 35 a from the assembled battery 30 is connected to the external terminal 36 a via the control circuit board 32. On the other hand, the negative electrode tab 35b is directly connected to the external terminal 36b. The Peltier element 31 is connected to the control circuit board 32 and is supplied with electric power as required.

A temperature control circuit 33 for managing the temperature of the assembled battery 30 is mounted on the control circuit board 32. The temperature control circuit 33 performs charge / discharge control for temperature control of the assembled battery based on the temperature information obtained from the temperature detection means 34 for detecting the temperature of the assembled battery, Control power supply and current direction. When it is determined that the temperature of the assembled battery is high, charge / discharge control of the assembled battery is performed so that the battery reaction becomes an endothermic reaction. At this time, the charge / discharge current is such that the endothermic amount Qs (= Tcell · ΔS) generated by the battery reaction exceeds the Joule heat amount Qj (= I ² · R) (I: charge / discharge current value, R: battery internal resistance). Controls the value I. When it is difficult to control the temperature by a method using these endothermic reactions, a current is allowed to flow in the direction in which the Peltier element 31 becomes endothermic. On the contrary, if it is determined that the temperature is low, the battery When it is difficult to control the temperature by the method using these exothermic reactions, it is preferable to control the Peltier element 31 to flow current in the heat generating direction. As the temperature detection means 34, a widely known technique such as a thermocouple or a thermistor can be used. In order to make it less susceptible to the environmental temperature, the temperature detecting means 34 is preferably arranged at the center of the flat battery 10 and arranged so that there is no gap between the heat transfer plate 7 and the unit cell 10. Is desirable. Specifically, a gap between the single cells 10 can be eliminated by sandwiching a thin thermistor between the layers and filling it with an adhesive. In FIG. 5, the temperature detection means 34 is simplified for convenience.

9) Exterior structure of assembled battery These assembled battery 30, Peltier element 31, and protection circuit 32 are housed in a battery case 38 and packaged by a lid 37. The case 38 and the lid 37 are filled or lined with a heat insulating material (not shown) to form a heat insulating structure. As the heat insulating material, not only resin-based heat insulating materials such as urethane, phenolic, polystyrene, and cellulose can be used, but also flame retardant heat insulating materials such as glass wool and rock wool can be applied. At this time, the aluminum case directly touches the surface opposite to the cell attachment surface of the Peltier element. This considers the case where the Peltier element 31 itself needs to dissipate heat. Since the Peltier element 31 itself does not have excellent heat conductivity, the heat insulating structure can be maintained by entering between the cell and the exterior.

  In the case of a laminated battery, the mechanism for directly cooling the battery is not very effective due to its low heat transfer performance, and the temperature rise of the battery is often determined by the heat capacity of the battery. Therefore, it is not efficient to have an external cooling mechanism. Rather, by providing a heat insulation structure, it is possible to avoid thermal influences from the outside such as the environmental temperature, and the thermal insulation and cooling efficiency by the Peltier element increases. preferable. In addition, by controlling the battery temperature using the exothermic / endothermic reaction during charging / discharging, the active material itself absorbs or generates heat, so heat transfer is faster than conventional cooling / heating methods. There is also an advantage that distribution is difficult to occur. It is known that a battery pack having a conventional configuration with temperature control using a heat medium causes a temperature difference between the battery surface and the inside, which leads to a reduction in battery life. In the configuration of the present invention, as described above, since the heat distribution hardly occurs, the life of the battery can be extended.

10) Charge control method for battery pack
The temperature control of the packaged assembled battery system is performed mainly by controlling the charge / discharge current, and only when the Peltier element 31 or the like is used when they do not function effectively or deviate from a predetermined temperature range. Temperature control is performed with a thermoelectric conversion element.

  FIG. 6 is a block diagram showing a control system having an assembled battery system 3 and an HEV drive system 4 as an application example to a hybrid electric vehicle (HEV). The temperature signal S1 sent from the temperature detection means 34 for detecting the battery temperature of the assembled battery 30 and the SOC information signal S7 sent from the SOC detection means 42 for managing and measuring the charge / discharge depth (SOC) of the battery are: To the arithmetic circuit 32a. When the cell temperature becomes higher than a predetermined temperature range during traveling, the power control circuit 44 of the HEV drive system 4 is urged to temporarily stop the motor power 45 and the main power is transferred to the engine power 46. Switch.

