Patent Description:
Electrochemical storage devices are also referred to in general as batteries or accumulators. Rechargeable batteries or accumulators, in particular, are used to enable electrical energy to be stored and used. To store large amounts of electrical energy, correspondingly powerful rechargeable batteries are required. For this purpose, it is possible to use batteries based on molten sodium and sulfur, for example. In order to achieve the corresponding capacity, a plurality of electrochemical cells that are electrically interconnected are generally used here in the electrochemical energy storage devices. Such electrochemical cells, which operate on the basis of a molten alkali metal as an anode and a cathodic reactant, generally sulfur, are described in <CIT>, for example. Here, the molten alkali metal and the cathodic reactant are separated by a solid electrolyte which allows cations to pass through. At the cathode, there is a reaction between the alkali metal and the cathodic reactant. Where sodium is used as the alkali metal and sulfur is used as the cathodic reactant, this is the reaction of sodium and sulfur to form sodium polysulfide, for example. To charge the electrochemical energy storage device, the sodium polysulfide is decomposed into sodium and sulfur again at the electrode by the application of electrical energy.

The individual electrochemical cells are generally stacked in "battery packs" or, as an alternative, are placed parallel to one another in a housing. However, this arrangement has the disadvantage that uniform temperature control of the individual cells is possible only with difficulty. Throughflow of a heat transfer medium, in particular if the heat transfer medium flows perpendicular to the orientation of the electrochemical cells, leads to a temperature increase of said heat transfer medium and hence poorer cooling and accelerated aging of the electrochemical cells with the increase in distance traveled by the flowing heat transfer medium, owing to the absorption of heat by the heat transfer medium from the individual cells. However, this is disadvantageous for the operation of the electrochemical energy storage device. In particular, there is the risk that, if the temperature increase is too great, damage will occur to the individual electrochemical cells. If this leads to damage to the solid electrolyte, it can result in an uncontrolled reaction, which may lead to a fire that can be controlled only with difficulty in the electrochemical energy storage device.

Corresponding energy storage devices having sodium-sulfur batteries are described in <CIT> or <CIT>, for example.

It is a problem of the known electrochemical energy storage devices to provide a uniform temperature control. To achieve a uniform temperature control, <CIT> suggests an electrochemical energy storage device in which at least one electrochemical cell is accommodated in suspended fashion in the support structure. However, arranging the electrochemical cells in suspended fashion as described in <CIT> requires a complex design. Further, accommodating the electrochemical cells in a suspended fashion has the disadvantage that the density in which the electrochemical cells can be packed is limited.

For controlling the temperature in sodium sulfur batteries it is known for example from <CIT> or <CIT> to provide tubes in the battery which run parallel to the battery cells and through which a heat transfer medium flows. <CIT> and <CIT> each describe using cooling fins which are in contact with the single cells for controlling the temperature. Due to the necessary distributors and collectors, cooling tubes through which a heat transfer medium, e.g. air, flows are technically complex to realize.

It is an objective of the present invention to provide an electrochemical energy storage device which allows controlling the temperature of electrochemical cells with little technical effort and a sufficient heat transfer.

This objective is achieved by an electrochemical energy storage device comprising a plurality of electrochemical cells in a containing space in a housing, wherein the electrochemical energy storage device comprises a first duct which runs parallel to the top or the bottom of the housing and one or more heat transfer members which are arranged in spaces between the electrochemical cells, wherein at least one of the heat transfer members protrudes into the first duct.

The electrochemical cells and the heat transfer members preferably are arranged in such a way that they run parallel, so that it is possible to minimize the distance between the electrochemical cells and the heat transfer members and optimize the heat transfer. Further, this arrangement allows for setting a homogeneous temperature in the whole electrochemical energy storage device.

The heat transfer members may be any type of heat transfer members, for example electrical elements like Peltier elements or electrical heating elements. However, particularly preferably, heat transfer members are used which have a shape of a plate, a solid rod-like shape or a hollow pipe shape. In this case, heat is transferred from the electrochemical cells to the heat transfer members and in the heat transfer members by heat conduction to at least one end of the heat transfer member at which the heat is transferred to the first duct, through which a heat transfer medium, particularly air, may flow. Besides air, the heat transfer medium also may be, for example, thermal oil or nitrogen. However, particularly preferably, the heat transfer medium is air.

The heat transfer members may have any shape. Preferably the heat transfer members are plates, solid rods or pipes having any cross sectional shape, for example circular, oval or polygonal with any number of edges, preferably <NUM> to <NUM> edges. Particularly preferably, the heat transfer members are plates, solid rods or pipes having a circular cross sectional shape.

For achieving a sufficient heating or cooling of the electrochemical cells, if the heat transfer members are in the form of pipes, the ratio of the number of electrochemical cells to the number of heat transfer members is in a range from <NUM> : <NUM> to <NUM> : <NUM>, more preferred, the ratio of the number of electrochemical cells to the number of heat transfer members is in a range from <NUM> : <NUM> to <NUM>:<NUM> and particularly <NUM> : <NUM>. The ratio of the number of electrochemical cells to the number of heat transfer members thereby depends on the size and shape of the electrochemical cells as well as on the size and shape of the heat transfer members.

Preferably, the electrochemical cells are arranged to form a square lattice in plan view, and the heat transfer members are each disposed at a central location of a unit lattice of the square lattice. Particularly preferably, the heat transfer members are each in contact with four cells constituting the unit lattice among the plurality of cells.

Independently of the arrangement of the electrochemical cells and the heat transfer members, each heat transfer member may be arranged in such a way that the distance between the heat transfer member and each electrochemical cell being adjacent to that electrochemical cell is the same. In this case, the heat transfer member is in the center of the space between the electrochemical cells. If the electrochemical cells are not in contact with the heat transfer member, it is also possible that the distances between the heat transfer member and the adjacent electrochemical cells differ. If the distances between the heat transfer member and the adjacent electrochemical cells differ, the heat transfer members are arranged off-center. However, preferably, the heat transfer members are arranged centrally.

If the heat transfer members are in the form of plates, it is preferred that the electrochemical cells are arranged in rows and the heat transfer members are placed between the rows of electrochemical cells.

