Battery monomer, battery and electric device

Abstract

The invention provides a battery monomer, a battery and a power utilization device, and belongs to the technical field of batteries. The single battery comprises a negative pole piece, the negative pole piece comprises a main body part and a tab, the main body part is provided with a first end and a second end which are opposite, the tab is arranged at the first end, the direction extending from the first end to the second end is the width direction of the negative pole piece, and the main body part comprises a first area, a second area and a third area which are sequentially distributed in the width direction; the ion diffusion coefficient of the first region is greater than that of the second region, and / or the ion diffusion coefficient of the third region is greater than that of the second region. According to the battery monomer, the dynamic performance of the middle region of the negative pole piece can be reduced, and the dynamic performance of the end region of the negative pole piece can be improved, so that the problem of non-uniform polarization of different regions in the cycle process of the battery monomer is counteracted or weakened, and the lithium precipitation problem or the sodium precipitation problem of the negative pole piece is improved; and the service life of the battery monomer is prolonged.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a battery cell, a battery and an electrical device. Background Art

[0002] In recent years, as the application scope of lithium-ion batteries has become more and more extensive, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As lithium-ion batteries have made great progress, higher requirements have been put forward for their energy density, cycle performance and safety performance.

[0003] As lithium batteries continue to develop towards high power and high energy density, capacity decay has become the main limiting factor of lithium batteries. Summary of the invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell, a battery and an electrical device, which can slow down the capacity decay of the battery cell and increase the service life of the battery cell.

[0005] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a battery cell, which includes an electrode assembly, the electrode assembly includes a negative electrode plate, the negative electrode plate includes a main body and a pole ear, the main body has a first end and a second end opposite to each other, the pole ear is arranged at the first end, the direction extending from the first end to the second end is the width direction of the negative electrode plate, the main body includes a first region, a second region and a third region distributed in sequence along the width direction, the ion diffusion coefficient of the first region is greater than the ion diffusion coefficient of the second region, and / or the ion diffusion coefficient of the third region is greater than the ion diffusion coefficient of the second region; the ion diffusion coefficient includes a lithium ion diffusion coefficient or a sodium ion diffusion coefficient.

[0006] Therefore, the battery cell of the present application divides the main body into a first region, a second region and a third region distributed in sequence along the width direction, and makes the lithium ion diffusion coefficient or the sodium ion diffusion coefficient of the first region greater than the lithium ion diffusion coefficient or the sodium ion diffusion coefficient of the second region, and / or the ion diffusion coefficient of the third region greater than the ion diffusion coefficient of the second region, wherein the second region is closer to the middle of the negative electrode plate than the first region and the third region, thereby reducing the kinetic performance of the middle region of the negative electrode plate, that is, slowing down the migration and diffusion of lithium ions or the migration and diffusion of sodium ions in the middle region of the negative electrode plate, increasing the polarization of the middle region of the negative electrode plate, and improving the kinetic performance of the end region of the negative electrode plate, that is, accelerating the migration and diffusion of lithium ions or the migration and diffusion of sodium ions in the end region of the negative electrode plate, reducing the polarization of the end region of the negative electrode plate, thereby offsetting or weakening the problem of uneven polarization in different regions during the battery cell cycle, improving the lithium precipitation problem or sodium precipitation problem of the negative electrode plate and the capacity attenuation of the battery cell, and improving the service life of the battery cell.

[0007] In any embodiment, the ratio of the lithium ion diffusion coefficient of the first region to the lithium ion diffusion coefficient of the second region is 2 to 1000, and / or the ratio of the lithium ion diffusion coefficient of the third region to the lithium ion diffusion coefficient of the second region is 2 to 1000. By making the ratio of the lithium ion diffusion coefficient of the first region to the lithium ion diffusion coefficient of the second region and / or the ratio of the lithium ion diffusion coefficient of the third region to the lithium ion diffusion coefficient of the second region within the above range, it is possible to avoid or improve the problem of lithium precipitation in the middle part and accelerated capacity decay of the battery cell in the late cycle due to the excessively high kinetic performance of the first region and / or the third region located at the end and the excessively low kinetic performance of the second region located in the middle.

[0008] In any embodiment, the main body is sequentially divided into the first region, the second region and the third region along the width direction, and the ratio of the lithium ion diffusion coefficient located in the first region and / or the third region to the lithium ion diffusion coefficient located in the second region is 5 to 500. When the main body is sequentially divided into the first region, the second region and the third region along the width direction, by making the ratio of the lithium ion diffusion coefficient located in the first region to the lithium ion diffusion coefficient located in the second region and / or the ratio of the lithium ion diffusion coefficient located in the third region to the lithium ion diffusion coefficient located in the second region within the above range, it is possible to avoid or improve the problem of lithium deposition in the middle part and accelerated capacity decay of the battery cell in the late cycle due to the excessively high kinetic performance of the first region and / or the third region located at the end and the excessively low kinetic performance of the second region located in the middle.

[0009] In any embodiment, the lithium ion diffusion coefficient in the first region and / or the third region is 10 -9 cm 2 / s~10 -11cm 2 / s, and the lithium ion diffusion coefficient in the second region is 10 -11 cm 2 / s~10 -12 cm 2 By making the lithium ion diffusion coefficient located in the first region and / or the lithium ion diffusion coefficient located in the third region, and the lithium ion diffusion coefficient located in the second region within the above range, it is beneficial to reduce the dynamic performance of the middle region of the negative electrode plate, increase the polarization of the middle region of the negative electrode plate, and improve the dynamic performance of the end region of the negative electrode plate, and reduce the polarization of the end region of the negative electrode plate.

[0010] In any embodiment, the area of ​​the second region accounts for 50% to 70% of the total area of ​​the main body. By making the area of ​​the second region account for the above range, the area size of the first region and the third region can be further divided according to the polarization of the negative electrode plate during the battery cell cycle, so as to more accurately offset or reduce the problem of uneven polarization of different regions during the battery cell cycle, improve the capacity attenuation of the battery cell, and increase the service life of the battery cell.

[0011] In any embodiment, the ratio of the dimensions of the first region, the second region, and the third region along the width direction is 15% to 25%: 50% to 70%: 15% to 25%. By making the ratio of the dimensions of the first region, the second region, and the third region along the width direction within the above range, it is beneficial to divide the first region, the third region, and the second region therebetween located at the two ends according to the polarization of the negative electrode sheet during the battery cell cycle, so as to more accurately offset or weaken the problem of uneven polarization of different regions during the battery cell cycle, improve the capacity attenuation of the battery cell, and increase the service life of the battery cell.

[0012] In any embodiment, the negative electrode plate includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, and the ion diffusion coefficient of the negative electrode active material located in the first region and / or the third region is greater than the ion diffusion coefficient of the negative electrode active material located in the second region. The battery cell of the present application can make the lithium ion diffusion coefficient or sodium ion diffusion coefficient of the first region and / or the third region greater than the lithium ion diffusion coefficient or sodium ion diffusion coefficient of the negative electrode active material located in the second region, thereby reducing the kinetic performance of the middle region of the negative electrode plate, increasing the polarization of the middle region of the negative electrode plate, and improving the kinetic performance of the end region of the negative electrode plate, reducing the polarization of the end region of the negative electrode plate, thereby offsetting or weakening the problem of uneven polarization in different regions during the battery cell cycle, improving the lithium or sodium precipitation problem of the negative electrode plate and the capacity attenuation of the battery cell, and improving the service life of the battery cell.

[0013] In any embodiment, the negative electrode plate includes a negative electrode active material layer, and the first region, the second region and the third region include the same conductive agent, based on the mass of the negative electrode active material layer in the first region, the mass proportion of the conductive agent in the negative electrode active material layer in the first region is W1, based on the mass of the negative electrode active material layer in the second region, the mass proportion of the conductive agent in the negative electrode active material layer in the second region is W2, based on the mass of the negative electrode active material layer in the third region, the mass proportion of the conductive agent in the negative electrode active material layer in the third region is W3, W1<W2 and / or W3<W2. When the conductive agent used in the first region, the second region and the third region is the same, the battery cell of the present application can reduce the kinetic performance of the middle region of the negative electrode plate by making the mass proportion of the conductive agent in the negative electrode active material layer located in the second region greater than the mass proportion of the conductive agent in the negative electrode active material layer located in the first region and / or the third region, that is, slowing down the migration and diffusion of lithium ions or the migration and diffusion of sodium ions in the middle region of the negative electrode plate, increasing the polarization of the middle region of the negative electrode plate, and improving the kinetic performance of the end region of the negative electrode plate, that is, accelerating the migration and diffusion of lithium ions or the migration and diffusion of sodium ions in the end region of the negative electrode plate, reducing the polarization of the end region of the negative electrode plate, thereby offsetting or weakening the problem of uneven polarization in different regions during the battery cell cycle, improving the lithium or sodium precipitation problem of the negative electrode plate and the capacity attenuation of the battery cell, and improving the service life of the battery cell.

