Battery module

The disclosure relates to a battery module and the technical field of energy storage. The battery module comprises: a frame having an accommodation space; and a plurality of batteries successively arranged in the accommodation space in a thickness direction of the battery, wherein a partition is arranged between adjacent batteries, wherein the partition has a compressibility and a coefficient of compressibility δ1 at a pressure equal to or smaller than 2 MPa, which meets a relation C0×δ1≤A0×0.2, wherein C0 is an initial thickness of the partition, and A0 is an initial thickness of the battery.

CROSS REFERENCE

This application is a National Stage of International Application No. PCT/CN2018/119125 filed on Dec. 4, 2018, which claims priority to Chinese Patent Application No. 201811013207.7 entitled “Battery Module” filed on Aug. 31, 2018, both of which are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to the technical field of energy storage, and in particular to a battery module.

BACKGROUND

A battery can convert chemical energy into electrical energy. The battery has stable voltage and current. It offers reliable performance, is friend to environment, has simple structure and is convenient to carry. The battery has become a main power source for electric vehicle. For high power and long run time, more than one battery cells is assembled into a battery module, or even more than one battery modules are assembled into a battery pack.

During charge-discharge of the battery cell of the battery module, its electrode plate will expand its volume due to different lithiation and dilithiation states of active materials. The expansion of the electrode plate will inevitably cause stress in the battery cell. Such stress cannot be effectively released and thus will cause distortion of the battery core. Accordingly, the cycle performance of the battery will be adversely affected. Moreover, the volume expansion and distortion occurred during charge-discharge of the battery cell of the battery module will close inner gaps between layers, which will decrease permeability of electrolyte and thus degrade the cycle performance of the battery module. It is clear such situation cannot meet higher market requirement for cycle performance of battery module in recent years.

SUMMARY

In view of the above existing problems in the field, an object of the disclosure is to provide a battery module which has a good cycle performance.

In order to achieve the above object, the present disclosure discloses a battery module, comprising: a frame having an accommodation space; and a plurality of batteries successively arranged in the accommodation space in a thickness direction of the battery, wherein a partition is arranged between adjacent batteries, wherein the partition has a compressibility and a coefficient of compressibility δ1at a pressure equal to or smaller than 2 MPa, which meets a relation C0×δ1≤A0×0.2, wherein C0is an initial thickness of the partition, and A0is an initial thickness of the battery.

As compared to prior art, the disclosure provide following advantageous.

Since the battery module according to the disclosure comprises the partition having a compressibility between adjacent batteries, the partition can meet the expansion requirement of the battery, can act as a buffer to reduce the expansion rate of the batteries and effectively release stress in battery cells due to expansion of electrode plates. Moreover, the partition has a coefficient of compressibility δ1at a pressure equal to or smaller than 2 MPa, which meets a relation C0×δ1≤A0×0.2. Accordingly, the partition can prevent further expansion of the battery, thereby effectively restricting the stress within the battery cells and preventing excessive expansion of the battery cells. Therefore, the disclosure can effectively prevent the battery cells from being twisted, restrict the volume expansion of the battery cells, and ensure sufficient permeability of electrolyte in the battery cell such that the battery module has good cycle performance.

REFERENCE SIGNS IN THE DRAWINGS

DETAILED DESCRIPTION

In order to make the objects, technical solutions, and advantageous technical effects of the present disclosure more clear, the present disclosure will be further described in detail below with reference to the embodiments. It is to be understood that the embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In the description of the present disclosure, it should be noted that, unless otherwise stated, the meaning of “a plurality” is two or more; “no less than” and “no more than” shall be construed as including the number itself; the orientation or positional relationship indicated by the terms “upper”, “lower”, “inner”, “outer” and the like are orientation or positional relationship based on the orientation shown in the drawings; it is merely simplified for convenience of describing the present disclosure and simplification of the description, and does not indicate or imply that the pointed device or element must have a particular orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the present disclosure.

In the description of the present disclosure, it should be noted that, unless otherwise stated, the terms “installation”, “connected to”, and “connected with” are to be understood broadly, and may be, for example, a fixed connection, a disassemble connection, or an integral connection; they can be connected directly or indirectly through an intermediate medium. The specific meaning of the above terms in the present disclosure can be understood by the person skilled in the art according to actual circumstance.

