Battery monomer, preparation method thereof, battery device and power utilization device

Abstract

The invention provides a battery monomer, a preparation method thereof, a battery device and a power utilization device. The height of the battery monomer is more than 200mm, the battery monomer comprises at least one battery cell, the battery cell comprises a pole piece and a diaphragm, the pole piece extends along a first direction, the length of the pole piece along the first direction is greater than that along a second direction, the second direction is perpendicular to the first direction and is the same as the height direction of the battery monomer, and the pole piece and the diaphragm are laminated along a third direction; the third direction is perpendicular to the first direction and the second direction, the cell has a large area in the cross section perpendicular to the height direction of the battery monomer, and the average gap between the pole piece and the adjacent diaphragm in the third direction in the large area is 6.3-24 [mu] m. The battery monomer provided by the invention has good cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a battery monomer, a preparation method of the battery monomer, a battery device and a power utilization device. BACKGROUND

[0002] In recent years, with the application range of battery monomers becoming more and more extensive, battery monomers are widely applied to energy storage power supply systems such as water, fire, wind and solar power stations, and many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, etc. With the rapid development of batteries, people have put forward higher requirements for the cycle performance of batteries, especially the cycle performance of battery monomers with large height.

[0003] Therefore, how to improve the cycle performance of battery monomers with large height has become a technical problem to be solved. SUMMARY

[0004] The present application is carried out in view of the above-mentioned problems, and aims to provide a battery monomer with large height, a preparation method thereof, a battery device and a power utilization device. The battery monomer of the present application has excellent cycle performance.

[0005] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a battery monomer, the height of the battery monomer is 200mm or more, the battery monomer comprises at least one battery cell, the battery cell comprises a pole piece and a diaphragm, the pole piece extends along a first direction, the length of the pole piece along the first direction is greater than the length along a second direction, the second direction is perpendicular to the first direction and the same as the height direction of the battery monomer, the pole piece and the diaphragm are stacked along a third direction, the third direction is perpendicular to the first direction and the second direction, the battery cell has a large area region in a cross section perpendicular to the height direction of the battery monomer, and the average gap between the pole piece and the adjacent diaphragm in the third direction in the large area region is 6.3μm-24μm. Thus, it is beneficial to improve the cycle performance of the battery monomer.

[0006] In some embodiments, the average gap between the pole piece and the adjacent diaphragm in the third direction in the large area region is 8.2μm-20.3μm. Thus, it is beneficial to further improve the electrolyte wettability of the battery cell, thereby improving the cycle performance of the battery monomer.

[0007] In some embodiments, the electric core is a wound electric core, the wound electric core comprises the large area and the bending area on both sides of the large area in the cross section perpendicular to the height direction of the battery monomer, and the average gap between the pole piece and the diaphragm is 8.7 μm-32.5 μm in the direction 45° to the third direction from the bending position of the innermost layer in the wound electric core. Thus, it is beneficial to improve the infiltration effect of the electrolyte, thereby improving the cycle performance of the battery monomer.

[0008] In some embodiments, the average gap between the pole piece and the diaphragm is 8.9 μm-28.7 μm in the direction 45° to the third direction from the bending position of the innermost layer in the wound electric core in the bending area. Thus, the cycle performance of the battery monomer is further improved.

[0009] In some embodiments, the gap between the pole piece and the diaphragm is 21.0 μm-58.5 μm in the direction 90° to the third direction from the bending position of the innermost layer in the wound electric core in the bending area. Thus, it is beneficial to improve the infiltration effect of the electrolyte, thereby improving the cycle performance of the battery monomer.

[0010] In some embodiments, the gap between the pole piece and the diaphragm is 23.5 μm-55.5 μm in the direction 90° to the third direction from the bending position of the innermost layer in the wound electric core in the bending area. Thus, it is beneficial to further improve the cycle performance of the battery monomer.

[0011] In some embodiments, the diaphragm comprises a base film and a functional layer provided on at least one side of the base film, and the functional layer comprises porous ceramic particles. Thus, it is beneficial to improve the liquid retention capacity of the diaphragm to the electrolyte, thereby improving the cycle performance of the battery monomer.

[0012] In some embodiments, the porous ceramic particles comprise one or more of boehmite, aluminum oxide, titanium dioxide, silicon dioxide, silicon carbide, barium sulfate, calcium sulfate, and glass fiber. Thus, it is beneficial to improve the cycle performance of the battery.

[0013] In some embodiments, the air permeability of the diaphragm is 156 s / 100 mL-175.5 s / 100 mL. Thus, it is beneficial to improve the cycle performance and safety performance of the battery monomer.

[0014] In some embodiments, the ionic conductivity of the diaphragm is 0.6 mS / cm-0.95 mS / cm. Thus, it is beneficial to improve the cycle stability of the battery monomer.

[0015] In some embodiments, the surface density of the separator is 3 g / m 2 ~7.6g / m 2 This is beneficial to improving the energy density, cycle performance and safety performance of battery cells.

[0016] In some embodiments, the thickness of the functional layer is less than or equal to 5 μm, which is beneficial to improving the cycle performance of the battery.

[0017] In some embodiments, the height of the battery cell is 200 mm to 300 mm, thereby improving the energy storage capacity of the battery.

[0018] A second aspect of the present application further provides a method for preparing a battery cell, wherein the battery cell is at least 200 mm tall and comprises stacking the electrode sheets and the separator in sequence and then cold pressing the layers at a pressure of 20T to 50T for a time of 20s to 150s. This method is beneficial for increasing the electrolyte's creep height and wettability within the battery cell, thereby enhancing the cycle performance of the prepared battery cell.

[0019] In some embodiments, the cold pressing pressure is 32T to 42.5T, and the cold pressing time is 20s to 60s, thereby further improving the cycle performance of the battery cell.

[0020] The third aspect of the present application further provides a battery device, comprising the battery cell described in the first aspect of the present application, or comprising a battery cell prepared according to the preparation method described in the second aspect of the present application. Thus, the battery device has at least the advantages of the battery cell of the present application.

