Battery cell, battery apparatus and electrical apparatus

Abstract

Provided in the present application are a battery cell, a battery apparatus and an electrical apparatus. The battery cell comprises a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer. A first film layer of the positive electrode film layer is provided at a lower layer, the first film layer comprising a first transition metal oxide, the lithium-containing first transition metal oxide comprising a first doping element, and the mass content of manganese in the lithium-containing first transition metal oxide being a1; and a second film layer is provided at an upper layer, the second film layer comprising a lithium-containing second transition metal oxide, the lithium-containing second transition metal oxide comprising an optional second doping element, the mass content of manganese in the lithium-containing second transition metal oxide being a2, a1>a2, and the first doping element and the second doping element each independently comprising one or more elements of Na, K, Be, Mg, Ca, Group IIIA, Group IB, Group IIB, Group IIIB, Group IVB, Group VB, Group VIB and Group VIII.

Description

Battery cell, battery device and electric device Cross-reference to related applications

[0001] This application claims priority to Chinese Patent Application No. 202411350103.0, filed on September 26, 2024, entitled “Battery cell, battery device and electric device”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, in particular to a battery cell, a battery device and an electric device. BACKGROUND

[0003] With the rapid development of society, low-cost and long-life lithium-ion batteries are gradually becoming the increasing demand of people. In NCM ternary positive electrode material, the cost of Co element is high, and increasing the nickel content or manganese content can reduce the cost of NCM ternary positive electrode material.

[0004] However, the increase of nickel content or manganese content is easy to cause the structural stability of NCM ternary positive electrode material to decrease, especially when charging at high voltage or storing at high temperature, the structural stability of NCM ternary positive electrode material is more unstable, therefore, how to realize low cost while realizing long life has been a topic of exploration in the industry. SUMMARY

[0005] The present application provides a battery cell and an electric device to realize long life of the battery cell while maintaining low cost.

[0006] The first aspect of the present application provides a battery cell, comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises: a first film layer arranged on at least one side of the positive electrode current collector, the first film layer comprising a first positive electrode active material, the first positive electrode active material comprising a first transition metal oxide containing lithium, the first transition metal oxide containing lithium comprising lithium elements, nickel elements, cobalt elements, manganese elements and first doping elements, the mass content of manganese elements in the first transition metal oxide containing lithium being a1; and a second film layer arranged on a side of the first film layer away from the positive electrode current collector, the second film layer comprising a second positive electrode active material, the second positive electrode active material comprising a second transition metal oxide containing lithium, the second transition metal oxide containing lithium comprising lithium elements, nickel elements, cobalt elements, manganese elements and optional second doping elements, the mass content of manganese elements in the second transition metal oxide containing lithium being a2, a1>a2; and the first doping elements and the second doping elements each independently comprise one or more elements of Na, K, Be, Mg, Ca, Group IIIA, Group IB, Group IIB, Group IIIB, Group IVB, Group VB, Group VIB and Group VIII.

[0007] The positive electrode film layer of the battery cell of the present application is arranged in layers, the first film layer is arranged close to the positive electrode current collector of the positive electrode sheet to which it belongs, the second film layer covers the first film layer and is arranged away from the positive electrode current collector of the positive electrode sheet to which it belongs, the first film layer and the second film layer use different transition metal oxides as components of the positive electrode active material, the content a2 of manganese elements in the second transition metal oxide containing lithium in the second film layer is lower than the content a1 of manganese elements in the first transition metal oxide containing lithium in the first film layer, so that the first transition metal oxide containing lithium in the first film layer is used to achieve a substantial reduction in cost, and the second transition metal oxide containing lithium in the second film layer has a low content of manganese elements, so that the problem of manganese elution is effectively controlled, thereby improving the cycle performance of the battery cell and prolonging the service life of the battery cell.

[0008] Moreover, since the first transition metal oxide containing lithium in the first film layer has a high content of manganese elements, its structural stability is naturally lower than that of the second transition metal oxide containing lithium, and the present application uses more first doping elements to improve the stability of the first transition metal oxide containing lithium, further reduces the manganese elution in the second film layer, and better improves the cycle performance of the battery cell and further prolongs the service life of the battery cell.

[0009] In any embodiment of the first aspect, the first doping element and the second doping element each independently comprise a first metal doping element, and the first metal doping element each independently comprises one or more of Na, K, Be, Mg and Ca. When an element of Na, K, Be, Mg and Ca is selected for doping, it is easier to form doping at the lithium site, thereby playing a role in supporting the layered material structure and reducing the risk of structure collapse during cycling; in addition, it can significantly reduce lithium / nickel mixing and increase the migration barrier of manganese dissolution and inhibit manganese dissolution.

[0010] In any embodiment of the first aspect, the first metal doping element each independently comprises one or more of Na, K and Mg, and further optionally comprises Na and / or Mg. Sodium, potassium and magnesium can better reduce lithium / nickel mixing and further increase the migration barrier of manganese dissolution and inhibit manganese dissolution.

[0011] In any embodiment of the first aspect, the mass ratio of the first metal doping element to lithium in the first lithium-containing transition metal oxide is b1, and the mass ratio of the first metal doping element to lithium in the second lithium-containing transition metal oxide is b2, and b1 > b2. In the positive electrode film layer away from the positive electrode current collector, the manganese content in the second lithium-containing transition metal oxide is low, and thus the structural stability thereof is improved, and in order to control the further reduction of the specific capacity thereof due to the doping element, the second lithium-containing transition metal oxide contains no or less first metal doping element; in the first film layer close to the positive electrode current collector, the manganese content in the first lithium-containing transition metal oxide is high, and in order to further improve the cycle performance of the battery cell, a high content of the first metal doping element is used to improve the structural stability of the first lithium-containing transition metal oxide.

[0012] In any embodiment of the first aspect, 39300 ppm > b1 > 0 ppm, and optionally 26300 ppm > b1 > 9900 ppm. Thus, on the basis of improving the cycle performance, the increase in the internal resistance of the battery is controlled.

[0013] In any embodiment of the first aspect, 26300 ppm > b2 > 0 ppm.