  Next, the SOC is adjusted in accordance with the endothermic reaction region of the assembled battery. The SOC is adjusted by battery power consumption or charging, and is controlled by the arithmetic circuit 32a. The basic thermal data of the battery, such as the SOC of the heat absorption region and the amount of heat absorbed, is mapped in advance, and these data are stored in the storage device 32b.

  Next, when the SOC enters the endothermic reaction region, the current is controlled in a direction in which the endothermic reaction of the assembled battery 30 occurs. That is, in the case of the battery 10 that absorbs heat by charging, control is performed in the charging direction and vice versa. Mainly, since there are many secondary batteries that absorb heat during charging, it is preferable to use regenerative energy generated from a running vehicle as the charging current during heat absorption. At this time, referring to the data in the storage device 32b, an appropriate current value is determined by the arithmetic circuit 32a. Whether or not the battery is being cooled by the endothermic reaction of the assembled battery 30 is confirmed by a signal S1 from the temperature detecting means 34. If the battery is cooled, a signal S6 is sent to the power control circuit 44 of the HEV drive system 4, Return to normal operation mode. At this time, when the temperature continues to rise without efficiently absorbing the amount of heat, such as when the heat generation rate of the battery is faster than the cooling rate of the battery, power is supplied from the arithmetic circuit 32a to the thermoelectric element 31 via the temperature control circuit 33. Supply and cool (signal S2 → signal S3).

  Next, when the temperature of the battery 10 becomes lower than the specified temperature range, the heat generation area of the battery 10 is heated using the Joule heat generation of the battery based on the information signal S5 from the storage device 32b. To do so, a signal S6 is sent to the power control circuit 44 of the HEV drive system 4. At this time, when the vehicle is started in an extremely low temperature environment or immediately after the start, the assembled battery 30 is heated by supplying power to the thermoelectric conversion element 31 via the temperature control circuit 33.

  In the present embodiment, the temperature control circuit 33 is housed in the battery pack, but the present invention is not limited to this installation method. For example, by providing temperature information from the assembled battery of the present invention to an external circuit by means of communication or the like, and supplying power to the electric heat exchanger from the outside, the temperature of the battery is completely from the external circuit. It is also possible to control. Moreover, when combining the some assembled battery 30 and using it as one module, it is preferable to equip the temperature control circuit 33 for every module. In this case, it is only necessary to have at least one circuit that collectively manages and controls the temperature information detected by the temperature detection means 34 from the assembled battery. In applications where the battery temperature can be controlled simply by using the endothermic reaction due to charging / discharging of the battery, it is possible to reduce the cost by omitting expensive thermoelectric conversion elements.

  As described above, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  Using the assembled battery which is one embodiment of the present invention configured as described above, a charge / discharge test was actually performed to confirm the temperature distribution inside the battery and the operational stability of the battery pack under different temperature environments. As a comparative example, a commercially available laminate-type lithium ion battery was used to construct a battery pack by a conventionally known method, and a charge / discharge test was performed using air as a cooling medium.

  Next, various examples and comparative examples will be described.

[Example 1]
Lithium cobalt oxide (LiCoO ₂ ) was used as the positive electrode active material. A positive electrode active material, a conductive material, and a binder were blended and dispersed in an n-methylpyrrolidone (NMP) solvent to prepare a slurry. The obtained slurry was applied to an aluminum foil (purity 99.99%) having a thickness of 15 μm and an average crystal particle diameter of 50 μm, followed by drying and pressing steps to produce a positive electrode.

Lithium titanate (Li ₄ Ti ₅ O ₁₂ ) was prepared as a negative electrode active material. A negative electrode active material, a conductive material, and a binder were blended and dispersed in an n-methylpyrrolidone (NMP) solvent to prepare a slurry. The obtained slurry was applied to an aluminum foil (purity 99.99%) having a thickness of 15 μm and an average crystal particle diameter of 50 μm, followed by drying and pressing steps to produce a negative electrode.

