Battery cell, battery device, and electric device

Abstract

The invention provides a battery monomer, a battery device and a power utilization device, and relates to the field of batteries. The battery monomer comprises an electrolyte, a positive pole piece and a negative pole piece; the positive pole piece comprises a positive pole current collector and a positive pole film layer arranged on at least one side of the positive pole current collector, the positive pole film layer comprises a positive pole active material, and the single-side coating weight of the positive pole film layer is 0.36 g / 1540.25 mm < 2 >-0.43 g / 1540.25 mm < 2 >; the negative electrode piece comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, and the single-side coating weight of the negative electrode film layer is 0.17 g / 1540.25 mm < 2 >-0.21 g / 1540.25 mm < 2 >; the electrolyte comprises a carbonic ester solvent, the carbonic ester solvent comprises methyl ethyl carbonate, and the mass content of the methyl ethyl carbonate is 24%-51% based on the mass of the electrolyte. The battery cell can give consideration to both low-temperature performance and energy density.

Description

Technical Field

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

[0002] In recent years, with the increasingly wide application range of secondary battery cells, secondary batteries are widely used in energy storage power systems such as hydraulic, thermal, wind, and solar power stations, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, and aerospace. Among them, lithium iron phosphate system batteries have received increasing attention in recent years due to their excellent safety performance.

[0003] With the rapid development of lithium iron phosphate system battery cells, higher requirements have been put forward for their low-temperature performance and energy density. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a battery cell, a battery device, and an electrical device, and the battery cell provided by the present application can take into account both low-temperature performance and energy density.

[0005] To achieve the above object, a first aspect of the present application provides a battery cell, including an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode tab and a negative electrode tab; the positive electrode tab includes a positive current collector and a positive electrode film layer provided on at least one side of the positive current collector. The positive electrode film layer includes a positive active material, and the single-sided coating weight of the positive electrode film layer is 0.36 g / 1540.25 mm 2 ~0.43 g / 1540.25 mm 2 ; the negative electrode tab includes a negative current collector and a negative electrode film layer provided on at least one side of the negative current collector. The negative electrode film layer includes a negative active material, and the single-sided coating weight of the negative electrode film layer is 0.17 g / 1540.25 mm 2 ~0.21 g / 1540.25 mm 2 ; the electrolyte includes a carbonate solvent, and the carbonate solvent includes ethyl methyl carbonate. Based on the mass of the electrolyte, the mass content of ethyl methyl carbonate is 24% - 51%.

[0006] In the present application, by making the single-sided coating weight of the positive electrode film layer 0.36 g / 1540.25 mm 2 ~0.43 g / 1540.25 mm 2 , the single-sided coating weight of the negative electrode film layer is 0.17 g / 1540.25 mm 2 ~0.21 g / 1540.25 mm 2, enabling the battery cell to obtain a high energy density. By selecting an ethylene carbonate dimethyl ester electrolyte with a mass ratio of 24% to 51%, the movement of lithium ions at low temperatures is promoted, thereby improving the low-temperature performance of the battery cell.

[0007] In some embodiments, based on the mass of the electrolyte, the mass content of ethylene carbonate dimethyl ester is 30% to 44%. This is beneficial for further balancing the low-temperature performance and energy density of the battery cell.

[0008] In some embodiments, the carbonate solvent further includes at least one of dimethyl carbonate and diethyl carbonate. Dimethyl carbonate and diethyl carbonate have low viscosities. By adding dimethyl carbonate and / or diethyl carbonate, it is beneficial to reduce the viscosity of the electrolyte, improve the electrolyte conductivity and wetting ability, thereby improving the low-temperature performance of the battery cell.

[0009] In some embodiments, based on the mass of the electrolyte, the mass content of dimethyl carbonate and / or diethyl carbonate is 8.5% to 22%. This is beneficial for further improving the low-temperature performance of the battery cell.

[0010] In some embodiments, based on the mass of the electrolyte, the mass content of dimethyl carbonate and / or diethyl carbonate is 11% to 20%. This is beneficial for further improving the low-temperature performance of the battery cell.

[0011] In some embodiments, the conductivity of the electrolyte is 8 mS / cm to 14 mS / cm. This is beneficial for reducing the internal impedance of the battery cell, reducing the energy loss due to resistance during charge and discharge, and extending the service life of the battery cell.

[0012] In some embodiments, the tap density of the positive electrode plate is 2.25 g / cm 3 ~2.65 g / cm 3 . This is beneficial for the battery cell to obtain a high energy density.

[0013] In some embodiments, the tap density of the positive electrode plate is 2.30 g / cm 3 ~2.45 g / cm 3 . This is beneficial for the battery cell to obtain a high energy density and balance the low-temperature performance.

[0014] In some embodiments, the porosity of the positive electrode plate is 23% to 32%. This can simultaneously ensure that the positive electrode plate has both a high tap density and good wetting performance, thereby being beneficial for the battery cell to balance a high energy density and good low-temperature performance.

[0015] In some embodiments, the positive electrode active material includes lithium-containing transition metal phosphate particles. The lithium-containing transition metal phosphate particles include a lithium-containing transition metal phosphate matrix and a coating layer located on at least a part of the surface of the lithium-containing transition metal phosphate matrix. The coating layer contains carbon elements. In the cumulative area distribution curve of the sphericity of the lithium-containing transition metal phosphate particles obtained from the cross-section of the positive electrode film layer in the thickness direction of the electrode sheet, the L of the sphericity A50 is 0.7 to 0.75. On the one hand, this is beneficial to improving the compaction density of the electrode sheet and enhancing the energy density during battery manufacturing; on the other hand, the stress generated during the lithium deintercalation and intercalation process of the positive electrode sheet can be released through the slip between particles, thereby alleviating the damage to the structure of the positive electrode sheet caused by stress release and improving the cycle performance of the battery.

[0016] In some embodiments, the chemical formula of the lithium-containing transition metal phosphate matrix is Li x1 A y1 Me a1 M b1 P 1- c1 X c1 Y z1 , where 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 0.8, 0.9 ≤ x1 + y1 ≤ 1.3; 0.9 ≤ a1 ≤ 1.5, 0 ≤ b1 ≤ 0.5, 0.9 ≤ a1 + b1 ≤ 1.5; 0 ≤ c1 ≤ 0.5; 3 ≤ z1 ≤ 5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, N, and P; Y includes one or more of O and F. Selecting the above lithium-containing transition metal phosphate matrix is beneficial to improving the cycle performance of the battery.

[0017] In some embodiments, the lithium-containing transition metal phosphate contains Ti element. Based on the mass of the lithium-containing transition metal phosphate particles, the mass content of the Ti element is 0.05% to 0.2%. By selecting the lithium-containing transition metal phosphate with the Ti element mass content in the above range, the transport barrier of lithium ions can be reduced, the lithium ion diffusion rate can be increased, thereby improving the kinetic performance of the battery monomer and enhancing the cycle performance.

[0018] In some embodiments, the primary average particle size of the lithium-containing transition metal phosphate is 100 nm to 2.5 μm. This is beneficial to improving the compaction density of the positive electrode sheet, thereby enhancing the energy density of the battery monomer.

[0019] In some embodiments, the compaction density of the negative electrode sheet is 1.3 g / cm 3 ~1.55 g / cm 3 . By making the compaction density of the negative electrode sheet within the above range, it is beneficial to improve the energy density of the battery cell.

[0020] In some embodiments, the compaction density of the negative electrode sheet is 1.4 g / cm 3 ~1.5 g / cm 3 . This is beneficial for the battery cell to obtain a high energy density and take into account the low-temperature performance.