[0014] In any embodiment of the first aspect, the first doping element and the second doping element each independently further comprise a second metal doping element, and the second metal doping element each independently comprises one or more of elements of Group IIIA, Group IB, Group IIB, Group IIIB, Group IVB, Group VB, Group VIB and Group VIII. This can better inhibit manganese dissolution and oxygen release, and also play a role in adjusting the growth of crystal grains to a favorable crystal direction for lithium ion extraction.

[0015] In any embodiment of the first aspect, the second metal doping element each independently comprises one or more of Al, Ti, W, Zr, Sr, Cr, Fe, Zn, Cu, Mo, V, Ce, Nb, Sb, Ta, Ge, Nb, Sc, and Y, more optionally one or more of Ti, W, Zr, Sr, Cr, Fe, Zn, Cu, Mo, V, Nb, Sb, Ta, Y, further optionally one or more of Ti, Mo, Nb, Sb, Ta.

[0016] In any embodiment of the first aspect, in the lithium-containing first transition metal oxide, the mass ratio of the second metal doping element to the total mass of the nickel element, the cobalt element, the manganese element and the second metal doping element is c1; in the lithium-containing second transition metal oxide, the mass ratio of the second metal doping element to the total mass of the nickel element, the cobalt element, the manganese element and the second metal doping element is c2, c1>c2. The structural stability of the lithium-containing first transition metal oxide and the lithium-containing second transition metal oxide is further improved.

[0017] In any embodiment of the first aspect, the mass content of the second metal doping element in the lithium-containing first transition metal oxide is 1700 ppm to 6700 ppm, optionally 1700 ppm to 3400 ppm; the mass content of the second metal doping element in the lithium-containing second transition metal oxide is 0 ppm to 3400 ppm. The introduction of the transition metal element has an impact on the conductivity of the transition metal oxide.

[0018] In any embodiment of the first aspect, in the lithium-containing first transition metal oxide, the molar content of the manganese element in the nickel element, the cobalt element and the manganese element is 0.05:1-0.4:1; in the lithium-containing second transition metal oxide, the molar content of the manganese element in the nickel element, the cobalt element and the manganese element is 0.02:1-0.3:1. The content of the manganese element in the upper and lower layers is further controlled, so that the problem of manganese dissolution can be further inhibited.

[0019] In any embodiment of the first aspect, in the same cross section, the cross-sectional area ratio of the first positive electrode active material in the first film layer is d1, the cross-sectional area ratio of the second positive electrode active material in the second film layer is d2, d1

[0020] In any embodiment of the first aspect, the first positive electrode active material further comprises a first lithium-containing phosphate, the second positive electrode active material further comprises a second lithium-containing phosphate, and the first lithium-containing phosphate and the second lithium-containing phosphate each independently comprise one or more of lithium iron phosphate and modified materials thereof, lithium manganese iron phosphate and modified materials thereof. This helps to improve the discharge power performance of the battery cell at low SOC (SOC refers to the state of charge of the battery cell, the ratio of the remaining capacity of the battery cell to the capacity of its fully charged state).

[0021] In any embodiment of the first aspect, the mass content of the first lithium-containing phosphate in the first positive electrode active material is e1, the mass content of the second lithium-containing phosphate in the second positive electrode active material is e2, and e1≤e2, and optionally 0≤(e1+e2)≤8. This avoids excessive impact of the lithium-containing phosphate on the energy density of the battery cell.

[0022] In any embodiment of the first aspect, 0≤e1≤4wt%; 0≤e2≤5wt%. This helps to maintain a high energy density as much as possible on the basis of improving the discharge power of the battery cell at low SOC by using the lithium-containing phosphate.

[0023] In any embodiment of the first aspect, the thickness of the first film layer is f1, the thickness of the second film layer is f2, and 0.25≤f1 / f2≤4. This helps to maintain the structural stability of the oxide in the first film layer as much as possible during long cycles.

[0024] In any embodiment of the first aspect, the first film layer further comprises a first conductive agent, the second film layer further comprises a second conductive agent, the mass content of the first conductive agent in the first film layer is g1, and the mass content of the second conductive agent in the second film layer is g2, and g1>g2. Since the content of Mn element in the second positive electrode active material of the second film layer is relatively low, the conductivity of the second film layer itself is relatively high, and therefore a relatively small amount of conductive agent can be used to achieve a comparable conductive effect to the first film layer. The reduction in the content of the conductive agent can correspondingly increase the content of the second positive electrode active material, and thus can increase the energy density of the battery cell to a certain extent.

[0025] In any embodiment of the first aspect, the first conductive agent and the second conductive agent each independently comprise one or more of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers, and optionally the first conductive agent and the second conductive agent each independently comprise carbon nanotubes. Carbon nanotubes, as one-dimensional linear conductive materials, have better conductivity.

[0026] After the problem of instability of the positive electrode material structure during high-voltage charging is improved, the battery cell can use high-voltage charging to improve the energy density of the battery cell, and in any embodiment of the first aspect, the charging voltage of the battery cell is 4.25V-4.5V. By increasing the charging voltage, the energy density of the battery cell can be further improved.

[0027] The second aspect of the present application provides a battery device, comprising a plurality of battery cells, the battery cell comprising the battery cell provided by any embodiment of the first aspect

[0028] The third aspect of the present application provides a power utilization device, comprising the battery cell comprising the battery cell provided by any embodiment of the first aspect or the power utilization device comprising the power utilization device provided by any embodiment of the second aspect. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings.

[0030] FIG. 1 is a structural schematic diagram of a positive electrode sheet of a battery cell according to an embodiment of the present application.

[0031] FIG. 2 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0032] FIG. 3 is an exploded view of the battery cell shown in FIG. 2 according to an embodiment of the present application.

[0033] FIG. 4 is a schematic diagram of a battery module according to an embodiment of the present application.

[0034] FIG. 5 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0035] FIG. 6 is an exploded view of the battery pack shown in FIG. 5 according to an embodiment of the present application.

[0036] FIG. 7 is a schematic diagram of a power utilization device using the battery pack as a power source according to an embodiment of the present application.

[0037] In the drawings, the drawings are not drawn according to the actual scale.

[0038] Explanation of reference numerals:

[0039] 11 positive electrode current collector; 12 first film layer, 13 second film layer; 1 battery pack; 2 upper box body; 3 lower box body; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 end cover. DETAILED DESCRIPTION

[0040] The embodiments of the present application will be described in further detail below with reference to the accompanying drawings and examples. The following detailed description of the examples and the accompanying drawings are provided to illustrate the principles of the present application, and should not be taken in a limiting sense. The present application is not limited to the examples described.

