Patent Description:
The present invention relates to the field of battery, and particularly relates to a battery pack and a vehicle.

A secondary battery has the advantages of high energy density, long working life, energy saving, environmental protection and the like, and has been widely applied to various fields, such as new energy vehicle, energy storage power station and the like.

A battery pack generally comprises a box assembly and a battery module accommodated in the box assembly; the battery module comprises batteries arranged sequentially. In known technology, the battery module fixes the batteries by providing an end plate and a side plate, the end plate is fixed to the box assembly via a bolt, and the batteries of the battery module are not directly connected with the box assembly, so the overall stiffness of the battery module is low. When the battery module vibrates, the battery positioned at middle of the battery module can not be easily fixed completely due to insufficient clamping force, thereby resulting in safety risk. Related technologies are known from <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

In view of the problem existing in the background, an object of the present invention is to provide a battery pack and a vehicle, which can ensure dynamics performance of the battery and connecting strength between the battery and the box assembly. The present invention is defined in the independent claim.

In order to achieve the above object, the present invention provides a battery pack as defined in claim <NUM> and a vehicle as defined in claim <NUM>. Preferred embodiments are defined in dependent claims <NUM>-<NUM> and <NUM>.

The present invention has the following beneficial effects: in the present invention, the first batteries are fixed to the box assembly via the first adhesive member, thereby increasing the connecting strength between the battery module and the box assembly, achieving the fixation of the first batteries, and reducing the safety risk when the battery pack vibrates. In the present invention, the area A of the first surface and the elastic modulus which is defined as Young's modulus B of the first adhesive member are comprehensively considered, when "<NUM><NUM>/MPa≤A/B≤<NUM><NUM>/MPa" is satisfied, it can ensure the dynamics performance of the first battery and the connecting strength between the first battery and the box assembly.

Reference numerals in figures are represented as follows:.

To make the object, technical solutions and advantages of the present invention more apparent, hereinafter the present invention will be further described in detail in combination with the accompanying figures and the embodiments. It should be understood that the specific embodiments described herein are merely used to explain the present invention but are not intended to limit the present invention.

The present invention provides a vehicle, the vehicle comprises a vehicle body and a battery pack, the battery pack is provided to the vehicle body. The vehicle is a new energy vehicle, for example, the vehicle may be a pure electric vehicle, hybrid power vehicle or extended range vehicle. The vehicle body is provided with a drive motor, the drive motor is electrically connected with the battery pack, the battery pack supplies electric energy, and the drive motor is connected with a wheel on the vehicle body via a transmission mechanism, thereby driving the vehicle. Preferably, the battery pack may be horizontally provided to a bottom of the vehicle body.

<FIG> is an exploded view of a battery pack according to the present invention. The battery pack comprises a battery module <NUM>, a box assembly <NUM> and a first adhesive member <NUM>.

The box assembly <NUM> comprises an upper box cover <NUM> and a lower box body <NUM>. In <FIG>, the upper box cover <NUM> and the lower box body <NUM> are separated. The upper box cover <NUM> and the lower box body <NUM> are connected together in sealing, and an accommodating cavity is formed between the upper box cover <NUM> and the lower box body <NUM>. The upper box cover <NUM> and the lower box body <NUM> may be made of aluminum, aluminum alloy or other metal.

The battery module <NUM> is accommodated in the accommodating cavity of the box assembly <NUM>. The battery module <NUM> may be provided as one or plurality in number. When the battery module <NUM> is provided as plurality in number, the plurality of the battery modules <NUM> may be arranged in the length direction X or arranged in the width direction Y. The battery module <NUM> comprises first batteries <NUM> arranged sequentially in the horizontal direction. The first batteries <NUM> are secondary batteries which can charge and discharge repeatedly. The first batteries <NUM> may be electrically connected via busbars.

The battery module <NUM> further comprises two end plates not shown in the figures and a strap not shown in the figures. The two end plates are respectively provided at two ends of the first batteries <NUM> in the horizontal direction, the strap encircles the first batteries <NUM> and the two end plates. The end plate may be made of metal material, such as aluminum, aluminum alloy or the like, or made from insulation material.

Referring to <FIG>, the first battery <NUM> comprises an electrode assembly <NUM>, a case <NUM> and a cap assembly <NUM>. The electrode assembly <NUM> is received in the case <NUM>, and the electrode assembly <NUM> comprises a first electrode plate 111a, a second electrode plate 111b and a separator 111c provided between the first electrode plate 111a and the second electrode plate 111b.