[0021] In some embodiments, the porosity of the negative electrode sheet is 23% - 32%. This can simultaneously ensure that the negative electrode sheet takes into account a high compaction density and good wetting performance, thus being beneficial for the battery cell to take into account a high energy density and good low-temperature performance.

[0022] In some embodiments, the negative electrode active material includes graphite, and the volume-average particle size Dv50 of the graphite is 13 μm - 22 μm. This is beneficial to increase the compaction density of the electrode sheet, thereby increasing the volume energy density of the battery cell; at the same time, it can ensure that the transmission path of lithium ions in the graphite is appropriate, reducing the risk of adverse effects on the low-temperature performance of the battery cell due to too long a path.

[0023] In some embodiments, the volume-average particle size Dv50 of the graphite is 14.5 μm - 20 μm. This is beneficial for the battery cell to further take into account the energy density and low-temperature performance.

[0024] In some embodiments, the electrode assembly includes a stacked electrode assembly. The stacked electrode assembly can arrange the positive electrode sheet and the negative electrode sheet more regularly and tightly, so that more active materials (positive electrode active material, negative electrode active material) can be accommodated per unit volume, thereby increasing the volume energy density of the battery cell.

[0025] In some embodiments, the electrode assembly further includes a separator, the separator includes a base film, ceramic layers provided on both sides of the base film, and a bonding layer provided on the side of at least one ceramic layer away from the base film side. The bonding layer is a continuous layer with a porous structure, and the bonding layer includes a polyvinylidene fluoride polymer. By selecting the above bonding layer, it is possible to improve the adhesion between the separator and the electrode sheet and improve the battery cell interface while reducing the influence on the migration of lithium ions.

[0026] In some embodiments, the thickness of the base film in the separator is 7 μm - 9 μm.

[0027] In some embodiments, the single-sided thickness of the ceramic layer in the separator is 0.5 μm - 4 μm.

[0028] In some embodiments, the thickness of the adhesive layer on one side of the separator membrane is 0.15 μm to 2 μm.

[0029] In some embodiments, the porosity of the separator membrane is 28% to 50%. This is beneficial for the separator membrane to have appropriate mechanical strength while reducing the influence of the separator membrane on the migration rate of lithium ions between the positive and negative electrodes.

[0030] In some embodiments, the porosity of the separator membrane is 31% to 40%. This is beneficial for further balancing the mechanical strength of the separator membrane and the migration rate of lithium ions.

[0031] The second aspect of the present application provides a battery device, including the battery cell provided in the first aspect.

[0032] The third aspect of the present application provides an electrical device, including the battery device provided in the second aspect. Description of the Drawings

[0033] Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present application; Figure 2 is Figure 1 the exploded view of the battery cell according to an embodiment of the present application shown in Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application; Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application; Figure 5 is Figure 4 the exploded view of the battery pack according to an embodiment of the present application shown in Figure 6 is a schematic diagram of an electrical device using the battery cell according to an embodiment of the present application as a power source.

[0034] Description of the Reference Numerals: 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Embodiments

[0035] Hereinafter, embodiments of the battery cell, battery device, and electrical device of the present application will be specifically disclosed with appropriate reference to the 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 identical structures are omitted. This is to avoid making the following description 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 present application.

[0036] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise stated, the numerical range "a - b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0038] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0039] If there is no special instruction, all steps of this application can be carried out in sequence or randomly, preferably in sequence. For example, if the method includes steps (a) and (b), it means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, if it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0040] If there is no special instruction, the terms used in this application have the well-known meanings commonly understood by those skilled in the art.

[0041] If there is no special instruction, the numerical values of the various parameters mentioned in this application can be measured by various commonly used testing methods in the art. For example, they can be measured according to the testing methods given in this application.

[0042] At present, lithium iron batteries (where the positive electrode active material includes lithium-containing transition metal phosphates) have attracted increasing attention due to their superior safety performance compared to ternary batteries. However, compared with ternary batteries, the energy density of a single lithium iron battery cell is relatively low. Therefore, in the prior art, the energy density is usually increased by increasing the coating weight of the electrode sheet.

[0043] During the R & D process, the inventors made an important discovery: when the coating weight of the electrode sheet increases, the thickness of the electrode sheet will correspondingly increase. The increase in the thickness of the electrode sheet has an adverse effect on the transmission of lithium ions, and this phenomenon is more prominent in low-temperature application scenarios, resulting in a serious deterioration of the low-temperature performance of the battery cell.

[0044] Based on this, the present application provides a battery cell, a battery device, and an electrical device. The battery cell provided by the present application can balance low-temperature performance and energy density.

[0045] Battery cell In the first aspect of the present application, a battery cell is provided, which includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet and a negative electrode sheet; the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material, and the single-sided coating weight of the positive electrode film layer is 0.36 g / 1540.25 mm 2 ~0.43 g / 1540.25 mm 2 ; the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material, and the single-sided coating weight of the negative electrode film layer is 0.17 g / 1540.25 mm 2 ~0.21 g / 1540.25 mm 2 ; the electrolyte includes a carbonate solvent, and the carbonate solvent includes ethyl methyl carbonate. Based on the mass of the electrolyte, the mass content of ethyl methyl carbonate is 24% - 51%.

[0046] In the present application, by making the single-sided coating weight of the positive electrode film layer 0.36 g / 1540.25 mm 2 ~0.43 g / 1540.25 mm 2 and the single-sided coating weight of the negative electrode film layer 0.17 g / 1540.25 mm 2 ~0.21 g / 1540.25 mm 2, enabling the battery cell to obtain a high energy density. By selecting an ethylene carbonate - dimethyl carbonate electrolyte with a mass ratio of 24% - 51%, the characteristics of low viscosity and low melting point of ethylene carbonate - dimethyl carbonate can be utilized, so that the electrolyte will not solidify at low temperatures and has good fluidity. At low temperatures, the electrolyte can still fully penetrate the electrode sheet, ensuring the rapid transfer of lithium ions between the electrode sheet and the electrolyte, thereby improving the low - temperature performance of the battery cell. In addition, the ethylene carbonate - dimethyl carbonate within this content range can keep the electrolyte maintaining a relatively high dielectric constant, enhancing the solvation ability of ions and promoting the easier dissociation and movement of lithium ions, thus further improving the low - temperature performance of the battery cell.

[0047] In this application, the types and contents of organic components (such as carbonate solvents) in the electrolyte can be detected by using equipment and methods well - known in the art. For example, qualitative and quantitative analysis of the organic components in the electrolyte can be carried out by gas chromatography with reference to GB / T9722 - 2006 General Rules for Gas Chromatography of Chemical Reagents. In the embodiments of this application, newly prepared electrolyte can be taken as a sample, or a free electrolyte obtained by reverse - disassembling a battery that has been fully discharged (discharged to the lower cut - off voltage so that the charged state of the battery is about 0% SOC) can be used as a sample, and gas chromatography analysis method can be used for detection.

[0048] In the embodiments of this application, the types and contents of inorganic components (such as electrolyte salts) in the electrolyte have meanings well - known in the art and can be detected by using equipment and methods well - known in the art. For example, qualitative or quantitative analysis of the inorganic components / lithium salt concentration in the electrolyte can be carried out by ion chromatography with reference to the standard JY / T020 - 1996 General Rules for Ion Chromatography Analysis Method. In the embodiments of this application, newly prepared electrolyte can be taken as a sample, or a free electrolyte obtained by reverse - disassembling a battery that has been fully discharged (discharged to the lower cut - off voltage so that the charged state of the battery is about 0% SOC) can be used as a sample, and ion chromatography analysis method can be used for detection.