[0021] The fourth aspect of the present application further provides an electrical device, the battery device described in the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic structural diagram of a cross section of a large area of ​​a battery cell according to one embodiment of the present application, perpendicular to the height direction of the battery cell.

[0023] Figure 2 1 is a schematic structural diagram of a cross section of a wound battery cell according to an embodiment of the present application, perpendicular to the height direction of the battery cell.

[0024] Figure 3 This is a CT image of an interface of a wound battery cell perpendicular to the height direction of a battery cell according to an embodiment of the present application. The battery cell includes two wound battery cells.

[0025] Figure 4 Schematic diagram of a battery cell according to one embodiment of the present application.

[0026] Figure 5 yesFigure 4 An exploded view of the battery cell of one embodiment of the present application.

[0027] Figure 6 A schematic view of the battery module of one embodiment of the present application.

[0028] Figure 7 A schematic view of the battery pack of one embodiment of the present application.

[0029] Figure 8 A schematic view of Figure 7 An exploded view of the battery pack of one embodiment of the present application.

[0030] Figure 9 A schematic view of the electric device using the secondary battery as a power source of one embodiment of the present application.

[0031] BRIEF DESCRIPTION OF DRAWINGS

[0032] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 case; 52 electrode assembly; 521 negative electrode sheet; 522 positive electrode sheet; 523 separator; 524 gap; 53 top cover assembly DETAILED DESCRIPTION

[0033] Hereinafter, the battery cell, the method for manufacturing the battery cell, the battery device, and the electric device of the present application will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters that are already well known, repeated description of substantially identical structures are omitted. This is to avoid the following description becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0034] The ranges disclosed herein are intended to be "open" ranges, i.e., the upper and lower limits of the range are not included. The ranges are also intended to include any and all sub-ranges of the same, wherein each sub-range is inclusive of the end values. For example, if a range is from 1 to 10, then the range includes any and all sub-ranges between (and including) the minimum of 1 and the maximum of 10, that is, any and all sub-ranges having a minimum of equal to or greater than 1 and a maximum of equal to or less than 10, e.g., 5-10. In other words, the range of "1 to 10" is intended to include the range of "5 to 10" as well as sub-ranges such as 7.1 to 8.3, 5.75 to 6.11, etc. Further, a range includes the singular when the variable includes the singular. For example, a range of "less than 10" is intended to include the variable "10" as well as "less than 10".

[0035] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, if not specifically stated otherwise.

[0036] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, if not specifically stated otherwise.

[0037] All steps of the present application can be performed in sequence or randomly, preferably in sequence, if not specifically stated otherwise. For example, a method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, it is mentioned that the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0038] The terms used in the present application have the commonly understood meanings understood by those skilled in the art, if not specifically stated otherwise.

[0039] The values of the parameters mentioned in the present application can be measured by various test methods commonly used in the art, if not specifically stated otherwise, for example, the test methods given in the present application can be used for measurement.

[0040] In the present application, the battery cell is a secondary battery, which can be activated by charging after discharging to continue to be used. The battery cell can be a lithium ion battery, a sodium ion battery, a sodium lithium ion battery, a lithium metal battery, a sodium metal battery, and the present application is not limited thereto.

[0041] Currently, in large-size battery cells, it is easy to cause uneven distribution of electrolyte. In the preparation stage of the battery cell, after the first liquid injection, the electrolyte infiltrates from the periphery to the center. Due to the chromatographic effect of electrolyte climbing, the concentration of electrolyte salt and additives in the electrolyte gradually decreases from the edge to the center, resulting in that the quality of the anode first film (SEI film) in the center of the battery cell is worse than that in other parts. During the operation of the battery, due to the continuous charging and discharging of the battery cell, the electrolyte is consumed, and at the later stage of the cycle, the electrolyte is mainly located at the bottom of the battery cell due to the action of gravity. For large-size battery cells, the climbing path of the electrolyte from the bottom of the battery cell to the top of the battery cell increases, resulting in insufficient infiltration at the top of the battery cell. Therefore, there is an urgent need for a method for improving the electrolyte infiltration capacity of the electrode sheet.

[0042] In view of the above problems, it is reported that the electrolyte infiltration rate can be improved by, for example, reducing the width and thickness of the electrode sheet, reducing the compaction density of the electrode sheet, etc. However, such treatment will affect the overall performance of the battery cell, such as reducing the capacity of the battery cell, etc. Especially for large-height battery cells, the middle / top of the battery cell is still difficult to be infiltrated by the electrolyte, resulting in uneven distribution of the electrolyte in the height direction of the battery cell, thereby causing inconsistent film-forming components during the formation stage, leading to problems such as lithium precipitation during the cycle, and affecting the cycle performance of the battery.

[0043] Based on this, the present application provides a large-size battery cell, a preparation method thereof, a battery device and a power utilization device. The battery cell of the present application has good electrolyte infiltration in the middle and top, and excellent cycle performance. The present application and optional embodiments will be described in more detail below.

[0044] Battery cell

[0045] The first aspect of the present application provides a battery cell, the height of the battery cell is 200 mm or more, the battery cell comprises at least one battery cell, the battery cell comprises an electrode sheet and a separator, the electrode sheet extends along a first direction, the length of the electrode sheet along the first direction is greater than the length along a second direction, the second direction is perpendicular to the first direction and the same as the height direction of the battery cell, the electrode sheet and the separator are stacked along a third direction, the third direction is perpendicular to the first direction and the second direction, the battery cell has a large area in the cross section perpendicular to the height direction of the battery cell, and the average gap between the electrode sheet and the adjacent separator in the third direction in the large area is 6.3 μm to 24 μm.

[0046] In the present application, for the battery monomer with a height of 200 mm or more, by making the average gap between the pole piece and the adjacent diaphragm in the stacking direction (third direction) in the large area of the cell to be 6.3-24 μm, the effect of capillary force between the positive and negative pole pieces and the diaphragm in the cell can be improved, the wicking height of the electrolyte in the cell is improved, thereby improving the electrolyte wettability of the cell, improving the electrolyte wettability of the battery monomer, thereby reducing the lithium precipitation problem caused by the lack of electrolyte in the middle and / or top of the cell during the later cycle process, thereby improving the cycle performance of the battery monomer.