  Next, a strip of porous polyethylene porous film having a thickness of 20 μm is placed horizontally, and a positive electrode piece cut into a strip shape is placed on the left end of the separator, and the separator is folded back to the left along the right end of the positive electrode piece. The negative electrode piece cut into strips is placed, and the separator is folded back along the left end of the negative electrode piece to the right, and the positive electrode and the negative electrode are stacked while sandwiching the separator folded in ninety-nine times between them, A power generation element having 31 positive electrodes and 30 negative electrodes was produced.

The produced power generation element was pressed and adjusted in shape, and then the positive electrode terminal and the negative electrode terminal were connected, sealed in an exterior member made of a laminate film, injected with a non-aqueous electrolyte, and a flat non-aqueous electrolyte with a capacity of 3 Ah. A water electrolyte secondary battery was produced. The full charge voltage V _H of the obtained secondary battery was 2.8V.

  In order to measure the entropy change ΔS of this single cell, a battery in which SOCs are aligned at 10% intervals between 0 to 100% is kept in a constant temperature phase of 20 ° C. for 24 hours or more, and then 10 to 40 ° C. DVo / dT was measured from the temperature change of the open circuit voltage Vo of the battery every 10 ° C. for 6 hours, and the entropy change ΔS was calculated from the equation (6).

ΔS = − (∂ΔG / ∂T) = n · F · (∂E / ∂T) (6)
As a result, as shown by the characteristic line A in FIG. 8, the total entropy change of the battery maintains 50% or more of the peak heat absorption in the region of 50% or more of the total charge / discharge depth during charging. There was found. Compared to the conventional carbon-based negative electrode, there was almost no heat generation during the charge of spinel type lithium titanate (Li ₄ Ti ₅ O ₁₂ ), and the endothermic reaction of lithium cobalt oxide of the positive electrode could be utilized to the maximum extent. It is.

  A tray-like heat transfer plate 7 shown in FIG. 1B was made of an aluminum plate, and the tray 7 and the cell 10 were attached with a heat conductive adhesive tape 20, and nine of them were connected in series and laminated. By combining the side protrusion covers 9 in a mosaic shape, both side surfaces of the assembled battery 30 are formed.

  The electrode tabs 12a and 12b of the battery described above were electrically joined by ultrasonic welding. In order to examine the in-plane temperature distribution, the laminated battery 10 was provided with thin temperature thermistors for temperature detection at the five measurement points 34a, 34b, 34c, 34d, and 34e shown in FIG. When installing the thermistor, it was carefully assembled so that there was no gap between it and the heat transfer plate 7.

  Next, aluminum foil was bonded to both side surfaces of the assembled battery 30 including the side protrusion cover 9 to facilitate soaking. A heat conductive adhesive was used for bonding the aluminum foil. Furthermore, the 1 step | paragraph general-purpose Peltier element 31 of the substantially same area as the side surface of the assembled battery 30 was affixed on both side surfaces, respectively. The Peltier element 31 is electrically connected to the temperature control circuit 33, and the temperature detection thermistor at the center of the battery is used as control temperature information. These assembled battery systems were housed in a heat insulating case 38 shown in FIG. The main body of the case 38 was made of aluminum, and urethane foam was lined on the case main body as a heat insulating material. The heat insulating material was filled so that the space between the assembled battery 30 and the main body of the case 38 was filled with the heat insulating material.

  In Example 1, the control circuit board 32 was connected to the outside of the battery case 38 for the experiment. In this example, the running pattern of the HEV vehicle was performed using a charge / discharge pattern that simply simulated the running pattern of the HEV vehicle. The assembled battery 30 was held in a temperature-controlled thermostat, and the experiment was conducted while maintaining the environmental temperature at 25 ° C. The SOC of the assembled battery at the time of the test was 50%, which is practical as a battery and easily uses an endothermic reaction. By performing 10C rate simulated HEV type pulse input / output, the temperature of the assembled battery was raised to 45 ° C., and then the cooling effect of the assembled battery was verified by continuously charging at 3C, and temperature control was performed. . Here, 1C is a current value required to completely discharge the cell in 1 hour, and for convenience, the nominal capacity value of the cell can be replaced with the 1C current value.