[0014] In any embodiment, the difference between W2 and W1 is 0.5wt% to 2wt%, and / or the difference between W2 and W3 is 0.5wt% to 2wt%. By making the difference between the mass ratio of the conductive agent in the negative electrode active material layer located in the second region and the mass ratio of the conductive agent in the negative electrode active material layer located in the first region and / or the difference between the mass ratio of the conductive agent in the negative electrode active material layer located in the second region and the mass ratio of the conductive agent in the negative electrode active material layer located in the third region within the above range, it is possible to avoid or improve the problem of lithium deposition in the middle part and accelerated capacity decay of the battery cell caused by excessively high kinetic performance of the first region and / or the third region located at the end and excessively low kinetic performance of the second region located in the middle in the late cycle.

[0015] In any embodiment, the negative electrode plate includes a negative active material layer, the negative active material layer includes a conductive agent, the first region includes a first conductive agent, the second region includes a second conductive agent, the third region includes a third conductive agent, the conductivity of the second conductive agent is greater than the conductivity of the first conductive agent, and / or the conductivity of the second conductive agent is greater than the conductivity of the third conductive agent. When the conductive agents used in the first region, the second region and the third region are different, the battery cell of the present application can reduce the kinetic performance of the middle region of the negative electrode plate, that is, slow down the migration and diffusion of lithium ions or the migration and diffusion of sodium ions in the middle region of the negative electrode plate, increase the polarization of the middle region of the negative electrode plate, and improve the kinetic performance of the end region of the negative electrode plate, that is, accelerate the migration and diffusion of lithium ions or the migration and diffusion of sodium ions in the end region of the negative electrode plate, reduce the polarization of the end region of the negative electrode plate, and then offset or weaken the problem of uneven polarization in different regions during the battery cell cycle, improve the lithium or sodium precipitation problem of the negative electrode plate and the capacity attenuation of the battery cell, and improve the service life of the battery cell.

[0016] In any embodiment, the negative electrode plate includes a negative electrode active material layer, the first region, the second region and the third region include the same binder, the mass proportion of the binder in the negative electrode active material layer located in the first region is W4, the mass proportion of the binder in the negative electrode active material layer located in the second region based on the mass of the negative electrode active material layer in the second region is W5, the mass proportion of the binder in the negative electrode active material layer located in the third region based on the mass of the negative electrode active material layer in the third region is W6, W4>W5 and / or W6>W5. When the binder used in the first region, the second region and the third region is the same, the battery cell of the present application can reduce the kinetic performance of the middle region of the negative electrode plate by making the mass proportion of the binder in the negative electrode active material layer located in the first region and / or the third region greater than the mass proportion of the binder in the negative electrode active material layer located in the second region, that is, slowing down the migration and diffusion of lithium ions or the migration and diffusion of sodium ions in the middle region of the negative electrode plate, increasing the polarization of the middle region of the negative electrode plate, and improving the kinetic performance of the end region of the negative electrode plate, that is, accelerating the migration and diffusion of lithium ions or the migration and diffusion of sodium ions in the end region of the negative electrode plate, reducing the polarization of the end region of the negative electrode plate, thereby offsetting or weakening the problem of uneven polarization in different regions during the battery cell cycle, improving the lithium or sodium precipitation problem of the negative electrode plate and the capacity attenuation of the battery cell, and improving the service life of the battery cell.

[0017] In any embodiment, the difference between W4 and W5 is 0.5wt% to 3.1wt%, and / or the difference between W6 and W5 is 0.5wt% to 3.1wt%. By making the difference between the mass ratio of the binder in the negative electrode active material layer located in the first region and the mass ratio of the binder in the negative electrode active material layer located in the second region and / or the difference between the mass ratio of the binder in the negative electrode active material layer located in the third region and the mass ratio of the binder in the negative electrode active material layer located in the second region within the above range, it is possible to avoid or improve the problem of lithium deposition in the middle part and accelerated capacity decay of the battery cell in the late cycle due to the excessively high kinetic performance of the first region and / or the third region located at the end and the excessively low kinetic performance of the second region located in the middle.

[0018] In any embodiment, the main body also includes a fourth region and a fifth region, and the main body includes a first region, a fourth region, a second region, a fifth region and a third region sequentially distributed along the width direction, and the ion diffusion coefficient of the fourth region and / or the fifth region is greater than the ion diffusion coefficient of the second region and less than the ion diffusion coefficient of the first region. The battery cell of the present application is divided into the main body into a first region, a fourth region, a second region, a fifth region and a third region sequentially distributed along the width direction, and the ion diffusion coefficient of the fourth region and / or the fifth region is greater than the ion diffusion coefficient of the second region and less than the ion diffusion coefficient of the first region, wherein the fourth region disposed between the second region and the first region and the fifth region disposed between the second region and the third region are transition regions, and the polarization difference between the second region and the adjacent region is reduced, so that the transition from the second region to the first region and the third region is more stable, thereby improving the service life of the battery cell.

[0019] In any embodiment, the ratio of the dimensions of the first region, the fourth region, the second region, the fifth region and the third region along the width direction is 10% to 15%: 5% to 10%: 50% to 70%: 5% to 10%: 10% to 15%. By making the ratio of the dimensions of the first region, the fourth region, the second region, the fifth region and the third region along the width direction within the above range, it is beneficial to more accurately offset or weaken the problem of uneven polarization of different regions during the battery cell cycle according to the polarization of the negative electrode plate during the battery cell cycle, improve the capacity attenuation of the battery cell, and increase the service life of the battery cell.

[0020] In any embodiment, the ratio of the lithium ion diffusion coefficient located in the fourth region and / or the fifth region to the lithium ion diffusion coefficient located in the second region is 5 to 100. By making the ratio of the lithium ion diffusion coefficient located in the fourth region and / or the fifth region to the lithium ion diffusion coefficient located in the second region within the above range, it is possible to avoid or improve the problem of lithium deposition in the middle part and accelerated capacity decay of the battery cell in the late cycle due to the excessively high kinetic performance of the fourth region and / or the fifth region and the excessively low kinetic performance of the second region located in the middle.

[0021] In any embodiment, the ion diffusion coefficient in the fourth region and / or the fifth region is 10 -10 cm 2 / s~5*10 -12 cm 2 / s. By making the ion diffusion coefficient located in the fourth region and / or the fifth region within the above range, the ion diffusion coefficient located in the fourth region and / or the fifth region can be greater than the ion diffusion coefficient of the second region and less than the ion diffusion coefficient of the first region and / or the third region, which is beneficial to reducing the dynamic performance of the middle region of the negative electrode sheet, increasing the polarization of the middle region of the negative electrode sheet, and improving the dynamic performance of the end region of the negative electrode sheet, reducing the polarization of the end region of the negative electrode sheet.

[0022] A second aspect of the present application provides a battery, which includes the battery cell in the above embodiment.

[0023] A third aspect of the present application provides an electrical device, which includes the battery in the above embodiment, and the battery is used to provide electrical energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0025] Figure 2 yes Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown.

[0026] Figure 3 It is a schematic diagram of a negative electrode plate according to one embodiment of the present application.

[0027] Figure 4 It is a schematic diagram of a negative electrode sheet according to another embodiment of the present application.

[0028] Figure 5 is a schematic diagram of a battery module according to an embodiment of the present application.

[0029] Figure 6 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0030] Figure 7 yes Figure 6 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0031] Figure 8 It is a schematic diagram of an electrical device using a battery cell according to an embodiment of the present application as a power source.

[0032] Fig. 9 This is a schematic diagram of the negative electrode sheet of the present application before it is cut.

[0033] Description of reference numerals:

[0034] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 cover plate; 6 negative electrode plate; 61 main body; 62 pole ear; 611 first end; 612 second end; 613-width direction; 614 first area; 615 second area; 616 third area; 617 fourth area; 618 fifth area; 619-blank area. DETAILED DESCRIPTION

[0035] Below, a battery cell, a battery, and an electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0036] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0038] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0039] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0040] As lithium batteries continue to develop towards high power and high energy density, the operating conditions of different areas of the battery cell are different, resulting in different temperatures, currents and expansion forces in each area. Under different operating conditions, the capacity decay of each area is different, which causes the overall reversible capacity of the battery cell to decay too quickly.

[0041] When adopting low-rate charging and high-power discharging conditions, the charging rate is low, and the effect on the temperature rise of the battery cell and the diffusion of lithium ions is small. During high-power discharge, the heat cannot be effectively dissipated in the middle of the battery cell and accumulates, which leads to a temperature rise in the middle area of ​​the negative electrode plate, small impedance, small expansion force, and fast lithium ion diffusion. The temperature of the end area of ​​the negative electrode plate is lower than that of the central area, the impedance is larger, and the expansion force is larger. When charging again, lithium ions remain in the end area. In the process of continuous cyclic charge and discharge, the lithium ions in the end area are continuously enriched, resulting in an increasing difference in polarization between the middle area and the end area of ​​the negative electrode plate, which causes the capacity of the middle area to be consumed first. Therefore, the uneven polarization inside the battery cell will lead to lithium or sodium precipitation problems in the negative electrode plate and accelerated reversible capacity decay of the battery cell.