[0047] The average gap between the pole piece and the adjacent diaphragm in the stacking direction (third direction) in the large area of the cell can be 6.3 μm, 7.2 μm, 8.21 μm, 9.5 μm, 11.0 μm, 12.5 μm, 14.0 μm, 15.5 μm, 16.52 μm, 18.5 μm, 19.5 μm, 20.21 μm, 20.3 μm, 23.52 μm, 24 μm or a value between a range consisting of any two of them. Alternatively, the gap between the pole piece and the adjacent diaphragm in the stacking direction (third direction) in the large area of the cell is 8.2-20.3 μm, thereby more conducive to improving the capillary force between the positive and negative pole pieces and the diaphragm in the cell, thereby further improving the electrolyte wettability of the cell, thereby improving the cycle performance of the battery monomer.

[0048] The height of the battery monomer of the present application is 200 mm or more, which can increase the internal space of the battery monomer, thereby accommodating more electrolyte and electrode material, improving the energy storage capacity of the battery; in addition, it is also conducive to optimizing the size of the pole piece, improving the utilization rate of materials, and improving the production efficiency. In the present application, the height of the battery monomer can be measured by micrometer or height gauge. Exemplarily, the height of the battery monomer of the present application can be 200 mm, 220 mm, 240 mm, 260 mm, 280 mm, 300 mm or a value between a range consisting of any two of them. Alternatively, the height of the battery monomer is 200-300 mm, and further alternatively 210-280 mm. By making the height of the battery monomer in the above range, it is conducive to improving the capacity and energy density of the battery, and also conducive to optimizing the size of the pole piece, improving the utilization rate of materials, while taking into account the production efficiency.

[0049] The battery cell of the present application includes at least one battery cell, for example, it may include 1, 2, 3, or 4. The battery cell includes a pole piece and a separator, and the pole piece and the separator are stacked along a third direction, and the third direction (i.e., the stacking direction) is perpendicular to the height direction of the battery cell. In some embodiments, the pole piece includes a positive pole piece and a negative pole piece, wherein the separator is arranged between the positive pole piece and the negative pole piece. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive pole piece and the negative pole piece. The electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece. The separator is arranged between the positive pole piece and the negative pole piece, mainly to prevent the positive and negative poles from short-circuiting, while allowing ions to pass through. In some embodiments, the positive pole piece, the negative pole piece, and the separator are stacked in sequence in the order of "separator-negative pole piece-separator-positive pole piece".

[0050] Figure 1 Schematic diagram of the structure of a large area of ​​a battery cell according to an embodiment of the present application is shown. Figure 1 As shown, the positive electrode sheet 521, the negative electrode sheet 522, and the separator 523 extend along a first direction (length direction), with the length in the first direction being greater than the length in a second direction, which is perpendicular to the first direction and coincides with the height direction of the battery cell. The positive electrode sheet 521, the negative electrode sheet 522, and the separator 523 are stacked along a third direction (stack direction, perpendicular to the first and second directions), with a gap 524 between the electrode sheet and the adjacent separator.

[0051] In some embodiments, the battery cell is a wound battery cell. Figure 2 As shown, the positive electrode sheet, negative electrode sheet, and separator extend along a first direction (lengthwise) and are wound into a wound structure. The wound structure includes a large surface area and bending regions located on both sides of the large surface area along the first direction in a cross-section perpendicular to the height direction of the battery cell. In the large surface area, the electrode sheet and separator are stacked in a third direction. In the bending region, the stacking direction of the electrode sheet and separator forms a certain angle with the stacking direction of the electrode sheet and separator in the large surface area.

[0052] In the present application, the term "large surface area" refers to the area in which the extension directions of the pole piece and the diaphragm are parallel to each other and perpendicular to the stacking direction in the cross section perpendicular to the height direction of the battery cell. The term "bending area" refers to the corner area formed at both ends in the length direction when the battery cell is wound. It can be understood that the battery cell of the present application includes a large surface area and a bending portion, wherein the bending portion is located on both sides of the large surface area. In the cross section perpendicular to the height direction of the battery cell, the cross section of the large surface area corresponds to the large surface area, and the cross section of the bending portion corresponds to the bending area.

[0053] In the present application, the average gap between the electrode sheet and the adjacent separator in the stacking direction can be tested by computer tomography (CT) technology. CT testing generates a three-dimensional image of the internal structure of the battery cell through X-ray penetration and computer reconstruction technology, which can clearly show the structures of the electrode sheet, separator, electrolyte, etc. inside the battery, so that the gap between the positive electrode sheet or negative electrode sheet and the separator can be measured. The specific test steps are as follows: place the battery cell prepared during the preparation of the battery monomer or the battery cell obtained by disassembling the battery monomer in the CT device (for example, Zeiss Xradia Computer tomography platform) for scanning, obtain the CT picture of the cross section perpendicular to the height direction in the battery cell, and use picture analysis tools such as Powerpoint software to assist in measuring the average gap between the electrode sheet and the adjacent separator in the stacking direction in the CT picture of the battery cell. The exemplary steps of analyzing the average gap include: marking the lowermost electrode sheet (positive or negative) and the uppermost electrode sheet (negative or positive) in the battery cell in the CT picture in the stacking direction, and measuring the vertical distance between them, and converting the actual total thickness according to the scale of the CT picture; recording the number of layers of positive electrode sheets, negative electrode sheets and separators between the lowermost electrode sheet and the uppermost electrode sheet, and their respective single layer thicknesses. Calculate the average gap, the average gap between the electrode sheet and the adjacent separator = (actual total thickness - single layer thickness of positive electrode sheet x number of layers of positive electrode sheet - single layer thickness of negative electrode sheet x number of layers of negative electrode sheet - single layer thickness of separator x number of layers of separator) / (total number of layers of positive electrode sheet, negative electrode sheet and separator - 1).