Besides using heat transfer members in the form of pipes or heat transfer members in the form of plates it is further possible to use heat transfer members in different shapes, for example heat transfer members in the form of pipes in the inner part of the electrochemical energy storage device and heat transfer members in the form of plates which are arranged close to the walls of the housing and which run parallel to the walls of the housing. If heat transfer members in the form of plates are placed parallel to the walls of the housing, it is further possible to place the heat transfer members in the space between the outermost electrochemical cells and the walls of the housing.

The electrochemical cells preferably each comprise a compartment for an anode material and a compartment for a cathode material, the compartments for the anode material and for the cathode material being separated by a solid electrolyte.

The anode material used in the electrochemical cells preferably is a reactant which is liquid at operating temperature of the electrochemical cell and which is supplied to the anode side during discharging. The anode material is preferably electrically conductive. Preferred anode materials are alkali metals like lithium, sodium or potassium. Particularly preferably the anode material is sodium or potassium and particularly sodium.

The cathode material is a reactant which also is liquid at the operating temperature of the electrochemical cell and which is electrochemically reacted with the anode material. The cathode material conventionally forms a salt by chemical reaction with the anode material. Suitable cathode materials are for example sulfur or polysulfides. Also suitable as cathode material is a mixture of sodium chloride and a metal from transition group <NUM>, as for example iron, nickel or cobalt, in combination with a liquid-melt electrolyte such as NaAlCl<NUM>.

Other suitable cathode materials in conjunction with an alkali metal as anode material are, for example, oxides of nitrogen (NO or NO<NUM>), halogen, as for example chlorine, iodine or bromine, a metal halide, for example NiCl<NUM> or FeCl<NUM>, a metalloide halide, for example SiCl<NUM> or Si<NUM>Cl<NUM>. Also possible is the use of a solid salt which is able to change its redox potential. An example of such a salt is NaFePO<NUM>.

However, particularly preferably, the cathode material is sulfur or a polysulfide.

The electrochemical energy storage devices preferably contains electrochemical cells which have a ratio of diameter to length in a range from <NUM> : <NUM> to <NUM> : <NUM>, more preferred in a range from <NUM> : <NUM> to <NUM> : <NUM> and particularly in a range from <NUM> : <NUM> to <NUM> : <NUM>.

The cross sectional area of the electrochemical cells may have any shape, however, it is particularly preferred if the shape of the cross sectional area is cylindrical.

If, in the context of the present invention, the term "diameter" is used for non-cylindrical shapes, this term refers to the hydraulic diameter which is defined by <MAT> wherein dh is the hydraulic diameter, A the cross sectional area and U the perimeter.

The number of cells used in the electrochemical energy storage device depends on the size of the electrochemical cells. Particularly preferably, the electrochemical cells which are used in the electrochemical energy storage device are sodium-sulfur cells. Such sodium-sulfur cells are usually cylindrical and have a diameter in a range of from <NUM> to <NUM> and a length in a range of from <NUM> to <NUM>. Corresponding sodium-sulfur cells are known to those skilled in the art and are described in <CIT>, for example.

For achieving a sufficient heat transfer from the electrochemical cells to the heat transfer members, it is possible that the heat transfer members and the electrochemical cells are in contact. Alternatively, it is also possible that there is no contact between the electrochemical cells and the heat transfer members or that only a part of the electrochemical cells and the heat transfer members are in contact.

Independently of whether the electrochemical cells are in contact with the heat transfer members or not, it is preferred that the space between the heat transfer members and the electrochemical cells is filled with a liquid or solid material. If the spaces are filled with a solid material, it is particularly preferred that the solid material is a particulate material, particularly a pulverulent material. The mean particle diameter of the particles of the particulate material preferably is in a range from <NUM> to <NUM>, more preferred in a range from <NUM> to <NUM>. The solid material used for filling the spaces between the electrochemical cells and the heat transfer members preferably is any inorganic solid material which is stable at operating temperature, such as sand, glass, metal or ceramics. A particularly preferred material is sand. It is a further advantage that by filling the space between the electrochemical cells and the heat transfer members, the heat transfer from the electrochemical cells to the heat transfer members is improved.

Using a solid material for filling the spaces between the electrochemical cells and the heat transfer members has the additional effect that the position of the electrochemical cells is stabilized and the electrochemical cells are fixed. Even if the electrochemical energy storage device moves, the electrochemical cells remain at their places and cannot bounce against each other which may result in a damage of the electrochemical cell. Therefore, it is particularly preferred to use a solid material for filling the spaces between the electrochemical cells and the heat transfer members. Using sand as solid material for filling the spaces between the electrochemical cells has the additional advantage that in case of a damage of an electrochemical cell, the solid material functions as a fire extinguisher.

Usually, electrochemical cells generate heat during operation. This heat is dissipated by the heat transfer members which in this case operate as cooling elements. Additionally a part of the heat is dissipated to the ambient via the outer walls of the electrochemical storage device. Due to this additional heat dissipation to the ambient, by uniform cooling of all electrochemical cells, the electrochemical cells which are close to the walls of the electrochemical energy storage device are cooler than the electrochemical cells which are placed closer to the center of the electrochemical storage device. For achieving a uniform temperature of all electrochemical cells it is therefore necessary to dissipate more heat from the electrochemical cells which are placed close to the center of the electrochemical energy storage device than from the electrochemical cells which are placed closer to the walls. This may be achieved for example by designing the heat transfer members in such a way that the surface area of outer heat transfer members which are arranged closer to the walls of the housing is smaller than the surface area of inner heat transfer members which are arranged in the middle of the housing or that the volume flow of the heat transfer medium through the heat transfer members which are arranged closer to the walls of the housing is smaller than the volume flow of the heat transfer medium through the heat transfer members which are arranged in the middle of the housing. Preferably the heat transfer members are designed such that the ratio of the surface area of the outer heat transfer members to the surface area of the inner heat transfer members is in a range from <NUM> to <NUM>.