[0041] Hereinafter, specific embodiments of the battery cell, the battery device, and the electric device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there are cases where unnecessary detailed description is omitted. For example, there are cases where detailed description of matters known well, repeated description of substantially identical 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 accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0042] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise specified, the numerical range "a-b" represents a shorthand notation for any real combination of numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, and "0-5" is just a shorthand notation for these numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0044] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0045] If not specifically stated, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c) means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0046] If not specifically stated, the present application refers to "including" and "comprising" as open-ended. For example, "including" and "comprising" can mean that other components not listed can also be included or contained.

[0047] If not specifically stated, in the present 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 A and B are both true (or exist).

[0048] [Battery cell]

[0049] In the embodiments of the present application, the battery cell can be a secondary battery, which refers to a battery that can be activated by charging after discharging to continue use.

[0050] The battery cell can be a lithium ion battery, a sodium ion battery, a sodium lithium ion battery, a lithium metal battery, a sodium metal battery, a lithium sulfur battery, a magnesium ion battery, a nickel hydrogen battery, a nickel cadmium battery, a lead-acid battery, etc. The embodiments of the present application are not limited thereto.

[0051] The battery cell generally includes an electrode assembly. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is disposed between the negative electrode sheet and the positive electrode sheet. During the charging and discharging process of the battery cell, active ions (such as lithium ions) are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, which can prevent the positive and negative electrodes from short-circuiting, and at the same time, the active ions can pass through.

[0052] In order to reduce the cost, the Co content in the NCM ternary positive electrode material can be reduced. Moreover, when low-cobalt NCM ternary positive electrode materials with different solid contents are mixed, the activity of the positive electrode material can be more flexibly adjusted. However, when the manganese content in the positive electrode material increases, the risk of manganese dissolution increases, which is more serious during high-voltage charging.

[0053] To solve the above problems, the first embodiment of the present application provides a battery monomer, comprising a positive pole piece, the positive pole piece comprising a positive pole current collector and a positive pole film layer arranged on at least one side of the positive pole current collector, wherein, as shown in FIG. 1, the positive pole film layer comprises a first film layer 12 and a second film layer 13, the first film layer 12 is arranged on at least one side of the positive pole current collector 11, the first film layer 12 comprises a first positive pole active material, the first positive pole active material comprises a first transition metal oxide containing lithium, the first transition metal oxide containing lithium comprises lithium elements, nickel elements, cobalt elements, manganese elements and first doping elements, the mass content of manganese elements in the first transition metal oxide containing lithium is a1; the second film layer 13 is arranged on the side of the first film layer 12 away from the positive pole current collector 11, the second film layer 13 comprises a second positive pole active material, the second positive pole active material comprises a second transition metal oxide containing lithium, the second transition metal oxide containing lithium comprises lithium elements, nickel elements, cobalt elements, manganese elements and second doping elements, the mass content of manganese elements in the second transition metal oxide containing lithium is a2, and a1>a2; the first doping elements and the second doping elements each independently comprise one or more elements of Na, K, Be, Mg, Ca, group IIIA, group IB, group IIB, group IIIB, group IVB, group VB, group VIB and group VIII.

[0054] To solve the above problems, the first embodiment of the present application provides a battery monomer, comprising a positive pole piece, the positive pole piece comprising a positive pole current collector and a positive pole film layer arranged on at least one side of the positive pole current collector, wherein, as shown in FIG. 1, the positive pole film layer comprises a first film layer 12 and a second film layer 13, the first film layer 12 is arranged on at least one side of the positive pole current collector 11, the first film layer 12 comprises a first positive pole active material, the first positive pole active material comprises a first transition metal oxide containing lithium, the first transition metal oxide containing lithium comprises lithium elements, nickel elements, cobalt elements, manganese elements and first doping elements, the mass content of manganese elements in the first transition metal oxide containing lithium is a1; the second film layer 13 is arranged on the side of the first film layer 12 away from the positive pole current collector 11, the second film layer 13 comprises a second positive pole active material, the second positive pole active material comprises a second transition metal oxide containing lithium, the second transition metal oxide containing lithium comprises lithium elements, nickel elements, cobalt elements, manganese elements and second doping elements, the mass content of manganese elements in the second transition metal oxide containing lithium is a2, and a1>a2; the first doping elements and the second doping elements each independently comprise one or more elements of Na, K, Be, Mg, Ca, group IIIA, group IB, group IIB, group IIIB, group IVB, group VB, group VIB and group VIII.

[0055] The positive pole film layer of the battery monomer of the present application is arranged in layers, the first film layer is arranged close to the positive pole current collector of the positive pole piece to which it belongs, the second film layer covers the first film layer and is arranged away from the positive pole current collector of the positive pole piece to which it belongs, the first film layer and the second film layer use different transition metal oxides as components of the positive pole active material, the content a2 of manganese elements in the second transition metal oxide containing lithium in the second film layer is lower than the content a1 of manganese elements in the first transition metal oxide containing lithium in the first film layer, so that the first transition metal oxide containing lithium in the first film layer is used to realize sufficient reduction of cost, and the second transition metal oxide containing lithium in the second film layer has a low content of manganese elements, so that the problem of manganese dissolution is effectively controlled, thereby the cycle performance of the battery monomer can be improved and the service life of the battery monomer can be prolonged. Moreover, the first transition metal oxide containing lithium in the first film layer has more first doping elements, the stability of the first transition metal oxide containing lithium is improved by using the first doping elements, the manganese dissolution is further reduced, and the cycle performance of the battery monomer is better improved and the service life of the battery monomer is further prolonged.

[0056] The comparison of the above manganese element content can be tested by the following method:

[0057] The positive electrode sheet is cut into a size of 6mm*6mm as a sample, attached to a sample stage coated with paraffin wax, and the sample slightly protrudes from the edge of the sample stage (<1mm). The polished end face is tested by a scanning electron microscope & energy spectrometer, equipment model Sigma300, and the detection method is operated according to the JY / T010-1996 regulation; the active material particles at different positions of the end face of the sheet are selected for energy spectrum analysis, and the element contents of the active material at different positions are calculated and compared.