The case <NUM> may be made of metal material or composite material. For example, in an embodiment, the case <NUM> is integrally made of metal material, such as aluminum, aluminum alloy, nickel-plated steel or the like. Alternatively, in another embodiment, the case <NUM> may comprises a base and an insulation layer, the base is made of metal material, such as aluminum, aluminum alloy, nickel-plated steel or the like, the insulation layer is provided to an outer surface of the base by coating, bonding or the like; at this time, the base made of metal material can ensure the strength of the case <NUM>, and the insulation layer can promote the insulating performance of the case <NUM>.

The case <NUM> may have a hexahedron shape or other shape. The case <NUM> has an opening, and the electrode assembly <NUM> can be placed into the case <NUM> via the opening. In an embodiment, the opening is positioned at an end of the case <NUM> in the width direction Y.

The cap assembly <NUM> comprises a cap plate 113a and an electrode terminal 113b, the electrode terminal 113b is provided to the cap plate 113a. The cap plate 113a may be made of metal material, such as aluminum, aluminum alloy or the like, a dimension of the cap plate 113a is matched with a dimension of the opening of the case <NUM>. The cap plate 113a is connected to the case <NUM> by welding and covers the opening of the case <NUM>, thereby sealing the electrode assembly <NUM> in the case <NUM>.

The electrode terminal 113b is fixed with the cap plate 113a by welding, riveting or the like. The electrode terminal 113b is provided as two in number and the two electrode terminals 113b are respectively electrically connected with the first electrode plate 111a and the second electrode plate 111b.

In the electrode assembly <NUM>, one of the first electrode plate 111a and the second electrode plate 111b is a positive electrode plate, the other one of the first electrode plate 111a and the second electrode plate 111b is a negative electrode plate, and the separator 111c is an insulator provided between the positive electrode plate and the negative electrode plate. For example, the first electrode plate 111a is the positive electrode plate, the first electrode plate 111a comprises a first current collector and a first active material layer coated on a surface of the first current collector; the first current collector may be an aluminum foil, the first active material layer comprises ternary material, lithium manganese oxide or lithium iron phosphate. The second electrode plate 111b is the negative electrode plate, and the second electrode plate 111b comprises a second current collector and a second active material layer coated on a surface of the second current collector; the second current collector may be copper foil, the second active material layer comprises graphite or silicon.

As shown in <FIG>, in an embodiment, the electrode assembly <NUM> is a winding structure. Specifically, the first electrode plate 111a, the second electrode plate 111b and the separator 111c are belt-shaped structures. The first electrode plate <NUM>11a, the separator 111c and the second electrode plate 111b are stacked sequentially and wound to two or more turns to form the electrode assembly <NUM>, and the electrode assembly <NUM> is in a flat shape. When preparing the electrode assembly <NUM>, the electrode assembly <NUM> is wound to a hollow cylindrical structure, and then the electrode assembly <NUM> is pressed to a flat shape after winding. <FIG> is a schematic view showing a profile of the electrode assembly <NUM>. The outer surface of the electrode assembly <NUM> comprises two flat surfaces 111d and two narrow surfaces 111e, the two flat surfaces 111d face each other in the vertical direction Z, the two narrow surfaces 111e face each other in the length direction X. The flat surface 111d is substantially parallel to a winding axis of the electrode assembly <NUM>. The flat surface 111d is a relatively flat surface and not required to be an absolute plane. At least a part of the narrow surface 111e is in the shape of arc. The flat surface 111d is flat relative to the narrow surface 111e, and an area of the flat surface 111d is larger than an area of the narrow surface 111e.

As shown in <FIG>, in another embodiment, the electrode assembly <NUM> is a stacking structure. Specifically, the electrode assembly <NUM> comprises first electrode plates 111a and second electrode plates 111b; the separator 111c is provided between the first electrode plate 111a and the second electrode plate 111b. The first electrode plates 111a and the second electrode plates 111b are stacked in the vertical direction Z. In the stacking structure, the first electrode plate 111a and the second electrode plate 111b are in the shape of plate and substantially perpendicular to the vertical direction Z.