The above summary of the present disclosure is not intended to describe each disclosed embodiment or every implementation. The following description more particularly exemplifies the exemplary embodiments. In many places throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. In each instance, the list is merely representative and should not be construed as exhaustive.

First, a battery module according to an aspect of the disclosure will be described. For better understanding of the disclosure, a battery module according to embodiments of the disclosure will be described below in detail with reference toFIGS. 1 to 8.

FIG. 1schematically shows an exploded structure of a battery module according to an embodiment of the disclosure. As shown inFIG. 1, a battery module100according to an embodiment of the disclosure comprises a frame110, batteries120and a partition130.

The frame110comprises two side plates111face to each other and spaced apart in a first direction and two end plates112face to each other and spaced apart in a second direction. The first direction intersects the second direction. Preferably, the first direction is perpendicular to the second direction. The adjacent side plates111connect with each other by the end plate112. That is to say, the two side plates111and the two end plates112enclose an accommodation space113. The batteries120are disposed successively in the accommodation space113along the second direction. The batteries120can be connected in series, in parallel or in mixed series-parallel arrangement. The second direction can be for example a thickness direction of the battery120. Referring toFIG. 2, the adjacent batteries120are spaced apart. That is to say, there is a gap121between the adjacent batteries120to accommodate expansion and deformation of the batteries120in actual use. The gap121has a width B, which is generally in a range of 1 mm to 4 mm, such as 1.3 mm to 3.6 mm, or for example 1.5 mm to 2.7 mm.

Furthermore, the partition130is provided in the gap121. The partition130has a compressibility and a coefficient of compressibility δ1at a pressure equal to or smaller than 2 MPa, which meets a relation C0×δ1≤A0×0.2, wherein C0is an initial thickness of the partition130, and A0is an initial thickness of the battery120. Referring toFIGS. 3 to 8, the partition130has a first surface131and a second surface132opposite to each other in its thickness direction. The first surface131is disposed to face one of the two adjacent batteries120, and the second surface132is disposed to face the other of the two adjacent batteries120. Preferably, the first surface131and the second surface132of the partition130can contact with the two adjacent batteries120respectively.

It will be appreciated that the first surface131and the second surface132are simply named to distinguish the two surfaces of the partition130in its thickness direction, and the disclosure is not limited to this. For example, the first surface131can be alternatively named as the second surface132, while the second surface132can be alternatively named as the first surface131.

It will also be appreciated that the frame110is not limited to the above structure. For example, the frame110can comprise two fixing members face to each other and spaced apart in the second direction, and the batteries120and the partitions130can be successively disposed between the two fixing members. The two fixing members can be connected through connecting members such that the batteries120and the partitions130are fixed between the two fixing members. The structure of the frame110is not specifically limited in the disclosure, so long as the frame110can receive and fix the batteries120and the partitions130.

In the disclosure, the coefficient of compressibility of the partition130means a ratio of a thickness change ΔC of the partition130and the initial thickness C0of the partition130. The initial thickness C0of the partition130means the thickness of the partition130in a new assembled battery module100. The initial thickness A0of the battery120means the thickness of the battery120in the new assembled battery module100.

For a battery module100after charge-discharge cycles, severe expansion will occur in the central regions on the main surface of the battery120, and there will be smaller expansion in the outside regions, especially there will be almost no expansion at the peripheral regions. In such battery module100, a thickness between the main surfaces of the battery120at its peripheral regions can be deemed as equal to the initial thickness A0of the battery120. The partition130will be barely compressed in its regions corresponding to the above thickness of the battery120, and a thickness of the partition130in these regions can be deemed as equal to the initial thickness C0of the partition130. A maximum thickness at the central regions on the main surfaces of the battery120can be considered as a thickness of the expanded battery120after charge-discharge cycles, and the partition130will have a thickness C10its regions corresponding to the maximum thickness of the battery120, wherein the thickness C10is a thickness of the partition130after being compressed by the batteries120after charge-discharge cycles. The thickness change ΔC of the partition130can be expressed as ΔC=C0−C10.