[0058] The above method is suitable for testing the following doped element content.

[0059] In some embodiments, the first doped element and the second doped element each independently include a first metal doped element, and the first metal doped element each independently includes one or more elements of Na, K, Be, Mg and Ca (indicating that the first metal doped element in the first doped element and the first metal doped element in the second doped element are each independently selected, the first doped element can or can not include the first metal doped element, and the second doped element can or can not include the first metal doped element, when both include the first metal doped element, the first metal doped elements of the two can be the same or different). When the elements of Na, K, Be, Mg and Ca are selected for doping, it is easier to form doping at the lithium site, thereby playing a role in supporting the structure of the layered material, reducing the risk of structure collapse during the cycle; in addition, it can significantly reduce lithium / nickel mixing, improve the migration barrier of manganese dissolution, and inhibit manganese dissolution.

[0060] In order to fully utilize the first metal element to improve the structural stability of the first transition metal oxide containing lithium, in some embodiments, the first metal doped element each independently includes one or more elements of Na, K, Mg, and further optionally includes Na and / or Mg. Sodium, potassium and magnesium can better reduce lithium / nickel mixing, further improve the migration barrier of manganese dissolution, and inhibit manganese dissolution.

[0061] In some embodiments, in order to control the influence of the first metal-doped element on the energy density of the battery cell, in some embodiments, the mass ratio of the first metal-doped element to lithium element in the first lithium-containing transition metal oxide is b1, and the mass ratio of the first metal-doped element to lithium element in the second lithium-containing transition metal oxide is b2, b1 > b2. In the positive electrode film layer away from the positive electrode current collector, the manganese content in the second lithium-containing transition metal oxide is low, so its structural stability is improved, and in order to control the further reduction of its specific capacity caused by the doped element, the second lithium-containing transition metal oxide does not contain or contains less first metal-doped element; in the first film layer close to the positive electrode current collector, the manganese element content in the first lithium-containing transition metal oxide is high, and in order to further improve the cycle performance of the battery cell, the first metal-doped element with high content is used to improve the structural stability of the first lithium-containing transition metal oxide.

[0062] In some embodiments, 39300 ppm ≥ b1 > 0 ppm, and optionally 26300 ppm ≥ b1 ≥ 9900 ppm. In some embodiments, 26300 ppm ≥ b2 ≥ 0 ppm. Thus, on the basis of improving cycle performance, the increase in battery internal resistance is controlled.

[0063] In some embodiments, the first doped element and the second doped element each independently further comprise a second metal-doped element (indicating that the second metal-doped element in the first doped element and the second metal-doped element in the second doped element are each independently selected, the first doped element can or can not comprise the second metal-doped element, and the second doped element can or can not comprise the second metal-doped element, when both comprise the second metal-doped element, the second metal-doped elements of the two can be the same or different), and the second metal-doped element each independently comprises one or more elements of Group IIIA, Group IB, Group IIB, Group IIIB, Group IVB, Group VB, Group VIB and Group VIII.

[0064] In some embodiments, the above-mentioned second metal-doped element each independently comprises one or more elements of Al, Ti, W, Zr, Sr, Cr, Fe, Zn, Cu, Mo, V, Ce, Nb, Sb, Ta, Ge, Nb, Sc, and Y, more optionally comprises one or more elements of Ti, W, Zr, Sr, Cr, Fe, Zn, Cu, Mo, V, Nb, Sb, Ta, Y, and further optionally comprises one or more elements of Ti, Mo, Nb, Sb, and Ta. The doping of the above-mentioned metal-doped element to the defect site can cause local lattice distortion of the crystal, thereby increasing the manganese-O bond strength, inhibiting manganese dissolution and oxygen release, and also can play a role in adjusting the grain growth in a favorable crystal direction for lithium ion extraction.

[0065] In some embodiments, in order to further improve the structural stability of the lithium-containing first transition metal oxide and the lithium-containing second transition metal oxide, the mass ratio of the second metal doping element in the lithium-containing first transition metal oxide is c1, and the mass ratio of the second metal doping element in the lithium-containing second transition metal oxide is c2, c1>c2.

[0066] When the amount of transition metal doping is large, it is easy to cause distortion of the oxide structure, affect the lithium ion deintercalation, and further affect the conductivity of the oxide. When applied to a battery cell, it will increase the DCR of the battery, and further affect the kinetic performance of the battery. The amount of doping of the transition metal element can be used as a reference for the conventional doping amount. In some embodiments, while the doping of the transition metal element plays the above-mentioned role, in order to further avoid the influence of the introduction of the transition metal element on the conductivity of the transition metal oxide, the mass content of the second metal doping element in the lithium-containing first transition metal oxide is 1700 ppm to 6700 ppm, and optionally 1700 ppm to 3400 ppm; the mass content of the second metal doping element in the lithium-containing second transition metal oxide is 0 ppm to 3400 ppm.

[0067] The content of manganese element in the lithium-containing first transition metal oxide and the content of manganese element in the lithium-containing second transition metal oxide are selected within a conventional range on the basis of meeting the above conditions. In some embodiments, in the lithium-containing first transition metal oxide, the molar content of manganese element in nickel element, cobalt element and manganese element is 0.05:1-0.4:1; in the lithium-containing second transition metal oxide, the molar content of manganese element in nickel element, cobalt element and manganese element is 0.02:1-0.3:1. The content of manganese element in the lithium-containing first transition metal oxide can reach 0.4 mol, so that the material cost is reduced as much as possible, and on this basis, the content of manganese element in the lithium-containing second transition metal oxide can be reduced to 0.02 mol, so that the problem of manganese dissolution can be further inhibited.

[0068] In some embodiments, the lithium-containing first transition metal oxide and the lithium-containing second transition metal oxide described above can be conventional lithium-containing layered transition metal oxides that meet the above conditions, such as NCM 333 (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), NCM 523 (such as LiNi 0.5 Co 0.2 Mn 0.3 O2), NCM211 such as LiNi 0.5 Co 0.25 Mn 0.25 O2), NCM 622 such as LiNi 0.6 Co 0.2 Mn 0.2 O2), NCM 811 such as LiNi 0.8 Co 0.1 Mn 0.1 O2).