[0049] In the embodiments of this application, after quantitatively and qualitatively detecting each component in the electrolyte, the mass content of ethylene carbonate - dimethyl carbonate can be determined based on the mass of the electrolyte.

[0050] Exemplarily, the mass content of ethylene carbonate - dimethyl carbonate is 24%, 30%, 35%, 40%, 45%, 51% or any numerical range between any two of them. Optionally, the mass content of ethylene carbonate - dimethyl carbonate is 30% - 44%.

[0051] In this application, the single-sided coating weight of the positive electrode film layer can be tested by methods known in the art. The positive electrode sheet to be tested can be the prepared positive electrode sheet or the positive electrode sheet obtained by disassembling the battery. Hereinafter, the test process will be described by taking the latter as an example. Disassemble the battery at 0% state of charge (SOC) to obtain the positive electrode sheet, soak the sheet in DMC for 6 hours and then dry it. Cut the dried positive electrode sheet into a circular piece with an area of 1540.25 mm 2 , weigh the mass of the circular piece as m1, then remove the positive electrode film layer provided on one side of the circular piece, weigh the mass of the circular piece as m2, and take m1 - m2 as the single-sided coating weight of the positive electrode film layer.

[0052] Exemplarily, the single-sided coating weight of the positive electrode film layer is 0.36 g / 1540.25 mm 2 , 0.37 g / 1540.25 mm 2 , 0.38 g / 1540.25 mm 2 , 0.39 g / 1540.25 mm 2 , 0.40 g / 1540.25 mm 2 , 0.41 g / 1540.25 mm 2 , 0.42 g / 1540.25 mm 2 , 0.43 g / 1540.25 mm 2 or any value range between any two of them.

[0053] In this application, the single-sided coating weight of the negative electrode film layer can be tested by methods known in the art. The negative electrode sheet to be tested can be the prepared negative electrode sheet or the negative electrode sheet obtained by disassembling the battery. Hereinafter, the test process will be described by taking the latter as an example. Disassemble the battery at 0% state of charge (SOC) to obtain the negative electrode sheet, soak the sheet in DMC for 6 hours and then dry it. Cut the dried negative electrode sheet into a circular piece with an area of 1540.25 mm 2 , weigh the mass of the circular piece as m3, then remove the negative electrode film layer provided on one side of the circular piece, weigh the mass of the circular piece as m4, and take m3 - m4 as the single-sided coating weight of the negative electrode film layer.

[0054] Exemplarily, the single-sided coating weight of the negative electrode film layer is 0.170 g / 1540.25 mm 2 , 0.175 g / 1540.25 mm 2 , 0.180 g / 1540.25 mm 2 , 0.185 g / 1540.25 mm 2 , 0.190 g / 1540.25 mm 2 , 0.195 g / 1540.25 mm 2 , 0.200 g / 1540.25 mm2 、 0.210 g / 1540.25 mm 2 or the numerical range between any two of them.

[0055] As used herein, the term "battery cell" refers to a battery module or a battery pack. The following are described separately. Usually, a battery cell includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are embedded and removed back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short - circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0056] Electrolyte The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. There is no specific limitation on the type of the electrolyte in this application, and it can be selected according to requirements.

[0057] In this application, the electrolyte includes a solvent, the solvent includes carbonate solvents, and the carbonate solvents include ethyl methyl carbonate.

[0058] In some embodiments, the carbonate solvents further include at least one of dimethyl carbonate and diethyl carbonate. Dimethyl carbonate and diethyl carbonate have low viscosities. By adding dimethyl carbonate and / or diethyl carbonate, it is beneficial to reduce the viscosity of the electrolyte, improve the conductivity and wetting ability of the electrolyte, thereby improving the low - temperature performance of the battery cell.

[0059] In this application, the test method for the mass content of dimethyl carbonate and / or diethyl carbonate in the electrolyte refers to the test method for the types and mass contents of organic components in the aforementioned electrolyte.

[0060] In some embodiments, based on the mass of the electrolyte, the mass content of dimethyl carbonate and / or diethyl carbonate is 8.5% - 22%. By controlling the mass content of dimethyl carbonate and / or diethyl carbonate within the above range, it is beneficial to reduce the viscosity of the electrolyte, improve the conductivity and wetting ability of the electrolyte, thereby further improving the low - temperature performance of the battery cell. Exemplarily, based on the mass of the electrolyte, the mass content of dimethyl carbonate and / or diethyl carbonate is 8.5%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22% or the values within the range composed of any two of them. Optionally, based on the mass of the electrolyte, the mass content of dimethyl carbonate and / or diethyl carbonate is 11% - 20%.

[0061] In some embodiments, the conductivity of the electrolyte is 8 mS / cm to 14 mS / cm. In the present application, by adjusting the mass content of ethyl methyl carbonate, dimethyl carbonate, and / or diethyl carbonate, the electrolyte has a relatively high conductivity, which can reduce the internal impedance of the battery cell, reduce the energy loss due to resistance during charge and discharge, and extend the service life of the battery cell. Exemplarily, the conductivity of the electrolyte is 8 mS / cm, 9 mS / cm, 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, 14 mS / cm, or a value within the range composed of any two of these values.

[0062] In the present application, the conductivity of the electrolyte can be tested by methods known in the art. The electrolyte to be tested can be the prepared electrolyte or the electrolyte obtained by disassembling the battery. Hereinafter, the testing process will be described taking the latter as an example. The battery is disassembled to obtain the electrolyte, and the obtained electrolyte is used as the sample to be tested. The testing method follows HG / T 4067-2015. The conductivity of the electrolyte to be tested is measured with a conductivity meter: Take about 100 mL of the sample to be tested with a dry, clean and corrosion-resistant sample bottle, seal it and place it in a constant temperature water bath at 25 ± 0.5 °C. When the temperature of the sample to be tested is constant, replace the sample bottle cap with a rubber stopper with electrodes inserted. When the temperature is within the range of 25 ± 0.5 °C, read the data, which is the conductivity of the sample to be tested.

[0063] In some embodiments, the electrolyte further includes an electrolyte salt.

[0064] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate) borate, lithium difluoro bis(oxalate) phosphate, and lithium tetrafluorooxalate phosphate.

[0065] In some embodiments, the electrolyte may further optionally include additives. For example, the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and can also include additives that can improve certain performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature or low-temperature performance of the battery, etc.

[0066] Positive electrode tab The positive electrode tab includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector. As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on either or both of the two opposite surfaces of the positive electrode current collector.

[0067] In some embodiments, the tap density of the positive electrode tab is 2.25 g / cm 3~2.65 g / cm 3 By making the compaction density of the positive electrode plate within the above range, it is beneficial for the battery cell to obtain a high energy density. Exemplarily, the compaction density of the positive electrode plate is 2.25 g / cm 3 , 2.26 g / cm 3 , 2.27 g / cm 3 , 2.28 g / cm 3 , 2.29 g / cm 3 , 2.30 g / cm 3 , 2.35 g / cm 3 , 2.40 g / cm 3 , 2.45 g / cm 3 , 2.50 g / cm 3 , 2.55 g / cm 3 , 2.60 g / cm 3 , 2.65 g / cm 3 or the numerical range between any two of them. Optionally, the compaction density of the positive electrode plate is 2.30 g / cm 3 ~2.45 g / cm 3 . Thus, it is beneficial for the battery cell to obtain a high energy density and take into account the low-temperature performance.