  FIG. 9 shows the relationship between the current (A) to the assembled battery and the cell temperature (° C.) in this test. It was found that the cell temperature monotonously increased in the region where pulse discharge was performed at a rate of 10C. This is a temperature rise accompanying the exothermic reaction and Joule heat of the battery. When the cell temperature in the center reached around 45 ° C, the temperature distribution inside the battery pack was not observed so much, so it was confirmed that the heat dissipation from the surface was small due to heat insulation, and the soaking effect by the heat transfer plate Was also confirmed. Next, after switching to the charging mode, each cell was gradually cooled down to 30 ° C. or less in about 5 minutes. Also, in this cooling process, the temperature distribution of each cell was hardly observed. In FIG. 9, since it was difficult to describe all measurement point temperatures, only representative cell temperatures were extracted and shown.

[Example 2]
In applications that require continuous discharge of the battery, the temperature rise gradient of the cell is larger than that of pulse discharge. Moreover, since it is necessary to perform cooling from during discharge, temperature control using an endothermic reaction as in Example 1 is difficult. Assuming such a situation, in Example 2, a cooling test was performed on a battery that is continuously discharged with a large current. An assembled battery system was prepared in the same manner as in Example 1, and the experiment was performed at an ambient temperature of 25 ° C. The assembled battery was continuously discharged at a discharge rate of 20 C, and when the battery temperature reached 30 ° C., cooling by the Peltier element 31 was performed to verify temperature control of the assembled battery. The SOC of the assembled battery was 100%, that is, the battery was continuously discharged from the fully charged state.

  FIG. 10 shows the temperature change of the battery when the Peltier element 31 is cooled while discharging at a 20 C rate. For comparison, a temperature change (characteristic line E indicated by a broken line in FIG. 10) when continuous discharge is performed without cooling is also shown. After the battery temperature reached 30 ° C., cooling of the assembled battery 30 was started by the Peltier element 31. The temperature rise was moderated immediately after the start of cooling, and the cell temperature during operation could be kept at 40 ° C. or lower until complete discharge. As for the temperature distribution, the temperature distribution in the stacking direction could hardly be confirmed, but it was confirmed that the temperature slightly decreased on the side closer to the Peltier element 31 in the plane. 10 characteristic line C (corresponding to the position of 34c in FIG. 7) and the Peltier element side (characteristic line D in FIG. 10; corresponding to the positions of 34b and 34d in FIG. 7) are within a maximum of 5 ° C. It was suppressed.

[Comparative Example 1]
An assembled battery of a flat battery generally used widely as Comparative Example 1 was prepared, and its characteristics were examined in comparison with the above-described Examples. In Comparative Example 1, a commercially available aluminum laminate type lithium ion secondary battery having a size almost equal to that of the battery prepared in Example 1 was used. As in Example 1, in order to measure the entropy change of this single cell, a battery in which SOCs were aligned at 10% intervals between 0 to 100% was kept in a constant temperature phase of 20 ° C. for 24 hours or more. DVo / dT was measured from the temperature change of the open circuit voltage Vo of the battery at 10 ° C between 10 and 40 ° C for 6 hours, and the entropy change ΔS was calculated from the above equation (6). Since a commercially available lithium ion secondary battery uses a carbon-based material for the negative electrode, the negative electrode generates heat during charging. For this reason, as shown by the characteristic line F in FIG. 11, the region that maintains 50% or more of the peak heat absorption during charging (the region indicated by the broken line of the characteristic line F) is only 30 of the full charge / discharge depth. It was found that it remained at about%.