[0042] Based on this, the present application proposes a battery cell, a battery and an electrical device. The present application and optional implementation methods are described in more detail below.

[0043] See also Figures 1 to 3 , Figure 1 It is a schematic diagram of a battery cell according to an embodiment of the present application. Figure 2 yes Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown. Figure 3 It is a schematic diagram of a negative electrode plate 6 according to an embodiment of the present application.

[0044] The present application provides a battery cell, which includes an electrode assembly, the electrode assembly includes a negative electrode plate 6, the negative electrode plate 6 includes a main body 61 and a pole ear 62, the main body 61 has a first end 611 and a second end 612 opposite to each other, the pole ear 62 is arranged at the first end 611, and the direction extending from the first end 611 to the second end 612 is the width direction 613 of the negative electrode plate 6, the main body 61 includes a first region 614, a second region 615 and a third region 616 distributed in sequence along the width direction 613, the ion diffusion coefficient of the first region 614 is greater than the ion diffusion coefficient of the second region 615, and / or the ion diffusion coefficient of the third region 616 is greater than the ion diffusion coefficient of the second region 615; the ion diffusion coefficient includes a lithium ion diffusion coefficient or a sodium ion diffusion coefficient.

[0045] The electrode assembly is a structure made of a positive electrode sheet, a negative electrode sheet 6 and a separator through a winding process or a lamination process.

[0046] The main body 61 of the negative electrode sheet 6 is a main structure that does not include the tab 62 .

[0047] The tab 62 of the negative electrode plate 6 is a metal conductor that leads the negative electrode and serves as a contact point during charging and discharging.

[0048] The first region 614 is a region close to the first end 611 of the main body 61 , the second region 615 is a region located in the middle of the main body 61 , and the third region 616 is a region close to the second end 612 of the main body 61 .

[0049] In such Figure 3 In the illustrated embodiment, the first region 614 , the second region 615 , and the third region 616 are all rectangular.

[0050] Optionally, the first region 614 and the third region 616 are of the same size.

[0051] It should be noted that the main body 61 can be divided into a first area 614, a second area 615 and a third area 616, and the negative electrode plate 6 can also include other areas besides the first area 614, the second area 615 and the third area 616. The shapes and sizes of the first area 614, the second area 615 and the third area 616 can be determined according to actual conditions.

[0052] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 A square-structured battery cell is used as an example.

[0053] In some embodiments, reference Figure 2, the outer packaging may include a shell and a cover plate. Among them, the shell may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell has an opening connected to the receiving cavity, and the cover plate can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet 6 and the isolation membrane can form an electrode assembly through a winding process or a lamination process. The electrode assembly is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly. The number of electrode assemblies contained in the battery cell can be one or more, and technicians in this field can choose according to specific actual needs.

[0054] The ion diffusion coefficient is the speed at which lithium ions in lithium-ion batteries or sodium ions in sodium-ion batteries diffuse in electrode materials. It is an important parameter for measuring the performance of lithium-ion batteries or sodium-ion batteries. The diffusion rate of lithium ions or sodium ions in electrode materials directly affects the battery's charge and discharge rate and overall battery performance. The larger the diffusion coefficient, the faster the lithium ions or sodium ions diffuse, the higher the battery's charge and discharge rate, and the better the battery's performance.

[0055] When the battery cell is a lithium ion battery, the lithium ion diffusion coefficient of the first region 614 is greater than that of the second region 615 , and / or the lithium ion diffusion coefficient of the third region 616 is greater than that of the second region 615 .

[0056] When the battery cell is a sodium ion battery, the sodium ion diffusion coefficient of the first region 614 is greater than the sodium ion diffusion coefficient of the second region 615 , and / or the sodium ion diffusion coefficient of the third region 616 is greater than the sodium ion diffusion coefficient of the second region 615 .

[0057] The ion diffusion coefficients of different regions of the negative electrode plate 6 can be measured by the following method:

[0058] The galvanostatic intermittent titration (GITT) method was used for determination: the negative electrode sheets 6 in different regions were cut into batteries, pulse current was applied to the battery to be tested and relaxation was performed, and the voltage change of the battery was recorded. The calculation formula of the ion diffusion coefficient derived from Fick's law is as follows:

[0059]

[0060] where τ is the relaxation time, n m is the number of moles, V m is the molar volume, S is the electrode / electrolyte contact area, ΔE S is the voltage change caused by the pulse, ΔE t It is the voltage change of constant current charging (discharging). The main parameters set by GITT are: current intensity (i) and relaxation time (τ).

[0061] The battery cell of the present application divides the main body 61 into a first region 614, a second region 615 and a third region 616 which are sequentially distributed along the width direction 613, and makes the lithium ion diffusion coefficient or the sodium ion diffusion coefficient of the first region 614 greater than the lithium ion diffusion coefficient or the sodium ion diffusion coefficient of the second region 615, and / or the ion diffusion coefficient of the third region 616 greater than the ion diffusion coefficient of the second region 615, wherein the second region 615 is closer to the middle of the negative electrode sheet 6 than the first region 614 and the third region 616, thereby reducing the middle of the negative electrode sheet 6. The kinetic performance of the region, that is, slowing down the migration and diffusion of lithium ions or the migration and diffusion of sodium ions in the middle region of the negative electrode plate 6, increasing the polarization of the middle region of the negative electrode plate 6, and being able to improve the kinetic performance of the end region of the negative electrode plate 6, that is, accelerating the migration and diffusion of lithium ions or the migration and diffusion of sodium ions in the end region of the negative electrode plate 6, reducing the polarization of the end region of the negative electrode plate 6, thereby offsetting or weakening the problem of uneven polarization in different regions during the cycle of the battery cell, improving the lithium or sodium precipitation problem of the negative electrode plate 6 and the capacity attenuation of the battery cell, and increasing the service life of the battery cell.

[0062] In some embodiments, the ratio of the lithium ion diffusion coefficient of the first region 614 to the lithium ion diffusion coefficient of the second region 615 is 2-1000, and / or the ratio of the lithium ion diffusion coefficient of the third region 616 to the lithium ion diffusion coefficient of the second region 615 is 2-1000.

[0063] As an example, the ratio of the lithium ion diffusion coefficient of the first region 614 to the lithium ion diffusion coefficient of the second region 615 can be 5, 10, 20, 50, 100, 200, 500, 800 or 1000, and the ratio of the lithium ion diffusion coefficient of the third region 616 to the lithium ion diffusion coefficient of the second region 615 can be 5, 10, 20, 50, 100, 200, 500, 800 or 1000.

[0064] By making the ratio of the lithium ion diffusion coefficient of the first region 614 to that of the second region 615 and / or the ratio of the lithium ion diffusion coefficient of the third region 616 to that of the second region 615 within the above range, it is possible to avoid or improve the problem of lithium deposition in the middle portion and accelerated capacity decay of the battery cell in the late cycle due to the excessively high kinetic performance of the first region 614 and / or the third region 616 located at the ends and the excessively low kinetic performance of the second region 615 located in the middle.

[0065] In some embodiments, the main body 61 includes a first region 614, a second region 615 and a third region 616 along the width direction 613, and the ratio of the lithium ion diffusion coefficient located in the first region 614 and / or the third region 616 to the lithium ion diffusion coefficient located in the second region 615 is 5-500.

[0066] As an example, the ratio of the lithium ion diffusion coefficient located in the first region 614 and / or the third region 616 to the lithium ion diffusion coefficient located in the second region 615 may be 5, 10, 20, 50, 100, 200, or 500.

[0067] When the main body 61 is composed of the first region 614, the second region 615 and the third region 616 in sequence along the width direction 613, by making the ratio of the lithium ion diffusion coefficient located in the first region 614 to the lithium ion diffusion coefficient located in the second region 615 and / or the ratio of the lithium ion diffusion coefficient located in the third region 616 to the lithium ion diffusion coefficient located in the second region 615 within the above range, it is possible to avoid or improve the problem of lithium deposition in the middle part and accelerated capacity decay of the battery cell in the late cycle due to the excessively high kinetic performance of the first region 614 and / or the third region 616 located at the end and the excessively low kinetic performance of the second region 615 located in the middle.

[0068] In some embodiments, the lithium ion diffusion coefficient in the first region 614 and / or the third region 616 is 10 - 9 cm 2 / s~10 -11 cm 2 / s, the lithium ion diffusion coefficient in the second region 615 is 10 -11 cm 2 / s~10 -12 cm 2 / s.

