A battery cell and a battery

Abstract

The utility model provides a battery cell and a battery, the battery cell comprises: a pole piece; a diaphragm, comprising: a substrate and a coating, the coating covering at least one side of the substrate, the coating comprising a first layer and a second layer; the first layer is bonded to the pole piece, and the second layer is used to contain electrolyte, that is, it has good bonding force and good ability to store electrolyte, so as to avoid the occurrence of lithium precipitation.

Description

Technical Field

[0001] The utility model relates to the technical field of new energy, and in particular to a battery cell and a battery. Background Art

[0002] In the prior art, the use of lithium batteries means that the lithium batteries are continuously charged and discharged in a cycle, and the volume of the lithium batteries will continue to expand during the process of cyclic charging and discharging of the lithium batteries. After the volume of the lithium battery expands, the pole pieces of the lithium battery will squeeze each other, so that the electrolyte is squeezed out, especially in the corner area of ​​the battery cell, the ability of the diaphragm to retain the electrolyte will be more affected, which can easily cause the pole pieces to lack electrolyte and insufficient electrolyte infiltration, resulting in lithium precipitation during the cyclic charging and discharging of the lithium battery. The ability of the lithium battery to retain the electrolyte is closely related to the diaphragm. The diaphragm needs to firmly bond the pole pieces of the battery, so it is necessary to coat the diaphragm with a coating with strong bonding force to ensure the bonding force of the diaphragm, so as to avoid the separation of the pole pieces and the lithium precipitation caused by the separation of the pole pieces. After the coating with strong bonding force is coated on the diaphragm, the ability of the diaphragm to retain the electrolyte is not guaranteed. After a long period of use, the lithium battery will still produce lithium precipitation. Because it is impossible to find a coating with strong bonding force and strong ability to retain electrolyte to form a diaphragm. Therefore, a diaphragm is needed that has both good adhesion and good ability to preserve electrolyte, so as to avoid the occurrence of lithium precipitation. Utility Model Content

[0003] The utility model aims to solve at least one of the technical problems existing in the prior art. To this end, the utility model provides a battery cell that can effectively avoid the occurrence of lithium deposition.

[0004] The utility model also provides a battery comprising the battery core.

[0005] A diaphragm according to an embodiment of the first aspect of the utility model includes: a pole piece; a diaphragm including: a substrate and a coating, wherein the coating covers at least one side of the substrate, and the coating includes a first layer and a second layer; the first layer is bonded to the pole piece, and the second layer is used to contain an electrolyte.

[0006] A diaphragm according to the embodiment of the first aspect of the utility model has at least the following beneficial effects: the first layer on both sides of the width direction of the substrate has a strong adhesive force, so that the diaphragm and the pole piece are firmly bonded, and the pole pieces are also firmly bonded to each other, avoiding the lithium precipitation phenomenon caused by the separation of the pole pieces. The second layer on the same substrate has a strong ability to preserve electrolyte, so that the lithium battery still has a good ability to preserve electrolyte after the volume expands, avoiding the lithium precipitation phenomenon caused by insufficient electrolyte in the lithium battery.

[0007] According to some embodiments of the utility model, the first layer, the second layer and the first layer are sequentially coated on the substrate along the width direction of the substrate, the wetting ability of the second layer is greater than the wetting ability of the first layer, and the bonding ability of the first layer is greater than the bonding ability of the second layer.

[0008] According to some embodiments of the present invention, adjacent edges of the first layer and the second layer overlap.

[0009] According to some embodiments of the present invention, an overlapping area is provided at the connection between the first layer and the second layer.

[0010] According to some embodiments of the present invention, when observed from the overlapping area, the substrate, the second layer and the first layer are arranged in sequence along the thickness direction of the substrate.

[0011] According to some embodiments of the present invention, the width of the overlapping area in the width direction of the substrate is L1, L1≤3mm, the width of the first layer in the width direction of the substrate is L2, 10mm≥L2≥3mm, the width of the substrate is L3, and the width of the second layer in the width direction of the substrate is L4, 3L4≥L3.

[0012] According to some embodiments of the present invention, the adhesion of the first layer is not less than 4 N / m.

[0013] According to some embodiments of the present invention, the coating is coated on two opposite sides of the substrate, and the adjacent edges of the first layer and the second layer in the same coating are fitting edges. In the thickness direction of the substrate, the projection of the fitting edge of the coating on one side of the substrate does not intersect with the projection of the fitting edge of the coating on the other side of the substrate.