Since the battery module100according to embodiments of the disclosure comprises the partition130between adjacent batteries120, when an expansion force occurs within the battery120, the partition130can meet the expansion requirement of the battery120since it has compressibility. The partition130can act as a buffer to reduce the expansion rate of the batteries and effectively release stress in battery cells due to expansion of electrode plates. Moreover, the partition130has a coefficient of compressibility δ1at a pressure equal to or smaller than 2 MPa, which meets a relation C0×δ1≤A0×0.2. Accordingly, the partition130can prevent further expansion of the battery120, thereby effectively restricting the stress within the battery cells and preventing excessive expansion of the battery cells. Therefore, the disclosure can effectively prevent the battery cells from being twisted and restrict the volume expansion of the battery cells, such that the gaps between the positive and negative electrode plates, between the positive electrode plate and the separator, and between the negative electrode plate and the separator can be in appropriate ranges. It ensures sufficient permeability of electrolyte in the battery cell such that the battery module100can have good cycle performance. Moreover, it can prevent short circuit in the battery due to twisting of the battery cell and squeezing of the electrode plate, and thus improve safety performance of the battery module100.

It should be appreciated that although the battery120shown inFIGS. 1 and 2comprises only one battery cell, the battery120can also comprise two or more battery cells. The two or more battery cells can be connected in series, in parallel or in mixed series-parallel arrangement. That is to say, the partitions130can be provided in the battery module100for every two or more battery cells. Therefore, the battery module100can have a smaller length and volume while its safety performance and cycle performance are improved.

The above battery cell comprises a positive electrode plate, a negative electrode plate, a separator and electrolyte. The positive and negative electrode plates can produce and conduct current. The positive electrode plate comprises a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The negative electrode plate can be a lithium plate, or can comprise a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The separator is disposed between the positive electrode plate and the negative electrode plate to separate them. The electrolyte is disposed between the positive electrode plate and the negative electrode plate to conduct ions.

The disclosure can be especially applied into a battery module comprising battery cells that have expansion benefit. As an example, the positive active material of said battery module comprising battery cells that have expansion benefit is Li1+xNiaMe1-aO2−yXy, wherein −0.1≤x≤0.2; 0<a≤1; 0≤y<0.2; Me is one or more of Mn, Co, Fe, Cr, Ti, Zn, V, Al, Zr and Ce; X is one or more of S, N, F, Cl, Br and I. Especially, a is expressed as 0.5≤a≤1. For example, Li1+xNiaMe1-aO2-yXyis LiNi0.5Co0.2Mn0.3O2, LiNi0.6Co0.2Mn0.2O2, LiNi0.8Co0.1Mn0.1O2and the like.

Preferably, the coefficient of compressibility δ1of the partition130at a pressure equal to or smaller than 2 MPa meets a relation C0×δ1≤A0×0.1. It can further improve the cycle performance and safety performance of the nickel-rich battery. Especially, the nickel-rich battery indicates the positive active material is Li1+xNiaMe1-aO2−yXy, such as LiNi0.8Co0.1Mn0.1O2, wherein −0.1≤x≤0.2; 0.7≤a≤1; 0≤y<0.2; Me is one or more of Mn, Co, Fe, Cr, Ti, Zn, V, Al, Zr and Ce; X is one or more of S, N, F, Cl, Br and I.

In some embodiments, a pressure of 0.06 MPa to 0.35 MPa is applied to a mother plate to obtain the above partition130. Therefore, the partition130can meet the assembling force requirement when the partition130is assembled in the gap121between the adjacent batteries120, and the partition130can have good effect. As an example, the batteries120and the mother plates are alternatively disposed between the two end plates112to form an assembling group. The assembling group is pre-tightened with a pressure of 0.06 MPa to 0.35 MPa applied in the second direction. Thus, the mother plate is compressed to a predetermined extend to form the partition130. The pre-tightened assembling group is disposed between the two side plates111of the frame110. Finally, the end plates112and the side plates111are welded together to form a new battery module100.

The mother plate has a thickness C1. Preferably, 0<C1−C0. It can provide a shearing force between the partition130and the battery cell such that the new assembled battery module100has a stable structure and shaking of the battery120and the partition130can be prevented. More preferably, 0<C1−C0≤1 mm. By maintaining a smaller thickness change from the mother plate to the partition130, the partition130can have good effect and space utilization of the gap121can be improved.