[0069] In some embodiments, in the same cross section, the cross-sectional area ratio of the first positive electrode active material in the first film layer is d1, and the cross-sectional area ratio of the second positive electrode active material in the second film layer is d2, d1 < d2. The compaction density of the first film layer with the above characteristics is less than that of the second film layer, so that the energy density of the battery is higher and the cycle life is better.

[0070] The test of the above cross-sectional area ratio can refer to the following method:

[0071] The positive electrode sheet is cut into a sample of 6mm*6mm size, attached to a sample table coated with paraffin, and the sample can protrude slightly from the edge of the sample table (<1mm). The polished end face of the positive electrode sheet is tested by a scanning electron microscope, equipment model Sigma300, detection according to JY / T010-1996 procedure operation; generally observed under 3000 times field, selected different positions for SEM photography (such as taking at least three cross-sectional areas), then using Avizo software to analyze and calculate the cross-sectional area ratio of the metal oxide in the corresponding film layer by using different material contrast, and then taking the average value of the three cross-sectional areas.

[0072] When the manganese element content satisfies a1 > a2, the power performance of the battery monomer in the low SOC state is deteriorated. In order to improve the discharge power performance of the battery monomer at low SOC, in some embodiments, the first positive electrode active material further comprises a first lithium-containing phosphates, and the second positive electrode active material further comprises a second lithium-containing phosphates, and the first lithium-containing phosphates and the second lithium-containing phosphates each independently comprise one or more of lithium iron phosphate and its modified material, lithium manganese iron phosphate and its modified material. The platform voltage of the lithium-containing phosphates is lower than that of the lithium-containing transition metal oxide, so it is helpful to improve the discharge power performance of the battery monomer at low SOC.

[0073] Since the gram capacity of lithium-containing phosphates is lower than that of lithium-containing transition metal oxides, in order to avoid excessive influence of lithium-containing phosphates on the energy density of the battery monomer, the content of lithium-containing phosphates in each film layer is adjusted to realize the improvement of the discharge power of the battery monomer at low SOC on the basis of the use of lithium-containing phosphates, and to reduce the influence of lithium-containing phosphates on the energy density of the battery monomer as much as possible. In some embodiments, the mass content of the first lithium-containing phosphate in the first positive electrode active material is e1, the mass content of the second lithium-containing phosphate in the second positive electrode active material is e2, and e1≤e2, and optionally 0≤(e1+e2)≤8. The second film layer is closer to the electrolyte than the first film layer, and more lithium-containing phosphates are arranged in the second film layer. The lithium-containing phosphates are more easily infiltrated by the electrolyte, so that the active ions are deintercalated in the lithium-containing phosphates in a shorter time during the charging and discharging process, so that the effect of lithium-containing phosphates on improving the discharge power of the battery monomer at low SOC is more easily exerted.

[0074] In some embodiments, 0≤e1≤4wt%; 0≤e2≤5wt%, and optionally, 0

[0075] The test of the above mass contents e1 and e2 can refer to the following method:

[0076] The battery monomer is disassembled to obtain a positive electrode sheet, the film layers at different positions of the positive electrode sheet are scraped to collect the positive electrode material, the inductively coupled plasma emission spectrometer ICP-OES is used to test the content of phosphorus element in the first film layer and the second film layer, and the mass proportion of phosphorus element in lithium iron phosphate and lithium manganese iron phosphate can be obtained from the molecular formula of lithium iron phosphate and lithium manganese iron phosphate, so as to calculate the mass content of the first lithium-containing phosphate in the first positive electrode active material and the mass content of the second lithium-containing phosphate in the second positive electrode active material.

[0077] In order to maintain the structural stability of the oxides in the first film layer as much as possible during the long cycle process, in some embodiments, the thickness of the first film layer is f1, the thickness of the second film layer is f2, and 0.25≤f1 / f2≤4. The thickness of the second film layer sufficiently protects the oxides in the first film layer.

[0078] The thickness of the above first film layer and second film layer is tested according to the following method:

[0079] Cut the positive electrode sheet into a sample of 6mm*6mm size, paste the sample on the sample stage coated with paraffin wax, and the sample can protrude slightly from the edge of the sample stage (<1mm). Polish the end face of the sample. Test the end face of the sample using a scanning electron microscope & energy spectrometer, model Sigma300, according to JY / T010-1996; test the manganese element of the sample end face (linear scanning) to distinguish the position distribution of different film layers, and combine the SEM measurement of the corresponding position thickness to obtain the thickness of the first film layer and the second film layer.

[0080] Since the manganese content of the lithium-containing first transition metal oxide in the first film layer is less, the lithium-containing first transition metal oxide has better conductivity, so the addition amount of the conductive agent in the first film layer can be appropriately reduced, and the lithium content of the second positive electrode active material can be increased accordingly, thereby the energy density of the battery cell can be improved to a certain extent. In some embodiments, the first film layer further comprises a first conductive agent, and the second film layer further comprises a second conductive agent, the mass content of the first conductive agent in the first film layer is g1, and the mass content of the second conductive agent in the second film layer is g2, g1>g2.

[0081] The first conductive agent and the second conductive agent can be selected from the conductive agents commonly used in positive electrode sheets. In some embodiments, the first conductive agent and the second conductive agent each independently comprise one or more of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Optionally, the first conductive agent and the second conductive agent each independently comprise carbon nanotubes. Carbon nanotubes, as one-dimensional linear conductive materials, have better conductivity.

[0082] In some embodiments, the coating weight CW of the positive electrode film layer satisfies: 100mg / 1540.25mm 2 ≤CW≤500mg / 1540.25mm 2 , optionally, 200mg / 1540.25mm 2 ≤CW≤400mg / 1540.25mm 2 . By controlling the coating weight, on the one hand, it is convenient for coating and is conducive to processing. Too thin coating can produce coating scratches, and too thick coating can cause demolding. On the other hand, it can also improve the adhesion of the positive electrode film layer and the positive electrode current collector in the later cycle, thereby improving the cycle life.

[0083] The test of the coating weight of the above-mentioned positive electrode film layer can refer to the following method:

[0084] After the battery cell is disassembled, the positive electrode sheet is obtained, and the positive electrode sheet is cut into a size of 1540.25mm 2A small disc is weighed as m1, and after the positive electrode film layer on the surface of the positive electrode current collector is wiped off using solvent NMP, it is weighed as m2, and the coating weight is m1-m2.