[0069] As an example, the lithium ion diffusion coefficient in the first region 614 and / or the third region 616 may be 10 - 11 cm 2 / s, 2*10 -11 cm 2 / s, 5*10 -11 cm 2 / s, 8*10 -11 cm 2 / s, 10 -10 cm 2 / s, 2*10 -10 cm 2 / s, 5*10 -10 cm 2 / s, 8*10-10 cm 2 / s or 10 -9 cm 2 / s, the lithium ion diffusion coefficient in the second region 615 may be 10 -12 cm 2 / s, 2*10 -12 cm 2 / s, 5*10 -12 cm 2 / s, 8*10 -12 cm 2 / s or 10 -11 cm 2 / s.

[0070] By making the lithium ion diffusion coefficient located in the first region 614 and / or the lithium ion diffusion coefficient located in the third region 616, as well as the lithium ion diffusion coefficient located in the second region 615 within the above-mentioned range, it is beneficial to reduce the kinetic performance of the middle region of the negative electrode plate 6, increase the polarization of the middle region of the negative electrode plate 6, and improve the kinetic performance of the end region of the negative electrode plate 6, thereby reducing the polarization of the end region of the negative electrode plate 6.

[0071] In some embodiments, the area of ​​the second region 615 accounts for 50% to 70% of the total area of ​​the main body 61 .

[0072] Please note that Figure 3 The negative electrode sheet 6 includes a front side and a back side, which can be understood as that on the front side or the back side of the negative electrode sheet 6 , the area of ​​the second region 615 accounts for 50% to 70% of the total area of ​​the main body 61 .

[0073] As an example, the area of ​​the second region 615 may be 50%, 55%, 60%, 65% or 70% of the total area of ​​the main body 61 .

[0074] By making the area ratio of the second region 615 within the above range, the area sizes of the first region 614 and the third region 616 can be further divided according to the polarization conditions of the negative electrode plate 6 during the battery cell cycle, so as to more accurately offset or weaken the problem of uneven polarization in different regions during the battery cell cycle, improve the capacity attenuation of the battery cell, and increase the service life of the battery cell.

[0075] In some embodiments, the ratio of the sizes of the first region 614 , the second region 615 , and the third region 616 along the width direction 613 is 15% to 25%: 50% to 70%: 15% to 25%.

[0076] As an example, the ratio of the sizes of the first region 614, the second region 615 and the third region 616 along the width direction 613 can be 15%:70%:15%, 20%:60%:20%, 25%:50%:25% or 15%:60%:25%.

[0077] By making the size ratio of the first region 614, the second region 615 and the third region 616 along the width direction 613 within the above range, it is helpful to divide the first region 614, the third region 616 and the second region 615 located at the two ends according to the polarization of the negative electrode plate 6 during the battery cell cycle process, so as to more accurately offset or weaken the problem of uneven polarization in different regions during the battery cell cycle process, improve the capacity attenuation of the battery cell, and increase the service life of the battery cell.

[0078] In some embodiments, the negative electrode plate 6 includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, and the ion diffusion coefficient of the negative electrode active material located in the first region 614 and / or the third region 616 is greater than the ion diffusion coefficient of the negative electrode active material located in the second region 615.

[0079] Optionally, the negative electrode active material located in the first region 614 , the negative electrode active material located in the second region 615 , and the negative electrode active material located in the third region 616 are all graphite.

[0080] It should be noted that the ion diffusion coefficient of the negative electrode active material may be affected by the following factors:

[0081] 1. Material structure and composition: Different negative electrode active materials have different crystal structures and chemical compositions, which directly affect the diffusion path and diffusion kinetics of lithium ions. For example, negative electrode active materials with more open and ordered crystal structures generally have higher lithium ion diffusion coefficients.

[0082] 2. Particle size and morphology: The particle size and morphology of the negative electrode active material will also affect the diffusion coefficient of lithium ions. Smaller particle size can reduce the distance that lithium ions diffuse, thereby increasing the diffusion coefficient.

[0083] 3. Specific surface area: Negative electrode active materials with larger specific surface area provide more active sites, which help to increase the diffusion rate of lithium ions.

[0084] 4. Tap density: The tap density affects the packing density of the negative electrode active material, which in turn may affect the diffusion path and diffusion coefficient of lithium ions.

[0085] 5. Electrochemical performance: including the diffusion kinetics of lithium ions and the electrochemical reduction rate. The differences in electrochemical performance of different negative electrode active materials will lead to different lithium ion diffusion coefficients.

[0086] 6. Material modification: By introducing high entropy elements or performing other material modifications, the crystal structure and diffusion capacity of the negative electrode active material can be adjusted, thereby affecting the diffusion coefficient of lithium ions.

[0087] 7. Surface treatment: Surface treatment of the negative electrode active material, such as expansion of the surface layer, can improve the diffusion kinetics of lithium ions and thus increase the diffusion coefficient.

[0088] The battery cell of the present application makes the lithium ion diffusion coefficient or sodium ion diffusion coefficient of the negative electrode active material located in the first region 614 and / or the third region 616 greater than the lithium ion diffusion coefficient or sodium ion diffusion coefficient of the negative electrode active material located in the second region 615, so that the lithium ion diffusion coefficient or sodium ion diffusion coefficient of the first region 614 and / or the third region 616 is greater than the lithium ion diffusion coefficient or sodium ion diffusion coefficient of the second region 615, thereby reducing the kinetic performance of the middle region of the negative electrode plate 6, increasing the polarization of the middle region of the negative electrode plate 6, and improving the kinetic performance of the end region of the negative electrode plate 6, reducing the polarization of the end region of the negative electrode plate 6, thereby offsetting or weakening the problem of uneven polarization in different regions during the battery cell cycle, improving the lithium or sodium precipitation problem of the negative electrode plate 6 and the capacity attenuation of the battery cell, and increasing the service life of the battery cell.

[0089] In some embodiments, the negative electrode sheet 6 includes a negative electrode active material layer, and the first region 614, the second region 615 and the third region 616 include the same conductive agent, based on the mass of the negative electrode active material layer in the first region 614, the mass proportion of the conductive agent in the negative electrode active material layer in the first region 614 is W1, based on the mass of the negative electrode active material layer in the second region 615, the mass proportion of the conductive agent in the negative electrode active material layer in the second region 615 is W2, based on the mass of the negative electrode active material layer in the third region 616, the mass proportion of the conductive agent in the negative electrode active material layer in the third region 616 is W3, W1<W2 and / or W3<W2.

[0090] When the conductive agent used in the first region 614, the second region 615 and the third region 616 is the same, the battery cell of the present application can reduce the kinetic performance of the middle region of the negative electrode plate 6 by making the mass proportion of the conductive agent in the negative electrode active material layer located in the second region 615 greater than the mass proportion of the conductive agent in the negative electrode active material layer located in the first region 614 and / or the third region 616, that is, slow down the migration and diffusion of lithium ions or the migration and diffusion of sodium ions in the middle region of the negative electrode plate 6, increase the polarization of the middle region of the negative electrode plate 6, and improve the kinetic performance of the end region of the negative electrode plate 6, that is, accelerate the migration and diffusion of lithium ions or the migration and diffusion of sodium ions in the end region of the negative electrode plate 6, reduce the polarization of the end region of the negative electrode plate 6, and thus offset or weaken the problem of uneven polarization in different regions during the battery cell cycle, improve the lithium or sodium precipitation problem of the negative electrode plate 6 and the capacity attenuation of the battery cell, and improve the service life of the battery cell.

[0091] In some embodiments, the difference between W2 and W1 is 0.5 wt % to 2 wt %, and / or the difference between W2 and W3 is 0.5 wt % to 2 wt %.

[0092] As an example, the difference between W2 and W1 can be 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt% or 2wt%, and the difference between W2 and W3 can be 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt% or 2wt%.

[0093] By making the difference between the mass ratio of the conductive agent in the negative electrode active material layer located in the second region 615 and the mass ratio of the conductive agent in the negative electrode active material layer located in the first region 614 and / or the difference between the mass ratio of the conductive agent in the negative electrode active material layer located in the second region 615 and the mass ratio of the conductive agent in the negative electrode active material layer located in the third region 616 within the above-mentioned range, it is possible to avoid or improve the problem of lithium deposition in the middle part and accelerated capacity decay of the battery cell in the late cycle due to the excessively high kinetic performance of the first region 614 and / or the third region 616 located at the ends and the excessively low kinetic performance of the second region 615 located in the middle.

[0094] In some embodiments, the negative electrode sheet 6 includes a negative active material layer, the negative active material layer includes a conductive agent, the first region 614 includes a first conductive agent, the second region 615 includes a second conductive agent, and the third region 616 includes a third conductive agent, the conductivity of the second conductive agent is greater than the conductivity of the first conductive agent, and / or the conductivity of the second conductive agent is greater than the conductivity of the third conductive agent.

[0095] As an example, the first conductive agent and the third conductive agent may be carbon black, and the second conductive agent may be carbon nanotubes; or the first conductive agent and the third conductive agent may be carbon black, and the second conductive agent may be graphene; or the first conductive agent and the third conductive agent may be carbon nanotubes, and the second conductive agent may be graphene.