In some embodiments, the partition130has a thickness Caat a pressure larger than 2 MPa and a thickness Cbat a pressure of 2 MPa, which meet a relation (Cb−Ca)/Cb×100%≤0.15%. It ensures that the thickness of the partition130do not change substantially when the expansion force of the battery120is larger than 2 MPa. It prevents further expansion of the battery120such that the gaps between the positive and negative electrode plates, between the positive electrode plate and the separator, and between the negative electrode plate and the separator can be in appropriate ranges. It ensures sufficient permeability of electrolyte in the battery cell, and maintains stability of the positive and negative active material layers.

Furthermore, the partition130also has thermal insulation property. The thickness Cbof the partition130at the pressure of 2 MPa is equal to above 0.015 mm, such as equal to above 0.1 mm. When a battery cell experiences thermal failure due to overheating, short circuit, overcharge and the like, the expansion force in the battery increases sharply, and the partition130will be compressed to its minimum thickness due to the expansion force. In this case, the partition130has still a thickness equal to or above 0.015 mm. It facilitates the thermal insulation of the partition130, prevents immense heat in the battery cell experiencing the thermal failure from being transferred to adjacent battery cells. Therefore, it can prevent thermal failure of the battery module100due to spreading of the thermal failure of the battery cell, and the battery module100can have good safety performance.

In some optional embodiments, when the requirements for heat insulation and module assembling are met, the thickness Cbof the partition130at the pressure of 2 MPa can be in a range of 0.015 mm to 4 mm, such as 0.1 mm to 2 mm.

Preferably, a thermal conductivity of the partition130at a temperature of 25° C. is equal to or smaller than 0.04 W·m−1·K−1. In this case, the partition130can have even better thermal insulation. At high temperature, the temperature difference between the first surface131and the second surface132of the partition130can be equal to or larger than 100° C. to 150° C., which significantly delays or even avoids propagation of thermal failure of adjacent battery cells.

In some embodiments, the partition130comprises a closed cell therein which has a diameter of 10 nm-120 μm, such as 15 μm-120 μm. The closed cell in the partition130inhibits the movement of the air molecule, and thereby reduces convective heat transfer of air. Moreover, the closed cell extends solid conduction path, restricts the solid thermal conduction and reduces thermal radiation. Therefore, the thermal insulation of the partition130can be greatly improved.

Furthermore, due to the compressibility of the partition130, it will be compressed by the expansion force of the battery, and the diameter of the closed cell in the partition130will be decreased, or even the diameter of the closed cell will be smaller than a mean free path of air molecule. Therefore, the convective heat transfer of air can be prevented. Moreover, by increasing the cell density of the closed cells in the partition130, it greatly extends the solid conduction path of heat, prevents the solid thermal conduction and reduces thermal radiation. Therefore, the thermal insulation of the partition130can be greatly improved.

Preferably, the partition130has a closed cell percentage of 60%-98%. More preferably, the partition130has a closed cell percentage of 80%-95%.

Referring toFIGS. 3 to 8, the above partition130comprises a functional layer133, which is exposed from at least the first surface131. However, as stated above, the functional layer133can be alternatively exposed from at least the second surface132. Alternatively, the functional layer133can be exposed from the first surface131and the second surface132.

Preferably, carbonization can take place in the functional layer133at a temperature of 400° C.-650° C. such that a carbon protective layer is formed. The carbon protective layer can prevent further thermal decomposition of the polymer, and prevent internal thermal decomposition products from being diffused to combust. It ensures the partition130has good effect, and its reliability is improved. Moreover, the heat generated when the battery experiences the thermal failure will melt the aluminum metal. Since the melting point of carbon is well above the melting point of the aluminum metal and carbon has a compact structure, the carbon protective layer can avoid liquid aluminum from permeating into heat absorbing surfaces of the adjacent battery cells, and a few of liquid aluminum can form carbon aluminum composite layer along with surface carbon on the carbon protective layer. It can reduce the liquid aluminum and prevent the permeation of the liquid aluminum, such that the carbon protective layer can protect the aluminum metal in the adjacent battery cells, and can prevent thermal failure of the adjacent battery cells due to liquid aluminum at a high temperature in the battery cell experiencing the thermal failure.

