Battery cell, battery device and electric device

Abstract

The invention provides a battery monomer, a battery device and a power utilization device. The battery monomer comprises an electrode assembly, the electrode assembly comprises a positive pole piece, a negative pole piece and an isolating membrane, the negative pole piece comprises a negative pole current collector and a negative pole active layer arranged on at least one side of the negative pole current collector, and the positive pole piece comprises a positive pole current collector and a positive pole active layer arranged on at least one side of the positive pole current collector; the positive electrode active layer comprises a positive electrode material, the positive electrode material comprises a nickel-containing lithium transition metal oxide and a lithium-containing phosphate positive electrode material, and the molar content of Ni element in the nickel-containing lithium transition metal oxide relative to other metal elements except the lithium element is greater than or equal to 50%; in the lithium-containing phosphate positive electrode material, the molar content of Mn element relative to other metal elements except lithium element is 50%-90%, and the surface density of the positive electrode active layer is 190 mg / 1540.25 mm < 2 >-380 mg / 1540.25 mm < 2 >.

Description

Technical Field

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

[0002] Lithium iron phosphate cathode materials are widely used in the cathode of secondary batteries due to their low cost, but their low energy density limits their application. In order to increase their energy density, some technologies have attempted to combine lithium iron phosphate and manganese phosphate to form lithium iron manganese phosphate. As the manganese content in lithium iron manganese phosphate increases, although the energy density is improved, its cycle performance deteriorates. Summary of the invention

[0001] The present application provides a battery cell, a battery device and an electrical device to improve the energy density output performance and cycle performance of the battery cell.

[0002] The first aspect of the present application provides a battery cell, including an electrode assembly, the electrode assembly including a positive electrode plate, a negative electrode plate, and a separator located between the positive electrode plate and the negative electrode plate, wherein the negative electrode plate includes a negative electrode current collector and a negative electrode active layer arranged on at least one side of the negative electrode current collector, the negative electrode active layer includes a negative electrode material, and the negative electrode material includes a carbon material; the positive electrode plate includes a positive electrode current collector and a positive electrode active layer arranged on at least one side of the positive electrode current collector, the positive electrode active layer includes a positive electrode material, and the positive electrode material includes a nickel-containing lithium transition metal oxide and a lithium-containing phosphate-based positive electrode material, and the molar content of the Ni element in the nickel-containing lithium transition metal oxide is greater than or equal to 50% based on the total molar amount of other metal elements other than lithium in the nickel-containing lithium transition metal oxide; the molar content of the Mn element in the lithium-containing phosphate-based positive electrode material is 50%-90% based on the total molar amount of other metal elements other than lithium in the lithium-containing phosphate-based positive electrode material, and the surface density of the positive electrode active layer is 190mg / 1540.25mm 2 -380mg / 1540.25mm 2 .

[0003] The addition of lithium-containing phosphate-based positive electrode materials makes the positive electrode materials lower in cost compared to pure systems of nickel-containing lithium transition metal oxide positive electrode materials.

[0004] The molar content of Ni in the lithium-containing transition metal oxide is greater than or equal to 50%, which is a lithium-containing transition metal oxide with a high nickel content and has a high gram capacity, so it can provide a higher energy density for the battery cell; the molar content of Mn in the lithium-containing phosphate positive electrode material is 50%-90%, which is a lithium iron manganese phosphate with a high manganese content and has a high platform voltage, so it can provide a higher energy density for the battery cell, and at the same time, the positive electrode active layer is set to have 190mg / 1540.25mm 2 -380mg / 1540.25mm 2 The high surface density makes the battery monomer with the above-mentioned positive electrode material have a high energy density output.

[0005] At the same time, when the surface density is too large, the positive active layer of the mixed positive electrode material is difficult to be compacted to the surface of the current collector due to the limitation of the processing technology, resulting in serious powder loss of the pole piece, which increases the difficulty of the preparation process of the battery cell, and thus it is difficult to achieve the production of high energy density battery cells. Therefore, the energy density is controlled at 380mg / 1540.25mm 2 In addition, when the Mn content in the lithium-containing phosphate-based positive electrode material is too high, the gram capacity of the lithium-containing phosphate-based positive electrode material is too low, resulting in limited improvement in the energy density of the battery cell. Therefore, the Mn content in the lithium-containing phosphate-based positive electrode material is controlled to be less than 90%.

[0006] In any embodiment of the first aspect of the present application, the surface density of the positive electrode active layer is 200 mg / 1540.25 mm 2 -350mg / 1540.25mm 2 .

[0007] In any embodiment of the first aspect of the present application, the mass ratio of the Fe element to the Ni element in the positive electrode material is in the range of (0.4-10):1.

[0008] In any embodiment of the first aspect of the present application, the molar content of the Ni element in the nickel-containing lithium transition metal oxide is 70%-95%, and can be optionally 80%-95%, based on the total molar amount of other metal elements except lithium in the nickel-containing lithium transition metal oxide.

[0009] In any embodiment of the first aspect of the present application, the molar content of the Mn element in the lithium-containing phosphate positive electrode material is 50%-70% based on the total molar amount of other metal elements except lithium in the lithium-containing phosphate positive electrode material.

[0010] In any embodiment of the first aspect of the present application, the compaction density of the positive electrode active layer corresponding to the battery cell when the battery cell is configured at 100% SOC is 2.32 g / cm 3-3.18g / cm 3 , optional 2.53g / cm 3 -2.84g / cm 3 .

[0011] In any embodiment of the first aspect of the present application, the powder compaction density of the positive electrode material at 30000N is ≥2.5g / cm 3 , optional 2.5g / cm 3 -2.8g / cm 3 .

[0012] In any embodiment of the first aspect of the present application, the nickel-containing lithium transition metal oxide includes a lithium-containing nickel-cobalt-manganese oxide, and the lithium-containing nickel-cobalt-manganese oxide contains one or more of the elements Zr, Al, B, Fe, Ca, Sr, Ti, V or Y.

[0013] In any embodiment of the first aspect of the present application, the nickel-containing lithium transition metal oxide includes a lithium-containing nickel cobalt manganese oxide including one or more of Zr, Al, B or Fe elements.

[0014] In any embodiment of the first aspect of the present application, in the lithium-containing nickel-cobalt-manganese oxide, the mass content of the elements satisfies at least one of the following: the content of Zr is 1000-3000 ppm, the content of Al is 100-1000 ppm, and the content of B is 50-300 ppm.

[0015] In any embodiment of the first aspect of the present application, the lithium-containing phosphate-based positive electrode material includes lithium iron manganese phosphate, which contains one or more of the elements Al, B, Ca, Cr, Cu, K, Mg, Na, P, Si, Ti, V or Zn.

[0016] In any embodiment of the first aspect of the present application, the lithium manganese iron phosphate includes one or more of Al, Ca, Na, Ti or V elements.

[0017] In any embodiment of the first aspect of the present application, in the lithium manganese iron phosphate, the mass content of the elements satisfies at least one of the following: the content of Al is 100-1000ppm, the content of Ca is 50-300ppm, the content of Na is 50-300ppm, the content of Ti is 100-1000ppm, and the content of V is 1000-3000ppm.

[0018] In any embodiment of the first aspect of the present application, the positive electrode active layer contains lithium iron manganese phosphate and nickel cobalt manganese oxide, and the positive electrode active layer contains one or more of Al, B, Ca, Fe, Sr, Ti, V, Y or Zn elements, and in the positive electrode material, the mass content of each element satisfies: Al: 0.005%-0.1%; Ca: 0.0001%-0.02%; Na: 0.005%-0.06%; Ti: 0.005%-0.15%; V: 0.0001%-0.3%; Zr: 0.005%-0.2%; B: 0.01%-0.1%.