[0014] According to some embodiments of the present invention, the coating is coated on two opposite sides of the substrate, and an overlapping area of ​​the coating on one side of the substrate does not intersect with an overlapping area of ​​the coating on the other side of the substrate.

[0015] A battery according to an embodiment of the second aspect of the utility model comprises a battery cell as described in any one of the above embodiments.

[0016] Additional aspects and advantages of the present invention will be given in part in the following description, and in part will become apparent from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A top view of the diaphragm in the first embodiment of the present invention excluding the overlapping area;

[0018] Figure 2 A top view of the diaphragm including the overlapping area in the second embodiment of the present invention;

[0019] Figure 3 It is a side view of the diaphragm in the first embodiment of the utility model excluding the overlapping area;

[0020] Figure 4 It is a side view of the diaphragm including the overlapping area in the second embodiment of the present invention.

[0021] Figure Number:

[0022] 1. Substrate; 11. Through hole; 2. Coating; 21. First layer; 22. Second layer; 23. Overlap area; 24. Lamination line. DETAILED DESCRIPTION

[0023] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0024] In the description of the present invention, it should be understood that the descriptions involving orientation, such as the orientation or positional relationship indicated as up, down, etc., are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0025] In the description of the present utility model, "a plurality" means more than two. If there is a description of "first" or "second", it is only for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0026] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0027] In the prior art, the diaphragm is usually formed by coating a coating 2 on a substrate. The material of the substrate 1 is mainly a polyolefin substrate mainly composed of polyethylene and polypropylene, wherein polypropylene is relatively more resistant to high temperatures, while polyethylene is more resistant to low temperatures. A through hole 11 is set on the polyolefin substrate to form the substrate 1 required for the diaphragm. After obtaining the substrate 1, the coating 2 is coated on the substrate 1 to obtain the diaphragm required for the lithium battery. The coating 2 is formed by mixing particles formed by polyvinylidene fluoride, polymethyl methacrylate, polyamide, acrylonitrile resin, polytetrafluoroethylene, polytrifluorochloroethylene, etc. and inorganic particles to form a slurry. At the same time, multiple materials can also be mixed to form a slurry. The diaphragm is an important component of the lithium-ion battery. It is a microporous membrane used to separate the positive and negative pole pieces. It is a polymer functional material with a nano-scale microporous structure. Its main function is to prevent the two poles from contacting and short-circuiting while allowing electrolyte ions to pass through. Its performance determines the interface structure and internal resistance of the battery, and directly affects the capacity, cycle and safety performance of the battery. At present, most lithium-ion battery separator products in the prior art are microporous membranes made of polyolefin materials. The main raw materials are high molecular weight polyethylene and polypropylene. The products include polyethylene PE single-layer membrane, polypropylene PP single-layer membrane and PP / PE / PP multi-layer microporous membrane composited by PP and PE. Polyolefin materials have the advantages of high strength, good acid and alkali corrosion resistance, waterproof, chemical resistance, good biocompatibility, and non-toxicity. Its industrial preparation is relatively mature. Other lithium-ion battery separators that are in the research stage or have not yet been widely used include PET / cellulose non-woven fabrics, polyvinylidene fluoride (PVDF) porous membranes, polyimide (PI) electrospun porous membranes, and various PE, PVDF, PP, PI modified membranes, etc.

[0028] At present, the production process of polyolefin diaphragms can be divided into two categories according to the dry method and the wet method. At the same time, the dry method can be further divided into the unidirectional stretching process and the bidirectional stretching process. The dry unidirectional stretching process is to prepare a low-crystallinity, highly oriented polypropylene or polyethylene film by producing hard elastic fibers, and obtain a high-crystallinity oriented film by annealing at high temperature. This film is first stretched at low temperature to form micro defects, and then the defects are pulled apart at high temperature to form micropores. After decades of development, this process has become very mature. The diaphragm produced by this method has a flat and long microporous structure. Since only unidirectional stretching is performed, the transverse strength of the diaphragm is relatively poor, but it is precisely because there is no transverse stretching that there is almost no thermal shrinkage in the transverse direction. The dry bidirectional stretching process adds a β-crystal modifier with a nucleating effect to polypropylene, and utilizes the density difference between different phases of polypropylene to form micropores during the stretching process. It is used to produce a single-layer PP film.