In the charge process or discharge process of the electrode assembly <NUM>, the electrode plate will expand along its thickness direction. In the electrode assembly <NUM> having winding structure, an expanding force along a direction perpendicular to the flat surface <NUM> is largest; in the electrode assembly <NUM> having stacking structure, an expanding force along a stacking direction of the first electrode plates 111a and the second electrode plates 111b is largest. This shows that whether the electrode assembly <NUM> is a winding structure or a stacking structure, the largest expanding force applied to the case <NUM> by the electrode assembly <NUM> is along a direction substantially parallel to the vertical direction Z. In other words, in the horizontal direction, the electrode assembly <NUM> applies a smaller expanding force to the case <NUM>. In the present invention, the first batteries <NUM> are arranged in the length direction X, so even though the expanding forces of all the electrode assemblies <NUM> in the length direction X are accumulated to form a composite force, and the composite force will not be excessive, thereby reducing a risk that the first batteries <NUM> is crushed.

The box assembly <NUM> has a connection portion, and the connection portion is positioned at a side of the battery module <NUM> in the vertical direction Z. An outer surface of the case <NUM> comprises a first surface 112a, and the first surface 112a is connected with the connection portion via the first adhesive member <NUM>. The first surface 112a is positioned at an end of the case <NUM> close to the connection portion, and the first adhesive member <NUM> may be provided between the first surface 112a and the connection portion and connected with the first surface 112a and the connection portion. The first batteries <NUM> and the box assembly <NUM> are connected via the first adhesive member <NUM>.

In an embodiment, a bottom wall of the lower box body <NUM> may act as the connection portion, the first adhesive member <NUM> is provided to the bottom wall of the lower box body <NUM>; at this time, the first batteries <NUM> can be provided close to the bottom wall of the lower box body <NUM>, the first surface 112a is connected with the bottom wall of the lower box body <NUM> via the first adhesive member <NUM>.

In another embodiment, a top wall of the upper box cover <NUM> also can act as the connection portion, the first adhesive member <NUM> is provided to the top wall of the upper box cover <NUM>; at this time, the first batteries <NUM> can be provided close to the top wall of the upper box cover <NUM>, and the first surface 112a is connected with the top wall of the upper box cover <NUM> via the first adhesive member <NUM>.

In still another embodiment, the box assembly <NUM> further comprises a fixing plate <NUM>, and the fixing plate <NUM> also can act as the connection portion. The fixing plate <NUM> is accommodated in the accommodating cavity and positioned at an upper side of the battery module <NUM> in the vertical direction Z, and the fixing plate <NUM> is fixed with the upper box cover <NUM> via a fastener. The first adhesive member <NUM> is provided on the fixing plate <NUM>, and the first surface 112a is connected with the fixing plate <NUM> via the first adhesive member <NUM>. A gap is kept between the fixing plate <NUM> and the top wall of the upper box cover <NUM>, and the gap can avoid deformation of the upper box cover <NUM> due to expansion of the first batteries <NUM> in the vertical direction Z.

In further another embodiment, referring to <FIG>, the fixing plate <NUM> is accommodated in the accommodating cavity and positioned at a lower side of the battery module <NUM> in the vertical direction Z, and the fixing plate <NUM> can be fixed with the lower box body <NUM> via a fastener. The first adhesive member <NUM> is provided on the fixing plate <NUM>, and the first surface 112a is connected with the fixing plate <NUM> via the first adhesive member <NUM>. A gap is kept between the fixing plate <NUM> and the bottom wall of the lower box body <NUM>, and the gap can avoid deformation of the lower box body <NUM> due to expansion of the first batteries <NUM> in the vertical direction Z.

The first adhesive member <NUM> is a solid adhesive, the adhesive is liquid or paste before solidification, the adhesive is coated between the connection portion and the first surface 112a of the first battery <NUM> and solidifies, thereby firmly connecting the first battery <NUM> and the box assembly <NUM>. The adhesive is one or more selected from a group consisting of epoxy resin, polyurethane and acrylic resin.

In the present invention, the first batteries <NUM> are fixed to the box assembly <NUM> via the first adhesive member <NUM>, thereby increasing the connecting strength between the battery module <NUM> and the box assembly <NUM>, achieving the fixation of the first batteries <NUM>, and reducing the safety risk when the battery pack vibrates.

In the charge process or discharge process of the electrode assembly <NUM>, the electrode assembly <NUM> applies an expanding force to a circumferential wall of the case <NUM>, and a first side wall of the case <NUM> corresponding to the first surface 112a is subjected to a largest expanding force and deforms most easily. Edge region of the first side wall corresponding to the first surface 112a is bound by other side walls, and an central region of the first side wall is subjected to a smaller bound force, so when the first side wall is subjected to the expanding force, the central region of the first side wall will bulge. Correspondingly, referring to <FIG>, a height difference h will exist between the central region of the first surface 112a and the edge region of the first surface 112a.