  In the same manner as in Example 1, the commercially available lithium ion secondary battery was laminated by connecting aluminum tray-like heat transfer plate heat with a sticky adhesive tape and connecting 9 cells in series. The battery electrode tabs described above were electrically joined by ultrasonic welding. In order to investigate the in-plane temperature distribution, the laminated batteries were provided with five thin thermistors for temperature detection in the plane. When installing the thermistor, it was carefully assembled so that there was no gap between it and the heat transfer plate. These assembled battery systems were housed in a case having a heat insulating structure in the same manner as in Example 1.

  Similarly in Comparative Example 1, the charging / discharging pattern that simply simulated the running pattern of the HEV vehicle was used. The assembled battery was held in a temperature-controlled thermostat and the experiment was conducted at an environmental temperature of 25 ° C. The SOC of the assembled battery at the time of the test was set to 20%, which is considered to be most likely to use the endothermic reaction from the result of ΔS measurement. By performing 10C rate simulated HEV type pulse input / output, the temperature of the assembled battery was raised to 45 ° C., and then the cooling effect of the assembled battery was verified by continuously charging at 3C, and temperature control was performed. . Here, 1C is a current value required to completely discharge the cell in one hour, and for convenience, the nominal capacity value of the cell can be replaced with the 1C current value.

  In FIG. 12, the horizontal axis represents time (minutes), and the vertical axis represents the battery temperature (° C.) and the supply current (A) to the battery pack. It is a characteristic diagram which shows the result of having investigated the correlation. In the figure, a plurality of characteristic line groups G indicate changes in temperature of each part of the assembled battery (temperature measurement points 34a, 34b, 34c, 34d in FIG. 7), and a characteristic line H indicates changes in the supply current to the assembled battery ( Charging and discharging).

  Since a commercially available lithium ion secondary battery has high internal resistance, when pulse discharge was repeated at a high rate of 10 C, the temperature rose within a short time and reached 45 ° C. Next, when switching from the discharge mode to the charge mode, almost no cooling phenomenon was observed, and after a slight temperature increase, a moderate temperature decrease was observed. This is because when charging is performed at 3C, Joule heat generation due to resistance overvoltage or the like becomes dominant, and as a result, a cooling effect cannot be obtained. Moreover, even if the charge rate was lowered to 1C, almost the same result was obtained. This is thought to be because the impedance of the positive electrode material is increased in a region where the SOC is as low as about 20%, and the amount of heat generated is higher due to the increase in impedance at low SOC than the amount of heat absorbed by the charging reaction. It suggests that it is trapped. From this, it has been found that a sufficient cooling effect cannot be obtained with a combination of active materials having a narrow endothermic reaction region.

  From the above results, in Comparative Example 1, the variations in the in-plane temperature distribution and the stacking temperature distribution of the assembled battery during high-speed charge / discharge are large. If the variation in these temperature distributions is large, an excessive load is applied to a specific unit cell in the assembled battery, so that the assembled battery of Comparative Example 1 has a short life. On the other hand, in Example 1, the variation in the in-plane temperature distribution and the stacking temperature distribution of the assembled battery during the high-speed charge / discharge is small, and the temperature variation between the single cells is also small. For this reason, the assembled battery of Example 1 has a long life.

[Comparative Example 2]
In Comparative Example 2, when flat batteries are stacked, a gap is formed by providing a spacer between the batteries as in a conventionally known technique, and the temperature of the battery is controlled by blowing air with a fan as a heat medium. The same methods as in Patent Documents 1 and 3 were compared.

  Similarly to Example 1, thin thermistors were arranged at five locations in the plane, and the temperature distribution was measured. When the pressure loss generated in the gap between the cells was calculated, it was found that the periphery of the assembled battery was covered with a wind tunnel-like shape and a gap of at least 5 mm or more was necessary. Therefore, as shown in FIG. 13, the batteries were stacked with a gap 11 of 5 mm between adjacent batteries, and housed in an aluminum case 110. The assembled battery was cooled by blowing air using an electric fan 111 so that the wind speed was 10 m / s from the side of the assembled battery.

  When continuous discharge was performed at a high rate of 20 C as in Example 2, the temperature of the commercially available lithium ion secondary battery increased in a short time because of high internal resistance. When the center battery temperature exceeded 30 ° C., air cooling with an electric fan was performed. The results are shown in FIG. Immediately after the start of air cooling, almost no temperature decrease was observed, and then the gradient of the cell temperature increase gradually decreased, but the in-plane temperature distribution increased. Three minutes after the end of the discharge, a temperature difference of 5 ° C. or more occurred in the surface.