[0054] In some embodiments, as shown in Figure 3 In the bending area, the average gap between the electrode sheet and the separator in the direction of 45° to the third direction is 8.7 μm to 32.5 μm, starting from the bending position of the innermost layer in the wound battery cell. Exemplarily, the gap is 8.7 μm, 8.9 μm, 9.9 μm, 10.5 μm, 15.5 μm, 18.30 μm, 20.5 μm, 25.5 μm, 28.65 μm, 30.5 μm, 32.31 μm, 32.5 μm or a value between any two of them. By making the gap between the electrode sheet and the separator in the above direction in the bending area within the above range, the capillary force between the positive and negative electrode sheets and the separator is further improved, thereby improving the climbing height of the electrolyte in the battery cell and improving the wettability of the electrolyte, thereby improving the cycle performance of the battery monomer. Alternatively, the gap between the electrode sheet and the separator in the bending area in the direction of 45° to the third direction is 8.7 μm to 28.7 μm, starting from the bending position of the innermost layer in the wound battery cell.

[0055] Figure 3An example of a battery cell including two electric cores is shown, but should not be construed as a limitation of the present application. Those skilled in the art can adjust the number of electric cores in the battery cell as needed. As shown in Figure 3 In each electric core, in the bending area on each side, there is a direction of 45° to the third direction on the upper and lower parts of the bending area.

[0056] In some embodiments, as shown in Figure 3 In the bending area, the gap between the pole piece and the separator is 21.0 μm to 58.5 μm, starting from the bending position of the innermost layer of the wound electric core, in the direction of 90° to the third direction. Exemplarily, the gap can be 21.0 μm, 23.72 μm, 25.23 μm, 25.65 μm, 28.5 μm, 30.5 μm, 35.5 μm, 40.5 μm, 45.5 μm, 50.5 μm, 55.23 μm, 58.23 μm, or a value between any two of them. By making the gap between the pole piece and the separator in the bending area, starting from the bending position of the innermost layer of the wound electric core, in the direction of 90° to the third direction, within the above range, the capillary force between the positive and negative pole pieces and the separator is improved, thereby improving the climbing height of the electrolyte in the electric core, thereby improving the wettability of the electrolyte and improving the cycle performance of the battery cell. Alternatively, the gap between the pole piece and the separator, starting from the bending position of the innermost layer of the wound electric core, in the direction of 90° to the third direction, is 23.5 μm to 55.5 μm.

[0057] In this application, in the bending area of the wound electric core, the average gap between the pole piece and the adjacent separator, starting from the bending position of the innermost layer of the wound electric core, in the direction of a certain angle to the third direction, the exemplary measurement method includes the following specific steps: using the same method as above to obtain the CT picture of the electric core, in the bending area, mark the ray starting from the bending position of the innermost layer of the wound electric core, in the direction of 45° or 90° to the third direction. In the direction of the marked ray, measure the total thickness of the electric core from the winding start position of the innermost layer to the 4th winding position, calculate the average gap between the measured 4 layers, average gap = (actual total thickness - single layer thickness of positive pole piece x number of positive pole pieces - single layer thickness of negative pole piece x number of negative pole pieces - single layer thickness of separator x number of separators) / (total number of positive pole pieces, negative pole pieces and separators - 1). Using the same method as above, continue to count 5 layers from the inside to the outside, calculate the average gap value between each 5 layers of the electric core, and finally calculate the average gap value of the part less than 5 layers as a group. The average of the calculated average gap values is taken as the average gap between the pole piece and the adjacent separator.

[0058] In some embodiments, the separator includes a base membrane and a functional layer disposed on at least one side of the base membrane, wherein the functional layer includes porous ceramic particles. The porous ceramic particles, due to their rich pore structure, can reduce electrolyte extrusion caused by respiration during battery cell cycling, thereby improving the separator's ability to retain electrolyte.

[0059] In some embodiments, the porous ceramic particles include one or more of boehmite, aluminum oxide, titanium dioxide, silicon dioxide, silicon carbide, barium sulfate, calcium sulfate, and glass fiber. These porous ceramic particles have a rich pore structure, stable structure and chemical properties, and good electrolyte retention, which helps reduce electrolyte loss in the middle and / or top portion of the battery cell during cycling, thereby improving the battery's cycling performance.

[0060] In some embodiments, the porous ceramic particles have a porosity of 10% to 80%. By ensuring that the porosity of the porous ceramic particles is within this range, the pores in the porous ceramic particles help improve the capillary force of the separator on the electrolyte, thereby increasing the height of the electrolyte climbing on the separator and improving the electrolyte wettability. Furthermore, the pores in the porous ceramic particles have good electrolyte retention capacity, which helps reduce electrolyte loss during circulation, thereby improving the cycle performance of the battery.

[0061] In the present application, the porosity of ceramic particles is a meaning well known in the art. The porosity of ceramic particles can be tested with reference to the following method: measure the tap density of ceramic particles and the true density of ceramic particles respectively, and calculate the porosity of ceramic particles according to the following formula: (1-tap density of ceramic particles / true density of ceramic particles) × 100%. Wherein, the testing method of the tap density of ceramic particles is as follows: ceramic particles are placed in a container under specified conditions and vibrated, the volume and mass after vibrating are measured, and the tap density of ceramic particles is calculated, and tap density=sample mass / volume after vibrating. The true density of ceramic particles is measured by gas adsorption method, and the testing method is as follows: a ceramic sample is placed in a true density meter, under a closed test system, helium is introduced according to the procedure, the gas pressure in the sample chamber and the expansion chamber is detected, and then the true volume of the sample is calculated according to Bohr's law (PV=nRT), and then the true density of ceramic particles is calculated according to the true volume and mass of the sample, and the true density of ceramic particles=sample mass / true volume of the sample.

