Patent Description:
The present technology relates to a battery assembly and a method of manufacturing the battery assembly.

In <CIT>, a structure in which a heat insulating material and an elastic body are placed on each other is disclosed as a structure of a separator disposed between a plurality of battery cells.

<CIT>, forming the basis for the preamble of claim <NUM>, discloses an elastic body in which a hard portion protrudes from a through hole of a soft portion. As can be also seen from its family member <CIT> the secondary battery module includes a nonaqueous electrolyte secondary battery and an elastic body. The elastic body has a compressive elastic modulus of <NUM> MPa to <NUM> MPa. The nonaqueous electrolyte secondary battery includes a positive electrode and a negative electrode. The positive electrode includes a positive electrode collector containing Ti as a main component and having a thickness of <NUM> to <NUM>. The negative electrode includes a first layer and a second layer sequentially formed from a side with the negative electrode collector. The first layer contains negative electrode active material particles containing first carbon-based active material particles with a <NUM>% proof stress of <NUM> MPa or less. The second layer contains negative electrode active material particles containing second carbon-based active material particles with a <NUM>% proof stress of <NUM> MPa or greater.

In addition, patent document <CIT> discloses a power supply device comprising a plurality of battery cells configured so that the external shape thereof is rectangular, a plurality of separators for insulating adjacent battery cells, and a restriction member for assembling the plurality of battery cells and the plurality of separators. Each of the separators includes a sandwiched plate part disposed between adjacent battery cells, at least one sheet-form insulation member disposed between the sandwiched plate part and the adjacent battery cell, and a peripheral wall that projects from the sandwiched plate part toward the adjacent battery cell. In addition, each of the battery cells is fitted into a space partitioned by the peripheral wall so that each of the separators restricts relative displacement between adjacent battery cells.

Since the separator described in <CIT> employs the two-layer structure with the heat insulating material and the elastic body, a total of a tolerance of the thickness of the heat insulating material and a tolerance of the thickness of the elastic body is a tolerance of the thickness of the separator.

Therefore, the tolerance of the thickness of the separator tends to be larger than that of a separator constituted of one member. When the thickness of the separator is large, a restraint load on battery cells become large even though design values of sizes of the battery cells in a stacking direction are the same. When the maximum value of the restraint load on the battery cells becomes large, strength of a strength member in the battery module needs to be improved, which can lead to increased weight and increased cost of the battery module.

In the elastic body described in <CIT>, and family member <CIT>, the soft portion is normally separated from an electrode assembly in a state in which it is incorporated in a secondary battery module. Further, since the hard portions interspersed in the elastic body are likely to be deformed, it is considered that a load is received from the electrode assembly.

It is an object of the present technology to provide: a battery assembly in which variation in reaction force acting on a battery cell is small; and a method of manufacturing the battery assembly.

The above object is solved by the subject-matters of claims <NUM> and <NUM>. Further advantageous configurations of the invention can be drawn from the dependent claims.

Hereinafter, embodiments of the present technology will be described. It should be noted that the same or corresponding portions are denoted by the same reference characters, and may not be described repeatedly.

In the present specification, the term "battery" is not limited to a lithium ion battery, and may include other batteries such as a nickel-metal hydride battery and a sodium ion battery.

In the present specification, the term "battery cell" is not necessarily limited to a prismatic battery cell and may include a cell having another shape, such as a cylindrical battery cell, a pouch battery cell, or a blade battery cell. Further, the "battery cell" can be mounted on vehicles such as a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and a battery electric vehicle (BEV). It should be noted that the use of the "battery cell" is not limited to the use in a vehicle.

<FIG> is a perspective view of a battery assembly 1A. Battery assembly 1A shown in <FIG> includes battery cells <NUM> and separators <NUM> (inter-cell separator). Battery cells <NUM> and separators <NUM> are alternately arranged along a Y axis direction (first direction).

The plurality of battery cells <NUM> are battery cells each having a prismatic shape, and are provided along the Y axis direction. The plurality of battery cells <NUM> are electrically connected together by a bus bar (not shown).

Separators <NUM> are provided between the plurality of battery cells <NUM>. Each of separators <NUM> prevents unintended electrical conduction between adjacent battery cells <NUM>. Separator <NUM> secures an electrical insulation property between adjacent battery cells <NUM>.

<FIG> is a perspective view of each battery cell <NUM>. As shown in <FIG>, battery cell <NUM> has a prismatic shape. Battery cell <NUM> has electrode terminals <NUM>, a battery case <NUM>, and a gas-discharge valve <NUM>.