[0085] In some embodiments, the charging voltage of the battery cell is 4.25V-4.5V. Increasing the charging voltage can further increase the energy density of the battery cell.

[0086] As an example, the positive electrode current collector can employ a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, a pure metal, an alloy, a surface-treated metal, including but not limited to stainless steel, copper, aluminum, nickel, nickel, titanium, or silver, etc. can be employed. The composite current collector can include a polymer material base layer and a metal layer. The composite current collector can 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 base material (such as a base material of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

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

[0088] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry for coating the lower layer and a positive electrode slurry for coating the upper layer; double-layer simultaneous coating, coating the positive electrode slurry for coating the lower layer on the positive electrode current collector, and coating the positive electrode slurry for coating the upper layer on the coated upper layer positive electrode slurry; and after processes such as drying, cold pressing, etc., the positive electrode tab is obtained.

[0089] Generally, the battery cell also includes a negative electrode tab, a separator, and an electrolyte. During the charging and discharging of the battery, active ions (such as lithium ions) are embedded and extracted between the positive electrode tab and the negative electrode tab. The separator is disposed between the positive electrode tab and the negative electrode tab, mainly to prevent short circuiting of the positive and negative electrodes, while allowing the active ions to pass through. The electrolyte is between the positive electrode tab and the negative electrode tab, mainly to conduct the active ions.

[0090] [Negative electrode tab]

[0091] The negative electrode tab includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0092] As an example, the negative current collector has two surfaces opposite in the thickness direction thereof, and the negative film layer is provided on either one or both of the two opposite surfaces of the negative current collector. As an example, the negative current collector can employ a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as the metal foil, a pure metal, an alloy, a surface-treated metal, including but not limited to stainless steel, copper, aluminum, nickel, nickel, titanium, or silver, and the like can be employed. The composite current collector can include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, and the like) on a polymer material base material (such as a base material of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, and the like).

[0093] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate, and the like. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery negative active material can also be used. These negative active materials can be used alone only one or in combination of two or more.

[0094] In some embodiments, the negative film layer can further optionally include a binder. As an example, the binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0095] In some embodiments, the negative film layer can further optionally include a conductive agent. As an example, the conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0096] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0097] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector; and subjecting the negative electrode slurry to drying, cold pressing, and the like to obtain the negative electrode sheet.

[0098] As an example, the negative electrode active material can be filled or / and deposited in the negative electrode current collector.

[0099] In some embodiments, the material of the positive electrode current collector can be aluminum, and the material of the negative electrode current collector can be copper.

[0100] [Electrolyte]

[0101] The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of the electrolyte is not particularly limited in the present application and can be selected as needed. For example, the electrolyte can be in a liquid state, a gel state, or a full solid state.

[0102] In some embodiments, the electrolyte is in a liquid state and includes an electrolyte salt and a solvent.

[0103] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium di-oxalate borate, lithium difluoro di-oxalate phosphate, and lithium tetrafluoro oxalate phosphate.

[0104] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butanedisulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent can also be selected from an ether solvent. The ether solvent can include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and a crown ether. In some embodiments, the electrolyte solution can also optionally include an additive. As an example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, and the like.

[0105] [Separator]

[0106] In some embodiments, a separator is further included in the battery cell. The type of the separator is not particularly limited in the present application, and any known porous separator film having good chemical stability and mechanical stability can be used.

[0107] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited. The separator can be a separate component located between the positive and negative electrodes, or can be attached to the surface of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can be applied to the surface of the separator film.

[0108] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film can be used to make an electrode assembly by a winding process or a stacking process.

[0109] In some embodiments, the electrode assembly has a winding structure. The positive electrode sheet and the negative electrode sheet are wound to form the winding structure.

[0110] In some embodiments, the electrode assembly has a stacking structure.

[0111] For example, a plurality of positive electrode sheets and a plurality of negative electrode sheets can be alternately stacked.

[0112] For example, a plurality of positive electrode sheets can be provided, and the negative electrode sheet can be folded to form a plurality of folded sections that are stacked. One positive electrode sheet can be clamped between adjacent folded sections.

[0113] For example, the positive electrode sheet and the negative electrode sheet can be both folded to form a plurality of folded sections that are stacked.

[0114] For example, a plurality of separators can be provided, and each of the separators can be disposed between any adjacent positive electrode sheet or negative electrode sheet.

[0115] For example, a plurality of separators can be provided, and each of the separators can be disposed between any adjacent positive electrode sheet or negative electrode sheet.

[0116] In some embodiments, the electrode assembly can have a cylindrical shape, a flat shape, or a polygonal shape.

[0117] In some embodiments, the electrode assembly is provided with a tab. The tab can guide the current out of the electrode assembly. The tab includes a positive tab and a negative tab.

[0118] In some embodiments, the battery cell can include a housing. The housing can be a steel housing, an aluminum housing, a plastic housing (e.g., polypropylene), a composite metal housing (e.g., copper-aluminum composite housing), or an aluminum-plastic film, etc. In some embodiments, the housing can be a sealed structure or a non-sealed structure. As an example, when the housing is a non-sealed structure, the housing serves to protect the electrode assembly, and a sealing bag is further included between the housing and the electrode assembly, which is used to encapsulate the electrode assembly and the electrolyte. Specifically, the sealing bag can be a bag-shaped insulating member or an aluminum-plastic film. When the housing is a sealed structure, it is used to encapsulate the electrode assembly and the electrolyte, etc.

[0119] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes, including a square battery cell, a blade battery cell, a multi-prismatic battery cell (e.g., a hexagonal battery cell), etc., without specific limitation in the present application.

[0120] In some embodiments, the housing includes a cap and a shell, and the shell is provided with an opening, and the cap is arranged on the opening. The shell can be provided with one or more openings. The cap can also be provided with one or more openings. In some embodiments, at least one electrode terminal is arranged on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab or indirectly connected to the tab through a current collecting member. The electrode terminal can be arranged on the cap or arranged on the shell.