If the heat transfer members are plates which extend from one wall of the housing to the opposite wall of the housing, the wall thickness of the plates may vary to achieve a homogeneous temperature in adjacent electrochemical cells. For such a homogenization of the temperature in the electrochemical cells, it is particularly preferred that the walls of the plates close to the walls of the housing are thicker. Further, for achieving a uniform temperature of the electrochemical cells is also possible to provide plates having a larger distance between the opposite walls of the plates in the center area of the housing of the electrochemical energy storage device and separate plates having a smaller distance between the walls close to the walls of the housing.

Besides only two different sizes of the heat transfer members it is further possible to provide heat transfer members in more than two different sizes, for example three or four or even more different sizes. The number of different sizes depends on the number of electrochemical cells and the arrangement of the cells. More than two different sizes for example may be advantageous if it is not possible to achieve an essentially uniform temperature in the housing.

According to the invention, the electrochemical energy storage device comprises a first duct which runs parallel to the top or the bottom of the housing and into which the heat transfer member protrude. By this design, the heat transfer from the heat transfer members to a heat transfer medium, preferably air, which flows through the first duct, is intensified.

Additionally, the electrochemical energy device also may comprise a second duct which is located at the bottom of the housing, if the first duct is located at the top of the housing, or at the top of the housing, if the first duct is located at the bottom of the housing.

If the electrochemical energy device comprises the additional second duct, the heat transfer members preferably are connected with the second duct or extend into the second duct.

As particularly for starting the charging or discharging of the electrochemical energy device it may be necessary to heat the electrochemical energy device, preferably a heater is disposed at the bottom below the cells, near the walls of the housing, above the cells, or a combination of these. If a bottom heater is used, it is further preferred, that the lower end of the heat transfer members ends above the bottom heater.

For facilitating mounting of the electrochemical energy device, it is preferred, that the housing comprises a box having an opening and a lid for closing the opening. To reduce the heat being transferred to the environment, particularly during heating of the electrochemical cells, it is further preferred that the box and the lid have insulating capability. For this purpose, the box and the lid may be equipped with an insulating material which either is mounted on the outside of the box or on the inner side of the walls of the box. The insulating material may be any insulating material known to a skilled person, for example mineral wool, glass wool, or other inorganic, microporous insulation materials.

Preferably, the first duct is disposed between the box and the lid above the electrochemical cells. This arrangement allows for an easy assembly of the electrochemical cell and further an easy access to the first duct for example for maintenance.

For transferring heat to a medium flowing through the first duct, at least one heat transfer member protrudes into the first duct. Particularly preferably, all heat transfer members have the same length, so that all heat transfer members protrude into the first duct.

The heat transfer members protruding into the first duct may be in contact with a surface of the first duct opposite of the containing space in a direction of extension of the heat transfer members.

For improving heat transfer, it is preferred that the electrochemical energy storage device further comprises a first intake fan capable of supplying air to the first duct from the outside, wherein the first duct includes a first intake port to which air is supplied from the first intake fan, a first internal space to allow heat to be transferred from the heat transfer members to air supplied from the first intake port, and a first exhaust port from which air having passed through the first internal space is discharged to the outside.

Particularly if a second duct at the bottom of the electrochemical energy storage device is provided, it is further preferred that the electrochemical energy storage device further comprises a second intake fan capable of supplying air to the second duct from the outside, wherein the second duct includes a second intake port to which air is supplied from the second intake fan, a second internal space to which air is supplied from the second intake port, the second internal space being located so that the bottom heater is interposed between the second internal space and a range of arrangement of the heat transfer members in the containing space, and a second exhaust port from which air having passed through the second internal space is discharged to the outside. The air which flows through the second duct in this case also improves cooling of the electrochemical cells because heat is transferred to the second duct and by air flowing through the second duct, this heat is dissipated to the environment by the air leaving the second duct.

As usually heat is dissipated to the ambient by the walls of the housing of the electrochemical energy storage device and for this reason, the electrochemical cells close to the wall of the housing need less cooling than the electrochemical cells in the center of the housing, the inner heat transfer members which are closer to the center of the housing and the outer heat transfer members which are closer to the walls of the housing may protrude into different fluid circuits in the first duct.

Besides providing only two fluid circuits, it is also possible to provide more than two fluid circuits. Increasing the number of fluid circuits allows for a more specific setting of the heat transfer parameters in the electrochemical energy storage device as each fluid circuit can be operated with different parameters.

If the first duct and/or the second duct comprises more than one closed fluid circuit, to control the temperature, each fluid circuit may comprise at least one external heat exchanger which is connected to an entrance into a sub-duct of the first duct and/or the second duct. If the flow circuits are open flow circuits, the first and/or second ducts each may be connected with at least one blower and if additional heating is required, also heating elements may be provided between the heat transfer members and/or in the heat transfer members, the first ducts and/or the entries into the first ducts.

For a sufficient heat transfer, it is preferred that the heat transfer members are made of a material which has good heat conducting properties. Suitable materials from which the heat transfer members may be made are one or more types of metal selected from the group consisting of aluminum, copper, steel, and alloys comprising at least one of these metals.

Illustrative embodiments of the invention are shown in the figures and explained in more detail in the following description.

<FIG> shows an electrochemical energy storage device with a schematically illustrated temperature control circuit.

An electrochemical energy storage device <NUM> comprises a housing <NUM> which encloses electrochemical cells and heat transfer members. To increase the energy efficiency of the electrochemical energy storage device <NUM>, it is preferred if the housing <NUM> is embodied in a thermally insulated way. Here, the thermal insulation can be applied to the inside or the individual housing walls or to the outside. Alternatively, it is also possible to produce the housing <NUM> from a thermally insulating material. By way of example, the housing <NUM> can be produced from metal sheets, in particular steel sheets, which are thermally insulated on the inside or on the outside. In this context, any desired insulating material known to those skilled in the art can be used for the thermal insulation. As an alternative, it is also possible to produce the housing from a mineral material, e.g. as masonry. However, the advantage of the housing <NUM> consisting of steel sheets is that, in this case, it is possible to provide a transportable electrical energy storage device <NUM>, whereas an electrochemical energy storage device <NUM> in a fixed location can also be enclosed with a brick housing <NUM>.