Electrode terminal <NUM> is formed on battery case <NUM>. Electrode terminals <NUM> have a positive electrode terminal <NUM> and a negative electrode terminal <NUM> arranged side by side along an X axis direction (second direction) orthogonal to the Y axis direction (first direction). Positive electrode terminal <NUM> and negative electrode terminal <NUM> are provided to be separated from each other in the X axis direction.

Battery case <NUM> has a rectangular parallelepiped shape and forms an external appearance of battery cell <NUM>. Battery case <NUM> includes: a case main body 120A that accommodates an electrode assembly (not shown) and an electrolyte solution (not shown); and a sealing plate 120B that seals an opening of case main body 120A. Sealing plate 120B is joined to case main body 120A by welding.

Battery case <NUM> has an upper surface <NUM>, a lower surface <NUM>, a first side surface <NUM>, a second side surface <NUM>, and two third side surfaces <NUM>.

Upper surface <NUM> is a flat surface orthogonal to a Z axis direction (third direction) orthogonal to the Y axis direction and the X axis direction. Electrode terminals <NUM> are disposed on upper surface <NUM>. Lower surface <NUM> faces upper surface <NUM> along the Z axis direction.

Each of first side surface <NUM> and second side surface <NUM> is constituted of a flat surface orthogonal to the Y axis direction. Each of first side surface <NUM> and second side surface <NUM> has the largest area among the areas of the plurality of side surfaces of battery case <NUM>. Each of first side surface <NUM> and second side surface <NUM> has a rectangular shape when viewed in the Y axis direction. Each of first side surface <NUM> and second side surface <NUM> has a rectangular shape in which the X axis direction corresponds to the long-side direction and the Z axis direction corresponds to the short-side direction when viewed in the Y axis direction.

The plurality of battery cells <NUM> are stacked such that first side surfaces <NUM> of battery cells <NUM>, <NUM> adjacent to each other in the Y direction face each other and second side surfaces <NUM> of battery cells <NUM>, <NUM> adjacent to each other in the Y axis direction face each other. Thus, positive electrode terminals <NUM> and negative electrode terminals <NUM> are alternately arranged in the Y axis direction in which the plurality of battery cells <NUM> are stacked.

Gas-discharge valve <NUM> is provided in upper surface <NUM>. When the temperature of battery cell <NUM> is increased (thermal runaway) and internal pressure of battery case <NUM> becomes more than or equal to a predetermined value due to gas generated inside battery case <NUM>, gas-discharge valve <NUM> discharges the gas to outside of battery case <NUM>.

<FIG> is a perspective view of battery module <NUM>. As shown in <FIG>, battery module <NUM> includes battery cells <NUM>, separators <NUM>, restraint members <NUM>, and end plates <NUM>.

Battery cells <NUM> and separators <NUM> alternately arranged along the Y axis direction (first direction) are pressed by end plates <NUM> and are restrained between two end plates <NUM>.

End plates <NUM> are disposed at both ends in the Y axis direction. Each of end plates <NUM> is fixed to a base such as a case that accommodates battery module <NUM>. Restraint member <NUM> connects two end plates <NUM> to each other to restrain the plurality of battery cells <NUM> and separators <NUM> along the Y axis direction.

Restraint member <NUM> is fixed to end plates <NUM> with a compression force in the Y axis direction being exerted to the stack of battery cells <NUM>, separators <NUM> and end plates <NUM>, and then the compression force is released, with the result that tensile force acts on restraint member <NUM> that connects two end plates <NUM> to each other. As a reaction thereto, restraint members <NUM> press two end plates <NUM> in directions of bringing them closer to each other. In this way, battery module <NUM> is constructed.

By accommodating battery module <NUM> in a pack case, a battery pack is formed (cell-module-pack structure). Instead of this, a structure (cell-to-pack structure) may be employed in which battery assembly 1A shown in <FIG> is directly supported by a wall surface of the pack case.

<FIG> is a cross sectional view of each separator <NUM>. <FIG> is a diagram showing a state in which separator <NUM> shown in <FIG> is disposed between battery cells <NUM>. <FIG> is a top view of a first member <NUM>, and <FIG> is a top view of a second member <NUM>.

As shown in <FIG>, separator <NUM> includes first member <NUM> and second member <NUM>. First member <NUM> and second member <NUM> are placed on each other in the stacking direction (Y axis direction) of the plurality of battery cells <NUM>.