[0019] In any embodiment of the first aspect of the present application, the lithium-containing phosphate-based positive electrode material includes a coating layer containing carbon, and the mass content of carbon in the lithium-containing phosphate-based positive electrode material is 1%-3%.

[0020] In any embodiment of the first aspect of the present application, in the positive electrode material, the mass content of Fe element in particles with a particle size less than or equal to Dv10 is M1, and the mass content of Fe element in particles with a particle size greater than or equal to Dv90 is M2, and M1 is greater than M2; and / or the mass content of Ni element in particles with a particle size less than or equal to Dv10 is M3, and the mass content of Ni element in particles with a particle size greater than or equal to Dv90 is M4, and M3 is less than M4.

[0021] In any embodiment of the first aspect of the present application, the particles of the nickel-containing lithium transition metal oxide are spherical or quasi-spherical polycrystalline particles, and the particles of the lithium-containing phosphate-based positive electrode material are single crystal particles.

[0022] In any embodiment of the first aspect of the present application, the particles of the nickel-containing lithium transition metal oxide are single crystal particles, and the particles of the lithium-containing phosphate-based positive electrode material are single crystal particles.

[0023] In any embodiment of the first aspect of the present application, the volume particle size Dv50 of the single crystal particles of the nickel-containing lithium transition metal oxide is 1 μm-5 μm, and can be optionally 1.5 μm-3 μm.

[0024] In any embodiment of the first aspect of the present application, the volume particle size Dv50 of the polycrystalline particles of the nickel-containing lithium transition metal oxide is 7 μm-12 μm.

[0025] In any embodiment of the first aspect of the present application, the volume particle size Dv50 of the lithium-containing phosphate-based positive electrode material is 0.1 μm-15 μm, or 0.5 μm-2 μm.

[0026] In any embodiment of the first aspect of the present application, the positive electrode plate further includes a positive electrode conductive layer, and the positive electrode conductive layer is disposed between the positive electrode current collector and the positive electrode active layer.

[0027] In any embodiment of the first aspect of the present application, the positive electrode conductive layer comprises a positive electrode binder and a positive electrode conductive material, and / or the thickness of the positive electrode conductive layer is 1 μm-2 μm.

[0028] In any embodiment of the first aspect of the present application, the thickness of the positive electrode current collector is 9 μm-17 μm, and can be optionally 10 μm-13 μm.

[0029] In any embodiment of the first aspect of the present application, the surface density of the negative electrode active layer is 95 mg / 1540.25 mm 2 -180mg / 1540.25mm 2 ; Optional: 130mg / 1540.25mm 2 -150mg / 1540.25mm 2 .

[0030] In any embodiment of the first aspect of the present application, the compaction density of the negative electrode active layer corresponding to the battery cell when the battery cell is configured to be in the 100% SOC state is 1.04 g / cm 3 -1.48g / cm 3 ; Optional: 1.23g / cm 3 -1.38g / cm 3 .

[0031] In any embodiment of the first aspect of the present application, the carbon material includes composite graphite particles, which include: a main particle, which includes secondary particles, and the main particle includes artificial graphite; and a coating layer, which is coated on the surface of the main particle, and the coating layer includes amorphous carbon.

[0032] In any embodiment of the first aspect of the present application, the mass content of amorphous carbon in the coating layer is 2% to 5% based on the total mass of the composite graphite particles.

[0033] In any embodiment of the first aspect of the present application, the powder compaction density of the composite graphite particles under a pressure of 20000N is 1.5g / cm 3 -1.7g / cm 3 , or 1.55g / cm 3 -1.65g / cm 3 .

[0034] In any embodiment of the first aspect of the present application, the negative electrode active layer includes: a first negative electrode active layer, arranged on one side of the negative electrode current collector, the first negative electrode active layer includes one or more of composite graphite particles and natural graphite, the volume average particle size Dv50 of the negative electrode material in the first negative electrode active layer is 7.5μm-19.5μm, which can be optionally 12.5μm-18.5μm, and a second negative electrode active layer, arranged on the side of the first negative electrode active layer away from the negative electrode current collector, the second negative electrode active layer includes composite graphite particles, and the volume average particle size Dv50 of the negative electrode material in the second negative electrode active layer is 7.5μm-19.5μm, which can be optionally 7.5μm-15.5μm.

[0035] In any embodiment of the first aspect of the present application, the negative electrode plate further includes a negative electrode conductive layer, and the negative electrode conductive layer is disposed between the negative electrode current collector and the negative electrode active layer.

[0036] In any embodiment of the first aspect of the present application, the negative electrode conductive layer comprises a negative electrode binder and a negative electrode conductive material, and the thickness of the negative electrode conductive layer is 1 μm-2 μm.

[0037] In any embodiment of the first aspect of the present application, the thickness of the negative electrode current collector is 4 μm-7 μm, and can be 4 μm-5 μm.

[0038] In any embodiment of the first aspect of the present application, the battery cell further includes an electrolyte, and the electrolyte includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0039] In any embodiment of the first aspect of the present application, the molar concentration ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is (2-5):10.

[0040] In any embodiment of the first aspect of the present application, the battery cell also includes a shell, the electrode assembly is arranged in the inner cavity of the shell, the positive electrode sheet and the negative electrode sheet are arranged in a stacked manner, the length of the shell is L1, the length of the positive electrode sheet is L2, L2 / L1 is 80%-99%, and can be optionally 88%-99%.

[0041] In any embodiment of the first aspect of the present application, the size of the shell has one or more of the following characteristics: the range of L1 is 300mm-950mm; the height of the shell is 85mm-140mm; the thickness of the shell is 10mm-20mm.

[0042] In any embodiment of the first aspect of the present application, the shell is an aluminum shell or a steel shell.

[0043] In any embodiment of the first aspect of the present application, the battery monomer injection coefficient is 1.9g / Ah-3.1g / Ah.

[0044] In any embodiment of the first aspect of the present application, the volume energy density of the battery cell is 470Wh / L-570Wh / L.

[0045] A second aspect of the present application provides a battery device, comprising a battery cell provided in any embodiment of the first aspect, wherein the battery device comprises a battery module, a battery pack or an energy storage device.

[0046] A third aspect of the present application provides an electrical device, comprising a battery cell provided in any embodiment of the first aspect, or a battery device provided in any embodiment of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0004] Figure 1 It is a schematic diagram of an electrode assembly according to one embodiment of the present application.

[0005] Figure 2 yes Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown.

[0006] Figure 3 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0007] Figure 4 yes Figure 3 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0008] Figure 5 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.

[0009] In the drawings, the drawings are not drawn to scale.

[0010] Description of reference numerals:

[0011] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0012] The following detailed description and drawings of the embodiments of the present application are used to illustrate the principles of the present application, but cannot be used to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0013] Hereinafter, the battery cells, battery devices and power devices 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 structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following descriptions 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.

[0014] "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.

[0015] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0016] 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.

[0017] 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.

[0018] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or comprised.

[0019] If not otherwise specified, in this application, the term "or" is inclusive. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0020] As analyzed in the background technology, as the manganese content in lithium manganese iron phosphate increases, although the energy density of the battery cell is improved, its cycle performance deteriorates. In order to increase the energy density output of the battery cell while maintaining high cycle performance, the present application provides a battery cell, a battery device and an electrical device.

[0021] [Battery Cell]

[0022] The first embodiment of the present application provides a battery cell, the battery cell includes an electrode assembly, the electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer arranged on at least one side of the negative electrode current collector, the negative electrode active layer includes a negative electrode material, the negative electrode material includes a carbon material, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer arranged on at least one side of the positive electrode current collector, the positive electrode active layer includes a positive electrode material, the positive electrode material includes a nickel-containing lithium transition metal oxide and a lithium-containing phosphate-based positive electrode material, based on the total molar amount of other metal elements other than lithium in the nickel-containing lithium transition metal oxide, the molar content of Ni in the nickel-containing lithium transition metal oxide is greater than or equal to 50%; based on the total molar amount of other metal elements other than lithium in the lithium-containing phosphate-based positive electrode material, the molar content of Mn in the lithium-containing phosphate-based positive electrode material is 50%-90%, and the surface density of the positive electrode active layer is 190mg / 1540.25mm 2 -380mg / 1540.25mm 2.