An area of the first surface 112a is defined as A. The larger the value of A is, the smaller the bound force applied to the central region of the first side wall is, and the more the deformation of the central region of the first side wall is, that is, the larger the value of h is. The smaller the value of A is, the larger the bound force applied to the central region of the first side wall is, and the less the deformation of the central region of the first side wall is, that is, the smaller the value of h is.

When the electrode assembly <NUM> expands, the first side wall applies a reaction force to the electrode assembly <NUM>. The larger the value of A is, the more the deformation of the first side wall is; the first side wall can release the expanding force by deformation, correspondingly, the reaction force applied to the electrode assembly <NUM> by the first side wall can be decreased. The smaller the value of A is, the less the deformation of the first side wall is, and the lower the capability of the first side wall to release the expanding force is; correspondingly, the first side wall will apply a larger reaction force to the electrode assembly <NUM>. When the reaction force applied to the electrode assembly <NUM> is excessively large, an electrolyte between the first electrode plate 111a and the second electrode plate 111b is easily extruded out, which leads to the infiltration capability of partial region being reduced, the lithium-ion being unable to pass through the separator 111c and causes the lithium precipitation.

An elastic modulus which is defined as the Young's modulus of the first adhesive member <NUM> is defined as B. The larger the value of B is, the higher the stiffness of the first adhesive member <NUM> is, and the less easily the first adhesive member <NUM> deforms when it is subjected to force. The smaller the value of B is, the lower the stiffness of the first adhesive member <NUM> is, and the more easily the first adhesive member <NUM> deforms when it is subjected to force. In addition, to a certain extent, the value of B is directly proportional to the bonding strength of the first adhesive member <NUM>.

When the electrode assembly <NUM> expands, the first side wall will deform under the influence of the expanding force. At the same time, referring to <FIG>, the first surface 112a will also press the first adhesive member <NUM>.

The larger the value of B is, the less easily the first adhesive member <NUM> deforms; the first adhesive member <NUM> is bonded with the first surface 112a, so the first adhesive member <NUM> will limit the deformation of the first surface 112a too. In other words, the larger the value of B is, the smaller the deformation of the first side wall is, the greater the reaction force applied to the electrode assembly <NUM> by the first side wall is, the more easily the electrolyte in the electrode assembly <NUM> is extruded out, and the higher a risk of lithium precipitation is.

The smaller the value of B is, the more easily the first adhesive member <NUM> deforms; in other words, the smaller the value of B is, the more the deformation of the first side wall is, the less the reaction force applied to the electrode assembly <NUM> by the first side wall is, and the lower a risk that the electrolyte is extruded out is. However, the easier the first surface 112a deforms, the larger the height difference h between the central region and the edge region is; referring to <FIG> and <FIG>, although a part of the first adhesive member <NUM> contacting the central region of the first surface 112a is pressed, a part of the first adhesive member <NUM> contacting the edge region of the first surface 112a is stretched easily. The smaller the value of B is, the lower the bonding strength of the first adhesive member <NUM> is; when the first adhesive member <NUM> is stretched, the first adhesive member <NUM> is easily separated from the first surface 112a or the connection portion, which leads to the connecting strength between the first battery <NUM> and the connection portion being lower, and results in a risk that the first battery <NUM> is detached from the box assembly <NUM>.

In conclusion, the area A of the first surface 112a and the elastic modulus B of the first adhesive member <NUM> have an significant influence on the dynamics performance of the first battery <NUM> and the connecting strength between the first battery <NUM> and the box assembly <NUM>. In the present invention, the area A of the first surface 112a and the elastic modulus B of the first adhesive member <NUM> are comprehensively considered, when "<NUM><NUM>/MPa≤A/B≤<NUM><NUM>/MPa" is satisfied, it can ensure the dynamics performance of the first battery <NUM> and the connecting strength between the first battery <NUM> and the box assembly <NUM>.

Specifically, if "A/B<<NUM><NUM>/MPa", the value of A is smaller and the value of B is larger. When the electrode assembly <NUM> of the first battery <NUM> expands, because the value of A is smaller, the deformation capability of the first side wall is limited; and because the value of B is larger, the first adhesive member <NUM> will further limit the deformation of the first side wall. At this time, the deformation of the first side wall is limited, so the first side wall will apply a larger reaction force to the electrode assembly <NUM>, the electrolyte in the electrode assembly <NUM> will be extruded out, which leads to the infiltration capability of partial region being reduced, the lithium-ion being unable to pass through the separator 111c and causes the lithium precipitation.