[0068] In the embodiments of the present application, the compaction density of the positive electrode plate refers to the compaction density of the positive electrode plate of the battery cell at 0% state of charge (SOC). It can be detected by the following method: disassemble the positive electrode plate from the battery cell at 0% SOC, and measure the compaction density of the positive electrode plate. For example, take a single-sided coated positive electrode plate (if it is a double-sided coated electrode plate, the positive electrode film layer on one side can be wiped off first), punch it into small round pieces with an area of S1, weigh it, record it as M1, and measure its thickness H1. Then wipe off the positive electrode film layer of the above-mentioned weighed positive electrode plate, weigh the weight of the positive electrode current collector, record it as M0, and measure its thickness H0. The single-sided coating weight of the positive electrode plate = (the weight M1 of the positive electrode plate - the weight M0 of the positive electrode current collector) / S1, the thickness of the positive electrode film layer = the thickness H1 of the positive electrode plate - the thickness H0 of the positive electrode current collector, and the compaction density of the positive electrode plate = the single-sided coating weight of the positive electrode film layer / the thickness of the positive electrode film layer.

[0069] In some embodiments, the porosity of the positive electrode plate is 23% - 32%. By controlling the porosity of the positive electrode plate within the above range, it is possible to ensure that the positive electrode plate takes into account both a high compaction density and good wetting performance, thereby ensuring that the battery has a high energy density and good low-temperature performance. Exemplarily, the porosity of the positive electrode plate is 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32% or the numerical range between any two of them.

[0070] In this application, the porosity of the positive electrode sheet can be measured by instruments and methods known in the art. For example, it can be measured with a true density tester with reference to GB / T24586-2009. Specifically: Cut the positive electrode sheet into a size of 3 mm × 3 mm, measure the apparent volume V0 of the sample (the apparent volume of the sample is the thickness of the positive electrode film layer × the area of the sample), and then use a true density tester to measure the true volume of the sample. Specifically, place the sample in the sample test chamber, introduce nitrogen into the sample test chamber, connect the sample test chamber with the reference chamber and record the pressure after stabilization. By detecting the pressure before the connection between the reference chamber and the sample chamber and the pressure after the connection between the reference chamber and the sample chamber is stabilized, and then calculate the volume of the pores according to Boyle's law PV = nRT. The porosity of the sample = pore volume / apparent volume.

[0071] In some embodiments, the positive electrode active material includes lithium-containing transition metal phosphate particles. The lithium-containing transition metal phosphate particles include a lithium-containing transition metal phosphate matrix and a coating layer located on at least a part of the surface of the lithium-containing transition metal phosphate matrix. The coating layer contains carbon. In the cumulative area distribution curve of the sphericity of the lithium-containing transition metal phosphate particles obtained from the cross-section of the positive electrode film layer in the thickness direction of the electrode sheet, the L A50 of the sphericity is 0.7 to 0.75. The L A50 of the sphericity of the lithium-containing transition metal phosphate particles within the above range indicates that the surface of the lithium transition metal phosphate particles is relatively smooth, and the friction between particles is relatively small, which can improve the slip degree between the lithium-containing transition metal phosphate particles. On the one hand, this is beneficial to improving the compaction density of the electrode sheet and enhancing the energy density during battery manufacturing; on the other hand, the stress generated during the lithium insertion and extraction process of the positive electrode sheet can be released through the slip between particles, thereby alleviating the damage to the electrode sheet structure caused by the stress release of the positive electrode sheet and improving the cycle performance of the battery. Exemplarily, in the cumulative area distribution curve of the sphericity of the lithium-containing transition metal phosphate particles obtained from the cross-section of the positive electrode film layer in the thickness direction of the electrode sheet, the L A50 of the sphericity is 0.70, 0.71, 0.72, 0.73, 0.74, 0.75 or the numerical range between any two of them.

[0072] In this application, the term "particle" refers to a particle with a recognizable complete boundary in the field of view of the positive electrode film layer at a certain magnification, such as 10,000 times. There may be defects and scratches inside the particle, but no complete boundary sufficient to divide the particle can be recognized inside the particle.

[0073] The method for identifying particles is as follows: Cut the positive electrode film layer along the thickness direction of the electrode plate by an argon ion beam. After exposing the cross-section, use a scanning electron microscope to observe the cross-section of the positive electrode film layer along the thickness direction of the electrode plate. Use a field emission scanning electron microscope to collect images in the secondary electron mode at a non-edge position (after observing the edge of the electrode plate under the scanning electron microscope, adjust the field of view to the central part of the sample) of the cross-section of the positive electrode film layer, take an electron microscope image at a magnification of 10k times, and analyze the particles in the electron microscope image using ImageJ software (version 1.46r, win64). The specific method of using ImageJ software is as follows: Load the scanning electron microscope image to be analyzed, use the Cellpose plug-in software in it to identify particles, and perform manual correction on this basis; Use Image J to read and count data. The specific method of using the Cellpose plug-in software to identify particles is as follows: Set the segmentation diameter parameter (diameter in the Segmantation module) to 15 pixels, click "run cyto3" to identify particles, and then manually mark the particles that are not recognized by the software, not completely recognized by the software, or have recognition errors in this image. The particles that are not recognized by the software, not completely recognized by the software, or have recognition errors in the image mainly include the following types: 1. Due to the particle being too large or having scratches on the particle surface, the particle cannot be recognized or cannot be completely recognized; 2. During the argon ion beam cutting process, scratches will be generated on the particle surface, and the software may misjudge the scratches as the particle boundary during the recognition process, resulting in recognition errors; 3. Due to the particle being too small, it is not successfully recognized; 4. The particle is located at the edge of the electron microscope field of view, and the interior of the particle is penetrated by the edge, and the morphology is not completely shown, and the local part is recognized instead of the whole, resulting in recognition errors. For the above unrecognized or misrecognized particles, manual calibration is carried out, and the specific process is as follows: Delete the large particles that are located at the four edges of the scanning electron microscope and cannot be completely shown; Judge whether there are gap scratches inside other unrecognized or misrecognized particles. If there are no gap scratches inside the particle, judge it as a particle, and manually mark it according to the particle boundary observed manually; In response to the presence of gap scratches inside the particle, judge whether the gap scratches penetrate the particle. If they do not penetrate the particle, judge it as a particle and perform manual marking; In response to the gap scratches penetrating the particle, judge whether the gap scratches are linear or irregular; In response to the gap scratches being irregular, judge it as the boundary between particles and divide the particles along this boundary; In response to the gap scratches being linear, perform contrast; In response to the contrast being not obvious and there being no sense of crack, judge it as a scratch and mark it as a particle; In response to the contrast being strong and there being a sense of crack, judge it as the boundary between particles and mark it as two particles. After manual marking, delete the information irrelevant to the particles during the automatic image processing process, and the determination and marking of the particles in the picture are completed.

[0074] Different from the state of the positive electrode active material in the Malvern laser scattering method and also different from the state of the positive electrode active material when directly observing the positive electrode active material by scanning electron microscopy. The particles in the positive electrode film layer are in a good dispersed state under the action of the roll pressure. Observing the positive electrode film layer is conducive to effectively characterizing the objective conditions of the particle size, particle area and quantity of the particles in the positive electrode film layer.

[0075] It can be understood that the particles in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, especially the particles above 50 nm, mainly come from the positive electrode active material. Therefore, by observing and counting the particle size of the particles in the cross-section of the positive electrode film layer in this application, the distribution of the lithium-containing transition metal phosphate particles in the positive electrode film layer in the electrode sheet can be accurately and objectively reflected.