[0023] During the battery charging and discharging process, active ions (such as lithium ions) are embedded and extracted between the positive electrode and the negative electrode. The separator is set between the positive electrode and the negative electrode, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing the active ions to pass through.

[0024] The addition of lithium-containing phosphate-based positive electrode materials makes the positive electrode materials lower in cost compared to pure systems of nickel-containing lithium transition metal oxide positive electrode materials.

[0025] The molar content of Ni in the lithium-containing transition metal oxide is greater than or equal to 50%, which is a lithium-containing transition metal oxide with a high nickel content and has a high gram capacity, so it can provide a higher energy density for the battery cell; the molar content of Mn in the lithium-containing phosphate positive electrode material is 50%-90%, which is a lithium iron manganese phosphate with a high manganese content and has a high platform voltage, so it can provide a higher energy density for the battery cell, and at the same time, the positive electrode active layer is set to have 190mg / 1540.25mm 2 -380mg / 1540.25mm 2 The high surface density makes the battery monomer with the above-mentioned positive electrode material have a high energy density output.

[0026] At the same time, when the surface density is too large, the positive active layer of the mixed positive electrode material is difficult to be compacted to the surface of the current collector due to the limitation of the processing technology, resulting in serious powder loss of the pole piece, which increases the difficulty of the preparation process of the battery cell, and thus it is difficult to achieve the production of high energy density battery cells. Therefore, the energy density is controlled at 380mg / 1540.25mm 2 the following.

[0027] In addition, when the Mn element content in the lithium-containing phosphate-based positive electrode material is too high, the gram capacity of the lithium-containing phosphate-based positive electrode material is too low, resulting in limited improvement in the energy density of the battery cell. Therefore, the Mn element content in the lithium-containing phosphate-based positive electrode material is controlled to be less than 90%.

[0028] In some embodiments, the elements in the positive electrode material can be determined by the following method:

[0029] The positive electrode sheet of the battery cell was fully cleaned with DMC (dimethyl carbonate), and the positive electrode sheet was dried and calcined before collecting the positive electrode material in the positive electrode active layer. The positive electrode material was tested using inductively coupled plasma atomic emission spectrometry (ICP-OES).

[0030] In some embodiments, the content of elements in the positive electrode material can be comprehensively determined by combining XRD, SEM-EDS, TEM-EDX, ICP-OES or other detection methods.

[0031] In some embodiments, the areal density is measured using the following method:

[0032] Take a single-sided coated positive electrode sheet (if it is a double-sided coated sheet, wipe off the positive electrode active layer on one side first), punch it into a small disc with an area of ​​S1, weigh it, record it as M1, and measure its thickness H1. Then wipe off the positive electrode active layer of the weighed positive electrode sheet, weigh the weight of the positive electrode collector, record it as M0, and measure its thickness H0. The single-sided coating weight of the positive electrode active layer (i.e., the surface density) = (weight of the positive electrode sheet M1-weight of the positive electrode collector M0) / S1.

[0033] In some embodiments, if a positive electrode conductive layer is disposed between the positive electrode active layer and the positive electrode current collector, the mass of the positive electrode conductive layer is significantly lower than that of the positive electrode active layer, so when testing the compaction density or surface density of the positive electrode active layer, the mass of the positive electrode conductive layer can be ignored. The same is true for the compaction density or surface density test of the negative electrode active layer.

[0034] In some embodiments of the present application, the surface density of the positive electrode active layer is 200 mg / 1540.25 mm 2 -350mg / 1540.25mm 2 . Thereby improving the high energy density output performance of battery cells more stably.

[0035] In some embodiments of the present application, in order to give full play to the respective advantages of the nickel-containing lithium transition metal oxide and the lithium-containing phosphate-based positive electrode material, the mass ratio of the Fe element to the Ni element in the positive electrode material is optionally in the range of (0.4-10): 1. Under the mixing ratio of the nickel-containing lithium transition metal oxide and the lithium-containing phosphate-based positive electrode material corresponding to the above molar ratio of the Fe element to the Ni element, the cycle stability and energy density of the battery cell are more fully improved, and the cost is more effectively controlled.

[0036] As the content of Ni increases, the gram capacity of the nickel-containing lithium transition metal oxide increases. In some embodiments, the molar content of Ni in the nickel-containing lithium transition metal oxide is 70%-95%, and can be 80%-95%, based on the total molar amount of other metal elements in the nickel-containing lithium transition metal oxide except lithium. The use of nickel-containing lithium transition metal oxides with high nickel content can further increase the gram capacity of the positive electrode material, thereby further improving the energy density of the battery cell.

[0037] In some embodiments, the molar content of the Mn element in the lithium-containing phosphate-based positive electrode material is 50%-70%, and can be further optionally 50%-60%, based on the total molar amount of other metal elements in the lithium-containing phosphate-based positive electrode material except the lithium element. Within the above range, as the Mn content increases, the gram capacity of the lithium-containing phosphate-based positive electrode material decreases, but the platform voltage of the battery cell can be increased, and thus the mass energy density of the battery cell can also be increased. Moreover, by controlling the Mn content within the above range, the excessive influence of the Mn content on the conductivity of the positive electrode material and the dissolution of manganese are controlled, thereby controlling the excessive negative impact on the rate performance and cycle performance of the battery cell.

[0038] The compaction density of the positive electrode active layer affects the stability of the electrolyte infiltration and volume expansion in the positive electrode plate, and also affects the volume energy density of the battery cell. Generally, the greater the compaction density, the smaller the pores between the positive electrode material particles, the worse the wettability of the electrolyte therein, and the smaller the buffer space reserved for the expansion of the positive electrode material, which affects the charging performance and cycle performance of the battery cell, but can improve the volume energy density of the battery cell; the smaller the compaction density, the larger the pores between the positive electrode material particles, the better the wettability of the electrolyte therein, and the larger the buffer space reserved for the expansion of the positive electrode material, so the charging performance and cycle performance of the battery cell are improved, but it will lead to a decrease in the volume energy density of the battery cell. In some embodiments, the compaction density of the positive electrode active layer corresponding to the battery cell when the battery cell is configured to be 2.32g / cm 3 -3.18g / cm 3 or 2.53g / cm 3 -2.84g / cm 3 . Thereby achieving the comprehensive performance improvement of energy density, charging performance and cycle performance.

[0039] The above-mentioned "100% SOC state" means a state in which the battery cell is charged at 25° C. at a rate of 0.33C to a voltage of 4.2V and then charged at a constant voltage to a current of less than 0.05C.

[0040] The test method for the compaction density of the positive electrode active layer can be implemented by referring to the following method:

[0041] Based on the above surface density test, the thickness of the positive electrode active layer = the thickness of the positive electrode plate H1-the thickness of the positive electrode collector H0, and the compaction density of the positive electrode active layer = the single-sided coating weight of the positive electrode active layer / the thickness of the single-sided positive electrode active layer.

[0042] In some embodiments, if a conductive layer is disposed between the positive electrode active layer and the positive electrode current collector, the mass of the conductive layer is significantly lower than that of the positive electrode active layer, so when testing the compaction density or surface density of the positive electrode active layer, the mass of the conductive layer can be ignored. The same is true for the test of the compaction density or surface density of the negative electrode active layer.

[0043] In some embodiments, the powder compaction density of the positive electrode material at 30000N is ≥2.5g / cm 3 , optional 2.5g / cm 3 -2.8g / cm 3 . Provide the material basis for achieving the largest possible compaction density of the active layer.