First member <NUM> includes a base portion <NUM> and a plurality of protrusions <NUM> protruding from base portion <NUM> in the Y axis direction. Each of protrusions <NUM> has a tapered shape having a diameter that is decreased toward its tip. In the example of <FIG>, base portion <NUM> and the plurality of protrusions <NUM> are integrally molded, but base portion <NUM> and protrusions <NUM> provided as separate members may be joined together.

Second member <NUM> is provided with hole portions <NUM>. Protrusions <NUM> of first member <NUM> are inserted into hole portions <NUM> of second member <NUM>. As a result, second member <NUM> is located between the plurality of protrusions <NUM>. As an example, the outer size of first member <NUM> and the outer size of second member <NUM> are substantially equal to each other.

Typically, as shown in <FIG>, in a state in which separator <NUM> is detached from battery assembly 1A, a protruding height of each of the plurality of protrusions <NUM> is larger than a thickness of second member <NUM>. After separators <NUM> each shown in <FIG> are prepared, the plurality of battery cells <NUM> and separators <NUM> are alternately arranged in the Y axis direction and are restrained along the Y axis direction. On this occasion, as shown in <FIG>, protrusions <NUM> of first member <NUM> are compressed together with second member <NUM>.

First member <NUM> is an elastic body. First member <NUM> can be composed of, for example, a silicone rubber, a fluororubber, a urethane rubber, a natural rubber, a styrene-butadiene rubber, a butyl rubber, an ethylene propylene rubber (EPM, EPDM), a butadiene rubber, an isoprene rubber, a norbornene rubber, or the like (is preferably composed of the silicone rubber or fluororubber).

In any case, first member <NUM> is composed of a material having an elastic modulus of about <NUM> MPa or more and <NUM> MPa or less as measured by the following method.

Further, it is preferable to form first member <NUM> using such a material that a sample thickness measured by a micrometer with resting of two hours after the pressure application test (after unloading) is about -<NUM>% or less from an initial state (before the pressure application test).

Second member <NUM> has such a property that second member <NUM> has a higher heat insulation property than that of first member <NUM> and is more likely to be deformed than first member <NUM>.

Second member <NUM> can be composed of a foamed resin. Second member <NUM> can be composed of, for example, an inorganic fiber (ceramic fiber or the like), a molding of an inorganic fiber and an organic binder, an inorganic filler and an organic binder, a foamed silicon sheet having a space therein, or the like.

Second member <NUM> preferably has a heat insulation property of about <NUM> W/mK or less, and more preferably has a heat insulation property of about <NUM> W/mK or less.

As shown in <FIG>, since separator <NUM> has the two-layer structure with first member <NUM> having a higher elastic modulus and second member <NUM> having a higher heat insulation property, both deformation absorption property and heat insulation property in separator <NUM> can be achieved.

<FIG> is a cross sectional view of a separator 200A according to a comparative example. <FIG> is a diagram showing a state in which separator 200A shown in <FIG> is disposed between battery cells <NUM>.

In separator 200A shown in <FIG> and <FIG>, a two-layer structure is disclosed in which a first member 210A having a higher elastic modulus and a second member 220A having a higher heat insulation property are placed on each other.

Since separator 200A employs the two-layer structure with first member 210A and second member 220A, a total of a tolerance of the thickness of first member 210A and a tolerance of the thickness of second member 220A is a tolerance of the thickness of separator 200A.

Thus, with the total of the tolerances of the thicknesses of the two members, the tolerance of the thickness of the separator becomes larger than that of a separator constituted of one member. As a result, a restraint load on battery cells <NUM> and separator 200A becomes large depending on the thickness of separator 200A even though design values of sizes of battery cells <NUM> in the stacking direction (Y axis direction) are the same. As a result, strength of a strength member in battery assembly 1A or battery module <NUM> needs to be improved, which can lead to increased weight and increased cost of battery module <NUM>.

On the other hand, in separator <NUM> according to the present embodiment, since the structure is employed in which second member <NUM> is provided between protrusions <NUM> of first member <NUM>, only the size tolerance of first member <NUM> of first member <NUM> and second member <NUM> needs to be managed, with the result that variation in the thickness of separator <NUM> becomes small as a whole. As a result, battery module <NUM> in which variation in reaction force acting on battery cell <NUM> is small is provided, thus contributing to reduced weight or reduced manufacturing cost of the battery module.