  As indicated by the characteristic line Q in FIG. 14, the temperature was about 50 ° C. at the windward position, that is, at the measurement point 34b in FIG. On the other hand, as indicated by the characteristic line P in FIG. 14, it was confirmed that the temperature was close to 55 ° C. at the leeward position, that is, at the measurement point 34 d in FIG. 7. From this, it has been found that an in-plane temperature difference of the battery occurs between the windward and leeward cooling air.

  A characteristic line R in FIG. 14 is a result of temperature change of the battery when no ventilation is performed. As is clear from this, in Comparative Example 2, the difference due to the presence or absence of cooling is smaller than that in Example 2. Furthermore, in the structure in which the cooling medium is taken into account, the case size of the assembled battery becomes large, and there is a problem that the volumetric energy density is lowered. Further, the cooling by fan air cooling not only has a low cooling efficiency, but also the temperature distribution tends to occur because the air volume changes due to the pressure loss of the flow path.

  In Comparative Example 2, since air is used as the heat medium, it is easily affected by the ambient temperature. In particular, at low temperatures, sufficient performance cannot be obtained outside the operating temperature range of the unit cell, and output characteristics are significantly reduced. The battery pack of Comparative Example 2 can cool the battery during high-speed charge / discharge when used at room temperature. However, when the ambient temperature is high, the temperature does not decrease even when the cooling fan is turned on. It turns out that deterioration becomes remarkable.

  On the other hand, when temperature control is performed in Example 1, it can be seen that the output characteristics are improved by maintaining the battery temperature to some extent at low temperatures. On the other hand, it can be seen that at a high temperature, the temperature rise of the battery can be suppressed due to the cooling effect of the Peltier element, and is hardly affected by the ambient environmental temperature.

  From the above results, Comparative Example 2 (conventional cooling method) is not only concerned about affecting the battery life but also more energy efficient than Example 1 when the power consumed by the fan is taken into account. Is low.

  The present invention can be used for various power sources such as portable electronic devices, hybrid vehicles, electric vehicles, and power storage facilities.

(A) is a perspective view which shows a square-shaped flat cell, (b) is a perspective view which shows a heat exchanger plate. The disassembled perspective view which shows a battery / heat-transfer plate assembly. The expanded sectional view which shows a part of assembled battery of this invention. The expanded sectional view which shows the laminate exterior which covers a cell. The disassembled perspective view which shows the battery pack provided with the assembled battery which concerns on embodiment of this invention. The control block diagram of the assembled battery which concerns on embodiment of this invention. The perspective view which shows the several temperature measurement point which measures the temperature of a battery. The characteristic line figure which shows the relationship between the charge depth (SOC) and heat flow in the assembled battery of Example 1. FIG. FIG. 3 is a characteristic diagram showing changes in current and temperature flowing through the assembled battery of Example 1 with time. The characteristic line figure which shows the temperature change of the assembled battery of Example 2 at the time of discharge. The characteristic line figure which shows the relationship between the charge depth (SOC) and heat flow in the assembled battery of the comparative example 1. FIG. 6 is a characteristic diagram showing changes in current and temperature flowing through the assembled battery of Comparative Example 1 with time. The cross-sectional schematic diagram which shows the assembled battery of the comparative example 2 seeing from the side. The characteristic line figure which shows the temperature change of the assembled battery of the comparative example 2 at the time of discharge.