[0076] In the prior art, the Malvern laser diffraction method is usually used to count the particle size of the positive electrode active material. However, the inventors' research shows that due to the easy agglomeration of lithium-containing phosphates, the test results obtained by the Malvern laser diffraction method based on the laser scattering principle often measure the particle size of its particle aggregates, and cannot truly reflect the particle size of the particles in the positive electrode active material, let alone reflect the dispersion state of the positive electrode active material in the film layer, because the dispersion degree of the positive electrode active material in the film layer will increase during the film-forming roll pressing process. The test results obtained by the Malvern laser diffraction method are closely related to the particle size, specific surface area and agglomeration degree of the positive electrode active material. Therefore, the particle size obtained by the Malvern laser diffraction method test cannot be equated or analogized to the particle size statistically obtained in this application.

[0077] In this application, in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the sphericity test method of the particles is as follows: Import the picture after particle determination and identification into ImageJ software for analysis. Complete the scale setting according to the scanning electron microscope image, and analyze the Feret diameter and Area of the particle cross-section in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet through the analysis functions of "Feret diameter", "Area", "Round", and "Solidity". According to the software manual (ImageJ User Guide IJ 1.46r), the "Feret" parameter obtained by analysis represents the maximum distance between all parallel lines of the outer contour of the particle cross-section, which characterizes the particle size; the "Area" parameter represents the pixel area of the particle, which characterizes the area of the particle. Since particles with a particle size less than 50 nm have large errors in the statistical process and are difficult to accurately identify, and the particle size of the conductive agent is generally less than 50 nm, which will cause large errors in the statistical results. Therefore, in the particle size statistics process of this application, particles with a particle size less than 50 nm are not statistically counted, and the particle statistical data corresponding to "NaN" displayed in Area is deleted. The "Round" parameter represents the ratio of the pixel area of the particle to the area of a circle with the fitted major axis as the diameter, which can be used to characterize the sphericity of the particle. When the particle is closer to a sphere, the ratio of the pixel area to the area of a circle with the fitted major axis as the diameter is closer to 1. Therefore, the "Round" parameter of the obtained particle is used to characterize the sphericity of the particle.

[0078] Arrange the sphericities of at least 5000 obtained particles in ascending order, and obtain the cumulative distribution curve of the sphericities of the particles in the positive electrode film layer with the sphericity as the horizontal axis and the cumulative area ratio as the vertical axis. L A50 It is the sphericity L value corresponding to the cumulative area ratio of 50% on the vertical axis in the cumulative distribution curve of the sphericity L value.

[0079] The sphericity L A50 Compared with the point value, it can reflect the overall sphericity of the particles in the positive electrode film layer, that is, the degree of approximate sphericity; compared with the mean value, it can reduce the influence of extreme values in the test process and improve the confidence level of the test results.

[0080] In some embodiments, the chemical formula of the lithium-containing transition metal phosphate matrix is Li x1 A y1 Me a1 M b1 P 1- c1 X c1 Y z1, wherein, 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 0.8, 0.9 ≤ x1 + y1 ≤ 1.3, 0.9 ≤ a1 ≤ 1.5, 0 ≤ b1 ≤ 0.5, 0.9 ≤ a1 + b1 ≤ 1.5, 0 ≤ c1 ≤ 0.5; 3 ≤ z1 ≤ 5, A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, N, and P; Y includes one or more of O and F. Selecting the above lithium-containing transition metal phosphate matrix is beneficial to improving the cycle performance of the battery.

[0081] In some embodiments, the lithium-containing transition metal phosphate includes lithium iron phosphate.

[0082] In some embodiments, the lithium-containing transition metal phosphate contains Ti element. Based on the mass of the lithium-containing transition metal phosphate particles, the mass content of the Ti element is 0.05% - 0.2%. By selecting the lithium-containing transition metal phosphate with the mass content of the Ti element in the above range, the transport barrier of lithium ions can be reduced, the diffusion rate of lithium ions can be increased, thereby improving the kinetic performance of the battery monomer and enhancing the cycle performance. Exemplarily, the mass content of the Ti element is 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2% or the numerical range between any two of them.

[0083] In some embodiments, the primary average particle size of the lithium-containing transition metal phosphate is 100 nm - 2.5 μm. By selecting the lithium transition metal phosphate with the primary average particle size in the above range, it is beneficial to improve the compaction density of the positive electrode sheet, thereby enhancing the energy density of the battery monomer. Exemplarily, the primary average particle size of the lithium-containing transition metal phosphate is 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 2000 nm, 2500 nm (2.5 μm) or the numerical range between any two of them.

[0084] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as 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.).

[0085] During the charge and discharge process of the battery, the insertion and extraction and consumption of Li will occur, and the molar content of Li is different when the battery is discharged to different states. In the listing of the positive electrode active material in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system, after charge and discharge cycles, the molar content of Li will change.

[0086] In the listing of the positive electrode active material in this application, the molar content of O is only the theoretical state 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.

[0087] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0088] In some embodiments, the positive electrode film layer may also optionally include a conductive agent. As an example, the conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] In some embodiments, the positive electrode plate can be prepared in the following manner: dispersing the above components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0090] Negative electrode plate The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector. As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0091] In some embodiments, the compaction density of the negative electrode plate is 1.3 g / cm 3 ~1.55 g / cm 3 . By making the compaction density of the negative electrode plate within the above range, it is beneficial to improve the energy density of the battery cell. Exemplarily, the compaction density of the negative electrode plate is 1.30 g / cm 3 , 1.35 g / cm 3 , 1.40 g / cm 3 , 1.41 g / cm 3 , 1.42 g / cm 3 , 1.43 g / cm 3 , 1.44 g / cm 3 , 1.45 g / cm 3 , 1.46 g / cm 3 , 1.47 g / cm 3 , 1.48 g / cm 3 , 1.49 g / cm 3 , 1.50 g / cm 3 , 1.51 g / cm 3 , 1.52 g / cm 3 , 1.53 g / cm 3 , 1.54 g / cm 3 , 1.55 g / cm 3 or any value range between any two of them. Optionally, the compaction density of the negative electrode plate is 1.40 g / cm 3 ~1.50 g / cm 3 . This is beneficial for the battery cell to obtain a high energy density and take into account the low-temperature performance.

[0092] In some embodiments, the porosity of the negative electrode plate is 23% - 32%. Exemplarily, the porosity of the negative electrode plate is 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32% or any value range between any two of them. By selecting a negative electrode plate with a porosity within the above range, it is possible to ensure that the negative electrode plate has a relatively high compaction density and good wetting performance, thereby ensuring that the battery cell has a high energy density and good cycling performance.

[0093] The negative electrode active material can be the negative electrode active material for battery cells known in the art. In some embodiments, the negative electrode active material includes graphite, and the volume average particle size Dv50 of the graphite is 13 μm to 22 μm. Exemplarily, the volume average particle size Dv50 of the graphite is 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, or the numerical range between any two of them. Optionally, the volume average particle size Dv50 of the graphite is 14.5 μm to 20 μm. By using graphite with a volume average particle size Dv50 within the above range, it is beneficial to increase the compaction density of the electrode sheet, thereby increasing the volume energy density of the battery cell; at the same time, it can ensure that the transmission path of lithium ions in the graphite is appropriate, reducing the risk of adversely affecting the low-temperature performance of the battery cell due to too long a path.

[0094] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as 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.).

[0095] In some embodiments, the thickness of the negative electrode current collector is 6 μm to 12 μm. Using a thicker current collector can improve the overall strength and support of the battery, and at the same time can also avoid the risk of the electrode sheet wrinkling or breaking during high-pressure rolling.

[0096] In some embodiments, the negative electrode film layer may also optionally include a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0097] In some embodiments, the negative electrode film layer may also optionally include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] In some embodiments, the negative electrode film layer may also optionally include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0099] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet described above, 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 current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained.