[0044] The nickel-containing lithium transition metal oxide used in the present application can be selected from conventional positive electrode materials of this type, such as one or more of lithium-containing nickel-cobalt-manganese oxide and lithium-containing nickel-cobalt-aluminum oxide.

[0045] In some embodiments, the nickel-containing lithium transition metal oxide includes a lithium-containing nickel-cobalt-manganese oxide, and the lithium-containing nickel-cobalt-manganese oxide contains one or more of the elements Zr, Al, B, Fe, Ca, Sr, Ti, V or Y. The elements in the above-mentioned modified materials can be present in the nickel-containing lithium transition metal oxide in the form of doping or coating.

[0046] By using some of the above elements, the distance between lithium layers is widened to promote the transmission of lithium ions; or the migration of nickel ions to the lithium layer is inhibited, the cation mixing is reduced, and the structural stability is maintained; or the transition metal-oxygen bond is strengthened, the harmful phase change during the cycle is inhibited, and the release of structural oxygen is inhibited. In some embodiments, the nickel-containing lithium transition metal oxide includes one or more of Zr, Al, B or Fe elements in the lithium-containing nickel cobalt manganese oxide.

[0047] In order to give full play to the role of each element, in some embodiments, in the lithium-containing nickel-cobalt-manganese oxide, the mass content of the elements satisfies at least one of the following: the content of Zr is 1000-3000 ppm, the content of Al is 100-1000 ppm, and the content of B is 50-300 ppm.

[0048] The lithium-containing phosphate-based positive electrode material used in the present application may be any conventional material of the same type, such as lithium iron manganese phosphate, which contains one or more of the elements Al, B, Ca, Cr, Cu, K, Mg, Na, P, Si, Ti, V or Zn. The elements in the above-mentioned modified materials may be present in the lithium-containing phosphate-based positive electrode material in the form of doping or coating.

[0049] In some embodiments, lithium manganese iron phosphate includes one or more of Al, Ca, Na, Ti or V. Among them, Al element can reduce the resistivity of the material, change the crystal structure, shorten the lithium ion transmission path, and enhance the electrochemical performance, Ca element can improve the structural stability of the material, increase the cycle life and rate performance of the battery cell, Na element and V element can improve the conductivity and cycle stability of the material, and Ti element can change the crystal structure and improve the charge and discharge performance of the material.

[0050] In order to give full play to the role of each element, in lithium manganese iron phosphate, the mass content of the elements meets at least one of the following requirements: Al content is 100-1000ppm, Ca content is 50-300ppm, Na content is 50-300ppm, Ti content is 100-1000ppm, and V content is 1000-3000ppm.

[0051] In some embodiments, the positive electrode active layer contains lithium manganese iron phosphate and nickel cobalt manganese oxide, and the positive electrode active layer contains one or more of Al, Ca, Na, Ti, V, Zr, B or Fe elements, and in the positive electrode material, the mass content of each element satisfies:

[0052] Al: 0.005%-0.1%; Ca: 0.0001%-0.02%; Na: 0.005%-0.06%; Ti: 0.005%-0.15%; V: 0.0001%-0.3%; Zr: 0.005%-0.2%; B: 0.01%-0.1%.

[0053] In order to improve the conductivity and surface stability of the lithium-containing phosphate-based positive electrode material, in some embodiments, the lithium-containing phosphate-based positive electrode material includes a carbon-containing coating layer, and the mass content of carbon in the lithium-containing phosphate-based positive electrode material is 1%-3%.

[0054] In some embodiments, the gram capacity of the positive electrode material is increased by size grading of the material particles in the positive electrode material. In the positive electrode material, the mass content of the Fe element in the particles with a particle size less than or equal to Dv10 is M1, and the mass content of the Fe element in the particles with a particle size greater than or equal to Dv90 is M2, and M1 is greater than M2; and / or the mass content of the Ni element in the particles with a particle size less than or equal to Dv10 is M3, and the mass content of the Ni element in the particles with a particle size greater than or equal to Dv90 is M4, and M3 is less than M4.

[0055] Through the above-mentioned particle size control, the small-particle lithium-containing phosphate-based positive electrode material and the large-particle nickel-containing lithium transition metal oxide are combined, and the small particles can fill the gaps between the large particles, thereby improving the compaction of the positive electrode material; and this combination method protects the lithium-containing phosphate-based positive electrode material, effectively reducing the chance of breakage when it is cold pressed at the same pressure.

[0056] In some embodiments, the particles of the nickel-containing lithium transition metal oxide are spherical or quasi-spherical polycrystalline particles, and the particles of the lithium-containing phosphate-based positive electrode material are single crystal particles. The polycrystalline form of the nickel-containing lithium transition metal oxide has a higher gram capacity, and thus can better improve the energy density of the battery cell.

[0057] In some embodiments, the particles of the nickel-containing lithium transition metal oxide are single crystal particles, and the particles of the lithium-containing phosphate-based positive electrode material are single crystal particles. The structure of the nickel-containing lithium transition metal oxide in single crystal form is more stable, so it can better improve the cycle performance of the battery cell.

[0058] In order to further improve the gram capacity of the nickel-containing lithium transition metal oxide, in some embodiments, the volume particle size Dv50 of the single crystal particles of the nickel-containing lithium transition metal oxide is 1 μm-5 μm, and can be 1.5 μm-3 μm.

[0059] In order to further improve the gram capacity of the nickel-containing lithium transition metal oxide, in some embodiments, the volume particle size Dv50 of the polycrystalline particles of the nickel-containing lithium transition metal oxide is selected to be 7 μm-12 μm.

[0060] In order to further increase the gram capacity of the lithium-containing phosphate-based positive electrode material, in some embodiments, the volume particle size Dv50 of the lithium-containing phosphate-based positive electrode material is 0.1 μm-15 μm, or 0.5 μm-2 μm.

[0061] In order to improve the rate performance of the battery cell, in some embodiments, the positive electrode plate further includes a positive electrode conductive layer, which is disposed between the positive electrode current collector and the positive electrode active layer. The positive electrode conductive layer is used to increase the electron transfer rate, thereby improving the rate performance of the battery cell.

[0062] In order to improve the bonding between the positive electrode current collector and the positive electrode active layer by using the conductive layer, in some embodiments, the positive electrode conductive layer includes a positive electrode binder and a positive electrode conductive material.

[0063] In some embodiments, the thickness of the positive electrode conductive layer is 1 μm-2 μm, so that the positive electrode conductive layer can be fully utilized to improve the conductivity, and the influence of the conductive layer thickness on the energy density of the battery cell is avoided.

[0064] The strength of the positive electrode current collector is related to its thickness. Generally, the greater the thickness, the greater the strength. However, the greater the strength, the worse the ductility, and it will also cause the energy density of the battery cell to decrease. During the charge and discharge cycle, the positive electrode material expands, so the positive electrode current collector needs to have a certain strength to restrain the expansion and also needs to have a certain ductility to adapt to the increase in the area of ​​the active layer caused by the expansion. In some embodiments, the thickness of the positive electrode current collector is 9μm-17μm, and can be optionally 10μm-13μm. The positive electrode current collector within this thickness range has little effect on the energy density, and it has a good matching ability of strength and ductility, thereby effectively reducing the risk of cracking of the current collector caused by the expansion of the battery cell during the charging process. At the same time, due to the increase in the thickness of the positive electrode current collector, the resistance of the metal parts in the single cell increases, which will also lead to an increase in the discharge DCR of the battery cell, that is, an increase in the internal resistance of the battery cell.

[0065] 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.).

[0066] In some embodiments, the positive electrode active 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.

[0067] In some embodiments, the positive electrode active layer may further include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0068] 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.