Preferably, cross-linking can take place in the functional layer133at a temperature of 400° C.-650° C. such that cross-linked solid matter is produced, which forms a cross-linking protective layer. The cross-linking protective layer can have the same effect as the above carbon protective layer.

The above polymer is preferably nitrogen-containing polymer, such as one or more of melamine polymer, polyamide (PA, commonly known as nylon), p-phenylene terephthalamide (PPTA, commonly known as aramid) and polyimide (PI). When the nitrogen-containing polymer is thermally decomposed at a high temperature, it is easy to release noncombustible gas, such as nitrogen, nitrogen oxide, water vapor and the like. The thermal decomposition of the nitrogen-containing polymer and the generation of the noncombustible gas will consume a lot of heat, which will substantially reduce the surface temperature of the functional layer133. Moreover, the noncombustible gas such as nitrogen will dilute oxygen in the battery module100and combustible gas generated when the polymer is thermally decomposed, and can react with the oxygen and the combustible gas such that the oxygen and the combustible gas will be converted into noncombustible gas, such as nitrogen, nitrogen oxide, water vapor and the like. According to chain reaction theory of combustion, when comburent and combustible for maintain the combustion are separated from each other and consumed, flame density in the combustion region will be reduced. Finally, the combustion reaction rate decreases and the combustion terminates, thus good flame retardation is achieved.

The nitrogen-containing polymer is preferably melamine polymer, such as melamine formaldehyde resin and its derivatives. When the melamine polymer is thermally decomposed, it can produce more noncombustible gas, such as nitrogen, nitrogen oxide, water vapor and the like, and can form a vitreous or stable foam covering layer at a high temperature (generally 400° C.-600° C.), which can prevent oxygen and combustible gas from escaping outward. When such nitrogen-containing polymer is heated, it is easy to form the cross-linking protective layer or the carbon protective layer to protect adjacent battery cells.

For example, for melamine formaldehyde resin, a monomer containing unsaturated bonds is made from melamine and formaldehyde by addition reaction to contain, which then is cross-linked with formaldehyde to form melamine formaldehyde resin. Melamine formaldehyde resin can be further provided with a foaming agent such as pentane foaming agent to initiate a foaming reaction so as to improve the closed cell percentage.

Referring toFIGS. 3 and 4, the partition130can have a single layer structure. As an example, the partition130in a single layer structure comprises a central region and an outside region which encloses the central region at a periphery of the central region. The functional layer133is provided at least in the central region of the partition130. At the outside region, the functional layer133or a supporting layer136can be provided there. Generally, as stated above, severe expansion will occur in the central regions on the main surface of the battery, and there will be smaller expansion in the outside regions. That is why functional layer133can be only provided in the central region of the partition130.

Preferably, the central region has an area which is 40%-100% of an area of the partition130. More preferably, the central region has an area which is 40%-65% of an area of the partition130, such as 40%-50%.

One or more holes135can be disposed in the outside region of the partition130. The above holes135can be one or more of through hole or blind hole. At one aspect, it can facilitate appropriate expansion of the outside region of the battery, which then shares the expansion force in the central region of the battery. On the other aspect, the holes can reduce material and cost.

The holes135at the outside region have a total area which is equal to or less than 40% of the area of the partition130, such as 25%-35%. It can ensure the supporting strength of the outside regions.

The shape of the hole135will not be specifically limited, and can be square, rhombus, polygon, circle, oval, irregular shape and the like.

It should be appreciated that when blind holes are provided at the outside region, the blind hole can be provided at one or both of the first surface131and the second surface132of the partition130.

As an example, as shown inFIG. 3, the functional layer133is disposed at both the central region and the outside region of the partition130, i.e., the partition130has a single layer structure composed of the functional layer133.

As an example, as shown inFIG. 4, the functional layer133is disposed at the central region of the partition130, and the supporting layer136is disposed at the outside region of the partition130. The supporting layer136encloses the functional layer133at its periphery. Accordingly, the partition130has a single layer composite structure composed of the functional layer133and the supporting layer136. It can reduce functional material and cost.