[0029] The wet method is also called phase separation method or thermal phase separation method. It mixes high-boiling hydrocarbon liquid or low-molecular-weight substance with polyolefin resin, heats and melts the mixture and spreads the melt on a sheet, then cools to separate the phases, and then orients the sheet longitudinally or biaxially, and finally extracts the liquid with a volatile solvent. Interpenetrating microporous membrane materials can be prepared, and the applicable materials are wide. The diaphragm produced by the wet biaxial stretching method has higher longitudinal and transverse strength due to biaxial stretching. It is currently mainly used for single-layer PE diaphragms.

[0030] From a theoretical analysis, the diaphragm produced by the dry biaxial stretching process is biaxially stretched. When the longitudinal tensile strength is not much different, the transverse tensile strength is significantly higher than that of the diaphragm produced by the dry uniaxial stretching process. The diaphragm produced by the dry biaxial stretching process is more advantageous in terms of physical and mechanical properties. However, the wet diaphragm can obtain higher porosity and better air permeability. It can meet the requirements of high current charging and discharging of power batteries, but the thermal stability is relatively poor.

[0031] A battery cell in the first embodiment of the utility model includes: a pole piece and a diaphragm, the diaphragm includes a substrate 1 and a coating 2, the coating 2 is coated on at least one side of the substrate 1, that is, the coating 2 can be coated on one side or both sides of the substrate 1. When the coating 2 is coated on one side of the substrate, it can meet the requirements of the lithium battery. When the coating 2 is coated on both sides of the substrate 1, the diaphragm has better performance. The coating 2 includes a first layer 21 and a second layer 22. The first layer 21 has an adhesive force, and a tool is used to bond the diaphragm to the pole piece. The second layer 22 has the ability to accommodate electrolyte, that is, the wetting ability, and can absorb the electrolyte. Figure 1 and Figure 2 In the figure, the left side shows the state where the coating 2 is applied, and the portion on the right side where the through hole 11 is exposed is to illustrate that the through hole 11 on the substrate 1 also needs to be coated with the coating 2.

[0032] Reference Figure 1 and Figure 3, preferably, the first layer 21, the second layer 22 and the first layer 21 are sequentially arranged along the first direction, and the first direction is the width direction of the substrate 1. Wherein the coating 2 includes the first layer 21 and the second layer 22 that are bonded, which means that after the first layer 21 and the second layer 22 are both arranged on the substrate 1, the first layer 21 and the second layer 22 are tightly bonded without a gap, that is, there is no substrate 1 exposed between the first layer 21 and the second layer 22. That is, the adjacent edges of the first layer 21 and the second layer 22 overlap. The wetting ability of the second layer 22 is greater than the wetting ability of the first layer 21, and the bonding ability of the first layer 21 is greater than the bonding ability of the second layer 22. Since the bonding force of the coating 2 and the ability of the coating 2 to preserve the electrolyte cannot be guaranteed at the same time, a first layer 21 with a strong bonding force is arranged at the edge of the substrate 1 to ensure that the edge of the battery cell can be more firmly bonded together, thereby avoiding the lithium precipitation phenomenon caused by the separation of the pole piece and the pole piece at the edge. Specifically, the proportion of the adhesive is increased in the slurry for forming the first layer 21, or an additional layer of adhesive is applied to ensure the bonding force of the first layer 21. The second layer 22 disposed between the two first layers 21 has poor adhesion or even no adhesion, but the second layer 22 has a strong ability to preserve electrolyte to ensure that the lithium battery still retains sufficient electrolyte after the volume expands due to cyclic charging and discharging, so that the lithium battery will not precipitate lithium due to insufficient electrolyte. The ability of the second layer 22 to preserve electrolyte can be specifically achieved by controlling the size of the particles in the slurry forming the second layer 22. Using larger particles can improve the ability of the second layer 22 to preserve electrolyte, and the size of the particles is controlled between 2um and 10um, preferably between 5um and 8um. Particles of this size are formed by agglomeration of particles of smaller size.

[0033] Preferably, the bonding position of the first layer 21 and the second layer 22 is set to be a straight line, i.e., the bonding line 24. At this time, the first layer 21 and the second layer 22 are both regular rectangles, which can make the first layer 21 have a more uniform bonding force and the electrolyte in the second layer 22 can be more evenly preserved.