If "A/B><NUM><NUM>/MPa", the value of A is larger and the value of B is smaller. When the electrode assembly <NUM> of the first battery <NUM> expands, because the value of A is larger, the deformation of the first side wall is also more; correspondingly, the first surface 112a is easier to deform, and the height difference h between the central region of the first surface 112a and the edge region of first surface 112a is also larger. Because the value of B is smaller, the first adhesive member <NUM> can not effectively limit the deformation of the first surface 112a, which leads to the height difference h between the central region of the first surface 112a and the edge region of first surface 112a being excessive large, and a part of the first adhesive member <NUM> contacting the edge region of the first surface 112a being stretched more easily. When the first adhesive member <NUM> is stretched, the first adhesive member <NUM> is more easily separated from the first surface 112a or the connection portion, which leads to the connecting strength between the first battery <NUM> and the connection portion being lower, and results in a risk that the first battery <NUM> is detached from the box assembly <NUM>.

Preferably, the area A of the first surface 112a and the elastic modulus B of the first adhesive member <NUM> satisfy a relationship: <NUM><NUM>/MPa≤A/B≤<NUM><NUM>/MPa.

The area A of the first surface 112a is <NUM><NUM>-<NUM><NUM>, preferably <NUM><NUM>-<NUM><NUM>. The elastic modulus B of the first adhesive member <NUM> is 100Mpa-1000Mpa, preferably 150MPa-800MPa.

A thickness of the first adhesive member <NUM> is defined as C. When the electrode assembly <NUM> of the first battery <NUM> expands, the part of the first adhesive member <NUM> contacting the edge region of the first surface 112a is stretched easily. The larger the value of C is, the greater a length of the first adhesive member <NUM> capable of being stretched before the first adhesive member <NUM> is separated from the first surface 111a or the connection portion is; otherwise, the smaller the value of C is, and the less the length of the first adhesive member <NUM> capable of being stretched is. In addition, the smaller the value of B is, the more easily the first adhesive member <NUM> is stretched.

When the electrode assembly <NUM> of the first battery <NUM> expands, if the value of B is smaller and the value of A is larger, the first surface 112a is easier to deform, the height difference h between the central region of the first surface 112a and the edge region of the first surface 112a is larger. At this time, the part of the first adhesive member <NUM> contacting the edge region of the first surface 112a needs to be stretched to a larger length, to avoid the first adhesive member <NUM> being separated from the first surface <NUM> or the connection portion. Therefore, the thickness C of the first adhesive member <NUM> needs to have a larger value.

When the electrode assembly <NUM> of the first battery <NUM> expands, if the value of B is larger and the value of A is smaller, the first surface 112a is less easy to deform, the height difference h between the central region of the first surface 112a and the edge region of the first surface 112a is smaller. At this time, the part of the first adhesive member <NUM> contacting the edge region of the first surface 112a will be stretched to a smaller length. Therefore, the thickness C of the first adhesive member <NUM> can has a smaller value, to decease the usage amount of the adhesive, reduce cost and improve energy density.

In conclusion, the elastic modulus B of the first adhesive member <NUM> and the thickness C of the first adhesive member <NUM> have an significant influence on the connecting strength between the first battery <NUM> and the box assembly <NUM>. In the present invention, the elastic modulus B of the first adhesive member <NUM> and the thickness C of the first adhesive member <NUM> are comprehensively considered, when a relationship, 2MPa·cm≤B·C≤500MPa·cm, is satisfied, it can ensure the connecting strength between the first battery <NUM> and the box assembly <NUM>.

If "B·C<2MPa·cm", both the value of B and the value of C are smaller, the first adhesive member <NUM> is easily separated from the first surface <NUM> or the connection portion. If "B·C>500MPa·cm", the value of C is larger, which results in waste of the adhesive, more inner space of the box assembly <NUM> being occupied.

The thickness C of the first adhesive member <NUM> is <NUM>-<NUM>, preferably <NUM>-<NUM>.

A roughness of the first surface 112a is <NUM>-<NUM>. If the roughness of the first surface 112a is smaller than <NUM>, the first surface 112a is excessively smooth, which is not beneficial for bonding the first surface 112a and the first adhesive member <NUM>, and reduces the connecting strength between the first surface 112a and the connection portion.