[0069] [Negative electrode]

[0070] The surface density of the negative electrode active layer is set according to the CB value of the battery cell. The design size varies with the surface density of the positive electrode active layer. The CB value is usually set between 1.04 and 1.20. In some embodiments, in order to fully utilize the capacity of the positive electrode material, the surface density of the negative electrode active layer is 95 mg / 1540.25 mm 2 -180 mg / 1540.25 mm 2 ; Optional: 130mg / 1540.25mm 2 -150mg / 1540.25mm 2 This forms a better match with the surface density of the positive active layer of the positive electrode sheet, allowing the capacity of the positive and negative electrode materials to be fully utilized.

[0071] When the battery cell is charged, the negative electrode material expands, resulting in a decrease in the compaction density of the negative electrode active layer. In some embodiments, the battery cell is configured to have a compaction density of 1.04 g / cm2 corresponding to the negative electrode active layer at 100% SOC. 3 -1.48g / cm 3 ; Optional: 1.23g / cm 3 -1.38g / cm 3 The negative electrode sheet with the above compaction density has small expansion deformation and good electrolyte infiltration, thereby improving the cycle performance of the battery cell.

[0072] In some embodiments, the carbon material includes composite graphite particles, the composite graphite particles include: a main body particle and a coating layer, the main body particle includes primary particles or secondary particles, the main body particle includes artificial graphite; the coating layer is coated on the surface of the main body particle, and the coating layer includes amorphous carbon. The artificial graphite coated with amorphous carbon has a simple structure and high conductivity.

[0073] On the basis of improving the conductivity of the composite graphite particles, the gram capacity of the composite graphite particles is improved as much as possible. In some embodiments, the mass content of amorphous carbon in the coating layer can be 2% to 5% based on the total mass of the composite graphite particles.

[0074] In order to maximize the contribution of the second negative electrode active layer to the energy density of the battery cell, in some embodiments, the powder compaction density of the composite graphite particles under a pressure of 20000N is 1.5g / cm 3 -1.7g / cm 3 , or 1.55g / cm 3 -1.65g / cm 3 .

[0075] In some embodiments, the negative electrode active layer includes: a first negative electrode active layer and a second negative electrode active layer, the first negative electrode active layer is arranged on one side of the negative electrode current collector, the first negative electrode active layer includes one or more of composite graphite particles and natural graphite, and the volume average particle size Dv50 of the negative electrode material in the first negative electrode active layer is optionally 7.5μm-19.5μm, and optionally 12.5μm-18.5μm; the second negative electrode active layer is arranged on the side of the first negative electrode active layer away from the negative electrode current collector, the second negative electrode active layer includes composite graphite particles, and the volume average particle size Dv50 of the negative electrode material in the second negative electrode active layer is optionally 7.5μm-19.5μm, and optionally 7.5μm-15.5μm. The first negative electrode active layer is used to improve the energy density of the battery cell, and the second negative electrode active layer is used to improve the charging rate of the battery cell.

[0076] In some embodiments, the negative electrode plate further includes a negative electrode conductive layer, which is disposed between the negative electrode current collector and the negative electrode active layer, and includes a negative electrode binder and a negative electrode conductive material, and the thickness of the negative electrode conductive layer is 0.5 μm-3 μm, or 1 μm-2 μm. The negative electrode conductive primer layer is used to improve the conductivity of the negative electrode plate, thereby improving the rate performance of the battery cell.

[0077] The same considerations as above for selecting the thickness of the positive electrode current collector, in some embodiments, the thickness of the negative electrode current collector is 4μm-7μm, and can be 4μm-5μm. The negative electrode current collector within this thickness range has little effect on the energy density, and has good strength and ductility matching capabilities, thereby effectively reducing the risk of current collector cracking caused by expansion during the charging process of the battery cell.

[0078] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a 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.).

[0079] In some embodiments, the negative electrode active layer may further include a binder. As an example, 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).

[0080] In some embodiments, the negative electrode active layer may further include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0081] In some embodiments, the negative electrode active layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0082] 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.

[0083] [Isolation film]

[0084] The present application has no particular limitation on the type of isolation membrane, and any known porous isolation membrane with good chemical stability and mechanical stability can be selected.

[0085] 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.

[0086] In some embodiments, the isolation membrane includes a porous base membrane and a functional layer disposed on at least one side of the porous base membrane. That is, the isolation membrane is a composite film. The corresponding functional layer is selected according to different functional requirements, and this application will not repeat it here.

[0087] [Electrolytes]

[0088] 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.

[0089] In some embodiments, the battery cell further includes an electrolyte solution including an electrolyte salt and a solvent.

[0090] 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0091] 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.

[0092] In some embodiments, the electrolyte may further include additives. As examples, the additives may include 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.

[0093] In some embodiments, the electrolyte includes lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI). Lithium bis(fluorosulfonyl)imide can improve the lithium ion transfer rate, thereby improving the charging rate of the battery cell; and it has high temperature stability, thereby improving the high temperature cycle performance of the battery cell.

[0094] In some embodiments, the molar concentration ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is (2-5): 10. Thus, the above lithium salt is used to improve the cycle stability and charging rate of the battery monomer, while controlling the excessive increase in the cost of the battery monomer.

[0095] In some embodiments, the battery cell includes a shell, the electrode assembly is arranged in the inner cavity of the shell, the positive electrode sheet and the negative electrode sheet are arranged in a stacked manner, the length of the shell is L1, the length of the positive electrode sheet is L2, and L2 / L1 is 80%-99%, and can be 88%-99%, thereby further improving the volume energy density of the battery cell.

[0096] In some embodiments, the dimensions of the housing have one or more of the following characteristics:

[0097] The range of L1 is 300mm-950mm;

[0098] The height of the shell is 85mm-140mm;

[0099] The thickness of the shell is 10mm-20mm.

[0100] 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.

[0101] In some embodiments, the housing is an aluminum housing or a steel housing.

[0102] In some embodiments, the battery cell filling factor is 1.9 g / Ah-3.1 g / Ah.

[0103] In some embodiments, the volume energy density of the battery cell is 470Wh / L-570Wh / L.

[0104] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0105] The shape of the battery cell in this application can be square or any other shape. For example, Figure 1 The electrode assembly 52 of the battery cell 5 having a square structure is used as an example.

[0106] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a top cover assembly 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 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 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.

[0107] 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. The specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0108] In the battery module, the plurality of battery cells may be arranged in sequence along the thickness direction of the battery module. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells may be fixed by fasteners.

[0109] Optionally, the battery module may further include a housing having a receiving space, and a plurality of battery cells are received in the receiving space.

[0110] 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.

[0111] Figure 3 and Figure 4 1 is a battery pack 1 as an example. Figure 3and Figure 4 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.

[0112] In addition, the present application also provides an electric device, which includes a battery cell provided in the present application. The battery cell can be used as a power source for the electric device, or as an energy storage unit for 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.

[0113] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0114] Figure 5 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.

[0115] [Example]

[0116] 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.

[0117] Example 1

[0118] Positive electrode

[0119] The positive electrode active layer includes positive electrode active materials, binder polyvinylidene fluoride, and conductive agent acetylene black (mass ratio is 96.7:2.3:1). In the positive electrode active material, the mass ratio of nickel-containing lithium transition metal oxide and lithium-containing phosphate positive electrode material is 4:6, and the mass content of carbon in the lithium-containing phosphate positive electrode material is about 1.7%. In the nickel-containing lithium transition metal oxide, the subscripts of Ni, Co and Mn in the chemical formula are rounded data. Since the content of other metal elements and oxygen elements M other than lithium is trace compared to the content of Ni, Co and Mn, these elements and their atomic numbers are not reflected in the chemical formula, but it does not mean that element M has no effect on battery performance. In the positive electrode material, the mass content of Al element is 0.063%, the mass content of B is 0.0039%, and the mass content of Zr is 0.256%. The thickness of the current collector aluminum foil is 12μm, the positive active layer is located on both sides of the aluminum foil, and there is a positive conductive layer between the positive active layer and the aluminum foil. The positive conductive layer includes a film layer formed by mixing the positive conductive agent superconducting carbon, the positive electrode binder polyacrylate and the solvent evenly and then coating it on the surface of the positive current collector and drying it. The thickness is 1μm, the mass content of the positive conductive agent in the positive conductive layer is 50%, and the mass content of the positive binder in the positive conductive layer is 50%. The length of the positive electrode sheet is 592mm.