[0096] When the conductive agents used in the first region 614, the second region 615, and the third region 616 are different, the battery cell of the present application can reduce the kinetic performance of the middle region of the negative electrode sheet 6 by making the conductivity of the conductive agent in the negative electrode active material layer located in the second region 615 greater than the conductivity of the conductive agent in the negative electrode active material layer located in the first region 614 and / or the conductivity of the conductive agent in the negative electrode active material layer located in the second region 615 greater than the conductivity of the conductive agent in the negative electrode active material layer located in the third region 616, that is, reducing It slows down the migration and diffusion of lithium ions or sodium ions in the middle area of ​​the negative electrode plate 6, increases the polarization of the middle area of ​​the negative electrode plate 6, and can improve the kinetic performance of the end area of ​​the negative electrode plate 6, that is, it accelerates the migration and diffusion of lithium ions or sodium ions in the end area of ​​the negative electrode plate 6, reduces the polarization of the end area of ​​the negative electrode plate 6, and then offsets or weakens the problem of uneven polarization in different areas during the cycle of the battery cell, improves the lithium or sodium precipitation problem of the negative electrode plate 6 and the capacity attenuation of the battery cell, and increases the service life of the battery cell.

[0097] In some embodiments, the negative electrode sheet 6 includes a negative electrode active material layer, and the first region 614, the second region 615 and the third region 616 include the same binder, the mass proportion of the binder in the negative electrode active material layer located in the first region 614 is W4, the mass proportion of the binder in the negative electrode active material layer located in the second region 615 based on the mass of the negative electrode active material layer in the second region 615 is W5, and the mass proportion of the binder in the negative electrode active material layer located in the third region 616 based on the mass of the negative electrode active material layer in the third region 616 is W6, W4>W5 and / or W6>W5.

[0098] When the binder used in the first region 614, the second region 615 and the third region 616 is the same, the battery cell of the present application can reduce the kinetic performance of the middle region of the negative electrode plate 6 by making the mass proportion of the binder in the negative electrode active material layer located in the first region 614 and / or the third region 616 greater than the mass proportion of the binder in the negative electrode active material layer located in the second region 615, that is, slowing down the migration and diffusion of lithium ions or the migration and diffusion of sodium ions in the middle region of the negative electrode plate 6, increasing the polarization of the middle region of the negative electrode plate 6, and improving the kinetic performance of the end region of the negative electrode plate 6, that is, accelerating the migration and diffusion of lithium ions or the migration and diffusion of sodium ions in the end region of the negative electrode plate 6, reducing the polarization of the end region of the negative electrode plate 6, thereby offsetting or weakening the problem of uneven polarization in different regions during the battery cell cycle, improving the lithium or sodium precipitation problem of the negative electrode plate 6 and the capacity attenuation of the battery cell, and improving the service life of the battery cell.

[0099] In some embodiments, the difference between W4 and W5 is 0.5 wt % to 3.1 wt %, and / or the difference between W6 and W5 is 0.5 wt % to 3.1 wt %.

[0100] As an example, the difference between W4 and W5 can be 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt%, 2.2wt%, 2.5wt%, 2.8wt%, 3wt% or 3.1wt%, and the difference between W6 and W5 can be 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt%, 2.2wt%, 2.5wt%, 2.8wt%, 3wt% or 3.1wt%.

[0101] By making the difference between the mass ratio of the binder in the negative electrode active material layer located in the first region 614 and the mass ratio of the binder in the negative electrode active material layer located in the second region 615 and / or the difference between the mass ratio of the binder in the negative electrode active material layer located in the third region 616 and the mass ratio of the binder in the negative electrode active material layer located in the second region 615 within the above-mentioned range, it is possible to avoid or improve the problem of lithium deposition in the middle part and accelerated capacity decay of the battery cell in the late cycle due to the excessively high kinetic performance of the first region 614 and / or the third region 616 located at the ends and the excessively low kinetic performance of the second region 615 located in the middle.

[0102] See also Figure 4 , Figure 46 is a schematic diagram of a negative electrode sheet 6 according to another embodiment of the present application. The main body 61 further includes a fourth region 617 and a fifth region 618. The main body 61 includes a first region 614, a fourth region 617, a second region 615, a fifth region 618 and a third region 616 sequentially distributed along a width direction 613. The ion diffusion coefficient of the fourth region 617 and / or the fifth region 618 is greater than the ion diffusion coefficient of the second region 615 and less than the ion diffusion coefficient of the first region 614.

[0103] The fourth region 617 is a transition region between the first region 614 and the second region 615 , and the fifth region 618 is a transition region between the third region 616 and the second region 615 .

[0104] In such Figure 4 In the illustrated embodiment, the first region 614 , the fourth region 617 , the second region 615 , the fifth region 618 , and the third region 616 are all rectangular.

[0105] Optionally, the fourth region 617 and the fifth region 618 are of the same size.

[0106] The battery cell of the present application divides the main body 61 into a first area 614, a fourth area 617, a second area 615, a fifth area 618 and a third area 616 which are sequentially distributed along the width direction 613, and makes the ion diffusion coefficient of the fourth area 617 and / or the fifth area 618 greater than the ion diffusion coefficient of the second area 615 and less than the ion diffusion coefficient of the first area 614, wherein the fourth area 617 arranged between the second area 615 and the first area 614 and the fifth area 618 arranged between the second area 615 and the third area 616 are transition areas, and the polarization difference between the second area 615 and the adjacent areas is reduced, so that the transition from the second area 615 to the first area 614 and the third area 616 is more stable, thereby improving the service life of the battery cell.

[0107] In some embodiments, the ratio of the sizes of the first region 614, the fourth region 617, the second region 615, the fifth region 618 and the third region 616 along the width direction 613 is 10% to 15%: 5% to 10%: 50% to 70%: 5% to 10%: 10% to 15%.

[0108] As an example, the ratio of the sizes of the first region 614, the fourth region 617, the second region 615, the fifth region 618 and the third region 616 along the width direction 613 is 10%:5%:70%:5%:10%, 15%:5%:60%:5%:15%, 10%:10%:60%:10%:10%, 15%:10%:50%:10%:15%, 10%:5%:65%:5%:15% or 10%:5%:60%:10%:15%.

[0109] By making the size ratios of the first region 614, the fourth region 617, the second region 615, the fifth region 618 and the third region 616 along the width direction 613 within the above range, it is beneficial to more accurately offset or weaken the problem of uneven polarization in different regions during the battery cell cycle according to the polarization conditions of the negative electrode plate 6 during the battery cell cycle, improve the capacity attenuation of the battery cell, and increase the service life of the battery cell.

[0110] In some embodiments, the ratio of the lithium ion diffusion coefficient located in the fourth region 617 and / or the fifth region 618 to the lithium ion diffusion coefficient located in the second region 615 is 5-100.

[0111] As an example, the ratio of the lithium ion diffusion coefficient located in the fourth region 617 and / or the fifth region 618 to the lithium ion diffusion coefficient located in the second region 615 may be 5, 10, 20, 50, 80, or 100.

[0112] By making the ratio of the lithium ion diffusion coefficient located in the fourth region 617 and / or the fifth region 618 to the lithium ion diffusion coefficient located in the second region 615 within the above range, it is possible to avoid or improve the problem of lithium precipitation in the middle part and accelerated capacity decay of the battery cell in the late cycle due to the kinetic performance of the fourth region 617 and / or the fifth region 618 being too high and the kinetic performance of the second region 615 located in the middle being too low.

[0113] In some embodiments, the ion diffusion coefficient located in the fourth region 617 and / or the fifth region 618 is 10 - 10 cm 2 / s~5*10 -12 cm 2 / s.

[0114] As an example, the ion diffusion coefficient in the fourth region 617 and / or the fifth region 618 may be 5*10 - 12 cm 2 / s, 8*10 -12 cm 2 / s, 10 -11 cm2 / s, 2*10 -11 cm 2 / s, 5*10 -11 cm 2 / s, 8*10 -11 cm 2 / s or 10 -10 cm 2 / s.

[0115] By making the ion diffusion coefficient located in the fourth region 617 and / or the fifth region 618 within the above-mentioned range, the ion diffusion coefficient located in the fourth region 617 and / or the fifth region 618 can be greater than the ion diffusion coefficient of the second region 615 and less than the ion diffusion coefficient of the first region 614 and / or the third region 616, which is beneficial to reducing the kinetic performance of the middle region of the negative electrode plate 6, increasing the polarization of the middle region of the negative electrode plate 6, and can improve the kinetic performance of the end region of the negative electrode plate 6 and reduce the polarization of the end region of the negative electrode plate 6.

[0116] In addition, a battery cell, a battery, and an electrical device of the present application are described below with reference to the accompanying drawings as appropriate.

[0117] [Battery Cell]

[0118] The present application has no particular limitation on the type of battery cells. For example, the battery cells may be lithium-ion batteries, etc.