[0121] In some embodiments, a pressure relief mechanism is arranged on the housing. The pressure relief mechanism is used to discharge the internal gas of the battery cell.

[0122] As an example, the internal pressure or temperature of the battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism performs an action or a weak structure provided in the pressure relief mechanism is broken, thereby forming an opening or a passage for the internal pressure or temperature to be released. The threshold value is designed differently according to different design requirements. The threshold value can depend on the material of one or more of the positive plate, the negative plate, the electrolyte, and the separator in the battery cell.

[0123] As an example, the pressure relief mechanism can be integrally formed with the housing.

[0124] As an example, the pressure relief mechanism can also be arranged separately from the housing and connected to the housing.

[0125] As used herein, "actuation" of the pressure relief mechanism refers to the pressure relief mechanism being activated or moved to a state in which the internal pressure and temperature of the battery cell can be released. The movement of the pressure relief mechanism can include, but is not limited to, movement of a component of the pressure relief mechanism to form a venting path, at least a portion of the pressure relief mechanism rupturing, breaking, tearing, or opening, and the like. Upon actuation of the pressure relief mechanism, the high temperature and pressure material inside the battery cell is released as an effluent from the actuated portion. In this manner, the battery cell can be depressurized and cooled in a controlled manner to avoid a potentially more severe accident.

[0126] In some embodiments, the housing is not a sealed structure, and the pressure relief mechanism can be a through hole for releasing the gas inside the battery cell.

[0127] As used herein, the effluent from the battery cell can include, but is not limited to, electrolyte, dissolved or broken positive and negative electrode sheets, fragments of the separator, high temperature and pressure gas generated by the reaction, flame, and the like.

[0128] FIG. 2 is a battery cell 5 in a square structure as an example.

[0129] In some embodiments, referring to FIG. 3, the housing can include a housing 51 and an end cap 53. The housing 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate can form an accommodation cavity. The housing 51 has an opening in communication with the accommodation cavity, and the end cap 53 can be arranged on the opening to close the accommodation cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the accommodation cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and a person skilled in the art can select according to the actual needs.

[0130] [Battery Apparatus]

[0131] The battery apparatus as referred to in the embodiments of the present application can include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly can include a plurality of battery cells connected in series, in parallel, or in a mixed connection through a busbar component.

[0132] In some embodiments, the battery cell assembly is generally formed by arranging a plurality of battery cells.

[0133] As an example, the battery cell assembly can be a battery module, which is formed by arranging and fixing a plurality of battery cells. As an example, the battery module can be formed by bundling a plurality of battery cells with a cable tie. The battery module

[0134] FIG. 4 is a battery module 4 as an example. Referring to FIG. 4, in the battery module 4, a plurality of battery cells 5 can be arranged in sequence in a length direction of the battery module 4. Of course, the plurality of battery cells 5 can be arranged in any other manner. The plurality of battery cells 5 can be further fixed by a fastener.

[0135] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of battery cells 5 can be accommodated in the accommodation space.

[0136] In some embodiments, the battery device can be a battery pack, which includes a case and one or more battery cell assemblies accommodated in the case.

[0137] As an example, the battery cell assembly can be a battery module, which can be accommodated in the case by fixing the battery module in the case. As an example, the battery cell assembly can also be accommodated in the case by directly fixing a plurality of battery cells in the case.

[0138] As an example, the case can include a first case and a second case. The first case and the second case are fastened so that an enclosed space is formed inside the case to accommodate the battery cell assembly. Here, the enclosed means covered or closed, which can be sealed or unsealed. The first case can be a top cover or a bottom plate.

[0139] As an example, the case can include a top cover, a frame, and a bottom plate. The top cover and the bottom plate are respectively connected to the frame so that an enclosed space is formed inside the case to accommodate the battery cell assembly.

[0140] In some embodiments, the case can be part of a chassis structure of a vehicle. For example, part of the case can be at least part of a floor of the vehicle, or part of the case can be at least part of a cross beam and a longitudinal beam of the vehicle.

[0141] FIGS. 5 and 6 are a battery pack 1 as an example. Referring to FIGS. 5 and 6, the battery pack 1 can include a battery case and a plurality of battery modules 4 arranged in the battery case. The battery case includes an upper case 2 and a lower case 3, and the upper case 2 can be placed on the lower case 3 to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery case in any manner.

[0142] The technical solutions described in the embodiments of the present application are applicable to various electric devices using battery monomers, such as mobile phones, portable devices, notebook computers, electric vehicles, electric toys, electric tools, vehicles, ships and spacecraft, such as aircraft, rockets, space shuttles and spaceships. As the electric device, the battery monomer, the battery module or the battery pack can be selected according to the use requirements.

[0143] FIG. 7 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electric device for battery monomers, a battery pack or a battery module can be used.

[0144] [Embodiments]

[0145] 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 cannot be understood as a limitation of the present application. If the specific technology or condition is not mentioned in the embodiments, the technology or condition described in the literature in the art or according to the product manual is used. If the reagent or instrument used is not mentioned by the manufacturer, it is a conventional product that can be obtained by purchase.

[0146] In the positive electrode active material used in each embodiment and comparative example, the type and mass content of the doping element are recorded in Table 1 unless otherwise specified.

[0147] Example 1

[0148] Preparation of the lower layer positive electrode slurry:

[0149] The positive electrode active material Li 0.995 Na 0.005 Ni 0.55 Co 0.07 Mn 0.38 O2 (volume particle size Dv50 is 3.7 μm), LiFePO4 (volume particle size Dv50 is 1.4 μm), acetylene black, positive electrode binder PVDF, carbon nanotubes are added in a mass ratio of 94.09:2.91:0.5:2:0.5 to a certain amount of solvent NMP, and stirred to form a uniform slurry 1;

[0150] Preparation of the upper layer positive electrode slurry:

[0151] LiNi 0.55 Co 0.16 Mn 0.29O2 cathode active material (volume particle size Dv50 is 3.3 μm), LiFePO4 (volume particle size Dv50 is 1.4 μm), acetylene black, positive electrode binder PVDF, carbon nanotubes are added in a certain amount of solvent NMP according to the mass ratio 94.09:2.91:0.5:2:0.5, and stirred to form a uniform slurry 2;

[0152] Preparation of positive electrode sheet

[0153] Using a double-layer coating device, the lower layer slurry and the upper layer slurry are simultaneously and uniformly coated on the positive electrode current collector, wherein the coating amount of the lower layer slurry is 136 mg / 1540.25 mm 2 , and the coating amount of the upper layer slurry is 136 mg / 1540.25 mm 2 ; after the double-sided coating is completed, drying, cold pressing and slitting are performed to prepare a positive electrode sheet having a first film layer as the lower layer and a second film layer as the upper layer, and the thickness of the first film layer and the thickness of the second film layer are both 28 μm, i.e. f1 / f2=1, g1 / g2=1.