The case <NUM> is substantially in a shape of hexahedron. Specifically, referring to <FIG> and <FIG>, the case <NUM> further comprises a second surface 112b, two third surfaces 112c and a fourth surface 112d. The second surface 112b is positioned at an end of the case <NUM> away from the connection portion in the vertical direction Z, the second surface 112b and the first surface 112a face each other in the vertical direction Z. The two third surfaces 112c are respectively positioned at two ends of the case <NUM> in the length direction X and face each other in the length direction X. The fourth surface 112d is positioned at and end of the case <NUM> in the width direction Y.

Before the electrode assembly <NUM> expands, the first surface 112a and the second surface 112b are substantially planar surfaces perpendicular to the vertical direction Z, the two third surfaces 112c are substantially planar surfaces perpendicular to the length direction X, the fourth surface 112d is substantially planar surface perpendicular to the width direction Y. The first surface 112a, the third surface 112c and the fourth surface 112d are connected with each other via transition surfaces in the shape of arc. The second surface 112b, the third surface 112c and the fourth surface 112d are connected with each other via transition surfaces in the shape of arc.

Both of the area of the first surface 112a and an area of the second surface 112b are larger than an area of the third surface 112c. The electrode assembly <NUM> generates gas in the charge process or discharge process, and the gas will apply a force to the case <NUM>, thereby intensifying outward expansion of the case <NUM>. In an embodiment, both of the area of the first surface 112a and the area of the second surface 112b are lager than the area of the third surface 112c, and the first surface 112a and the second surface 112b face each other in the vertical direction Z, so a direction of a largest force applied to the case <NUM> by the gas is along the vertical direction Z. Compared to known technology, it can further decrease the largest expanding force of the battery module <NUM>.

A contacting area between the first adhesive member <NUM> and the first surface 112a is defined as S1, a total area of the outer surface of the case <NUM> is defined as S2, a value of S1/S2 is larger than <NUM>%. The total area of the outer surface of the case <NUM> is a sum of the area of the first surface 111a, the area of the second surface 111b, the areas of the two third surfaces 111c, an area of the fourth surface 111d and areas of the transition surfaces in the shape of arc.

The larger a value of S1 is, the greater a bonding force between the first adhesive member <NUM> and the first battery <NUM> is; otherwise, the smaller the value of S1 is, the less the bonding force between the first adhesive member <NUM> and the first battery <NUM> is. The larger a value of S2 is, the larger a volume of the first battery <NUM> is, the larger a weight of the first battery <NUM> is, and the greater the bonding force the first battery <NUM> needs to have is; otherwise, the smaller the value of S2 is, the less the bonding force the first battery <NUM> needs to have is. In the present invention, the value of S1 and the value of S2 are comprehensively considered, when the value of S1/S2 is larger than <NUM>%, it can ensure the connecting strength between the first adhesive member <NUM> and the first battery <NUM>.

The battery module <NUM> further comprises second batteries <NUM> arranged sequentially in the horizontal direction, the second battery <NUM> and the first battery <NUM> are stacked in the vertical direction Z, and the second battery <NUM> is positioned at a side of the first battery <NUM> close to the second surface 112b. The second battery <NUM> and the first battery <NUM> are the same battery.

A dimension of the battery module <NUM> in the horizontal direction is larger than a dimension of the battery module <NUM> in the vertical direction Z. In the present invention, it can reduce a number of layers of the batteries stacked in the vertical direction Z, so as to decrease the largest expanding force of the battery module <NUM>, and avoid the batteries being crushed. In addition, a height dimension of a chassis of the vehicle body is limited, so the battery module <NUM> preferably has a smaller dimension in the vertical direction Z.

Referring to <FIG>, the battery pack further comprises a second adhesive member <NUM>, and the second adhesive member <NUM> connects the second surface 112b and the second battery <NUM>. The second adhesive member <NUM> is provided between the second surface 112b and the second battery <NUM>, and bonds the first battery <NUM> and the second battery <NUM> together. The second adhesive member <NUM> is an adhesive.

An area of the second surface 112b is defined as D, and an elastic modulus of the second adhesive member <NUM> is defined as E. In the present invention, the area D of the second surface 112b is substantially same as the area A of the first surface 112a. The second adhesive member <NUM> and the first adhesive member <NUM> can use the same adhesive, the elastic modulus E of the second adhesive member <NUM> is substantially same as the elastic modulus B of the first adhesive member <NUM>. Preferably, <NUM><NUM>/MPa ≤D/E≤ <NUM><NUM>/MPa.