The housing has an inlet <NUM> and an outlet <NUM> for a heat transfer medium. The heat transfer medium may flow from top to bottom as shown here or, as an alternative, from bottom to top. The inlet preferably is connected to a distributor by which the heat transfer medium is distributed to the heat transfer members which run parallel to the electrochemical cells in the housing <NUM>. For withdrawing the heat transfer medium from the electrochemical energy storage device <NUM>, the heat transfer members are connected to a collector which is connected to the outlet <NUM>. As an alternative to the embodiment shown in <FIG> with the distributor above the electrochemical cells and the collector below the electrochemical cells, it is also possible to arrange both, the distributor and the collector above the electrochemical cells or below the electrochemical cells, preferably above the electrochemical cells.

If it is intended to provide at least two fluid circuits for the heat transfer medium, each fluid circuit comprises an inlet <NUM> and an outlet <NUM> which are connected to the heat transfer members of the respective fluid circuit.

For controlling the temperature, the heat transfer medium removed from the housing <NUM> via the outlet <NUM> is then passed through a heat exchanger <NUM>, a heating device <NUM>, and a delivery device <NUM> and is then re-introduced into the housing <NUM> via the inlet <NUM>. In this case, the heat exchanger <NUM>, the heating device <NUM> and the delivery device <NUM> are preferably arranged in a channel, wherein the channel can be embodied as a pipe or as a channel with any other cross section, e.g. as a rectangular channel.

The heat exchanger <NUM> is used, in particular, to cool the heat transfer medium when the heat transfer medium is used to cool the electrochemical cells, as is necessary, for example, in the case of alkali metal-sulfur cells during the charging and discharging process. During this process, the heat transfer medium in the heat exchanger <NUM> releases heat to another heat transfer medium, wherein water or any other desired conventional heat transfer medium, e.g. a thermal oil, can be used as a heat transfer medium here, for example.

If heat has to be supplied either for the operation of the electrochemical cells or for starting up the electrochemical cells, the heating device <NUM> is provided. In the heating device <NUM>, the heat transfer medium is heated. Here, heating can be accomplished directly or indirectly, wherein indirect heating is accomplished, for example, by using a heating medium which releases heat to the heat transfer medium for controlling the temperature of the electrochemical cells. However, it is only possible here to use heating media which are stable at temperatures above the temperature to which the heat transfer medium for heating the electrochemical cells is to be heated. Suitable heating media would be molten salts, for example. There is therefore a preference for the use of a heating device in which the heat transfer medium is heated electrically or inductively or, alternatively, by burning a fuel.

As an alternative to the embodiment illustrated here having a heat exchanger <NUM> for cooling and a separate heating device <NUM>, it is also possible to use just one heat exchanger, which is used both for heating and for cooling. For this purpose, the temperature of the heat transfer medium can be varied, either for heating or for cooling, or a combination unit is used which cools by means of a heat transfer medium and additionally contains electric heating elements for heating, by means of which the heat transfer medium can be heated when required to control the temperature of the electrochemical cells.

The delivery device <NUM> is dependent on the heat transfer medium used. For a fluid, which is preferably used, the delivery device <NUM> is a pump, for example. The delivery device <NUM> is dimensioned in such a way that a quantity of heat transfer medium sufficient to control the temperature of the electrochemical cells can be passed through the heat transfer members.

Besides the embodiment shown in <FIG> having a closed fluid circuit for the heat transfer medium, it is also possible to provide an open circuit. Such an open circuit preferably is used if the heat transfer medium is air. In this case, ambient air is fed through the inlet <NUM> into the housing <NUM> and removed from the housing through the outlet <NUM>. In difference to the embodiment shown here, the air is blown from the outlet into the surroundings. For feeding the air through the electrochemical energy storage device, the delivery device <NUM>, particularly a blower, is connected to the inlet <NUM> and/or the outlet <NUM>. If an additional heating is intended, it is possible to provide the heating device <NUM> in the inlet to heat the air which is sucked in by the blower. Alternatively, it is possible to arrange the heater in the distributor or in the heat transfer members through which the air flows. Further, it is also possible to arrange heating devices between the electrochemical cells and the heat transfer members.

<FIG> and <FIG> show a sectional view of an electrochemical energy storage device and a plan view on the respective energy storage device having heat transfer members by which heat is transferred by heat conduction.

The electrochemical energy storage device <NUM> comprises a battery pack <NUM> which is composed of a plurality of single electrochemical cells <NUM>. The electrochemical cells <NUM> are placed in the housing <NUM>, which comprises a box <NUM>, which preferably has a rectangular parallelepiped shape and encloses the space <NUM> in which the electrochemical cells <NUM> are placed. The box <NUM> has an opening <NUM> which is closed by a lid <NUM>. As can be seen in <FIG>, the lid <NUM> preferably comprises a rim <NUM> which extends downwards and surrounds the upper part of the box <NUM>. The size of the lid <NUM> is such that a first duct is formed between the box <NUM> and the lid <NUM>.

Besides the battery pack <NUM>, the box <NUM> comprises a second duct <NUM> below the electrochemical cells <NUM> and heat transfer members <NUM>, which are arranged between the electrochemical cells <NUM>. The space <NUM> which is not filled with the electrochemical cells <NUM> and the heat transfer members <NUM> preferably is filled with a solid or liquid medium, particularly a solid particulate medium, for example sand like vermiculite or silica sand. The liquid or solid medium particularly is used to reduce the influence of the surroundings in the event of failure such as breakage, abnormal heating or leakage of active material in a single electrochemical cell <NUM>.

For connecting the electrochemical cells <NUM> to form the battery pack <NUM>, each electrochemical cell comprises a negative electrode terminal <NUM> which projects from the center of the upper end of the electrochemical cell <NUM> in the state mounted in the housing <NUM>, and a positive electrode terminal <NUM> which projects from the peripheral edge of the electrochemical cell <NUM>. In the battery pack <NUM>, one positive electrode terminal <NUM> and a negative electrode terminal <NUM> arranged adjacent to each other are electrically connected by a connection terminal <NUM>, thereby forming a string in which a plurality of electrochemical cells <NUM> are connected in series. A part of the connection terminals <NUM> is shown in <FIG>. In the battery pack <NUM>, a plurality of strings are connected in parallel to form a block, and the plurality of blocks are connected in series.