[0119] Generally, a battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0120] The present application has no particular restrictions on the type of the electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte). Battery cells using electrolytes, and some battery cells using solid electrolytes.

[0121] [Positive electrode]

[0122] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0123] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0124] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0125] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may adopt a positive electrode active material for lithium-ion batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may 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 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05at least one of O2) and its modified compounds. Examples of the lithium phosphate with olivine structure may include but are not limited to lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0126] In some embodiments, in order to further improve the energy density of the battery cell, the positive electrode active material for the lithium ion battery may include a general formula of Li a Ni b Co c M d O e A f and one or more of its modified compounds of lithium transition metal oxides. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0127] In some embodiments, by way of example, the positive electrode active material for the lithium ion battery may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O2, LiFePO4, and LiMnPO4.

[0128] In this application, the modified compounds of the above positive electrode active materials may be doping modification and / or surface coating modification of the positive electrode active materials.

[0129] As an optional technical solution of this application, the polyanion-type compound may be Li 1+x Mn 1-y A y P 1-z R zO4; wherein x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N;

[0130] As an optional technical method of the present application, the polyanionic compound can be Li a A e Mn 1-f B f P 1-g C g O 4-n D n , wherein A includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from the group consisting of B, S, Si, and N; D includes one or more elements selected from the group consisting of S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the second positive electrode active material is electrically neutral.

[0131] The battery will be accompanied by Li deintercalation and consumption during the charge and discharge process, and the molar content of Li is different when the battery is discharged to different states. In the list of positive electrode materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode material is used in the battery system, and the molar content of Li will change after charge and discharge cycles.

[0132] In the list of positive electrode materials in this application, the molar content of O is only a theoretical value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0133] When the battery cell is a sodium ion battery, the positive electrode active material may be a positive electrode active material for a sodium ion battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: a polyanion compound, a sodium transition metal oxide, a Prussian blue compound, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0134] As an optional technical solution of the present application, the polyanionic compound may be Na 4+x R 3-y P 4-m O 15 / C; where 0 < x < 0.5, 0 < y ≤ 0.5, 0 < m ≤ 0.2, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0135] As an optional technical solution of the present application, the polyanionic compound may be Na x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q d , where the A element represents an alkali metal element that dopes and replaces the Na element, the M element represents a metal element that replaces the V element, the D element represents a doping element that replaces the P element, the Q element represents a doping element that replaces the F element, the D element includes at least one of Si and S, the Q element includes at least one of Cl and O; 3.5 ≤ x ≤ 4.5, 0 ≤ a ≤ 0.15x, 0.8 ≤ y ≤ 1.1, 0 ≤ b ≤ 0.3y, 0 ≤ c ≤ 0.15, 0.8 ≤ z ≤ 1.1, 0 ≤ d ≤ 0.2z. Optionally, the A element includes at least one of K and Li; the M element includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0136] As an optional technical solution of the present application, the polyanionic compound may be a type of compound having sodium ions, transition metal ions, and tetrahedral (YO4) n- anion units. The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be at least one of P, S, and Si; n represents the valence state of (YO4) n- .

[0137] The polyanionic compound may also be a type of compound having sodium ions, transition metal ions, tetrahedral (YO4) n- anion units and halogen anions. The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be at least one of P, S, and Si; n represents the valence state of (YO4) n- ; the halogen may be at least one of F, Cl, and Br.

[0138] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedral unit (ZO y ) m+ and an optional halogen anion. Y can be at least one of P, S and Si, n represents the valence state of V; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, m represents (ZO y ) m+ valence state; the halogen may be at least one of F, Cl and Br.

[0139] Polyanionic compounds include NaFePO4, Na3V2(PO4)3, NaM'PO4F (M' is one or more of V, Fe, Mn and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0140] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. The sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0 <x≤1。

[0141] As an optional technical solution of the present application, the Prussian blue compound can be a compound having sodium ions, transition metal ions and cyanide ions (CN - ). The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Prussian blue compounds are, for example, Na a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 <a≤2,0<b<1,0<c<1。

[0142] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may 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 acrylate resin.

[0143] In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0144] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0145] [Negative electrode]

[0146] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

[0147] 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 any one or both of the two opposite surfaces of the negative electrode current collector.

[0148] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0149] In some embodiments, the negative electrode film layer includes a negative electrode active material. The negative electrode active material may be a negative electrode active material for a battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0150] In some embodiments, the negative electrode film layer may further include a binder. The binder may 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).

[0151] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0152] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0153] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0154] In other embodiments, the current collector of the negative electrode plate may generally include a current collector body and an undercoat layer, the undercoat layer may be disposed on at least one side of the current collector body, the undercoat layer substantially does not contain negative electrode active materials, and may include a small amount of carbon material, but the thickness of the coating formed by the carbon material is thin and cannot function as a negative electrode active material. In this embodiment, the negative electrode plate may be a plate without a negative electrode active material layer. For a negative electrode plate without a negative electrode active material layer, when the current collector of the negative electrode plate does not contain an undercoat layer, the film layer may be disposed on the surface of at least one side of the current collector; when the current collector of the negative electrode plate includes an undercoat layer, the film layer may be disposed on the surface of the undercoat layer on the side away from the current collector.

[0155] In some embodiments, the film layer may further include a binder, which is used to fix the additive on the negative electrode plate. The type of the binder is not particularly limited, and those skilled in the art may flexibly select the binder according to actual needs.

[0156] [Electrolytes]

[0157] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0158] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0159] In some embodiments, when the battery cell is a lithium ion battery, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. When the battery cell is a sodium ion battery, the electrolyte salt may be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bisfluorosulfonyl imide, and sodium difluorooxalate borate.

[0160] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl 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, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0161] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0162] [Isolation film]

[0163] In some embodiments, the battery cell further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0164] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0165] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0166] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0167] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The battery cell 5 is a square structure as an example.

[0168] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0169] In some embodiments, battery cells may be assembled into a battery module. The number of battery cells contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0170] Figure 5 4 is an example of a battery module. Figure 5 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0171] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0172] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0173] Figure 6 and Figure 7 1 is a battery pack 1 as an example. Figure 6 and Figure 7 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0174] In addition, the present application also provides an electric device, which includes at least one of the battery cells, battery modules, or battery packs provided in the present application. The battery cells, battery modules, or battery packs can be used as the power source of the electric device, and can also be used as the energy storage unit of the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0175] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0176] Figure 8 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the power consumption device's requirements for high power and high energy density of battery cells, a battery pack or a battery module can be used.

[0177] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be light and thin, and a battery cell may be used as a power source.

[0178] Example

[0179] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0180] Embodiments 1 to 8 of the present application provide a battery cell and a method for preparing the same, which comprises the following steps:

[0181] S1. Preparation of positive electrode sheet

[0182] Lithium iron phosphate (LiFePO4), conductive carbon black sp, and polyvinylidene fluoride were mixed in a weight ratio of 97:1:2 and dissolved in a solvent N-methylpyrrolidone (NMP) to prepare a positive electrode slurry; the positive electrode slurry was then evenly coated on a 15 μm aluminum foil with a coating weight of 0.068 CW / 1540.25 mm 2 After being fully dried, the positive electrode sheet is obtained by cold pressing, die cutting and slitting.

[0183] S2. Preparation of negative electrode sheet

[0184] Preparation of slurry: preparing two graphites with different kinetics, mixing high kinetic graphite, conductive carbon black sp and styrene butadiene rubber in a weight ratio of 97.5:1:1.5 and dissolving them in solvent deionized water to prepare a first negative electrode slurry, and mixing low kinetic graphite, conductive carbon black sp and styrene butadiene rubber in a weight ratio of 97.5:1:1.5 and dissolving them in solvent deionized water to prepare a second negative electrode slurry, wherein the lithium ion diffusion coefficient of the high kinetic graphite is greater than the lithium ion diffusion coefficient of the low kinetic graphite; then coating the first negative electrode slurry on a specific area of ​​the electrode collector copper foil to form a first area and a third area of ​​the negative electrode sheet, and coating the second negative electrode slurry on a specific area of ​​the electrode collector copper foil to form a second area of ​​the negative electrode sheet, and the coating weight of the first negative electrode slurry and the second negative electrode slurry are both 0.162CW / 1540.25mm 2 After drying, cold pressing and cutting, the negative electrode sheet is obtained. Fig. 9 As shown, the blank area 619 is an area for forming a tab.

[0185] S3. Preparation of isolation film

[0186] A conventional PE base film with a thickness of 5 μm was used. Ceramic fiber, styrene-butadiene rubber, polyvinylidene fluoride and water were mixed evenly in a mass ratio of 4:0.9:0.1:5 to obtain a ceramic fiber slurry, which was then evenly coated on the surface of the base film by gravure coating to form a ceramic fiber layer, and dried at 45°C to obtain an isolation membrane.