[0120] Negative electrode

[0121] The negative electrode active layer includes an upper layer (away from the current collector) and a lower layer (close to the current collector). The lower layer includes a 96:1:2:1 negative electrode active material, a conductive agent acetylene black, a binder styrene-butadiene rubber, and a thickener sodium carboxymethyl cellulose. The negative electrode active material is composed of composite graphite particles (the composite graphite particles include artificial graphite and a carbon coating layer, the carbon coating layer is coated on the surface of the artificial graphite, and the mass content of the carbon coating layer is 3.5%) and natural graphite in a mass ratio of 5:5, wherein the Dv50 of the composite graphite particles is 17μm, and the Dv50 of the natural graphite is 18μm. The negative electrode active material in the upper layer is a composite graphite particle with a Dv50 of 10μm. The powder compaction density of the composite graphite material in the negative electrode active layer of the above-mentioned negative electrode sheet under a pressure of 20000N is 1.6g / cm 3 .

[0122] The negative electrode current collector is a 5μm copper foil. There is a negative electrode conductive layer between the copper foil and the lower active layer. The conductive layer is a film layer formed by mixing the negative electrode conductive agent superconducting carbon, the negative electrode binder styrene butadiene rubber SBR, the thickener sodium carboxymethyl cellulose (CMC-Na) and the solvent water evenly and then coating it on the surface of the negative electrode current collector and drying it. The thickness is 1μm. The mass content of the negative electrode conductive agent in the negative electrode conductive layer is 35%, the mass content of the negative electrode binder in the negative electrode conductive layer is 60%, and the mass content of the thickener in the negative electrode conductive layer is 5%. Under the following test conditions, the compaction density of the negative electrode active layer is 1.32g / cm3 .

[0123] The electrolyte includes organic solvents ethyl acetate EA, ethylene carbonate EC, ethyl methyl carbonate EMC (mass ratio 50:35:15), 0.9 mol / L lithium hexafluorophosphate (LiPF6) and 0.3 mol / L lithium bis(fluorosulfonyl)imide LiFSI as lithium salts, 2.5% additives vinylene carbonate VC, 1% fluoroethylene carbonate FEC, 0.5% 1,3 propene sultone PS, 0.5% vinyl sulfite DTD and 0.5% lithium difluorophosphate LiPO2F2. The conductivity of the electrolyte is 11 mS / cm.

[0124] Isolation film

[0125] A polyethylene (PE) film coated with nano-aluminum oxide was used as the isolation film.

[0126] Battery Cell

[0127] The electrode assembly is obtained by stacking the positive electrode sheet, the separator and the negative electrode sheet. The electrode assembly is added to the outer packaging square aluminum shell (length 600mm, thickness 19mm, height 105mm), and the electrolyte is injected after drying, and the injection coefficient is 2.9. After packaging, high temperature standing, formation, secondary injection, aging, capacity and other processes, a battery cell is obtained.

[0128] Pole piece test

[0129] Compacting density of positive electrode active layer

[0130] The density refers to the compaction density of the positive electrode active layer after the battery cell is charged to a voltage of 4.2V at a rate of 0.33C at 25°C and then charged at a constant voltage to a current less than 0.05C.

[0131] Test methods for surface density and compacted density:

[0132] Take a single-sided coated positive electrode sheet (if it is a double-sided coated sheet, wipe off the positive electrode active layer on one side first), punch it into small discs with an area of ​​S1, weigh it, record it as M1, and measure its thickness H1. Then wipe off the positive electrode active layer of the weighed positive electrode sheet, weigh the weight of the positive electrode collector, record it as M0, and measure its thickness H0. The single-sided coating weight of the positive electrode active layer (also known as the surface density) = (the weight of the positive electrode sheet M1-the weight of the positive electrode collector M0) / S1, the thickness of the positive electrode active layer = the thickness of the single-sided positive electrode sheet H1-the thickness of the positive electrode collector H0, and the compacted density of the positive electrode active layer = the single-sided coating weight of the positive electrode active layer / the thickness of the single-sided positive electrode active layer.

[0133] Battery Cell Test

[0134] Volume energy density test method:

[0135] The battery cell is placed at 25°C, charged to 4.2V at a constant current of 0.33C, and then charged to 0.05C at a constant voltage; discharged to 2.5V at a constant current of 0.33C, and the discharge energy A0 at this time is obtained, in units of Wh; the length, width, and height of the battery cell are measured with a caliper (generally calculated based on the outer shell size of the battery, excluding the height of the electrode terminals and the insulating film outside the outer shell), and the volume V0 of the battery cell is calculated, in units of L; the volume energy density of the battery cell is VED = A0 / V0, in units of Wh / L.

[0136] DC internal resistance DCR test of battery cells

[0137] You can refer to the method in GB / T 31467 "Performance Test Specification for High Power Lithium-ion Power Batteries for HEV". The details are as follows:

[0138] At room temperature, charge the battery cell to 4.2V at 0.33C constant current, let stand for 1min, then charge to 4.2V at 0.1C constant current, discharge to 2.0V at 0.33C constant current, record the discharge capacity A0 at this time, unit Ah, then charge 0.5A0 Ah at 0.33C constant current, adjust SOC to 50%.

[0139] After the battery cell is placed at 25°C for 2 hours, it is discharged at a constant current of 2C for 10 seconds, and ΔU discharge and ΔI discharge are recorded. The discharge DCR data of the lithium-ion battery is calculated by the following formula: R discharge = ΔU discharge / ΔI discharge,

[0140] Here, ΔUdischarge represents the voltage change within 10 seconds after the start of discharge, and ΔIdischarge represents the current value within 10 seconds after the start of discharge.

[0141] Cycle life test method:

[0142] The number of cycles of the battery cell to 80% SOH:

[0143] At 45°C, charge the battery cell at 1C constant current to a charge cutoff voltage of 4.2V, and then discharge it at 1C constant current to 2.0V. This is a charge and discharge cycle. Repeat the above charge and discharge cycle steps until the cycle capacity retention rate (i.e. Cn / C0×100%) is 80% (the discharge capacity at 1C constant current to 2.0V is recorded as C0, and Cn is the discharge capacity of the nth cycle). Record the number of cycles. The more cycles, the better the cycle performance of the battery cell.

[0144] In Example 2, Example 3, and Comparative Examples 1 to 3, the composition or surface density of the positive electrode material is adjusted on the basis of Example 1, and other parameters are consistent with Example 1. The mass content of other elements M in the positive electrode material in the positive electrode active layer in Example 2 is Al 0.060%, B 0.0050%, and Zr 0.249%; in Example 3, the mass content of other elements is Al 0.060%, B 0.0043%, and Zr 0.257%. The specific adjustments are shown in Table 1 below, and the volume energy density test results of each embodiment and comparative example are recorded in Table 1.

[0145] Table 1

[0146] According to the comparison between the above embodiments and comparative examples, it can be seen that when the molar content of Ni element in nickel-containing lithium transition metal oxide relative to transition metal element is less than 50%, or the molar content of Mn element in lithium phosphate positive electrode material relative to transition metal element is less than 50% or greater than 90%, or the surface density of the positive electrode active layer is too small, the energy density of the battery cell will be significantly reduced.