The box <NUM> is mounted and fixed on a base <NUM>, which supports the box <NUM> downward. The box <NUM> preferably is composed of a metallic outer plate <NUM> facing the outside, metallic inner plate <NUM> facing the inside, and a heat insulating material <NUM>, having electrical insulating properties and which is filled between the outer plate <NUM> and the inner plate <NUM>.

The lid <NUM> preferably is detachably attached to the box <NUM> and is placed on the box <NUM> when the electrochemical energy storage device <NUM> is used, and is removed from the box <NUM> when the battery pack <NUM> is taken in and out.

The lid <NUM> preferably is composed of a metallic outer plate <NUM> facing the outside, a metallic inner plate <NUM> facing the inside, and a heat insulating material <NUM> being filled between the outer plate <NUM> and the inner plate <NUM>.

Preferably, the heat insulating materials <NUM>, <NUM> are used in an atmospheric atmosphere, and the box <NUM> and the lid <NUM> have an atmospheric heat insulating structure. More preferably, the outer plate <NUM> and the inner plate <NUM> are provided in such a shape and arrangement that they do not contact each other via the heat insulating material <NUM>, and the outer plate <NUM> and the inner plate <NUM> are also provided in such a shape and arrangement that they do not contact each other via the heat insulating material <NUM>. For example, a configuration is adopted in which the outer plate <NUM> and the inner plate <NUM> as well as the outer plate <NUM> and the inner plate <NUM> include a space in between, by which in addition to the thermal insulation also electrical insulation is ensured.

By configuring the box <NUM> and the lid <NUM> as described above, a gap <NUM> is formed between the outer plate <NUM> and the inner plate <NUM> and a gap <NUM> is formed between the outer plate <NUM> and the inner plate <NUM>. If air is present inside the box <NUM> and the lid <NUM> and is heated and expands during use, the air flows out to the outside through the gaps <NUM>, <NUM>. As a result, deformation of the box <NUM> and the lid <NUM> due to thermal expansion of air is suppressed.

Alternatively, the box <NUM> and/or the lid <NUM> may have a vacuum heat insulating structure by adopting a vacuum heat insulating board as the heat insulating material <NUM>, <NUM>. In this case, the inner plates <NUM>, <NUM> and the outer plates <NUM>, <NUM> are tightly connected.

For forming the first duct <NUM> between the box <NUM> and the lid <NUM>, preferably an insulating cushioning material <NUM> is disposed on the open end portion of the box <NUM> having the gap <NUM> formed therein. The first duct <NUM> is formed on the cushioning material <NUM> and extends between the outer plate <NUM> of the box <NUM> and the inner plate <NUM> of the lid <NUM>.

The first and second ducts <NUM>, <NUM> are respectively provided with a first fan <NUM> and a second fan <NUM> which may be electric intake fans. The first fan <NUM> and the second fan <NUM> are provided for supplying external air to the first duct <NUM> and the second duct <NUM>, respectively. The operation of the first and second fans <NUM>, <NUM> may be controlled by a fan control unit.

In addition, side heaters <NUM> may be provided on the surface of the inner plates <NUM> on each side of the box <NUM>. Further, a bottom heater <NUM> may be provided on the top surface <NUM> of the second duct <NUM>.

The upper surface of the bottom heater <NUM> is horizontal, and the battery pack <NUM> is arranged on the upper surface of the bottom heater <NUM>. More specifically, a plate-like or sheet-like insulator <NUM> mode of, for example mica, is interposed between the bottom heater <NUM> and the battery pack <NUM>, thereby ensuring insulation between the bottom heater <NUM> and the battery pack <NUM>.

The side heaters <NUM> and the bottom heater <NUM> preferably are electric heaters for heating the inside of the box <NUM>. Typically, the side heaters <NUM> and the bottom heater <NUM> are used to maintain the inside of the box <NUM> at an operating temperature so as to keep the active material of each electrochemical cell <NUM> of the battery pack <NUM> in a molten state when the electrochemical energy storage device <NUM> is in a standby state in which the battery pack <NUM> is not charged or discharged. The operation of the side heaters <NUM> and the bottom heater <NUM> is controlled by a heater control unit.

For releasing heat generated in the single electrochemical cells <NUM> during operation to the outside of the space <NUM>, rod shaped heat transfer members <NUM> are provided. In the embodiment shown in <FIG> and <FIG>, having heat transfer members for transferring heat by heat conduction, the heat transfer members <NUM> are made of a material having high thermal conductivity, typically a metal having high thermal conductivity. Preferably, aluminum is used as the material of the heat transfer members <NUM>. However, aluminum, steel, copper or an alloy of some of these metals may be used.

As can be seen in <FIG>, the electrochemical cells <NUM> are circular in plan view. If heat transfer members operating by heat conduction in the material of the heat transfer members, it is further preferred, that each electrochemical cell <NUM> is in contact with the adjacent electrochemical cells <NUM>. The electrochemical cells preferably are arranged in a rectangular lattice and the heat transfer members <NUM> are arranged in the space which is surrounded by four electrochemical cells <NUM>. As adjacent electrochemical cells <NUM> are in contact, the distance from center to center of two adjacent electrochemical cells <NUM> corresponds to the diameter of one electrochemical cell <NUM>. The heat transfer member is located at the intersection point of the diagonal lines of the rectangular lattice.

The heat transfer members <NUM> also preferably have a circular cross sectional area and are disposed in the space surrounded by the electrochemical cells <NUM> such that the longitudinal axes of the electrochemical cells <NUM> and the heat transfer members <NUM> run parallel and in a manner in which the heat transfer members <NUM> are in contact with all electrochemical cells <NUM> surrounding the respective heat transfer member <NUM>.