[0187] S4. Preparation of electrolyte

[0188] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly in a volume ratio of 3:7, 1 mol / L LiPF6 lithium salt was added and dissolved in the organic solvent, and stirred evenly to obtain an electrolyte.

[0189] S5. Assembly

[0190] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare cell, the bare cell is welded with a pole ear, and the bare cell is placed in an aluminum shell and baked at 80°C to remove water, and then the electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery is then subjected to the processes of static, formation, shaping, and capacity testing in sequence to obtain a battery cell, such as Figures 1 to 3 shown.

[0191] Embodiments 9 to 12 of the present application provide a battery cell and a method for preparing the same, which comprises the following steps:

[0192] S1. Preparation of positive electrode sheet

[0193] Lithium iron phosphate (LiFePO4), conductive carbon black sp, and polyvinylidene fluoride were mixed in a weight ratio of 97:1:2 and dissolved in a solvent N-methylpyrrolidone (NMP) to prepare a positive electrode slurry; the positive electrode slurry was then evenly coated on a 15 μm aluminum foil with a coating weight of 0.068 CW / 1540.25 mm 2 After being fully dried, the positive electrode sheet is obtained by cold pressing, die cutting and slitting.

[0194] S2. Preparation of negative electrode sheet

[0195] Preparation of slurry: preparing three kinds of graphite with different kinetics, mixing high kinetic graphite, conductive carbon black sp and styrene butadiene rubber in a weight ratio of 97.5:1:1.5 and dissolving them in solvent deionized water to prepare a first negative electrode slurry, mixing low kinetic graphite, conductive carbon black sp and styrene butadiene rubber in a weight ratio of 97.5:1:1.5 and dissolving them in solvent deionized water to prepare a second negative electrode slurry, mixing medium kinetic graphite, conductive carbon black sp and styrene butadiene rubber in a weight ratio of 97.5:1:1.5 and dissolving them in solvent deionized water to prepare a third negative electrode slurry, wherein high kinetic graphite, conductive carbon black sp and styrene butadiene rubber are mixed in a weight ratio of 97.5:1:1.5 and dissolved in solvent deionized water to prepare a third negative electrode slurry. The lithium ion diffusion coefficient of the mechanical graphite is greater than that of the medium kinetic graphite, which is greater than that of the low kinetic graphite; then the first negative electrode slurry is coated on a specific area of ​​the electrode collector copper foil to form a first area and a third area of ​​the negative electrode sheet, and the second negative electrode slurry is coated on a specific area of ​​the electrode collector copper foil to form a second area of ​​the negative electrode sheet, and the third negative electrode slurry is coated on a specific area of ​​the electrode collector copper foil to form a fourth area and a fifth area of ​​the negative electrode sheet, and the coating weights of the first negative electrode slurry, the second negative electrode slurry and the third negative electrode slurry are all 0.162CW / 1540.25mm 2 After drying, cold pressing and cutting, the negative electrode sheet is obtained.

[0196] S3. Preparation of isolation film

[0197] A conventional PE base film with a thickness of 5 μm was used. Ceramic fiber, styrene-butadiene rubber, polyvinylidene fluoride and water were mixed evenly in a mass ratio of 4:0.9:0.1:5 to obtain a ceramic fiber slurry, which was then evenly coated on the surface of the base film by gravure coating to form a ceramic fiber layer, and dried at 45°C to obtain an isolation membrane.

[0198] S4. Preparation of electrolyte

[0199] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly in a volume ratio of 3:7, 1 mol / L LiPF6 lithium salt was added and dissolved in the organic solvent, and stirred evenly to obtain an electrolyte.

[0200] S5. Assembly

[0201] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare cell, the bare cell is welded with a pole ear, and the bare cell is placed in an aluminum shell and baked at 80°C to remove water, and then the electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery is then subjected to the processes of static, formation, shaping, and capacity testing in sequence to obtain a battery cell, such as Figures 1-2 and 4.

[0202] Comparative Examples 1 to 3 of the present application provide a battery cell and a method for preparing the same, which comprises the following steps:

[0203] S1. Preparation of positive electrode sheet

[0204] Lithium iron phosphate (LiFePO4), conductive carbon black sp, and polyvinylidene fluoride were mixed in a weight ratio of 97:1:2 and dissolved in a solvent N-methylpyrrolidone (NMP) to prepare a positive electrode slurry; the positive electrode slurry was then evenly coated on a 15 μm aluminum foil with a coating weight of 0.068 CW / 1540.25 mm 2 After being fully dried, the positive electrode sheet is obtained by cold pressing, die cutting and slitting.

[0205] S2. Preparation of negative electrode sheet

[0206] Preparation of slurry: Prepare graphite, mix graphite, conductive carbon black sp and styrene butadiene rubber in a weight ratio of 97.5:1:1.5 and dissolve in solvent deionized water to prepare negative electrode slurry; then apply the negative electrode slurry on the surface of the electrode current collector copper foil to form a negative electrode sheet, and the coating weight of the negative electrode slurry is 0.162CW / 1540.25mm 2 After drying, cold pressing and cutting, the negative electrode sheet is obtained.

[0207] S3. Preparation of isolation film

[0208] A conventional PE base film with a thickness of 5 μm was used. Ceramic fiber, styrene-butadiene rubber, polyvinylidene fluoride and water were mixed evenly in a mass ratio of 4:0.9:0.1:5 to obtain a ceramic fiber slurry, which was then evenly coated on the surface of the base film by gravure coating to form a ceramic fiber layer, and dried at 45°C to obtain an isolation membrane.

[0209] S4. Preparation of electrolyte

[0210] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly in a volume ratio of 3:7, 1 mol / L LiPF6 lithium salt was added and dissolved in the organic solvent, and stirred evenly to obtain an electrolyte.

[0211] S5. Assembly

[0212] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare cell, the bare cell is welded with a pole ear, and the bare cell is placed in an aluminum shell and baked at 80°C to remove water, and then the electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery is then subjected to the processes of static, formation, shaping, and capacity testing in sequence to obtain a battery cell, such as Figures 1-2 shown.

[0213] The types of graphite used in different regions of the battery cells of Examples 1 to 12 and Comparative Examples 1 to 3 are shown in Table 1.

[0214] Table 1 Graphite types used in different regions of battery cells of Examples 1 to 12 and Comparative Examples 1 to 3

[0215]

[0216] Among them, the lithium ion diffusion coefficient of graphite A is 1.8*10 -11 , the lithium ion diffusion coefficient of graphite B is 6.6*10 -12 , the lithium ion diffusion coefficient of graphite C is 1*10 -9 , the lithium ion diffusion coefficient of graphite D is 1*10 -11 , the lithium ion diffusion coefficient of graphite E is 1*10 -12 , the lithium ion diffusion coefficient of graphite F is 1.7*10 -12 , the lithium ion diffusion coefficient of graphite G is 1*10 -10 , the lithium ion diffusion coefficient of graphite H is 1.1*10 -11 .

[0217] The lithium ion diffusion coefficient of graphite is determined by the current intermittent titration method (GITT): different graphites are made into negative electrode sheets, and then the negative electrode sheets are made into batteries (the preparation method of the battery is the same as the preparation method of Comparative Examples 1 to 3). The battery to be tested is subjected to pulse current and relaxation, and the voltage change of the battery is recorded. The calculation formula of the lithium ion diffusion coefficient derived from Fick's law is as follows:

[0218]

[0219] where τ is the relaxation time, n m is the number of moles, Vm is the molar volume, S is the electrode / electrolyte contact area, ΔE S is the voltage change caused by the pulse, ΔE t It is the voltage change of constant current charging (discharging). The main parameters set by GITT are: current intensity (i) and relaxation time (τ).

[0220] Table 2 shows the relevant parameters of the battery cells of Examples 1 to 12 and Comparative Examples 1 to 3.

[0221] Table 2 Related parameters of battery cells of Examples 1 to 12 and Comparative Examples 1 to 3

[0222]

[0223]

[0224] The lithium ion diffusion coefficient of different regions of the negative electrode sheet is determined by the current intermittent titration method (GITT): the negative electrode sheets in different regions are cut into batteries, and the battery to be tested is subjected to pulse current and relaxation, and the voltage change of the battery is recorded. The lithium ion diffusion coefficient calculation formula derived from Fick's law is as follows:

[0225]

[0226] where τ is the relaxation time, n m is the number of moles, V m is the molar volume, S is the electrode / electrolyte contact area, ΔE S is the voltage change caused by the pulse, ΔE t It is the voltage change of constant current charging (discharging). The main parameters set by GITT are: current intensity (i) and relaxation time (τ).

[0227] In addition, the cycle performance of the battery cells of Examples 1 to 12 and Comparative Examples 1 to 3 was measured, and the results are shown in Table 3.