Referring to <FIG> and <FIG>, the battery pack further comprises a third adhesive member <NUM>, the third adhesive member <NUM> bonds the third surfaces 112c of two adjacent first batteries <NUM>. A connecting area between the third adhesive member <NUM> and the third surface 112c is defined as S3, an area of the third surface 112c is defined as S4, and the value of S3/S4 is <NUM>-<NUM>. If the value of S3/S4 is smaller than <NUM>, the connecting strength between the third adhesive member <NUM> and the third surface 112c will be poor; on the premise that the connecting strength is satisfied, it can decrease the value of S3 and save adhesive; therefore, the value of S3/S4 is preferably smaller than <NUM>.

Hereinafter the present invention will be further described in detail in combination with the examples.

A battery pack of an example <NUM> could be prepared according to the following steps:.

In addition, it could adjust the thickness C of the first adhesive member <NUM> by changing the coated thickness of the adhesive in step (vii), and it could adjust the elastic modulus B of the first adhesive member <NUM> by changing the component of the adhesive. After step (viii), it could cut a part of the first adhesive member <NUM>, and measure the elastic modulus B of the first adhesive member <NUM> by using a DMA-Q800 detector. A thickness of the battery in a direction perpendicular to the first surface 111a was <NUM>.

Battery packs of examples <NUM>-<NUM> and battery packs of comparative examples <NUM>-<NUM> all could be prepared in accordance with the preparing method of the battery pack of the example <NUM>. The differences among the battery packs of the examples <NUM>-<NUM> and the battery packs of comparative examples <NUM>-<NUM> were the area A of the first surface 111a, the elastic modulus B of the first adhesive member <NUM> and the thickness C of the first adhesive member <NUM>. Specific parameters were shown in the table <NUM>.

Hereinafter test processes of the battery packs prepared in the examples <NUM>-<NUM> and the comparative examples <NUM>-<NUM> were described.

At <NUM>, the batteries prepared in the examples <NUM>-<NUM> and the comparative examples <NUM>-<NUM> were charged at a constant current of <NUM> C and discharged at a constant current of <NUM> C for <NUM> cycles. After <NUM> cycles of charge and discharge, the metal plate <NUM> was fixed to a jig <NUM> of a shear testing machine, and the battery was clamped by a detector <NUM>; then the detector <NUM> moved the battery at a speed of <NUM>/min along a direction parallel to the first adhesive member <NUM>, and the detector <NUM> would automatically generate values of pull forces and record a value F of pull force when the metal plate <NUM> was separated from the battery. The value of F/A was a shear strength. When the value of F/A was larger than 2MPa, it could satisfy battery's requirement of shear strength. The shear testing machine might be a microcomputer control electronic universal testing machine (type: MTS-CMT <NUM> or MTS-CMT4104-BZ).

At <NUM>, the batteries prepared in the examples <NUM>-<NUM> and the comparative examples <NUM>-<NUM> were charged at a constant current of <NUM> C and discharged at a constant current of <NUM> C for <NUM> cycles. After <NUM> cycles of charge and discharge, the second electrode plate 111b was disassembled from the battery, and the lithium precipitation of the second electrode plate was observed. A ratio of the lithium-precipitation area of the second electrode plate <NUM>1b to the total area of the second electrode plate 111b less than <NUM>% was considered to be slight lithium precipitation, a ratio of the lithium-precipitation area of the second electrode plate 111b to the total area of the second electrode plate 111b between <NUM>%-<NUM>% was considered to be moderate lithium precipitation, a ratio of the lithium-precipitation area of the second electrode plate 111b to the total area of the second electrode plate 111b more than <NUM>% was considered to be serious lithium precipitation.

In order to avoid the test of shear strength and the test of dynamics performance influencing each other, each example was provided as ten sets; five sets of each example were used for testing the shear strength, and the values of F/A obtained in the five sets were averaged; the other five sets of each example were used for testing dynamics performance, and the ratios obtained in the other five sets were averaged.

Referring to the examples <NUM>-<NUM> and the comparative examples <NUM>-<NUM>, when the value of A/B was smaller than <NUM><NUM>/MPa, the case <NUM> would apply a larger reaction force to the electrode assembly <NUM>, the electrolyte in the electrode assembly <NUM> would be extruded out, which lead to the infiltration capability of partial region being reduced, the lithium-ion being unable to pass through the separator 111c and caused a larger lithium precipitation area of the second electrode plate 111b. When the value of A/B was larger than or equal to <NUM><NUM>/MPa, it could effectively decrease the reaction force applied to the electrode assembly <NUM>, and promote the infiltration capability of the electrode assembly <NUM> and reduce the lithium precipitation area of the second electrode plate 111b.