Preferably, the area of the functional layer133is 40%-100% of the area of the partition130. More preferably, the area of the functional layer133is 40%-65% of the area of the partition130, such as 40%-50%.

The supporting layer136comprises hard polymer, such as one or more of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polycarbonate (PC), polyethylene (PE), polypropylene (PP) and polypropylene (PPE). However, the hard polymer is not limited to the above. The above hard polymer means it has a much smaller coefficient of compressibility at a same pressure as compared to the functional layer133. For example, at a pressure of 0.06 MPa-2 MPa, the supporting layer136has a coefficient of compressibility of 0-10%, such as 0.1%-5%.

The partition130can also have a multi layer structure.

In some embodiments, as shown inFIGS. 5 to 7, the partition130has a multi-layer composite structure composed of the supporting layer136and the functional layer133. The functional layer133and the supporting layer136are stacked such that the supporting layer136can support the functional layer133. Specifically, the supporting layer136comprises two opposite surfaces. The functional layer133can be provided at any of the two surfaces of the supporting layer136, or can be provided at both surfaces of the supporting layer136.

The supporting layer136and the functional layer133can be attached through squeezing force from the battery cells, or can be combined by bonding or external film encapsulation. The disclosure is not limited to the above.

The supporting layer136can comprise the above hard polymer. The disclosure is not limited to the above material.

As described above, the functional layer133can be disposed only at the central region of the partition130. Therefore, in some embodiments, the central region of the supporting layer136can comprise a recess, and the functional layer133can be arranged in the recess.

The supporting layer136has two opposite surfaces. The central region of one of the two surfaces of the supporting layer136is inward depressed to form the recess for receiving the functional layer133. Alternatively, the recesses can be formed in the central regions by inward depressing at both surfaces of the supporting layer136to receive the functional layers133respectively. The shape of the recess is not specifically limited, and can be square, polygon, circle, oval, irregular shape and the like.

Preferably, the exposed surface of the functional layer133is flush with the surface of the supporting layer136.

As an example, as shown inFIG. 5, the central region of one of the two surfaces of the supporting layer136is inwardly depressed to form the recess for receiving the functional layer133. Two ends of the recess extend to respective edges of the supporting layer136. Accordingly, the recess is a U-shaped recess. The functional layer133is disposed in the recess.

As an example, as shown inFIG. 6, the central region of one of the two surfaces of the supporting layer136is inwardly depressed to form the recess for receiving the functional layer133. One end of the recess extends to an edge of the supporting layer136such that a side opening is formed at the edge. The functional layer133is disposed in the recess.

As another example, as shown inFIG. 7, the central region of one of the two surfaces of the supporting layer136is inwardly depressed to form the recess for receiving the functional layer133. The recess is closed at every side. The functional layer133is disposed in the recess.

Preferably, the recess has an area which is 40%-100% of a total area of the partition130, i.e., the area of the functional layer133is 40%-100% of the total area of the partition130. More preferably, the area of the recess is 40%-65% of a total area of the partition130, i.e., the area of the functional layer133is 40%-65% of the total area of the partition130.

The partition130has side surface which are connected with edges of the first surface131and the second surface132respectively. Furthermore, at least one protrusion134is provided on the side surface.

One protrusion134can be arranged corresponding to a positive electrode terminal or a negative electrode terminal of the battery cell. Alternatively, both of two protrusions134can be arranged corresponding to a positive electrode terminal and a negative electrode terminal of the battery cell, respectively. The one or two protrusions134can provide positioning function such that the partition130can be conveniently aligned with the battery cell.

Two or more protrusions134can be disposed at the bottom side of the partition130to provide supporting effect.