Explanation of symbols

3 ... Battery system,
7 ... Heat transfer plate, 8 ... Recess, 9 ... Side projection cover,
10 ... single battery, 10a ... battery body, 10b, 10c, 10d ... laminate exterior material,
11 ... Gap (air passage),
12a ... positive electrode tab, 12b ... negative electrode tab,
13 ... Battery / heat transfer plate assembly,
20 ... Joining member (adhesive tape, adhesive), 21 ... protective plate,
30 ... assembled battery,
31 ... Thermoelectric element (Peltier element),
32 ... Control circuit board, 32a ... Arithmetic circuit, 32b ... Storage device,
33 ... temperature control circuit,
34 ... temperature detection means (thermocouple, thermistor),
34a, 34b, 34c, 34d ... temperature measurement points,
35a ... Positive electrode tab, 35b ... Negative electrode tab, 36a, 36b ... External terminal,
37 ... Lid (exterior member), 38 ... Battery case (exterior member),
4 ... HEV drive system, 42 ... SOC detection means, 44 ... power control circuit,
45: Motor power, 46: Engine power, 47: Regenerative power.

Claims (9)

An assembled battery in which a plurality of flat secondary batteries are stacked,
A heat transfer plate having a main surface in contact with the main surface of the secondary battery so as to be able to exchange heat with the secondary battery, and combined with the secondary battery to form a battery / heat transfer plate assembly;
At least one thermoelectric conversion element provided on a side surface of the battery / heat transfer plate assembly so as to exchange heat with a plurality of the battery / heat transfer plate assemblies stacked;
An exterior member having a heat insulating layer surrounding the battery / heat transfer plate assembly and the thermoelectric conversion element;
The secondary battery has a combination of a negative electrode active material and a positive electrode active material having a region where the entropy change ΔS of all battery reactions under normal temperature and atmospheric pressure is endothermic. The secondary battery is a single cell that maintains 50% or more of the endothermic amount of the battery reaction in a region of 50% or more of the total charge / discharge depth during charging or discharging. The assembled battery according to Item 1. The assembled battery according to claim 1, wherein the secondary battery is covered with a laminate exterior material having an outermost resin layer. The secondary battery is rectangular, and the heat transfer plate is rectangular.
The heat transfer plate has at least one side protrusion cover that rises from the periphery of the main surface so as to be orthogonal to the main surface, and a recess corresponding to the side protrusion cover of another adjacent heat transfer plate, Have
When the secondary battery and the heat transfer plate are alternately stacked to form a battery / heat transfer plate assembly laminate, the side protrusion cover is disposed at the recess, and the side surface of the laminate is The assembled battery according to claim 1, wherein the battery pack is covered with the side protrusion cover. The assembled battery according to claim 1, wherein the thermoelectric conversion element is an element using a Peltier effect that generates or absorbs heat according to a direction of a supplied current. The assembled battery according to claim 1, wherein the heat transfer plate is made of aluminum. Temperature detecting means for detecting the temperature of the assembled battery; and a temperature control circuit for adjusting the power supply to the thermoelectric conversion element based on the detected temperature and controlling the temperature of the battery / heat transfer plate assembly; The assembled battery according to claim 4, further comprising: A titanium-containing metal composite oxide is used as the negative electrode active material, and the positive electrode active material is selected from the group consisting of a lithium cobalt composite oxide, a lithium nickel cobalt composite oxide, and a lithium nickel cobalt manganese composite oxide. The assembled battery according to any one of claims 1 to 7, wherein the above complex oxide is used. A plurality of secondary batteries having a combination of a negative electrode active material and a positive electrode active material having a region where the entropy change ΔS of all battery reactions under normal temperature and atmospheric pressure is endothermic, and having a flat shape;
A heat transfer plate having a main surface in contact with the main surface of the secondary battery so as to be able to exchange heat with the secondary battery, and combined with the secondary battery to form a battery / heat transfer plate assembly;
At least one thermoelectric conversion element provided on a side surface of the battery / heat transfer plate assembly so as to exchange heat with a plurality of the battery / heat transfer plate assemblies stacked;
In the method of charging or discharging an assembled battery comprising: the battery / heat transfer plate assembly and an exterior member having a heat insulating layer surrounding the thermoelectric conversion element;
In order to control the assembled battery to an appropriate temperature range using the endothermic reaction during charging / discharging of the secondary battery, the current generated so that the amount of heat generated by the Joule heat of the secondary battery is less than the endothermic amount. A method for charging and discharging an assembled battery, comprising controlling the battery pack.

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