Referring to the examples <NUM>-<NUM> and the comparative examples <NUM>-<NUM>, when the value of A/B was larger than <NUM><NUM>/MPa, the shear strength between the battery and the metal plate <NUM> was smaller than 2MPa, which could not satisfy the battery's requirement of shear strength. In an actual battery pack, if the shear strength between the battery and the box assembly <NUM> was smaller than 2MPa, when the battery pack vibrated, the battery was easily separated from the box assembly <NUM>. When the value of A/B was smaller than or equal to <NUM><NUM>/MPa, the shear strength between the battery and the metal plate <NUM> was larger than 2MPa, which satisfied the battery's requirement of shear strength.

According to the examples <NUM>-<NUM> and the comparative examples <NUM>-<NUM>, when "<NUM><NUM>/MPa≤A/B≤<NUM><NUM>/MPa", it could ensure the dynamics performance of the battery and the connecting strength between the battery and the box assembly <NUM> at the same time.

Referring to the examples <NUM>-<NUM>, when the value of area A of the first surface 111a and the value of thickness C of the first adhesive member <NUM> were constant, by changing the elastic modulus B of the first adhesive member <NUM>, it could adjust the shear strength between the battery and the metal plate <NUM>. According to the examples <NUM>-<NUM>, when the value of area A and the value of thickness C were constant, the value of B was substantially directly proportional to the shear strength (the value of F/A).

Referring to the example <NUM> and the examples <NUM>-<NUM>, when the value of the elastic modulus B of the first adhesive member <NUM> and the value of the thickness C of the first adhesive member <NUM> were constant, by changing the area A of the first surface <NUM>1a, it could adjust the shear strength between the battery and the metal plate <NUM>. According to example <NUM> and examples <NUM>-<NUM>, when the value of the elastic modulus B and the value of thickness C were constant, the value of A was substantially inversely proportional to the shear strength (the value of F/A).

Referring to the example <NUM> and the examples <NUM>-<NUM>, when the value of area A of the first surface 111a and the value of the elastic modulus B of the first adhesive member <NUM> were constant, by changing the thickness C of the first adhesive member <NUM>, it could adjust the shear strength between the battery and the metal plate <NUM>. According to the example <NUM> and the examples <NUM>-<NUM>, when the value of the area A and the value of the elastic modulus B were constant, the value of C was substantially directly proportional to the shear strength (the value of F/A).

Referring to the comparative examples <NUM>-<NUM>, when the value of A/B was larger than <NUM><NUM>/MPa, the shear strength between the battery and metal plate <NUM> was insufficient. However, according to the comparative examples <NUM>-<NUM>, by increasing the value of C, it might improve the shear strength between the battery and the metal plate <NUM>.

Claim 1:
A battery pack, comprising a battery module (<NUM>), a box assembly (<NUM>) and a first adhesive member (<NUM>);
the box assembly (<NUM>) having an accommodating cavity, the battery module (<NUM>) being positioned in the accommodating cavity of the box assembly (<NUM>);
the battery module (<NUM>) comprising first batteries (<NUM>) arranged sequentially in a horizontal direction;
the first battery (<NUM>) comprising an electrode assembly (<NUM>) and a case (<NUM>), and the electrode assembly (<NUM>) being received in the case (<NUM>);
the electrode assembly (<NUM>) comprising a first electrode plate (111a), a second electrode plate (<NUM>1b) and a separator (111c) provided between the first electrode plate (111a) and the second electrode plate (<NUM>1b);
the electrode assembly (<NUM>) being a winding structure and in a flat shape, and the electrode assembly (<NUM>) comprising two flat surfaces (111d), the two flat surfaces (111d) facing each other in a vertical direction (Z); or, the electrode assembly (<NUM>) being a stacking structure, the first electrode plate (111a), the separator (<NUM>1c) and the second electrode plate (111b) being stacked in the vertical direction (Z);
the box assembly (<NUM>) having a connection portion, and the connection portion being positioned at a side of the battery module (<NUM>) in the vertical direction (Z);
an outer surface of the case (<NUM>) comprising a first surface (112a), and the first surface (112a) being connected with the connection portion via the first adhesive member (<NUM>);
an area A of the first surface (112a) and an elastic modulus B of the first adhesive member (<NUM>) satisfying a relationship: <MAT>
the elastic modulus B of the first adhesive member (<NUM>) is 150MPa-800MPa;
the elastic modulus B is Young's modulus.