[0062] In some embodiments, the air permeability of the separator is 156 s / 100 mL to 175.5 s / 100 mL. By having the air permeability of the separator within the above range, on one hand, it is beneficial to improve the absorption rate and absorption of the electrolyte by the separator, to better absorb and retain the electrolyte, and to improve the cycle performance of the battery cell; on the other hand, it is also beneficial to the passage of active ions in the electrolyte, to improve the ionic conductivity of the battery; in addition, it is also beneficial to improve the strength and thermal stability of the separator, to improve the safety of the battery. Illustratively, the air permeability of the separator can be 156 s / 100 mL, 156.4 s / 100 mL, 160.3 s / 100 mL, 162.2 s / 100 mL, 174.4 s / 100 mL, 175.1 s / 100 mL, 175.5 s / 100 mL, or a value between any two of them.

[0063] In the present application, the air permeability of the separator is the meaning known in the art, and can be tested by methods known in the art. Illustratively, using a gas permeability instrument (such as MODEL 4110N gas permeability instrument of Gurly, USA), the time required for a certain volume (such as 100 mL) of gas (such as air) to pass through a unit area (such as 1 inch 2 ) of the sample at a constant temperature (such as 20-25°C) and a unit pressure difference (such as 1.23 kPa) is determined, i.e. the air permeability. The illustrative test steps include: at room temperature (25°C), the separator obtained by disassembling the secondary battery is laid flat, a flat and oil-free position is selected, placed at the air outlet of the air compression cylinder of the gas permeability instrument, tightened and fixed, the separator is fixed at the work station, the self-weight of the cylinder floating on the liquid is used to compress the air in the cylinder, so that the pressure difference on both sides of the separator is 1.23 kPa, and the test area is one square inch (about 6.45 cm 2 ). As the air passes through the sample, the cylinder will fall smoothly, the time required for 100 mL of air to pass through the separator is measured, and the air permeability is calculated accordingly.

[0064] In some embodiments, the ionic conductivity of the separator is 0.6 mS / cm to 0.95 mS / cm. By having the ionic conductivity of the separator within the above range, it is beneficial to improve the ionic conductivity of the electrolyte by the separator, to reduce the internal resistance of the battery, to reduce the polarization phenomenon in the battery, and to improve the cycle stability of the battery cell.

[0065] In the present application, the ionic conductivity of the separator is the meaning known in the art, which can be tested by methods known in the art. Exemplarily, the specific test steps are as follows: the separator is disassembled from the secondary battery, the thickness of the separator is measured using a micrometer, which can be measured multiple times to ensure the accuracy of the thickness data. The separator is clamped between two electrodes to assemble a test battery. The resistance value of the single-layer separator is measured using a resistance tester. According to the measured resistance value and the thickness of the separator, the conductivity is calculated. The formula is as follows: conductivity = 1 / (resistance x thickness), unit: mS / cm.

[0066] In some embodiments, the areal density of the separator is 3 g / m 2 ~ 7.6 g / m 2 By making the areal density of the separator within the above range, it is shown that the areal density of the separator is low, which on the one hand is conducive to reducing the overall volume and weight of the battery monomer, thereby improving the energy density of the battery monomer. On the other hand, the low areal density of the separator indicates that the thermal shrinkage rate of the separator is low, thereby facilitating the improvement of the safety performance of the battery. In addition, the low areal density is conducive to improving the uniformity of the thickness of the separator, improving the mechanical strength of the separator, and also conducive to improving the cycle performance of the battery.

[0067] In the present application, the areal density of the separator refers to the mass per unit area of the separator, which can be tested by methods known in the art. Exemplarily, the test steps are as follows: the separator is disassembled from the secondary battery, a certain area of the separator sample is cut, for example, 100 cm 2 The mass of the cut separator sample is weighed using a high-precision electronic balance, and the areal density of the separator is calculated according to the following formula: areal density = mass / area.

[0068] In some embodiments, the thickness of the functional layer is less than or equal to 5 μm. By making the thickness of the functional layer within the above range, it is conducive to improving the liquid climbing ability and liquid retention ability of the separator, thereby improving the wettability of the electrolyte to the battery cell and improving the cycle performance of the battery. Exemplarily, the thickness of the functional layer can be less than or equal to 5 μm, less than or equal to 4 μm, less than or equal to 3 μm, less than or equal to 2 μm, less than or equal to 1 μm.

[0069] The battery cell of the present application also includes an electrolyte. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The present application does not have specific limitations on the type of electrolyte, which can be selected according to the needs. The electrolyte can be liquid, gel or solid.

[0070] The second aspect of the present application provides a method for preparing a battery cell, which includes the steps of stacking the pole pieces and the diaphragm in sequence and then cold pressing them, the cold pressing pressure is 20T to 50T, and the cold pressing time is 20s to 150s. The pole pieces and the diaphragm are stacked in sequence and then cold pressed, and by making the cold pressing pressure and the cold pressing time within the above range, the average gap between the pole piece and the adjacent diaphragm is 6.3μm-24μm. This is beneficial to improving the capillary force between the pole piece and the diaphragm in the prepared battery cell, improving the liquid climbing height and wettability of the electrolyte in the battery cell, and thus improving the cycle performance of the prepared battery cell. In the present application, cold pressing is a battery cell preparation process well known in the art, which includes placing the stacked pole pieces and diaphragm into a cold press, applying a certain pressure for cold pressing for a period of time, and the temperature is usually room temperature, such as 25°C. For example, the cold pressing pressure may be 20T, 24T, 26T, 28T, 30T, 32T, 33.0T, 34.0T, 35.0T, 36.0T, 37.0T, 37.5T, 38.0T, 38.5T, 39.0T, 40.0T, 42.0T, 42.5T, 44T, 46T, 48T, 50T, or a value between the ranges consisting of any two of them. The cold pressing time may be 20s, 30s, 40s, 50s, 60s, 70s, 90s, 110s, 130s, 150s, or a value between the ranges consisting of any two of them. In some optional embodiments, the cold pressing pressure is 32T to 42.5T, and the cold pressing time is 20s to 60s. This helps to achieve an appropriate average gap between the positive and negative electrodes and the separator in the prepared battery cell, increasing the electrolyte's climbing height and wettability in the battery cell, and improving the battery's cycling performance. It also helps to compact the positive and negative electrode sheets and separator layers, reducing the resistance of the separator layer, increasing the adhesion between the electrode sheets and / or separator, and improving the surface quality of the positive and negative electrode sheets and / or separator.