[0034] Reference Figure 2 and Figure 4 , an overlapping area 23 is provided at the connection between the first layer 21 and the second layer 22, and the first layer 21 and the second layer 22 are coated on the substrate 1 in the overlapping area 23. The first layer 21 and the second layer 22 are formed by coating layers, and during the coating process, it is difficult to align and fit the edges of the first layer 21 and the second layer 22, and even the substrate 1 may be exposed. Therefore, the overlapping area 23 is provided between the first layer 21 and the second layer 22, so that the substrate 1 can be completely covered with less difficulty in operation.

[0035] Reference Figure 4, the overlapping area 23 is the substrate 1, the second layer 22 and the first layer 21 in the thickness direction of the substrate 1. The second layer 22 is arranged below the first layer 21 so that the bonding force of the first layer 21 can play its role better. Specifically, the second layer 22 is first coated on the substrate 1, and then the first layer 21 is coated on the substrate 1, and a part of the first layer 21 is coated on the second layer 22 to form the overlapping area 23. The preferred projection of the overlapping area 23 on the substrate 1 is also a rectangle.

[0036] The width of the overlapping region 23 in the width direction of the substrate 1 does not exceed 3 mm. Since the overlapping region 23 has the substrate 1, the first layer 21 and the second layer 22, the thickness of the overlapping region 23 is thicker than other regions. Therefore, if the width of the overlapping region 23 is too large, the separator will become thicker, thereby affecting the energy density of the battery.

[0037] The width of the first layer 21 in the width direction of the substrate 1 is not less than 3 mm and not more than 10 mm. The first layer 21 has good adhesion, but it will reduce the ability of the diaphragm to store electrolyte. When the width of the first layer 21 is small, the adhesion of the diaphragm cannot be guaranteed. Therefore, it is necessary to set the first layer 21 with a width of not less than 3 mm to ensure the adhesion of the diaphragm, so that the diaphragm can firmly bond the pole pieces to each other, ensuring that the lithium battery will not cause lithium precipitation due to the separation of the pole pieces.

[0038] The width of the substrate 1 is L, the width of the second layer 22 in the width direction of the substrate 1 is H, and 3H is not less than L. If the width of the second layer 22 is smaller than the width of the substrate 1, the wettability of the edge of the diaphragm will be insufficient, that is, there will not be enough electrolyte on both sides of the diaphragm. The reason is that if the width of the second layer 22 becomes smaller, the width of the first layer 21 will increase, and the position of the first layer 21 does not have a good ability to preserve the electrolyte. Therefore, it is necessary to ensure the width of the second layer 22 to ensure the ability of the diaphragm to preserve the electrolyte.

[0039] The bonding capacity of the first layer 21 is not less than 4N / ㎡. Under the condition of ensuring the strong bonding between the diaphragm and the electrode, the stronger the bonding capacity of the first layer 21, the smaller the first layer 21 can be set, and the wider the second layer 22 can be set, thereby improving the ability of the diaphragm to store electrolyte, thereby avoiding the occurrence of lithium deposition in lithium batteries.

[0040] Reference Figure 3, the coating 2 is coated on two opposite sides of the substrate 1, and the adjacent edges of the first layer 21 and the second layer 22 in the same coating are the bonding edges, and the bonding edges of the coating on one side of the substrate 1 do not overlap with the bonding edges of the coating 2 on the other side of the substrate 1. When the first layer 21 and the second layer 22 are bonded, a gap may be generated between the first layer 21 and the second layer 22, causing the substrate 1 to be exposed. In order to avoid both sides of the substrate 1 being exposed at the same time, the bonding lines 24 formed by the bonding edges on both sides of the substrate 1 are offset. Even if a gap appears at the bonding edge position, both sides of the substrate 1 will not be exposed at the same time, and the performance of the diaphragm can still be maintained. Specifically, the width of the first layer 21 on one side of the substrate 1 is set to 4 mm, and the width of the first layer 21 on the other side of the substrate 1 is set to 5 mm, so that the bonding line 24 is offset. Specifically, the width of the substrate 1 is 20 mm, and the first surface of the substrate 1 is sequentially provided with a 4 mm wide first layer 21, a 10 mm wide second layer 22, and a 6 mm wide first layer 21 along the width direction of the substrate 1, and the second surface of the substrate 1 is sequentially provided with a 6 mm wide first layer 21, a 10 mm wide second layer 22, and a 4 mm wide first layer 21 along the width direction of the substrate 1. Not only are the bonding lines 24 on both sides of the substrate 1 offset, but also the bonding forces on both sides of the substrate 1 are equal, and the substrate 1 has the same ability to store electrolyte.