However, if the heat transfer members are designed as shown in <FIG>, the heat transfer members <NUM> are only in line contact (point contact in the cross-sectional view shown in <FIG>) with the surrounding electrochemical cells <NUM>. From the viewpoint of improving heat transfer performance, a cross-sectional shape perpendicular to the longitudinal direction of the heat transfer members <NUM> may be determined so that the heat transfer members <NUM> and the electrochemical cells <NUM> are in surface contact. For example, all or most of the space between the electrochemical cells <NUM> may be a region in which the heat transfer member <NUM> is to be disposed and the heat transfer members <NUM> have a cross sectional shape corresponding to the cross sectional shape of this region. In such a case, the side surface of the heat transfer members <NUM> are in wide contact with the side surface of the electrochemical cells <NUM> and high heat transfer performance is obtained.

If a suitable heat transfer can be obtained in another way, it is further possible, that the heat transfer members <NUM> and the electrochemical cells <NUM> are not in contact. In this case, heat is transferred from the electrochemical cells <NUM> to the heat transfer members <NUM> by heat conduction through the medium which is in the space between the electrochemical cells <NUM> and the heat transfer members <NUM>.

Besides having a circular cross sectional area, the heat transfer members <NUM> also may have any other shape, for example the shape of a rectangular column, a triangular column or even a shape with irregularities on the side surface along the longitudinal direction so as to increase the surface area, as long as the heat transfer members <NUM> ca be disposed in the space between the electrochemical cells <NUM>. Further, it is also possible, that a plurality of heat transfer members <NUM> is arranged in each space between the electrochemical cells <NUM>.

The heat transfer members <NUM> may have a hollow pipe shape or a solid rod shape as long as good heat transfer performance is ensured. A hollow pipe shape is advantageous not only in the terms of costs but also in that sand can be filled inside. More specifically, from the viewpoint of reducing the interior of the box <NUM> with a certain amount of electrochemical cells <NUM>, it is necessary to fill the interior of the box <NUM> with a predetermined amount or more of sand material. The type of sand material to be filled in the space <NUM> may be the same as or different from the type of sand material to be filled in the pipe-like heat transfer members <NUM>. Further, in one electrochemical energy storage device <NUM>, pipe-shaped heat transfer members <NUM> and rod-shaped heat transfer members <NUM> may coexist.

When the heat transfer members <NUM> have a pipe shape, both ends of the heat transfer members <NUM> may be closed or opened independently. Alternatively, both ends may each independently be provided with a removable lid.

Besides being disposed in all spaces surrounded by electrochemical cells <NUM> as shown in <FIG>, the heat transfer members <NUM> also may be arranged only in the spaces between the electrochemical cells <NUM> near the center of the battery pack <NUM> and the arrangement of heat transfer members <NUM> may be omitted in the spaces between the electrochemical cells <NUM> close to the walls of the box <NUM>. This is possible as heat is more likely to be released outside in the vicinity of the walls of the box <NUM> than in the vicinity of the center of the box <NUM>.

As can be seen in <FIG>, the lower end <NUM> of each heat transfer member <NUM> is in contact with the insulator <NUM>. On the other hand, the upper end <NUM> of the heat transfer members <NUM> is disposed so as to protrude at least partly into the first duct <NUM>. Preferably, the upper end <NUM> of the heat transfer member <NUM> is disposed so as to be close to the inner plate <NUM> of the lid <NUM> forming the upper surface of the first duct <NUM>, and particularly so as to be in contact with the upper surface of the first duct <NUM>.

For controlling the electrochemical cell, it is preferred to provide a controller for controlling the operation of each part. The controller may be constituted by a general-purpose or special-purpose computer having a CPU, ROM, RAM or the like, and functions as the controller by executing an operation program stored in a predetermined storage medium incorporated in or externally connected to the computer. The controller mainly includes a battery operation control unit and a temperature control unit as virtual components realized by execution of the operation program.

The battery operation control unit controls charging and discharging operations of the electrochemical energy storage device <NUM> in the battery pack <NUM>, power supply and reception operations between the electrochemical energy storage device <NUM> and the outside, and the like.

The temperature control unit controls the temperature inside the electrochemical energy storage device <NUM> (in particular, the temperature of the space <NUM>) during the operation (charging and discharging) and the standby of the electrochemical energy storage device <NUM> on the basis of an output signal (temperature signal) from a temperature sensor provided at a predetermined position of the box <NUM>. The temperature control unit includes a fan control unit for controlling the operations of the first fan <NUM> and the second fan <NUM>, and a heater control unit for controlling the operations of the side heaters <NUM> and the bottom heater <NUM>.

During the operation of the electrochemical energy storage device <NUM>, charging and discharging operations in the battery pack <NUM>, power supply and reception operations between the battery pack <NUM> and the outside are executed under the control of the battery operation control unit, and at this time, the fan control unit appropriately operates the first fan <NUM> and the second fan <NUM> to blow low-temperature air from the outside into the first duct <NUM> and the second duct <NUM>, thereby maintaining the operating temperature in the electrochemical energy storage device <NUM>. Thus, the charge/discharge operation and the power supply/reception operation are performed while the operating temperature is maintained.

On the other hand, during standby, the electrochemical energy storage device is maintained at the operating temperature mainly by turning on/off the energization states of the side heaters <NUM> and the bottom heater <NUM> based on the output signal from the temperature sensor by the heater control unit.

During operation, reaction heat is generated in each electrochemical cell <NUM>. The reaction heat is transferred to the periphery of the respective electrochemical cell <NUM> an then is transferred to the heat transfer member <NUM> having higher thermal conductivity than the medium filled in the space <NUM>. The heat transferred from the electrochemical cell <NUM> to the heat transfer member <NUM> is indicated by arrows <NUM> in <FIG>.

As shown by arrows <NUM>, <NUM>, the heat transferred to the heat transfer member <NUM> rapidly moves to the upper end <NUM> and the lower end <NUM> of the heat transfer member <NUM>.

During operation of the electrochemical energy storage device, external air <NUM> having a temperature below the temperature inside the box <NUM> is introduced into the first duct <NUM> by activating the first fan <NUM>. The air flows through the first duct <NUM> as shown with arrow <NUM>. The air flowing through the first duct <NUM> absorbs heat generated from the electrochemical cells <NUM> by cooling the lower surface of the first duct <NUM>. Additionally, the upper ends <NUM> of the heat transfer members <NUM> are cooled by the air flowing through the first duct <NUM>. The thus heated air then is released to the environment as shown with arrows <NUM>.