[0071] In some embodiments, the preparation method further comprises injecting electrolyte into the bare battery cell obtained after cold pressing.

[0072] The components of the battery cell of the present application are introduced in detail below.

[0073] Negative electrode

[0074] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0075] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0076] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0077] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination of two or more.

[0078] In some embodiments, the negative film layer can further optionally include a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0079] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0080] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0081] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-described components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry, coating the negative electrode slurry on a negative current collector, and then performing processes such as drying, cold pressing, etc.

[0082] Positive electrode sheet

[0083] The positive electrode tab includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including the positive electrode material of the present application or the positive electrode material prepared according to the preparation method of the present application.

[0084] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector. In some embodiments, the positive electrode current collector can adopt a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0085] In some embodiments, when the battery cell is a lithium ion battery, the positive electrode active material can adopt a positive electrode active material commonly known in the art for lithium ion batteries. As an example, the positive electrode active material can include at least one of the following materials: lithium-containing phosphate of olivine structure, lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination with two or more. Among them, examples of lithium transition metal oxides can include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3Mn 1 / 3 O2(also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2(also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn0.1 O2(also can be referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.1 Al 0.05 O2) and modified compounds thereof. Examples of lithium-containing phosphates of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4(also can be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon.

[0086] The battery will be accompanied by Li de-intercalation and consumption during charging and discharging, and the molar content of Li is different when the battery is discharged to different states. In the enumeration of the positive electrode active material in the present application, the molar content of Li is the initial state of the material, i.e. the state before feeding. When the positive electrode active material is applied to the battery system, the molar content of Li will change after charging and discharging cycles.

[0087] In the enumeration of the positive electrode active material in the present application, the molar content of O is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will appear to be floating.

[0088] In some embodiments, when the battery monomer is a sodium ion battery, the positive electrode active material can use the positive electrode active material known in the art for sodium ion batteries. As an example, the positive electrode active material can include sodium transition metal oxide, polyanion compound, prussian blue compound, etc.

[0089] In some embodiments, the positive electrode film layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic ester resin.

[0090] In some embodiments, the positive electrode film layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0091] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, in a solvent (such as N-methyl pyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying, cold pressing, etc., the positive electrode sheet can be obtained.

[0092] Electrolyte

[0093] The electrolyte functions to conduct ions between the positive electrode and the negative electrode. The type of electrolyte is not particularly limited in the present application and can be selected as desired. For example, the electrolyte can be liquid, gel, or all-solid.

[0094] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0095] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0096] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0097] In some embodiments, the electrolyte solution can optionally further include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0098] In some embodiments, the battery cell can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte described above.

[0099] In some embodiments, the outer package of the battery cell can be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The outer package of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed.

[0100] The shape of the battery cell is not particularly limited in the present application and can be cylindrical, square, or any other arbitrary shape. For example, Figure 4 is a square structure battery cell 5 as an example.

[0101] In some embodiments, referring to Figure 5The outer package can include a housing 51 and a top cover assembly 53. The housing 51 can include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening in communication with the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator film can form the electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of the electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by a person skilled in the art according to specific actual needs.

[0102] Battery device

[0103] In addition, the application also provides a battery device, which includes the battery cell of the application.

[0104] In some embodiments, the battery cell can be assembled into a battery module, and the number of the battery cells contained in the battery module can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0105] Figure 6 The battery module 4 is taken as an example. Refer to Figure 6 In the battery module 4, the plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be adopted. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0106] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0107] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of the battery modules contained in the battery pack can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0108] Figure 7 And Figure 8 The battery pack 1 is taken as an example. Refer to Figure 7 And Figure 8 In the battery pack 1, a battery box and a plurality of battery modules 4 arranged in the battery box can be included. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in an arbitrary manner.

[0109] Battery device

[0110] In addition, the application also provides a power utilization device comprising the battery device provided by the application. The battery device can be used as a power supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0111] As the power utilization device, a battery cell, a battery module or a battery pack can be selected according to the use requirement thereof.

[0112] Figure 9 The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the power utilization device, a battery pack or a battery module can be used.

[0113] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and a battery cell can be used as a power supply.

[0114] Embodiment

[0115] Hereinafter, the embodiments of the application are described. The embodiments described below are exemplary and are only used to explain the application, and cannot be understood as a limitation of the application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument used is not indicated by the manufacturer, it is a conventional product that can be obtained by purchase.

[0116] Embodiment 1

[0117] Preparation of battery cells

[0118] Preparation of the positive electrode tab: the active material lithium iron phosphate, the conductive agent carbon black and the binder PVDF were mixed in a weight ratio of 98.2:0.3:1.5, a solvent N-methyl pyrrolidone was added, and the mixture was fully stirred and uniformly mixed to obtain a positive electrode slurry. The positive electrode slurry was coated on two surfaces of a positive electrode current collector aluminum foil, wherein the coating weight of the positive electrode slurry was 0.3196 g / 1540.25 mm 2 (determined by the weight excluding the solvent), and after drying and cold pressing, a positive electrode tab was obtained.

[0119] Preparation of the negative electrode tab:

[0120] The active material artificial graphite (330 mAh / g of capacity), the conductive agent carbon black, the binder carboxymethyl cellulose and water are mixed in a weight ratio of 97.9:0.4:1.7:100, and are fully stirred and mixed uniformly to obtain a negative electrode slurry. The negative electrode slurry is coated on the surfaces of both sides of a negative electrode current collector copper foil, wherein the coating weight of the negative electrode slurry is 0.1563 g / 1540.25 mm 2 (100 by weight excluding the solvent), and after drying and cold pressing, a negative electrode sheet is obtained.