[0041] Reference Figure 4 , the coating 2 is coated on the two opposite sides of the substrate 1, and the overlapping area 23 of the coating 2 on one side of the substrate 1 does not intersect with the overlapping area 23 of the coating 2 on the other side of the substrate 1. In the overlapping area 23, since there are substrate 1, the first layer 21 and the second layer 22, the thickness of the diaphragm in the overlapping area 23 is relatively large. If the overlapping areas 23 intersect, the thickness of the area where the overlapping areas 23 intersect will be greater, which not only affects the flatness of the diaphragm, but also reduces the energy density of the lithium battery. Therefore, the overlapping areas 23 on both sides of the substrate 1 cannot intersect, avoiding the situation where the thickness of the diaphragm is locally large. The overlapping area 23 is equivalent to overlapping the first layer 21 and the second layer 22 together. Preferably, the second layer 22 is first coated on the substrate 1, and then the first layer 21 is coated on the substrate 1. At the same time, when the first layer 21 is coated, a part of the first layer 21 is coated on the edge of the second layer 22 adjacent to the first layer 21. This coating method ensures that the substrate 1 can be completely covered by the coating 2.

[0042] A battery according to an embodiment of the second aspect of the utility model includes a battery cell in any one of the above embodiments.

[0043] There are two situations of lithium precipitation in this scheme. One is caused by the separation of the pole pieces and the gap between them. When the pole pieces are spaced apart, the negative pole piece is not fully infiltrated by the electrolyte, and the lithium ions cannot be embedded in the inside of the negative pole piece through the electrolyte and the diaphragm in time, so that lithium precipitation will occur on the negative pole piece. The second is that the diaphragm cannot store enough electrolyte between the pole pieces, so that the inside of the negative pole piece is not infiltrated by the electrolyte, so that the lithium ions cannot be transferred to the negative pole piece in time, so that lithium precipitation will occur on the negative pole piece. Therefore, this scheme adopts a first layer 21 with strong bonding force so that the pole pieces can be firmly connected to avoid the generation of gaps, and at the same time adopts a second layer 22 with a strong ability to preserve electrolyte to ensure that there is enough electrolyte between the pole pieces. In order to ensure that the second layer 22 has a strong ability to preserve electrolyte, larger granular materials are used in the slurry of the second layer 22 to increase the gap between the particles to increase the space for storing electrolyte.

[0044] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A battery cell, characterized in that: include: Pole piece; A diaphragm comprises: a substrate and a coating, wherein the coating covers at least one side of the substrate, and the coating comprises a first layer and a second layer; The first layer is bonded to the pole piece, and the second layer is used to contain electrolyte.

2. A battery cell according to claim 1, characterized in that: The substrate is coated with the first layer, the second layer and the first layer in sequence along the width direction of the substrate, the second layer has a wettability greater than that of the first layer, and the first layer has a bonding ability greater than that of the second layer.

3. A battery cell according to claim 2, characterized in that: Adjacent edges of the first layer and the second layer overlap.

4. A battery cell according to claim 2, characterized in that: An overlapping area is provided at a connection between the first layer and the second layer.

5. A battery cell according to claim 4, characterized in that: Observed from the overlapping region, the substrate, the second layer and the first layer are arranged in sequence along the thickness direction of the substrate.

6. A battery cell according to claim 4, characterized in that: The width of the overlapping area in the width direction of the substrate is L1, L1≤3mm, the width of the first layer in the width direction of the substrate is L2, 10mm≥L2≥3mm, the width of the substrate is L3, and the width of the second layer in the width direction of the substrate is L4, 3L4≥L3.

7. A battery cell according to claim 1, characterized in that: The adhesion of the first layer is not less than 4 N / m.

8. A battery cell according to claim 1, characterized in that: The coating is coated on two opposite sides of the substrate, and the adjacent edges of the first layer and the second layer in the same coating are bonding edges. In the thickness direction of the substrate, the projection of the bonding edge of the coating on one side of the substrate does not intersect with the projection of the bonding edge of the coating on the other side of the substrate.

9. A battery cell according to claim 4, characterized in that: The coating is coated on two opposite sides of the substrate, and the overlapping area of ​​the coating on one side of the substrate does not intersect with the overlapping area of ​​the coating on the other side of the substrate.

10. A battery, characterized in that: A battery cell comprising any one of claims 1 to 9.

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