If present, also the second fan <NUM> is operated during operation of the electrochemical energy storage device <NUM> to introduce external air <NUM> into the second channel <NUM>. The air flows through the second channel <NUM> as indicated with arrow <NUM>, thereby cooling the upper surface of the second duct <NUM> and thus the space <NUM> which contains the battery pack <NUM> and also the lower end <NUM> of the heat transfer members <NUM>. Heat transfer from the space <NUM> to the air flowing through the second duct <NUM> is possible even though the insulator <NUM> and the bottom heater <NUM>, which is not in operation during normal operation of the electrochemical energy storage device <NUM>, are provided between the electrochemical cells <NUM> and the heat transfer members <NUM> due to the high temperature differences between the electrochemical cells at operation and the external air.

To further improve heat transfer from the heat transfer members <NUM> to the air flowing through the second duct <NUM>, it is possible to design the heat transfer members <NUM> such that the lower end <NUM> of the heat transfer members <NUM> protrudes into the second duct <NUM>.

It is a further advantage of the heat transfer members <NUM>, that also during standby of the electrochemical energy storage device <NUM>, when the battery pack <NUM> is heated by the side heaters <NUM> and the bottom heater <NUM>, heat from the bottom heater <NUM> is transferred to the electrochemical cells <NUM> by heat transfer through the heat transfer members <NUM>, thereby maintaining the temperature more efficiently in the electrochemical cells <NUM>.

According to the invention, at least one heat transfer member protrudes into the first duct. The further heat transfer members may be arranged as shown in <FIG>.

The arrangement shown in <FIG> corresponds to the arrangement of <FIG>, where all heat transfer members <NUM> protrude into the first duct <NUM> and in which the heat transfer members <NUM> are cooled by the air flowing around the upper end <NUM> of the heat transfer members <NUM> which protrudes into the first duct <NUM>, thereby ensuring heat dissipation during operation.

However, even if at least one of the heat transfer members <NUM> does not protrude into the first duct <NUM>, sufficient heat dissipation by the heat transfer members <NUM> can be realized. The heat transfer members may have a length as shown in <FIG>, not according to the invention, where the upper end of the heat transfer members <NUM> is in contact with the lower surface of the first duct <NUM>. In this case, the lower surface of the first duct <NUM> does not need any through holes through which the heat transfer members <NUM> are guided. In this embodiment, the heat is transferred from the upper end of the heat transfer members <NUM> to the lower surface of the first duct <NUM> and from the lower surface of the first duct <NUM> to the air flowing through the first duct.

It even may be sufficient as shown in <FIG>, also not according to the invention, if the upper end of at least one heat transfer member <NUM> ends at a distance d below the lower surface of the first duct <NUM>. In this case heat is transferred by the medium between the upper end of the heat transfer members <NUM> and the lower surface of the first duct <NUM> to the lower surface of the first duct <NUM> and then from the lower surface of the first duct <NUM> to the air flowing through the first duct <NUM>. If the heat transfer members <NUM> have a length as shown in <FIG>, it is possible to manufacture the upper duct <NUM> without the through holes for the heat transfer members <NUM>.

For example, considering that the temperature in the vicinity of the center of the electrochemical energy storage device <NUM> tends to be higher than that in the outer peripheral portion, the heat transfer members <NUM> in the vicinity of the center of the electrochemical energy storage device may protrude into the first duct <NUM> and may not protrude into the first duct <NUM> in the outer peripheral portion.

As an alternative or additionally, it is also possible to provide solid heat transfer members <NUM> near the center of the electrochemical energy storage device <NUM> and pipe-shaped heat transfer members <NUM> in the outer peripheral portion, and/or to provide heat transfer members <NUM> having a larger cross sectional area nearer to the center of the electrochemical energy storage device and having a smaller cross sectional area if located in the outer peripheral portion.

In this way, by selectively using the heat transfer members <NUM> having different geometry and thus different cooling capacities, depending on the locations in accordance with the required cooling performance, the temperature distribution of the electrochemical energy storage device <NUM> as a whole can be made uniform.

When the heat transfer member <NUM> penetrates the first duct <NUM>, at least one heat radiation fin may be attached the portion of the heat transfer member <NUM> protruding into the first duct <NUM>. In this case, heat dissipation from the heat transfer member <NUM> in the first duct <NUM> is further enhanced.

The heat transfer members <NUM> used in the electrochemical energy storage device may have any suitable cross sectional shape. Examples of possible shapes are shown in <FIG>.

<FIG> shows a top view on electrochemical cells and heat transfer members of an electrochemical energy storage device, the heat transfer members being plates.

If the heat transfer members <NUM> are in the form of plates as shown in <FIG>, the electrochemical cells <NUM> are arranged in rows and the heat transfer members <NUM> are arranged between the rows of the electrochemical cells <NUM>.

Embodiments with heat transfer members <NUM> being pipes or rods are shown in <FIG> and <FIG>. For achieving a sufficient heat transfer from the electrochemical cells <NUM> to the heat transfer members <NUM>, the electrochemical cells <NUM> are arranged around the heat transfer members <NUM>. Besides arranging four electrochemical cells <NUM> around one heat transfer member <NUM> it is also possible to arrange any other number of electrochemical cells <NUM> around one heat transfer member <NUM>, for example <NUM>, <NUM>, <NUM> or <NUM> electrochemical cells <NUM>. The number of electrochemical cells <NUM> being arranged around one heat transfer member <NUM> particularly depends on the diameters of the heat transfer members <NUM> and the electrochemical cells <NUM>. The larger the diameter of the electrochemical cells <NUM> and the smaller the diameter of the heat transfer members <NUM>, the smaller is the number of electrochemical cells <NUM> which can be arranged around a heat transfer member <NUM> without forming a space which is too large for a satisfying heat transfer.