[0121] Preparation of electrolyte:

[0122] In an argon atmosphere glove box with a water content of <10 ppm, ethylene carbonate, diethyl carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1:1, and LiPF6 is dissolved in the above solution to obtain an electrolyte. In the electrolyte, the concentration of LiPF6 is 1 mol / L.

[0123] Preparation of separator:

[0124] Preparation of functional layer: aluminum oxide porous ceramic particles, acrylic block polymer dispersant and polyvinylidene fluoride binder are mixed in a weight ratio of 93:0.5:6.5, and are dispersed in an acetone solvent to obtain a functional layer slurry.

[0125] A polyethylene porous membrane is used as a base film, and the functional layer slurry is uniformly coated on both sides of the base film. After drying and cold pressing, a separator is obtained, wherein the thickness of the functional layer on one side of the base film is 2 μm.

[0126] Assembly of battery monomer:

[0127] The negative electrode sheet, the positive electrode sheet and the separator are sequentially stacked in the order of "separator-negative electrode sheet-separator-positive electrode sheet", so that the separator is located between the positive and negative electrode sheets to play a separating role, and a roll structure is obtained by winding. The above winding structure is placed in a cold press, and a cold pressing pressure of 38.5T and a cold pressing time of 30s are set for cold pressing to obtain a wound bare cell. The above wound bare cell is placed in an outer package, the above electrolyte is injected, and is packaged for formation to obtain a battery monomer, and the height of the battery monomer is L (239 mm).

[0128] Parameter testing

[0129] Parameter test of separator:

[0130] The separator is obtained by disassembling the secondary battery, and the performance of the separator is tested according to the following method.

[0131] (1) Air permeability

[0132] The measurement was performed using a MODEL 4110N air permeability meter from Gurley, USA. The membrane was laid flat and a clean, oil-free area was selected. The membrane was placed over the air outlet of the air compression cylinder of the air permeability meter, and was fastened tightly. After the membrane was fixed in place, the cylinder was compressed by its own weight, which caused a pressure difference of 1.23 kPa across the membrane. The test area was 1 square inch (about 6.45 cm 2 ). As air passed through the sample, the cylinder fell steadily. The time required for 100 mL of air to pass through the membrane was measured, and was reported as the air permeability (in s / 100 mL).

[0133] (2) Ionic conductivity

[0134] The thickness of the membrane was measured using a micrometer. The measurement was repeated several times to ensure accuracy. The membrane was sandwiched between two electrodes to form a test cell. The resistance of the single layer of the membrane was measured using a resistance tester. The conductivity was calculated from the measured resistance and the thickness of the membrane. The formula was as follows: conductivity = 1 / (resistance x thickness), and was reported in mS / cm.

[0135] (3) Area density

[0136] A 100 cm 2 square sample of the membrane was cut. The mass of the cut sample was measured using a high-precision electronic balance. The area density of the membrane was calculated according to the following formula: area density = mass / area.

[0137] Parameter testing of battery cells

[0138] (1) Test of the gap between the electrode and the adjacent separator in the large area

[0139] The battery cell was placed in a CT device for scanning to obtain a CT image of the battery cell. Using image analysis software, the lowest positive electrode (or negative electrode) and the uppermost negative electrode (or positive electrode) in the stacking direction of the battery cell were marked in the CT image, and the vertical distance between them was measured. The actual total thickness was converted according to the scale of the CT image; the number of layers of the positive electrode, the negative electrode, and the separator between the lowest positive electrode (or negative electrode) and the uppermost negative electrode (or positive electrode) was recorded, and the thickness of each layer was measured. The average gap was calculated according to the following formula:

[0140] The average gap between the electrode and the adjacent separator = (actual total thickness - thickness of a single layer of the positive electrode x number of layers of the positive electrode - thickness of a single layer of the negative electrode x number of layers of the negative electrode - thickness of a single layer of the separator x number of layers of the separator) / (total number of layers of the positive electrode, the negative electrode, and the separator - 1).

[0141] (2) Test of the gap between the electrode and the adjacent separator in the bending area

[0142] The cell taken apart from the battery monomer is placed in the CT device to scan and obtain the CT picture of the cell. By using the picture analysis software, the bending area in the CT picture is marked, the total thickness of the cell between the winding start position of the innermost layer and the 4th winding position is measured in the direction of the marked ray at 45° or 90° to the third direction, the average gap between the measured 4 layers is calculated, average gap = (actual total thickness - single layer thickness of positive electrode sheet x number of layers of positive electrode sheet - single layer thickness of negative electrode sheet x number of layers of negative electrode sheet - single layer thickness of separator x number of layers of separator) / (total number of layers of positive electrode sheet, negative electrode sheet and separator - 1). The same method is used to calculate, and the average gap value between each 5 layers of the cell is calculated from the inside to the outside, and the last part less than 5 layers is calculated as a group. The average gap value of each calculated average gap value is taken as the average gap between the electrode sheet and the adjacent separator.

[0143] (3) Winding infiltration rate

[0144] A fan is used to circulate the hot air to keep the test at a uniform and stable temperature, and the ambient temperature of the test is 25±5℃. The prepared cell is placed in a tray containing electrolyte for infiltration, and the weight of the cell is recorded every time interval after the cell is placed in the tray and the infiltration process is completed. The weight of the electrolyte is obtained, and the curve of the weight of the electrolyte changing with time is obtained. The curve is fitted by using data processing software, and the slope of the curve is obtained, which is the winding infiltration rate, with the unit of g / s. 0.5 .

[0145] Performance testing of battery cells

[0146] Cycle performance test:

[0147] At 25℃, the battery monomer is first charged at 1C (i.e. the current value of completely discharging the theoretical capacity within 1h) to a voltage of 3.65V, then charged at 3.65V to a current of 0.05C, and then discharged at 1C to a voltage of 2.5V after 5min of standing, which is a charge and discharge cycle process. The discharge capacity of this time is the discharge capacity of the first cycle. The lithium ion secondary battery is subjected to multiple cycle charge and discharge tests according to the above method until the discharge capacity of the lithium ion secondary battery decays to 80%, and the cycle number of the battery is recorded.