[0147] The following examines the effect of changes in the Mn element content in lithium-containing phosphate-based positive electrode materials on the energy density and cycle performance of battery cells.

[0148] The nickel-containing lithium transition metal oxide used in Examples 4 to 7 is the same as that in Example 2, the surface density of the positive electrode active layer is the same as that in Example 2, the mass ratio of the nickel-containing lithium transition metal oxide to the lithium-containing phosphate positive electrode material is 4:6, and the negative electrode plate, electrolyte and separator are the same as those in Example 2. The remaining variable settings are recorded in Table 2.

[0149] Table 2

[0150] According to the data comparison in Table 2, as the Mn content in the lithium-containing phosphate-based positive electrode material increases, the volume energy density and cycle number of the battery cell are deteriorated, especially when the molar ratio of the Mn element to the iron element is greater than 7:3, the energy density and cycle number are significantly deteriorated. Therefore, controlling the Mn content in the lithium-containing phosphate-based positive electrode material is conducive to maintaining the high energy density and high cycle performance of the battery cell.

[0151] The following examines the effect of the ratio of nickel-containing lithium transition metal oxides to lithium-containing phosphate-based positive electrode materials on the energy density and cycle performance of battery cells.

[0152] The nickel-containing lithium transition metal oxide and lithium-containing phosphate-based positive electrode materials used in Examples 8 to 11 are the same as those in Example 2, and the surface density of the positive electrode active layer is also the same as that in Example 2, but the mass ratio of the nickel-containing lithium transition metal oxide and the lithium-containing phosphate-based positive electrode material is adjusted according to Table 3 to adjust the element mass ratio of Fe and Ni in the positive electrode material, and the negative electrode sheet, electrolyte and separator are the same as those in Example 2. The remaining variable settings are recorded in Table 3.

[0153] Table 3

[0154] According to the data comparison in Table 3, it can be seen that as the content of lithium-containing phosphate-based positive electrode materials increases, the energy density of the battery cell decreases, but the cycle performance is improved.

[0155] The following is an investigation of the effect of the surface density of the positive electrode active layer on the energy density of the battery cell. Based on Example 2, the surface density of the positive electrode active layer is adjusted as shown in Table 4, and the surface density of the negative electrode active layer is adaptively adjusted so that each example has the same CB value. The test results are recorded in Table 4.

[0156] Table 4

[0157] According to the data in Table 4, it can be seen that the increase in the positive electrode surface density is beneficial to improving the energy density of the battery cell.

[0158] The following examines the effect of the compaction density change of the positive electrode active layer corresponding to the battery cell being configured at 100% SOC on the volume energy density and cycle performance of the battery cell. Based on Example 2, the pressure conditions during the preparation of the positive electrode active layer were adjusted to obtain the compaction shown in Table 5, and the test results are also recorded in Table 5.

[0159] Table 5

[0160] According to the data in Table 5, it can be seen that as the compaction density increases, the volume energy density of the battery cell increases, but it also leads to a decrease in the cycle performance.

[0161] The following examines the effect of the compaction density change of the negative electrode active layer corresponding to the battery cell being configured at 100% SOC on the volume energy density and cycle performance of the battery cell. Based on Example 2, the pressure conditions during the preparation of the negative electrode active layer were adjusted to obtain the compaction shown in Table 6, and the test results are also recorded in Table 6.

[0162] Table 6

[0163] According to the data in Table 6, it can be seen that as the compaction density increases, the volume energy density of the battery cell increases, but it also leads to a decrease in the cycle performance.

[0164] The influence of the thickness of the positive electrode sheet and the thickness of the negative electrode sheet on the battery energy density and DCR internal resistance is considered below. Based on Example 2, the thickness of the positive electrode sheet or the thickness of the negative electrode sheet is adjusted, and the rest remains unchanged. The test results are recorded in Table 7.

[0165] Table 7

[0166] According to the data in Table 7, it can be seen that as the thickness of the positive electrode current collector increases or the thickness of the negative electrode current collector increases, the energy density of the battery cell decreases, the cycle performance improves, but the discharge DCR increases significantly, indicating that the increase in the thickness of the current collector leads to an increase in the resistance of the metal structural parts in the cell, causing the battery cell discharge DCR to increase.

[0167] The effect of the length of the positive electrode sheet on the energy density of the battery cell is investigated below. Based on Example 2, the length of the positive electrode sheet is adjusted as recorded in Table 8, and the test results are also recorded in Table 8.

[0168] Table 8 Positive electrode length / mm Volume energy density / Wh / L Number of cycles Embodiment 27 300 540 1156 Example 2 592 550 1143 Embodiment 28 950 563 1111

[0169] It can be seen from the data in Table 8 that as the length of the positive electrode sheet increases, the proportion of the positive electrode active layer that can play an energy role in the battery cell increases, thereby improving the energy density of the battery cell.

[0170] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, The battery cell comprises an electrode assembly, wherein the electrode assembly comprises a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet, wherein: The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active layer comprises a negative electrode material, and the negative electrode material comprises a carbon material. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active layer comprises a positive electrode material, and the positive electrode material comprises a lithium transition metal oxide containing nickel and a lithium phosphate-based positive electrode material containing lithium, wherein: The molar content of the Ni element in the nickel-containing lithium transition metal oxide is greater than or equal to 50%, based on the total molar amount of other metal elements except the lithium element in the nickel-containing lithium transition metal oxide; The molar content of the Mn element in the lithium-containing phosphate-based positive electrode material is 50%-90% based on the total molar amount of other metal elements except the lithium element in the lithium-containing phosphate-based positive electrode material, and The surface density of the positive electrode active layer is 190 mg / 1540.25 mm 2 -380mg / 1540.25mm 2 .

2. The battery cell according to claim 1, wherein: The surface density of the positive electrode active layer is 200 mg / 1540.25 mm 2 -350mg / 1540.25mm 2 .

3. The battery cell according to claim 1 or 2, wherein: The mass ratio of the Fe element to the Ni element in the positive electrode material is in the range of (0.4-10):

1.

4. The battery cell according to any one of claims 1 to 3, wherein: Based on the total molar amount of other metal elements except lithium in the nickel-containing lithium transition metal oxide, the molar content of Ni in the nickel-containing lithium transition metal oxide is 70%-95%, and can be optionally 80%-95%.

5. The battery cell according to any one of claims 1 to 4, wherein: The molar content of the Mn element in the lithium-containing phosphate-based positive electrode material is 50%-70% based on the total molar amount of other metal elements except the lithium element in the lithium-containing phosphate-based positive electrode material.

6. The battery cell according to any one of claims 1 to 5, wherein: The battery cell is configured such that the compaction density of the positive electrode active layer corresponding to the 100% SOC state is 2.32 g / cm 3 -3.18g / cm 3 , optional 2.53g / cm 3 -2.84g / cm 3 .

7. The battery cell according to any one of claims 1 to 6, wherein: The powder compaction density of the positive electrode material at 30000N is ≥2.5g / cm 3 , optional 2.5g / cm 3 -2.8g / cm 3 .

8. The battery cell according to any one of claims 1 to 7, wherein: The nickel-containing lithium transition metal oxide includes lithium-containing nickel-cobalt-manganese oxide, and the lithium-containing nickel-cobalt-manganese oxide contains one or more of Zr, Al, B, Fe, Ca, Sr, Ti, V or Y elements.

9. The battery cell according to claim 8, wherein: The nickel-cobalt-manganese oxide contains one or more of the elements Zr, Al, B or Fe; optionally, in the lithium-containing nickel-cobalt-manganese oxide, the mass content of the elements satisfies at least one of the following: the content of Zr is 1000-3000ppm, the content of Al is 100-1000ppm, and the content of B is 50-300ppm.