[0100] Separator In some embodiments, the battery cell further includes a separator. The present application does not particularly limit the type of the separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0101] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0102] In some embodiments, the electrode assembly includes a stacked electrode assembly. The stacked electrode assembly can make the positive electrode sheet and the negative electrode sheet arranged more regularly and tightly, so that more active substances (positive electrode active material, negative electrode active material) can be accommodated per unit volume, thereby improving the volumetric energy density of the battery cell.

[0103] In some embodiments, the separator includes a base film, ceramic layers provided on both sides of the base film, and a bonding layer provided on the side of at least one ceramic layer away from the base film. The bonding layer is a continuous layer with a porous structure, and the bonding layer includes a vinylidene fluoride polymer.

[0104] In some embodiments, the battery cell further includes a separator disposed between the positive electrode sheet and the negative electrode sheet. The separator includes a base film, ceramic layers provided on both sides of the base film, and a bonding layer provided on the side of at least one ceramic layer away from the base film.

[0105] The ceramic layers provided on both sides of the base film are beneficial to improving the mechanical strength of the separator and reducing the risk of internal short circuit.

[0106] In some embodiments, the battery cell further includes a separator disposed between the positive electrode sheet and the negative electrode sheet. The separator includes a base film, ceramic layers provided on both sides of the base film, and bonding layers provided on the sides of the ceramic layers away from the base film.

[0107] In some embodiments, the vinylidene fluoride-based polymers include one or more of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP).

[0108] In some embodiments, the vinylidene fluoride-based polymer includes polyvinylidene fluoride (PVDF).

[0109] In the prior art, the adhesive layer of the separator membrane usually uses aqueous PVDF, which presents an island-like structure in the separator membrane. On the one hand, this is beneficial for providing a gap for the expansion of the electrode assembly (electric core), and on the other hand, it is convenient for manufacturing. However, the contact area between such an adhesive layer of the separator membrane and the electrode tab is small, and the adhesive force is weak.

[0110] The separator membrane provided by the embodiments of the present application uses a continuous layer with a porous structure as the adhesive layer. Compared with the adhesive layer in the prior art, its bonding area with the electrode tab is larger, so that the bonding between the separator membrane and the electrode tab is more firm and uniform. Further, when the positive electrode film layer rebounds, it is beneficial to maintain the interfacial contact between the separator membrane and the positive electrode film layer, reducing the risk of performance deterioration caused by electrical contact failure.

[0111] It can be understood that the continuous adhesive layer may break and deform into a block structure during the manufacture or cycling process of the electrode tab due to contact or extrusion stress with the positive electrode tab or the negative electrode tab. The continuous structure referred to in the present application means that at the microscopic level, such as observed under a scanning electron microscope or an optical microscope, the adhesive layer of the separator membrane is continuous. In order to reflect the true morphology of the separator membrane, during the sampling process, it is preferably sampled in the area where the adhesive layer of the separator membrane in the battery has not adhered to the positive electrode tab or the negative electrode tab. As an example, it is sampled at the position of the separator membrane beyond the positive electrode tab and the negative electrode tab; or it is sampled at the separator membrane near the surface of the electrode assembly. The bonding between the sampling area of the separator membrane and the positive electrode tab or the negative electrode tab is less, and it can better reflect the true state of the separator membrane.

[0112] Relative to the wound electrode assembly (wound electric core), in the stacked electrode assembly (stacked electric core), the extrusion between the separator membrane and the electrode tab is smaller, and the separator membrane and the electrode tab are prone to relative displacement, thereby disturbing the membrane layer (negative electrode film layer, positive electrode film layer), and the membrane layer is prone to powder falling or peeling off; in addition, it may also cause the positive and negative electrodes to overlap each other, increasing the risk of internal short circuit of the electrode assembly. Therefore, the separator membrane provided by the embodiments of the present application is particularly suitable for the stacked electrode assembly. The increase in the adhesive force between the porous adhesive layer and the electrode tab helps to improve the adhesive force between the separator membrane and the electrode tab, reducing the relative displacement between the separator membrane and the electrode tab, which not only helps to reduce the disturbance to the positive electrode film layer and reduce the probability of membrane layer peeling off, but also helps to reduce the risk of short circuit of the electrode assembly caused by the overlap of the positive and negative electrodes.

[0113] In the present application, the "wound electrode assembly" refers to a battery core assembly with a specific shape and performance formed by tightly winding a positive electrode tab, a negative electrode tab, and a separator membrane located between the positive and negative electrode tabs in a certain manner.

[0114] In this application, the "laminated electrode assembly" refers to the core component of the battery formed by alternately stacking the positive electrode sheet, the separator membrane, and the negative electrode sheet in sequence.

[0115] In summary, when the polyvinylidene fluoride-based polymer in the adhesive layer of the embodiments of this application is selected from the above materials, it helps to form a continuous and uniform porous adhesive layer. First, the adhesion between this adhesive layer and the electrode sheet is improved and evenly distributed, which helps to reduce the stress concentration phenomenon in the thick-coated lithium-containing transition metal phosphate positive electrode film layer and reduce the risk of film layer peeling, thereby helping to further improve the cycle life of the battery. Second, the adhesive layer stably adheres to the positive electrode sheet or the negative electrode sheet, which helps to reduce the direct contact between the positive electrode sheet and the negative electrode sheet caused by the relative displacement of the electrode sheet and the separator membrane, reduce the risk of internal short circuit, and help to improve the battery safety performance. Third, the porous adhesive layer helps to maintain the porosity of the separator membrane, reserve space for the expansion of the electrode assembly, and further improve the cycle life of the battery.

[0116] In some embodiments, the material of the base film may include but is not limited to one or more of glass fiber, non-woven fabric, polyethylene (PE), and polypropylene (PP).

[0117] In some embodiments, the ceramic layer includes aluminum oxide ( ), zirconium oxide ( ), titanium oxide ( ), silicon oxide ( ), boron nitride ( ), or one or more of them.

[0118] The ceramic particles have flame retardancy and a relatively high hardness value, and are not easily deformed by heat, so their dimensional stability is excellent. The low thermal conductivity of the ceramic material can further prevent the expansion of certain thermal runaway points in the battery to form an overall thermal runaway, thereby improving the safety performance of the battery cell.

[0119] In some embodiments, the thickness of the base film in the separator membrane is 7 μm to 9 μm.

[0120] In some embodiments, the thickness of the base film in the separator membrane can be selected as 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, or the numerical range between any two of them.

[0121] In some embodiments, the unilateral thickness of the ceramic layer in the separator membrane is 0.5 μm to 4 μm.

[0122] In some embodiments, the unilateral thickness of the ceramic layer in the separator membrane can be selected as 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, or the numerical range between any two of them.

[0123] In some embodiments, the thickness of the adhesive layer on one side of the separator membrane is 0.15 μm to 2 μm.

[0124] In some embodiments, the thickness of the adhesive layer on one side of the separator membrane can be selected as 0.15 μm, 0.25 μm, 0.35 μm, 0.45 μm, 0.55 μm, 0.65 μm, 0.75 μm, 0.85 μm, 0.95 μm, 1 μm, 1.5 μm, 2 μm, or the numerical range between any two of them.

[0125] If the thickness of the adhesive layer is too low, the void space in the separator membrane is small and the adhesion between the separator membrane and the electrode is low. On the one hand, after the film layer expands, the stress increases and the probability of the film layer peeling off increases, affecting the cycle life of the battery. On the other hand, the probability of positive-negative lap short circuit increases, thus affecting the safety performance of the battery. If the thickness of the adhesive layer is too large, it occupies a large space in the battery and affects the transmission of lithium ions, thus affecting the volumetric energy density and cycle performance of the battery. In the embodiments of the present application, when the thickness of the adhesive layer is within the above range, it helps to balance the cycle life, safety performance and volumetric energy density of the battery.