In some embodiments, on the side surface of the partition130corresponding to the side plate111of the frame110, at least one protrusion134can be arranged corresponding to the side plate111. On the side surface of the partition130corresponding to a top plate of the frame110, at least one protrusion134can be arranged corresponding to the top plate. On the side surface of the partition130corresponding to a bottom plate of the frame110, at least one protrusion134can be arranged corresponding to the bottom plate. These protrusions can provide buffering effect. When a compression force is applied to the partition130, since material expands in all directions, the material may extend beyond the periphery of the battery cell to contact or even press the frame110. On one side, excess material accumulates outside of the gap121such that the gap121will have a large positional deviation and thus cannot effectively protect the battery120. On the other side, since the partition130presses the frame110, one or more of the side plates111, the top plate and the bottom plate will have large assembly deviation and thus cannot fit with the end plate112. In this case, there will be wide welding seam in welding zone between the end plate112and one or more of the side plates111, the top plate and the bottom plate, or even the welding cannot be normally performed. Through the buffering effect of these protrusions134, the above problem can be effectively solved.

Furthermore, the disclosure further provides a battery pack comprising one or more categories of the above battery modules100. There are two or more battery modules100, which can be connected in series, in parallel or in mixed series-parallel arrangement. Since the battery pack according to embodiments of the disclosure comprises the battery module100according to embodiments of the disclosure, the battery pack also has good cycle performance and safety performance.

EXAMPLES

The present disclosure is more particularly described in the following examples that are intended as illustrations only, since numerous modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise noted, all parts, percentages, and ratios reported in the following examples are on a weight basis, and all reagents used in the examples are commercially available or synthesized through routine methods, and used directly as they were originally received, and all instruments used in the examples are commercially available.

Preparation of Positive Electrode Plate

A positive slurry is prepared by mixing LiNi0.8Co0.1Mn0.1O2as positive active material, conductive carbon black and polyvinylidene difluoride (PVDF) as a binder at a weight ratio 8:1:1 in N-Methyl-2-pyrrolidone (NMP) as a solvent and stirring them uniformly. The positive slurry is coated onto an aluminum foil of a positive current collector. After drying, cold pressing, slitting and slicing process, a positive electrode plate is obtained.

Preparation of Negative Electrode Plate

A negative slurry is prepared by mixing synthetic graphite as negative active material, conductive carbon black, carboxymethyl cellulose (CMC) as a thickening agent and styrene-butadiene rubber (SBR) as a binder at a weight ratio 89:6:3:2 in deionized water as a solvent and stirring them uniformly. The negative slurry is coated onto a copper foil of a negative current collector. After drying, cold pressing, slitting and slicing process, a negative electrode plate is obtained.

Preparation of Electrolyte

An organic solvent is prepared by uniformly mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) at a volume ratio 1:1:1. An electrolyte is prepared by dissolving LiPF6with a concentration of 1 mol/L into the above organic solvent.

Preparation of Battery Cell

A battery cell is prepared by successively stacking the positive electrode plate, a separator and the negative electrode plate, winding them to form a battery core, placing the battery core into an aluminum case and performing subsequent processes including top-side sealing, electrolyte injection and the like, wherein the separator comprises a PP/PE/PP composite film and is disposed between the positive electrode plate and the negative electrode plate to separate them.

Preparation of Battery Module

Six battery cells as prepared above are arranged side by side, and mother plates are disposed between every two adjacent battery cells. A pressure of 0.2 MPa is applied to an assembly including the battery cells, the mother plates and two end plates, and thereby the mother plate is compressed to a predetermined extend to form a partition, which has a structure as shown inFIG. 8. Then, the assembly is disposed between two side plates and is welded to an assembly including the end plates and the side plates. After that, the six battery cells are connected in series to form a battery module. Specific parameters are shown in Table 1.

Different from Example 1, relevant parameters of the partition are adjusted, as shown in Table 1.

Different from Example 2, the partitions are disposed between every two adjacent batteries, each battery comprises two battery cells, and relevant parameters of the partition are adjusted, as shown in Table 1.

Different from Example 2, the positive active material is LiNi0.5Co0.2Mn0.3O2.

Comparative Example 1

Different from Example 1, there is no partition between the battery cells in the battery module, and a width of the gap between two adjacent battery cells is kept at 2.6 mm by fixing holder.

Comparative Example 2

Different from Example 1, there is no partition between the battery cells in the battery module, and a width of the gap between two adjacent battery cells is kept at 3.6 mm by fixing holder.