<FIG> is a top view of a separator <NUM> according to a modification. <FIG> is a cross sectional view along XI-XI in <FIG>.

In the modification shown in <FIG> and <FIG>, a foam having an air layer therein is used as each second member <NUM>. When preparing separator <NUM>, a resin is foamed in a recess <NUM> surrounded by a series of protrusions <NUM> of first member <NUM>. As a result, second member <NUM> composed of the foamed resin is formed between the plurality of protrusions <NUM> of first member <NUM>.

Next, a relation between the elastic modulus of first member <NUM> and the elastic modulus of second member <NUM> will be described with reference to <FIG>.

<FIG> is a diagram showing deformation when a load is applied to first member <NUM> of separator <NUM>. <FIG> is a diagram showing deformation when a load is applied to second member <NUM> of separator <NUM>.

As shown in <FIG>, when first member <NUM> having a thickness T under application of no load is fed with a load F1, protrusions <NUM> are mainly compressed and deformed, with the result that the thickness of first member <NUM> is decreased to T'.

As shown in <FIG>, when second member <NUM> having a thickness S under application of no load is fed with a load F2, second member <NUM> is compressed and deformed, with the result that the thickness of second member <NUM> is decreased to S'.

<FIG> is a graph showing an exemplary load-thickness curve of each of first member <NUM> and second member <NUM> in separator <NUM>. In <FIG>, a curve <NUM> is an exemplary load-thickness curve of first member <NUM> in separator <NUM>, and each of curves 20A, 20B is an exemplary load-thickness curve of second member <NUM> in separator <NUM>. In <FIG>, the vertical axis represents a load acting on each of first member <NUM> and the second member in separator <NUM>, and the horizontal axis represents the thickness of separator <NUM> (first member <NUM>).

As indicated by curves <NUM>, 20A, 20B in <FIG>, each of the loads acting on first member <NUM> and second member <NUM> in separator <NUM> is increased as the thickness of separator <NUM> (first member <NUM>) is decreased.

According to the invention, the load (elastic force of first member <NUM>) acting on first member <NUM> is larger than the load (elastic force of second member <NUM>) acting on second member <NUM> in a region (region of T50 to T90 in <FIG>) in which at least the thickness of separator <NUM> (first member <NUM>) is <NUM>% to <NUM>% of thickness T that is under application of no load (the same applies to each example of curves 20A, 20B). More preferably, the load (elastic force of first member <NUM>) acting on first member <NUM> is larger than the load (elastic force of second member <NUM>) acting on second member <NUM> in a region (region of T40 to T95 in <FIG>) in which at least the thickness of separator <NUM> (first member <NUM>) is <NUM>% to <NUM>% of thickness T that is under application of no load (the same applies to each example of curves 20A, 20B).

In this way, second member <NUM> can be provided so as not to affect the deformation absorption property of first member <NUM> excessively within a practical use range of separator <NUM>.

Claim 1:
A battery assembly comprising:
a plurality of battery cells (<NUM>) arranged in a first direction (Y);
a separator (<NUM>) disposed between the plurality of battery cells (<NUM>); and
a restraint member (<NUM>) that restrains the plurality of battery cells (<NUM>) and the separator (<NUM>) along the first direction (Y), wherein:
- the separator (<NUM>) includes
a first member (<NUM>) including a base portion (<NUM>) and a plurality of protrusions (<NUM>) each protruding from the base portion (<NUM>) in the first direction (Y), and
a second member (<NUM>) disposed between the plurality of protrusions (<NUM>), the second member (<NUM>) having a higher heat insulation property than a heat insulation property of the first member (<NUM>),
- -in a state in which the separator (<NUM>) is detached from the battery assembly (<NUM>), a protruding height of each of the plurality of protrusions (<NUM>) is larger than a thickness of the second member (<NUM>),
characterised in that the first member (<NUM>) and the second member (<NUM>) are selected such that:
- the first member (<NUM>) is composed of a material having an elastic modulus of about <NUM> MPa or more and <NUM> MPa or less,
- the second member (<NUM>) has a lower elastic modulus than the first member (<NUM>), and
- when a load is applied to the separator (<NUM>) and its thickness is reduced to between <NUM>% and <NUM>% of its thickness (T) in an unloaded state, the separator (<NUM>) undergoes elastic deformation, and the load acting on the first member (<NUM>) is greater than the load acting on the second member (<NUM>).