[0148] Examples 2-6

[0149] The battery cell was prepared in the same manner as in Example 1, except that the pressure and the cold-pressing time of the cold-pressing and the height of the battery cell were adjusted according to Table 1 so that the gap between the electrode tab and the separator had the values shown in Table 2.

[0150] Comparative Example 1

[0151] The battery cell was prepared in the same manner as in Example 1, except that the pressure and the cold-pressing time of the cold-pressing were adjusted according to Table 1 so that the gap between the electrode tab and the adjacent separator in the large surface area of the cell was less than 6.3 μm.

[0152] Comparative Example 2

[0153] The battery cell was prepared in the same manner as in Example 1, except that the pressure and the cold-pressing time of the cold-pressing were adjusted according to Table 1 so that the gap between the electrode tab and the adjacent separator in the large surface area of the cell was greater than 24 μm.

[0154] Table 1

[0155]

[0156] Example 1 to Example 6 and Comparative Examples 1, 2 were tested in the same manner as in Example 1, and the results are shown in Table 2.

[0157] Table 2

[0158]

[0159] The results show that, by controlling the cold-pressing pressure in the range of 20T-50T and the cold-pressing time in the range of 20s-150s during the preparation of the battery, the average gap between the positive and negative electrode tabs and the adjacent separator in the large surface area in the third direction of the battery cell prepared in Examples 1-6 is in the range of 6.3 μm-24 μm, which is beneficial to improve the infiltration rate of the electrolyte and thus improve the cycle performance of the battery. In contrast, the cold-pressing time of Comparative Example 1 during the preparation of the battery cell is more than 150s, so that the average gap between the electrode tab and the adjacent separator in the large surface area of the cell of the battery cell prepared is less than 6.3 μm. Comparative Example 2 uses a cold-pressing pressure of less than 20T to prepare the battery cell, so that the average gap between the electrode tab and the adjacent separator in the large surface area of the cell of the battery cell prepared is greater than 24 μm. The winding infiltration rate of the cell of Comparative Examples 1 and 2 is small, and the electrolyte infiltration effect is poor, so that the cycle performance of the battery cell is poor.

[0160] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. Furthermore, other modes constructed by applying various modifications to the embodiments, or by combining part of the configurations of the embodiments, which can be conceived by those skilled in the art without departing from the spirit of the present application, are also included in the scope of the present application.

Claims

1. A battery cell, characterized in that: The height of the battery cell is more than 200 mm. The battery cell includes at least one battery cell, and the battery cell includes a pole piece and a separator. The pole piece extends along a first direction, the length of the pole piece along the first direction is greater than the length along a second direction, the second direction is perpendicular to the first direction and is the same as the height direction of the battery cell, the pole piece and the diaphragm are stacked along a third direction, the third direction is perpendicular to the first direction and the second direction, The battery cell has a large surface area in a cross section perpendicular to the height direction of the battery cell, and in the large surface area, an average gap between the electrode and the adjacent separator in the third direction is 6.3 μm-24 μm.

2. The battery cell according to claim 1, wherein: In the large area, an average gap between the pole piece and the adjacent diaphragm in the third direction is 8.2 μm-20.3 μm.

3. The battery cell according to claim 1 or 2, characterized in that: The battery cell is a wound battery cell, and the wound battery cell includes the large area and bending areas located on both sides of the large area along the first direction in a cross section perpendicular to the height direction of the battery cell. In the bending region, starting from the innermost bending position of the wound battery cell, in a direction at 45° to the third direction, the average gap between the pole piece and the diaphragm is 8.7 μm to 32.5 μm.

4. The battery cell according to claim 3, characterized in that In the bending region, starting from the bending position of the innermost layer of the wound battery cell, in a direction at 45° to the third direction, the average gap between the pole piece and the diaphragm is 8.9 μm to 28.7 μm.

5. The battery cell according to claim 3 or 4, characterized in that: In the bending region, starting from the innermost bending position of the wound battery cell, in a direction 90° to the third direction, the average gap between the pole piece and the diaphragm is 21.0 μm to 58.5 μm.

6. The battery cell according to claim 5, characterized in that In the bending region, starting from the innermost bending position of the wound battery cell, in a direction 90° to the third direction, the average gap between the pole piece and the diaphragm is 23.5 μm to 55.5 μm.

7. The battery cell according to claims 1 to 6, characterized in that: The separator includes a base membrane and a functional layer disposed on at least one side of the base membrane, wherein the functional layer includes porous ceramic particles.

8. The battery cell according to claim 7, characterized in that The porous ceramic particles include one or more of boehmite, aluminum oxide, titanium dioxide, silicon dioxide, silicon carbide, barium sulfate, calcium sulfate, and glass fiber.

9. The battery cell according to claim 7 or 8, characterized in that: The air permeability of the diaphragm is 156s / 100mL-175.5s / 100mL.

10. The battery cell according to any one of claims 7 to 9, characterized in that: The ionic conductivity of the separator is 0.6 mS / cm to 0.95 mS / cm.

11. The battery cell according to any one of claims 7 to 10, characterized in that: The surface density of the diaphragm is 3g / m 2 ~7.6g / m 2 .

12. The battery cell according to any one of claims 7 to 11, characterized in that: The thickness of the functional layer is less than or equal to 5 μm.

13. The battery cell according to any one of claims 1 to 12, characterized in that: The height of the battery cell is 200mm-300mm.

14. A method for preparing a battery cell, characterized in that: The height of the battery cell is above 200 mm. The preparation method includes the steps of stacking the pole pieces and the diaphragm in sequence and then cold pressing them. The cold pressing pressure is 20T to 50T and the cold pressing time is 20s to 150s.

15. The preparation method according to claim 14, characterized in that The cold pressing pressure is 32T to 42.5T, and the cold pressing time is 20s to 60s.

16. A battery device, characterized in that: A battery cell comprising any one of claims 1 to 13, or a battery cell prepared by the preparation method according to claim 14 or 15.

17. An electrical device, characterized in that: A battery device comprising the battery device of claim 16.

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