Test Section

1. Thermal Propagation Test of Battery Module

After sufficient charge-discharge cycles of a new battery module, a compression force applied to a partition in the battery module comes up to 2 MPa. The battery module is charged at a temperature of 25±3° C. and an atmospheric pressure of 101 KPa, wherein the battery cell in the battery module is charged at a constant current at a rate of 1C until its voltage reaches 4.2V and then charged at a constant voltage until the current is equal to or less than 0.05C. The battery module is then placed in a nail penetration testing equipment. The testing environment is maintained at a temperature of 25±3° C. and an atmospheric pressure of 101 KPa. A fire resistant steel nail with a diameter of 3.0 mm and a taper angle of 30°-60° is used to penetrate at a speed of 0.1 mm/s a first battery cell of the battery module at its central position. The order of battery cells are calculated from an overall negative terminal to an overall positive terminal. The penetration depth is 5 mm-10 mm. The nail penetration is stopped when the first battery cell comes into thermal failure. Thermal propagation in the battery module is detected, and thermal failure times in second to sixth battery cells are recorded. A starting point of the thermal failure times in second to sixth battery cells is the time when the first battery cell comes into thermal failure.

2. Cycle Performance Test of Battery Module

A new battery module is charged at a temperature of 25±3° C. and an atmospheric pressure of 101 KPa, wherein the battery cell in the battery module is charged at a constant current at a rate of 1C until its voltage reaches 4.2V and then charged at a constant voltage until the current is equal to or less than 0.05C, and after that, discharged at a constant current at a rate of 1C until its voltage reaches 3.0V. This is a charge-discharge cycle. The discharge capacity at this time is recorded as the discharge capacity of the first cycle of the lithium-ion secondary battery. 1000 cycles of the charge-discharge testing are performed according to the above method, and the discharge capacity at each cycle is recorded.

Capacity retention rate of the lithium-ion secondary battery (%) after 1000 cycles=discharge capacity at the 1000thcycle/the discharge capacity at the first cycle×100%.

3. Direct Current Resistance (DCR) Test of Battery Module

A new battery module is charged at a temperature of 25±3° C. and an atmospheric pressure of 101 KPa, wherein the battery cell in the battery module is charged at a constant current at a rate of 1C until its voltage reaches 4.2V and then charged at a constant voltage until the current is equal to or less than 0.05C and after that, discharged at a constant current at a rate of 1C until the state of charge (SOC) of the lithium-ion secondary battery is adjusted to 20% of its full charge capacity. After resting for 60 min, it is discharged at a constant current at a rate of 4C for 30s, and is subjected to a DCR test with a recording interval time of 0.1s. An initial DCR of the battery module is obtained. 1000 cycles of the charge-discharge testing are performed according to the above method, and the DCR after the 1000 cycles is recorded.

The test results of Examples 1 to 12 and Comparative Examples 1-2 were shown in Table 2 below.

As can be seen from the comparison of Examples 2, 10, 11 to Comparative Example 2 and the comparison of Examples 3, 4, 5, 9 to Comparative Example 1, when the partition is disposed between the batteries, the capacity retention rate of the battery module after 1000 cycles is significantly improved, the DCR of the battery module after 1000 cycles is significantly reduced. Therefore, the cycle performance of the battery module according to the disclosure is significantly improved.

As can be seen from the test results of the Examples 1 to 12, after 1000 cycles at a rate of 1C, the capacity retention rate of the battery module according to the disclosure is still equal to or above 80% of its initial capacity, such as equal to or above 90%. After 1000 cycles of the battery module at a rate of 1C, its direct current resistance is still equal to or below 1.10 mΩ, such as equal to or below 1.00 mΩ, especially equal to or below 0.85 mΩ, more especially equal to or below 0.80 mΩ. The battery module according to embodiments of the disclosure has good cycle performance.

As can be seen from the comparison of Examples 1-3, 6, 8-12 to Comparative Examples 1-2, when the partition is disposed between the batteries, the thermal failure propagation time of the battery module is significantly increased while the battery module has good cycle performance. The thermal failure propagation can be greatly retarded, thus the battery module has good safety performance.

The above is only the specific embodiment of the present application, but the scope of the present application is not limited thereto. Various equivalent modifications and variations of the present application that can be easily conceived by those skilled in the art are intended to be included within the scope of the present application. Therefore, the scope of the invention should be determined by the scope of the claims.