[0126] The test method for the thickness of each layer in the separator membrane is as follows: Cut the separator membrane along the thickness direction. After exposing the cross-section, use a scanning electron microscope to observe the cross-section of the separator membrane in the thickness direction. Adjust the electron microscope to an appropriate magnification so that the base film, ceramic layer and adhesive layer contained in the separator membrane can be completely observed. Then perform a mapping test on the separator membrane. The coating with the distribution of metal elements in the test results is the ceramic layer, and the coating with higher carbon and fluorine element contents is the adhesive layer. Then measure the thickness T1 of the ceramic layer on one side of the base film and the thickness t1 of the adhesive layer respectively. According to the above operation steps, measure the thicknesses T1, T2, T3, T4, T5 of the ceramic layer in 5 different fields of view; calculate the average value, which is the thickness of the ceramic layer.

[0127] Measure the thickness values t1, t2, t3, t4, t5 of the adhesive layer in 5 different fields of view, and calculate the average value, which is the thickness of the adhesive layer.

[0128] In some embodiments, the porosity of the separator membrane is 28% to 50%. Exemplarily, the porosity of the separator membrane is 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or the numerical range between any two of them. Optionally, the porosity of the separator membrane is 31% to 40%. By making the porosity of the separator membrane within the above range, while enabling the separator membrane to have appropriate mechanical strength, the influence of the separator membrane on the migration rate of lithium ions between the positive and negative electrodes can be reduced.

[0129] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator are made into an electrode assembly by a stacking process.

[0130] In some embodiments, the battery cell may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0131] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed, etc.

[0132] This application does not particularly limit the shape of the battery cell, and it can be cylindrical, square, or any other shape. For example, Figure 1 is a battery cell 5 with a square structure as an example.

[0133] In some embodiments, referring to Figure 2 , the outer package may include a housing 51 and a top cover assembly 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 through a winding process or a stacking 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 included in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0134] In some embodiments, the battery cells can be assembled into a battery module. The number of battery cells included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0135] Figure 3 is a battery module 4 as an example. Referring to Figure 3 , in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0136] Optionally, the battery module 4 can further include a housing with a receiving space, and a plurality of battery cells 5 are accommodated in the receiving space.

[0137] In some embodiments, the above-mentioned battery module can be further assembled into a battery pack. The number of battery modules included in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0138] Figure 4 and Figure 5 The battery pack 1 is taken as an example. Referring to Figure 4 and Figure 5 , 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 be covered on the lower box body 3 to 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.

[0139] Battery device The second aspect of the present application provides a battery device, including the battery cell provided in the first aspect.

[0140] Power-consuming device The third aspect of the present application provides a power-consuming device, which includes the battery device provided in the second aspect of the present application.

[0141] The power-consuming device can be used as the power source of the power-consuming device or as the energy storage unit of the power-consuming device. The power-consuming device may include mobile devices (such as mobile phones, laptop computers, 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, satellites, energy storage systems, etc., but is not limited thereto.

[0142] As a power-consuming device, the battery cell, battery module or battery pack can be selected according to its usage requirements.

[0143] Figure 6 The power-consuming device is taken as an example. The power-consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the power-consuming device for the battery cell, a battery pack or a battery module can be adopted.

[0144] Another example of the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires thinness and lightness, and a battery cell can be used as the power source.

[0145] Embodiment 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 a limitation to the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0146] Embodiment 1 (1) Preparation of the positive electrode plate: The positive electrode active material (lithium iron phosphate), polyvinylidene fluoride and conductive carbon black are mixed in a weight ratio of 97:2:1 and added to a solvent N-methylpyrrolidone, and stirred evenly to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector aluminum foil to form a positive electrode film layer, and the positive electrode sheet is obtained after drying and cold pressing.

[0147] (2) Preparation of negative electrode sheet: The negative electrode material graphite, the conductive agent Super-P, the dispersant CMC, and the binder SBR are fully stirred and mixed in a proper amount of deionized water at a mass ratio of 96.4:0.4:1.0:2.2 to form a negative electrode slurry; the negative electrode slurry is coated on a copper foil to form a negative electrode film layer, and the negative electrode sheet is obtained after drying and cold pressing.

[0148] (3) Preparation of electrolyte: In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), carbonate solvents: ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed evenly. Lithium hexafluorophosphate was added and dissolved in an organic solvent so that the concentration of lithium hexafluorophosphate in the electrolyte was 1.05 mol / L, and vinylene carbonate (Vc) was added and stirred evenly to obtain the electrolyte of Example 1.

[0149] Among them, based on the total mass of the electrolyte, the mass content of dimethyl carbonate is 16.7%, the mass content of ethyl methyl carbonate is 39.5%, the mass content of ethylene carbonate is 29%, and the mass content of vinylene carbonate is 2.6%.

[0150] (4) Isolation film: Preparation of ceramic layer slurry: Inorganic particle boehmite, binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose (CMC-Na), and wetting agent silicone-modified polyether are mixed uniformly in an appropriate amount of solvent deionized water at a dry weight ratio of 85:13:1:1 to obtain ceramic layer slurry.

[0151] Preparation of bonding layer slurry: dissolve polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP), stir evenly, add polyethylene glycol (PEG) as a pore-forming agent, and stir and mix thoroughly to obtain bonding layer slurry.

[0152] A polyethylene PE with a thickness of 7 μm was used as the base film, and the ceramic layer slurry was coated on both surfaces of the PE substrate by a coating machine. After drying, the bonding layer slurry was applied to the base film with ceramic layers on both sides, and after pre-evaporation at 80°C and drying at 110°C, it was immersed in deionized water to dissolve PEG to obtain a separator. Among them, the thickness of the base film is 7 μm, the thickness of the single-sided ceramic layer is 2 μm, and the thickness of the single-sided bonding layer is 1 μm.

[0153] (5) Preparation of battery cells: Stack the above-mentioned positive electrode plate, separator membrane, and negative electrode plate in sequence, with the separator membrane placed between the positive electrode plate and the negative electrode plate to play a role in isolation. Then, form an electrode assembly through the lamination process. Place the electrode assembly in the outer packaging, inject the above-mentioned electrolyte after drying, and obtain the battery cell through processes such as vacuum packaging, standing, formation, and shaping.

[0154] Testing of battery cell performance (1) Testing of volumetric energy density: At 25 °C, charge the battery cell at a constant current of 0.33C to the cut-off voltage of 3.65V, and then charge it at a constant voltage of 3.65V until the current is 0.05C. At this time, the battery cell is in a fully charged state. After standing the fully charged battery cell for 5 minutes, discharge it at a constant current of 0.33C to the cut-off voltage of 2.5V, and record the discharge energy as Q0.

[0155] Measure the length, width, and thickness of the battery cell, and calculate the volume of the battery cell, denoted as V; then the volumetric energy density of the battery = Q0 / V, unit: Wh / L.

[0156] (2) Testing of low-temperature performance: At 25 °C, charge the battery cell at 0.33C to 3.65V, charge it at a constant voltage until 0.05C, then stand for 10 minutes, and discharge it at 0.33C to 2.5V, and record the discharge capacity as D0. Subsequently, charge the battery cell at 0.33C to 3.65V, charge it at a constant voltage until 0.05C, and stand for 10 minutes; place the battery at -10 °C, stand for 2 hours, and discharge it at 0.33C to 2.5V, and record the discharge capacity as D1; then the low-temperature capacity retention rate of the battery cell at -10 °C = D1 / D0 * 100%.