10. The battery cell according to any one of claims 1 to 9, wherein: The lithium-containing phosphate-based positive electrode material includes lithium iron manganese phosphate, which contains one or more of the elements Al, B, Ca, Cr, Cu, K, Mg, Na, P, Si, Ti, V or Zn.

11. The battery cell according to claim 10, wherein: The lithium manganese iron phosphate includes one or more of Al, Ca, Na, Ti or V elements; optionally, in the lithium manganese iron phosphate, the mass content of the elements satisfies at least one of the following: the Al content is 100-1000ppm, the Ca content is 50-300ppm, the Na content is 50-300ppm, the Ti content is 100-1000ppm, and the V content is 1000-3000ppm.

12. The battery cell according to any one of claims 1 to 11, wherein: The positive electrode material includes lithium iron manganese phosphate and nickel cobalt manganese oxide, and the positive electrode material includes one or more of Al, B, Ca, Fe, Sr, Ti, V, Y or Zn elements, and in the positive electrode material, the mass content of each element satisfies: Al:0.005％-0.1％； Ca: 0.0001%-0.02%; Na: 0.005%-0.06%; Ti: 0.005%-0.15%; V:0.0001％-0.3％； Zr:0.005％-0.2％； B:0.01％-0.1％。 13. The battery cell according to any one of claims 1 to 12, wherein: The lithium-containing phosphate-based positive electrode material comprises a carbon-containing coating layer, and the mass content of carbon in the lithium-containing phosphate-based positive electrode material is 1%-3%.

14. The battery cell according to any one of claims 1 to 13, wherein: In the positive electrode material, The mass content of Fe in particles with a particle size less than or equal to Dv10 is M1, and the mass content of Fe in particles with a particle size greater than or equal to Dv90 is M2, where M1 is greater than M2; and / or The mass content of Ni element in particles with a particle size less than or equal to Dv10 is M3, and the mass content of Ni element in particles with a particle size greater than or equal to Dv90 is M4, and M3 is less than M4.

15. The battery cell according to any one of claims 1 to 14, wherein: The particles of the nickel-containing lithium transition metal oxide are spherical or quasi-spherical polycrystalline particles, and the particles of the lithium-containing phosphate-based positive electrode material are single crystal particles.

16. The battery cell according to any one of claims 1 to 14, wherein: The particles of the nickel-containing lithium transition metal oxide are single crystal particles, and the particles of the lithium-containing phosphate-based positive electrode material are single crystal particles.

17. The battery cell according to claim 15, wherein: The volume particle size Dv50 of the polycrystalline particles of the nickel-containing lithium transition metal oxide is 7 μm-12 μm.

18. The battery cell according to claim 16, wherein: The volume particle size Dv50 of the single crystal particles of the nickel-containing lithium transition metal oxide is 1 μm-5 μm, and can be optionally 1.5 μm-3 μm.

19. The battery cell according to any one of claims 15 to 18, wherein: The volume particle size Dv50 of the single crystal particles of the lithium-containing phosphate-based positive electrode material is 0.1 μm-15 μm, and can be optionally 0.5 μm-2 μm.

20. The battery cell according to any one of claims 1 to 19, wherein: The positive electrode plate includes a positive electrode conductive layer, and the positive electrode conductive layer is arranged between the positive electrode collector and the positive electrode active layer.

21. The battery cell according to claim 20, wherein: The positive electrode conductive layer comprises a positive electrode binder and a positive electrode conductive material, and the thickness of the positive electrode conductive layer is 1 μm-2 μm.

22. The battery cell according to any one of claims 1 to 21, wherein: The thickness of the positive electrode current collector is 9 μm-17 μm, and can be 10 μm-13 μm.

23. The battery cell according to any one of claims 1 to 22, wherein: The surface density of the negative electrode active layer is 95 mg / 1540.25 mm 2 -180 mg / 1540.25 mm 2 ; Optional: 130mg / 1540.25mm 2 -150 mg / 1540.25 mm 2 .

24. The battery cell according to any one of claims 1 to 23, wherein the battery cell is configured such that the compaction density of the negative electrode active layer corresponding to the battery cell at 100% SOC is 1.04 g / cm 3 -1.48g / cm 3 ; Optional: 1.23g / cm 3 -1.38g / cm 3 .

25. The battery cell according to any one of claims 1 to 23, wherein: The carbon material includes composite graphite particles, and the composite graphite particles include: A bulk particle, the bulk particle comprising a secondary particle, the bulk particle comprising artificial graphite; and The coating layer is coated on the surface of the main particle, and the coating layer includes amorphous carbon.

26. The battery cell according to claim 25, wherein: The mass content of amorphous carbon in the coating layer is 2% to 5% based on the total mass of the composite graphite particles.

27. The battery cell according to claim 25 or 26, wherein: The powder compaction density of the composite graphite particles under a pressure of 20000N is 1.5g / cm 3 -1.7g / cm 3 , or 1.55g / cm 3 -1.65g / cm 3 .

28. The battery cell according to any one of claims 25 to 27, wherein: The negative electrode active layer comprises: A first negative electrode active layer is disposed on one side of the negative electrode current collector, the first negative electrode active layer comprises one or more of composite graphite particles and natural graphite, and optionally the volume average particle size Dv50 of the negative electrode material in the first negative electrode active layer is 7.5 μm-19.5 μm, and optionally 12.5 μm-18.5 μm, and The second negative electrode active layer is arranged on the side of the first negative electrode active layer away from the negative electrode current collector, and the second negative electrode active layer includes composite graphite particles. Optionally, the volume average particle size Dv50 of the negative electrode material in the second negative electrode active layer is 7.5μm-19.5μm, and can be optionally 7.5μm-15.5μm.

29. The battery cell according to any one of claims 1 to 28, wherein: The negative electrode plate includes a negative electrode conductive layer, and the negative electrode conductive layer is arranged between the negative electrode collector and the negative electrode active layer.

30. The battery cell according to claim 29, wherein: The negative electrode conductive layer comprises a negative electrode binder and a negative electrode conductive material, and the thickness of the negative electrode conductive layer is 1 μm-2 μm.

31. The battery cell according to any one of claims 1 to 30, wherein: The thickness of the negative electrode current collector is 4 μm-7 μm, and can be 4 μm-5 μm.

32. The battery cell according to any one of claims 1 to 31, wherein: The electrode assembly further includes an electrolyte, wherein the electrolyte includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

33. The battery cell according to claim 32, wherein: The molar concentration ratio of the lithium bis(fluorosulfonyl)imide to the lithium hexafluorophosphate is (2-5):

10.

34. The battery cell according to claim 32 or 33, wherein: The conductivity of the electrolyte is 10-20 mS / cm, and can be optionally 12-17 mS / cm.

35. The battery cell according to any one of claims 1 to 34, wherein: The battery cell also includes a shell, the electrode assembly is arranged in the inner cavity of the shell, the positive electrode sheet and the negative electrode sheet are arranged in a stacked manner, the length of the shell is L1, the length of the positive electrode sheet is L2, L2 / L1 is 80%-99%, and can be optionally 88%-99%.

36. The battery cell according to claim 35, wherein: The dimensions of the housing have one or more of the following characteristics: The range of L1 is 300mm-950mm; The height of the housing is 85 mm to 140 mm; The thickness of the shell is 10mm-20mm.

37. The battery cell according to claim 35 or 36, wherein: The shell is an aluminum shell or a steel shell.

38. The battery cell according to any one of claims 1 to 37, wherein: The liquid injection coefficient of the battery monomer is 1.9g / Ah-3.1g / Ah.

39. The battery cell according to claims 1 to 38, wherein: The volume energy density of the battery cell is 470Wh / L-570Wh / L.

40. A battery device comprising the battery cell according to any one of claims 1 to 39, wherein the battery device comprises a battery module, a battery pack or an energy storage device.

41. An electrical device comprising the battery cell according to any one of claims 1 to 39, or the battery device according to claim 40.

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