The embodiments shown in <FIG> and <FIG> differ in the cross sectional shape of the heat transfer members <NUM>. In the embodiment shown in <FIG>, the heat transfer members <NUM> have a circular cross sectional shape and in the embodiment shown in <FIG>, the heat transfer members <NUM> have a square cross sectional shape.

Besides the shapes shown in <FIG> and <FIG>, the heat transfer members <NUM> may have any other shape, for example oval, or polygonal with any number of edges. However, particularly preferably, the heat transfer members <NUM> have a circular cross sectional shape as shown in <FIG>.

If the heat transfer members <NUM> are pipes, it is possible to use pipes having different cross sectional shapes and/or different diameters in one electrochemical energy storage device. However, it is particularly preferred that all heat transfer members <NUM> have the same shape. Different diameters may be preferred, if the quantity of heat which has to be dissipated by the heat transfer members or which has to be supplied by the heat transfer members is different at different positions in the electrochemical energy storage device <NUM>. In this case, for removing a larger quantity of heat, a larger diameter is preferred in those areas of the electrochemical energy storage device where the larger quantity of heat occurs. Accordingly, for supplying a larger amount of heat, a larger diameter is preferred in those areas the larger quantity of heat is needed.

In the embodiments shown above, the electrochemical cells <NUM> are arranged adjacent to each other in a rectangular lattice. However, the arrangement of the electrochemical cells <NUM> is not limited thereto.

For example, the electrochemical cells may be arranged in a closest packing manner. Such is shown in a plan view in <FIG>. In this case, the electrochemical cells having a circular cross sectional shape are arranged in an equilateral triangular lattice. The heat transfer members <NUM> then are disposed in such a way that they contact three electrochemical cells <NUM>.

However, besides the rectangular lattice and the triangular lattice shown here, the electrochemical cells may be arranged in any other lattice shape.

A simulation experiment was carried out to evaluate the effect of the presence or absence of the heat transfer member <NUM> transferring heat by heat conduction in the solid material and the positional relationship between the heat transfer member <NUM> and the first duct <NUM> on the temperature characteristics at the time of discharge of the electrochemical energy storage device.

For examples <NUM> to <NUM>, <NUM> single electrochemical cells <NUM> each having diameters of about <NUM> and lengths of <NUM> were arranged adjacent to each other in a grid of <NUM> times <NUM> as shown in <FIG> and <FIG> in a storage space <NUM> of a box <NUM> closed by a lid <NUM>, each made of stainless steel (SUH409L, thermal conductivity <NUM> W/m*K). A hollow pipe-shaped heat transfer member <NUM> having an outer radius of <NUM> and an inner radius of <NUM> was arranged in the <NUM> spaces formed thereby. The remaining storage space <NUM> is filled with sand material. In the examples <NUM> to <NUM> only the arrangement of the heat transfer members <NUM> is different from each other. It is noted that each electrochemical cell <NUM> can be continuously discharged for four hours at an output of <NUM> W/DC.

In example <NUM>, the heat transfer members <NUM> penetrate into the first duct <NUM> and the upper end <NUM> is brought into contact with the upper surface of the first duct <NUM> as shown in <FIG>.

In example <NUM>, not according to the invention, the heat transfer members <NUM> do not pass into the first duct <NUM> and the upper end <NUM> of the heat transfer members <NUM> is brought into contact with the lower surface of the first duct <NUM> as shown in <FIG>.

According to example <NUM>, not according to the invention, the upper end <NUM> of the heat transfer members <NUM> is separated from the lower surface of the first duct <NUM> by a distance d=<NUM> as shown in <FIG>.

For comparison, an electrochemical energy storage device in which the electrochemical cells were arranged in the same ways as in examples <NUM> to <NUM> and which does not contain heat transfer members is used.

With respect to these examples and comparative example, temperature distributions at three different height positions of the electrochemical cell <NUM>, i.e. "upper portion", "middle portion", and "lower portion" were simulated in the case where discharge was performed at a target temperature of <NUM> ° C. "Upper part", "Middle part", and "Lower part" are respectively set to the position of <NUM>. <NUM> from the bottom surface of the electrochemical cell <NUM>.

<FIG> is a view showing the temperature distributions in the "upper part", the "middle part", and the "lower part" for examples <NUM> to <NUM> and the comparative example obtained by simulation, and the maximum temperature in the temperature distribution. As shown in the lower part of the figure, in each temperature distribution, the battery pack <NUM> composed of <NUM> electrochemical cells <NUM> is arranged in the storage space <NUM> surrounded by the box <NUM>. However, illustration of the heat transfer member <NUM> is omitted.

In addition, in the part of the battery pack <NUM> occupying the central portion in the storage space <NUM>, the temperature becomes higher as the color becomes darker. The white circle indicates the maximum temperature position.

From <FIG>, it can be seen that the temperature tends to be highest at approximately at the center of any electrochemical cell and at any height position.

Further, in the comparative example in which no heat transfer members <NUM> are provided, the maximum temperature exceeds <NUM> regardless of the height position, whereas in the first to third embodiments in which heat transfer members <NUM> are provided, the temperature is kept at <NUM> or less at the maximum. These results indicate that providing the heat transfer members <NUM> is effective for heat dissipation during discharge of the electrochemical energy storage device.

In particular, with regard to example <NUM> in which the heat transfer members <NUM> penetrate into the first duct <NUM>, although the maximum temperature at the "middle portion" slightly exceeded <NUM> the temperature was almost <NUM> or less regardless of the height position, and was below the target temperature of <NUM>. Moreover, the temperature difference in the plane was small. This shows that the configuration of the first embodiment is extremely effective for heat dissipation during discharge of the electrochemical energy storage device.

Claim 1:
An electrochemical energy storage device comprising a plurality of electrochemical cells (<NUM>) in a containing space in a housing (<NUM>), wherein the electrochemical energy storage device (<NUM>) comprises a first duct which runs parallel to the top or the bottom of the housing (<NUM>) and one or more heat transfer members (<NUM>) which are arranged in spaces (<NUM>) between the electrochemical cells (<NUM>), characterized in that at least one of the heat transfer members (<NUM>) protrudes into the first duct (<NUM>).