[0228] Among them, the test method is as follows:

[0229] S1. Keep the battery cell at rest for 2 hours;

[0230] S2, 1C is discharged to 2.5V;

[0231] S3, rest for 5 minutes;

[0232] S4, 1C charge to 3.65V;

[0233] S5, rest for 60 minutes;

[0234] S6, 358W constant power discharge to 2.5V;

[0235] S7, rest for 2 hours;

[0236] S8. Repeat steps S4 to S7 until the battery cell SOC reaches 80%, and record the number of cycles.

[0237] Table 3 Cyclic performance of battery cells of Examples 1 to 12 and Comparative Examples 1 to 3

[0238] project 80% SOC cycle number (cls) Example 1 1683 Example 2 2126 Example 3 1557 Example 4 1466 Example 5 2264 Example 6 1585 Example 7 1446 Example 8 1934 Example 9 2347 Example 10 2262 Embodiment 11 2388 Example 12 2160 Comparative Example 1 1316 Comparative Example 2 989 Comparative Example 3 1229

[0239] It can be seen from Examples 1 to 8 that the main body of the negative electrode sheets of Examples 1 to 8 is divided into a first region, a second region and a third region, and the negative electrode sheets are sequentially the first region, the second region and the third region along the width direction, and the number of 80% SOC cycles of the battery cell is 1446 to 2264.

[0240] By comparing Example 2 and Example 8, it can be seen that the ratio of the lithium ion diffusion coefficient of the graphite in the first region of Example 2 to the lithium ion diffusion coefficient of the graphite in the second region is 100, the ratio of the lithium ion diffusion coefficient of the graphite in the third region of Example 2 to the lithium ion diffusion coefficient of the graphite in the second region is 100, the ratio of the lithium ion diffusion coefficient of the graphite in the first region of Example 8 to the lithium ion diffusion coefficient of the graphite in the second region is 588, and the ratio of the lithium ion diffusion coefficient of the graphite in the third region of Example 8 to the lithium ion diffusion coefficient of the graphite in the second region is 588. The ratio of the lithium ion diffusion coefficient of the graphite in the first region of Example 8 to the lithium ion diffusion coefficient of the graphite in the second region is too different, and the ratio of the lithium ion diffusion coefficient of the graphite in the third region of Example 8 to the lithium ion diffusion coefficient of the graphite in the second region is too different, resulting in the number of 80% SOC cycles of the battery cell of Example 8 being less than the number of 80% SOC cycles of the battery cell of Example 2.

[0241] It can be seen from Examples 9 to 12 that the main body of the negative electrode sheets of Examples 9 to 12 is divided into the first region, the fourth region, the second region, the fifth region and the third region, and the number of cycles of the battery cell at 80% SOC is 2160 to 2388.

[0242] From the comparison between comparative example 1 and embodiment 1, it can be seen that the main body of the negative electrode plate of comparative example 1 has no divided area, and the lithium ion diffusion coefficient of the graphite of the entire negative electrode plate is the same as the lithium ion diffusion coefficient of the graphite of the first area or the third area of ​​embodiment 1, which is 1.8*10 -11 , the number of cycles of 80% SOC of its battery cell is only 1316.

[0243] From the comparison between Comparative Example 2 and Example 1, it can be seen that the main body of the negative electrode plate of Comparative Example 2 has no divided area, and the lithium ion diffusion coefficient of the graphite of the entire negative electrode plate is the same as the lithium ion diffusion coefficient of the graphite in the second area of ​​Example 1, which is 6.6*10 -12, the number of cycles of 80% SOC of its battery cell is only 989 cycles.

[0244] By comparing Comparative Example 3 with Example 1, it can be seen that the negative electrode plate of Comparative Example 3 has no divided regions, and the lithium ion diffusion coefficient of the graphite of the entire negative electrode plate is the same as the average of the lithium ion diffusion coefficients of the graphite of the first region, the second region and the third region of Example 1, which is 1.1*10 -11 , the number of cycles of 80% SOC of its battery cell is only 1229.

[0245] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A battery cell, characterized in that: The battery cell comprises an electrode assembly, the electrode assembly comprises a negative electrode sheet, the negative electrode sheet comprises a main body and a tab, the main body comprises a first end and a second end opposite to each other, the tab is arranged at the first end, the direction extending from the first end to the second end is the width direction of the negative electrode sheet, the main body comprises a first region, a second region and a third region sequentially distributed along the width direction, the ion diffusion coefficient of the first region is greater than the ion diffusion coefficient of the second region, and / or the ion diffusion coefficient of the third region is greater than the ion diffusion coefficient of the second region; The ion diffusion coefficient includes a lithium ion diffusion coefficient or a sodium ion diffusion coefficient.

2. The battery cell according to claim 1, characterized in that: The ratio of the lithium ion diffusion coefficient of the first region to the lithium ion diffusion coefficient of the second region is 2-1000, and / or the ratio of the lithium ion diffusion coefficient of the third region to the lithium ion diffusion coefficient of the second region is 2-1000.

3. The battery cell according to claim 1, characterized in that: The main body is divided into the first region, the second region and the third region in sequence along the width direction, and the ratio of the lithium ion diffusion coefficient in the first region and / or the third region to the lithium ion diffusion coefficient in the second region is 5-500.

4. The battery cell according to claim 1, characterized in that: The lithium ion diffusion coefficient in the first region and / or the third region is 10 -9 cm 2 / s~10 -11 cm 2 / s, the lithium ion diffusion coefficient in the second region is 10 -11 cm 2 / s~10 -12 cm 2 / s.

5. The battery cell according to claim 1, characterized in that: The area of ​​the second region accounts for 50% to 70% of the total area of ​​the main body.

6. The battery cell according to claim 5, characterized in that: The ratio of the sizes of the first region, the second region and the third region along the width direction is 15% to 25%: 50% to 70%: 15% to 25%.

7. The battery cell according to claim 1, characterized in that: The negative electrode plate includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, and the ion diffusion coefficient of the negative electrode active material located in the first region and / or the third region is greater than the ion diffusion coefficient of the negative electrode active material located in the second region.

8. The battery cell according to claim 1, characterized in that: The negative electrode plate includes a negative electrode active material layer, and the first region, the second region and the third region include the same conductive agent, based on the mass of the negative electrode active material layer in the first region, the mass proportion of the conductive agent in the negative electrode active material layer in the first region is W1, based on the mass of the negative electrode active material layer in the second region, the mass proportion of the conductive agent in the negative electrode active material layer in the second region is W2, based on the mass of the negative electrode active material layer in the third region, the mass proportion of the conductive agent in the negative electrode active material layer in the third region is W3, W1<W2 and / or W3<W2.

9. The battery cell according to claim 8, characterized in that: The difference between W2 and W1 is 0.5 wt % to 2 wt %, and / or the difference between W2 and W3 is 0.5 wt % to 2 wt %.

10. The battery cell according to claim 1, characterized in that: The negative electrode plate includes a negative electrode active material layer, the negative electrode active material layer includes a conductive agent, the first region includes a first conductive agent, the second region includes a second conductive agent, the third region includes a third conductive agent, the conductivity of the second conductive agent is greater than the conductivity of the first conductive agent, and / or the conductivity of the second conductive agent is greater than the conductivity of the third conductive agent.

11. The battery cell according to claim 1, characterized in that: The negative electrode sheet includes a negative electrode active material layer, the first region, the second region and the third region include the same binder, the mass proportion of the binder in the negative electrode active material layer located in the first region is W4, the mass proportion of the binder in the negative electrode active material layer located in the second region based on the mass of the negative electrode active material layer in the second region is W5, the mass proportion of the binder in the negative electrode active material layer located in the third region based on the mass of the negative electrode active material layer in the third region is W6, W4>W5 and / or W6>W5.

12. The battery cell according to claim 11, characterized in that: The difference between W4 and W5 is 0.5 wt % to 3.1 wt %, and / or the difference between W6 and W5 is 0.5 wt % to 3.1 wt %.

13. The battery cell according to claim 1, characterized in that: The main body also includes a fourth region and a fifth region, and the main body includes the first region, the fourth region, the second region, the fifth region and the third region distributed in sequence along the width direction, and the ion diffusion coefficient of the fourth region and / or the fifth region is greater than the ion diffusion coefficient of the second region and less than the ion diffusion coefficient of the first region.

14. The battery cell according to claim 13, characterized in that: The ratio of the sizes of the first region, the fourth region, the second region, the fifth region and the third region along the width direction is 10% to 15%: 5% to 10%: 50% to 70%: 5% to 10%: 10% to 15%.

15. The battery cell according to claim 13, characterized in that: A ratio of a lithium ion diffusion coefficient located in the fourth region and / or the fifth region to a lithium ion diffusion coefficient located in the second region is 5-100.

16. The battery cell according to claim 13, characterized in that: The ion diffusion coefficient located in the fourth region and / or the fifth region is 10 -10 cm 2 / s~5*10 -12 cm 2 / s.

17. A battery, characterized in that: The battery comprises the battery cell according to any one of claims 1 to 16.

18. An electrical device, characterized in that: The electrical device comprises the battery according to claim 17, and the battery is used for providing electrical energy.

Images