[0157] Examples 2 - 9 The preparation methods of Examples 2 - 9 are similar to those of Example 1, except that the coating weight of the positive electrode plate, the coating weight of the negative electrode plate, or the formula of the electrolyte is adjusted according to Table 1.

[0158] Comparative Examples 1 and 2 The preparation methods of Comparative Examples 1 and 2 are similar to those of Example 1, except that the mass content of ethyl methyl carbonate is adjusted according to Table 1.

[0159] Comparative Example 3 The preparation method of Comparative Example 3 is similar to that of Example 1, except that dimethyl carbonate is used to replace ethyl methyl carbonate.

[0160] Comparative Example 4 The preparation method of Comparative Example 4 was similar to that of Example 1, except that diethyl carbonate was used to replace ethyl methyl carbonate.

[0161] The viscosities of the electrolytes prepared in Examples 1 to 9 and Comparative Examples 1 to 4 were tested in the same manner as in Example 1. The test results are recorded in Table 2.

[0162] The performance of the battery monomers prepared in Examples 1 to 9 and Comparative Examples 1 to 4 was tested in the same manner as in Example 1. The test results are recorded in Table 1.

[0163] Table 1 It can be seen from the data in Table 1 that compared with Comparative Example 1 (the mass content of ethyl methyl carbonate is greater than 51%), Comparative Example 2 (the mass content of ethyl methyl carbonate is less than 24%), Comparative Example 3 and 4 (the electrolyte does not contain ethyl methyl carbonate). The battery monomers prepared in Examples 1 to 9 can balance low-temperature performance and energy density.

[0165] Examples 10 to 13 The preparation methods of Examples 10 to 13 were similar to that of Example 1, except that the electrolyte formula was adjusted as shown in Table 2.

[0166] And the performance of the battery monomers prepared in Examples 10 to 13 was tested according to the above test method for the performance of battery monomers, and the test results are shown in Table 2.

[0167] Table 2

[0168] It can be seen from the data in Table 2 that when the mass content of dimethyl carbonate and / or diethyl carbonate is 8.8% - 22%, it is beneficial for the battery monomer to balance low-temperature performance and energy density.

[0169] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same structure and the same function and effect as the technical idea within the technical solution scope of this application are included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be thought of by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, It includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet and a negative electrode sheet; The positive electrode sheet includes a positive current collector and a positive electrode film layer provided on at least one side of the positive current collector. The positive electrode film layer includes a positive active material, and the single-sided coating weight of the positive electrode film layer is 0.36 g / 1540.25 mm 2 ~0.43 g / 1540.25 mm 2 ; The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material, and the single-sided coating weight of the negative electrode film layer is 0.17 g / 1540.25 mm 2 ~0.21 g / 1540.25 mm 2 ; The electrolyte includes a carbonate solvent, and the carbonate solvent includes ethyl methyl carbonate. Based on the mass of the electrolyte, the mass content of ethyl methyl carbonate is 24% - 51%.

2. The battery cell according to claim 1, characterized in that Based on the mass of the electrolyte, the mass content of ethyl methyl carbonate is 30% - 44%.

3. The battery cell according to claim 1, wherein The carbonate solvent further includes at least one of dimethyl carbonate and diethyl carbonate.

4. The battery cell according to claim 3, characterized in that, Based on the mass of the electrolyte, the mass content of dimethyl carbonate and / or diethyl carbonate is 8.5% - 22%.

5. The battery cell according to claim 4, wherein Based on the mass of the electrolyte, the mass content of dimethyl carbonate and / or diethyl carbonate is 11% - 20%.

6. The battery cell according to any one of claims 1 to 5, characterized in that The conductivity of the electrolyte is 8 mS / cm - 14 mS / cm.

7. The battery cell according to any one of claims 1 to 5, characterized in that, The tap density of the positive electrode sheet is 2.25 g / cm 3 ~2.65 g / cm 3 .

8. The battery cell according to claim 7, characterized in that, The tap density of the positive electrode sheet is 2.30 g / cm 3 ~2.45 g / cm 3 .

9. The battery cell according to any one of claims 1 to 5, characterized in that The porosity of the positive electrode sheet is 23% - 32%.

10. The battery cell according to any one of claims 1 to 5, characterized in that, The positive electrode active material includes lithium-containing transition metal phosphate particles. The lithium-containing transition metal phosphate particles include a lithium-containing transition metal phosphate matrix and a coating layer located on at least part of the surface of the lithium-containing transition metal phosphate matrix. The coating layer contains carbon. In the cumulative area distribution curve of the sphericity of the lithium-containing transition metal phosphate particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the L of the sphericity A50 is 0.7 to 0.

75.

11. The battery cell according to claim 10, wherein The chemical formula of the lithium-containing transition metal phosphate matrix is Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 , Wherein, 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 0.8, 0.9 ≤ x1 + y1 ≤ 1.3, 0.9 ≤ a1 ≤ 1.5, 0 ≤ b1 ≤ 0.5, 0.9 ≤ a1 + b1 ≤ 1.5, 0 ≤ c1 ≤ 0.5; 3 ≤ z1 ≤ 5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce; X includes one or more of S, Si, Cl, B, C, N, P; Y includes one or more of O and F.

12. The battery cell according to claim 10, wherein The lithium-containing transition metal phosphate contains Ti element. Based on the mass of the lithium-containing transition metal phosphate particles, the mass content of the Ti element is 0.05% - 0.2%.

13. The battery cell according to claim 10, wherein The primary average particle size of the lithium-containing transition metal phosphate is 100 nm - 2.5 μm.

14. The battery cell according to any one of claims 1 to 5, characterized in that, The compaction density of the negative electrode plate is 1.3 g / cm 3 ~1.55 g / cm 3 .

15. The battery cell according to claim 14, wherein The compaction density of the negative electrode sheet is 1.4 g / cm 3 ~1.5 g / cm 3 .

16. The battery cell according to any one of claims 1 to 5, characterized in that, The porosity of the negative electrode sheet is 23% - 32%.

17. The battery cell according to any one of claims 1 to 5, characterized in that, The negative electrode active material includes graphite, and the volume average particle size Dv50 of the graphite is 13 μm - 22 μm.

18. The battery cell according to claim 17, wherein, The volume average particle size Dv50 of the graphite is 14.5 μm - 20 μm.

19. The battery cell according to any one of claims 1 to 5, characterized in that, The electrode assembly includes a stacked electrode assembly.

20. The battery cell according to any one of claims 1 to 5, characterized in that, The electrode assembly further includes a separator. The separator includes a base film, a ceramic layer provided on both sides of the base film, and an adhesive layer provided on the side of at least one of the ceramic layers away from the base film side. The adhesive layer is a continuous layer with a porous structure, and the adhesive layer includes a polyvinylidene fluoride polymer.

21. The battery cell according to claim 20, wherein, The separator satisfies at least one of the following conditions: (1) The thickness of the base film is 7 μm - 9 μm; (2) The single-side thickness of the ceramic layer is 0.5 μm - 4 μm; (3) The single-side thickness of the adhesive layer is 0.15 μm - 2 μm.

22. The battery cell according to claim 20, wherein, The porosity of the separator is 28% to 50%.

23. The battery cell according to claim 22, wherein, The porosity of the separator is 31% to 40%.

24. A battery device, characterized in that, Comprising the battery cell according to any one of claims 1 to 23.

25. An electrical device, characterized in that, Comprising the battery device according to claim 24.

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