[0154] Preparation of negative electrode sheet

[0155] The negative electrode active material graphite, the negative electrode binder styrene-butadiene rubber (SBR), the negative electrode thickening agent sodium carboxymethyl cellulose (CMC-Na), and the negative electrode conductive agent carbon black (Super P) are mixed in a certain amount of solvent deionized water according to the mass ratio 96:1.5:0.5:2, and a uniform negative electrode slurry is formed; the negative electrode slurry is coated on the surface of the negative electrode current collector copper foil, and a negative electrode sheet is prepared after drying, cold pressing and slitting.

[0156] Separator film: a porous polyethylene (PE) film is used as the separator film.

[0157] The solvent composition of the electrolyte is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1, the lithium salt is LiPF6 and its concentration in the solvent is 1 mol / L, FEC (fluoroethylene carbonate) is used as an additive and its mass content in the electrolyte is 1 wt%.

[0158] Battery cell assembly

[0159] The positive electrode sheet, the separator film and the negative electrode sheet are stacked in order, with the separator film between the positive and negative electrodes to play a separating role, and a bare cell is obtained by winding. The bare cell is placed in an outer package, electrolyte is injected, and packaging, liquid injection, formation and exhaust processes are performed to obtain a battery cell.

[0160] The thickness of the film layer is tested according to the following method:

[0161] The positive electrode sheet is cut into a sample of 6mm*6mm size, which is attached to a sample stage coated with paraffin wax, and the sample slightly protrudes the edge of the sample stage (<1mm). The end face of the sample is polished. The end face of the sample is tested by using a scanning electron microscope & energy spectrometer, the equipment model is Sigma300, and the detection is based on JY / T010-1996. The manganese element of the end face of the sample is detected (linear scanning) to distinguish the position distribution of different film layers, and the thickness of the corresponding position is measured by SEM to obtain the thickness of the first film layer and the second film layer. The relationship between the measured thickness of the first film layer and the second film layer is consistent with the relationship of the coating amount of each film layer.

[0162] The test of the cross-sectional area ratio of the active material can refer to the following method:

[0163] The positive electrode sheet is cut into a sample of 6mm*6mm size, which is attached to a sample stage coated with paraffin wax, and the sample slightly protrudes the edge of the sample stage (<1mm). The end face of the positive electrode sheet is polished. The polished end face is tested by using a scanning electron microscope, the equipment model is Sigma300, and the detection is based on JY / T010-1996 procedure operation. Three positions are selected for SEM photographing at 3000 times magnification. Then, the cross-sectional area ratio of the metal oxide in the cross-sectional area of the corresponding film layer is analyzed and calculated by using different material contrasts by using Avizo software. The average value of three positions is taken. The cross-sectional area ratio of the first positive active material in the first film layer is d1, and the cross-sectional area ratio of the second positive active material in the second film layer is d2. The d1 of each example is basically around 83% (the d1 of example 10 below is 79%, and the d1 of comparative example 3 is 85%). The d2 of each example is basically around 87%.

[0164] Battery performance test

[0165] (1) Normal temperature cycle performance test:

[0166] In a constant temperature environment of 25℃, the prepared battery is charged to an upper limit voltage of 4.4V at 0.5C constant current, then charged at a constant voltage of 4.4V until the current is ≤0.05C, and then rested for 5min. Then, the battery is discharged at 1C constant current to 2.5V, which is one cycle of charge and discharge process. The discharge capacity at this time is recorded, which is the discharge capacity of the first cycle. The battery is tested by the above method for cycle charge and discharge, and the discharge capacity after each cycle is recorded until the discharge capacity of the battery decays to 80% of the discharge capacity of the first cycle. The cycle number at this time is used to represent the cycle performance of the battery. The higher the cycle number of the battery, the better the cycle performance.

[0167] (2) Battery internal resistance growth rate test within 500 cycles:

[0168] The prepared battery was charged at 0.5 C to an upper limit voltage of 4.4 V at a constant temperature of 25 °C, and then charged at a constant voltage of 4.4 V until the current was less than or equal to 0.05 C, and then rested for 30 min. At this time, the voltage of the battery was recorded as V1. The battery was discharged at 1 C for 30 s, and the voltage at the end of the discharge was recorded as V2. The internal resistance DCR of the battery before cycling was recorded, and DCR = (V1-V2) / 1C.

[0169] The battery was cycled according to the above cycle performance test method for 500 cycles. The internal resistance DCR of the battery after 500 cycles was tested according to the above method.

[0170] The internal resistance growth rate of the battery after 500 cycles was (internal resistance after 500 cycles / internal resistance before cycling)-1.

[0171] (3) High-temperature storage performance test:

[0172] The prepared battery was charged at 0.5 C to an upper limit voltage of 4.4 V at a constant temperature of 25 °C, and then charged at a constant voltage of 4.4 V until the current was less than or equal to 0.05 C, and then rested for 5 min. Then, the battery was discharged at 1 C to 2.5 V, which was one cycle of charging and discharging. The discharge capacity at this time was recorded as the initial capacity C0 (calibrated capacity).

[0173] Then, the battery was charged at 0.5 C to an upper limit voltage of 4.4 V at a constant temperature of 25 °C, and then charged at a constant voltage of 4.4 V until the current was less than or equal to 0.05 C, and then rested for 5 min (adjusted to 100% SOC).

[0174] The battery cell in a 100% SOC state was placed in a 60 °C oven for different periods of time. During the resting process, the battery was taken out of the oven every 10 days or so, and the capacity Cn (n is the number of test days) was tested. The capacity retention rate was calculated by Cn / C0. When the capacity retention rate was less than or equal to 80%, the high-temperature storage time was recorded. The higher the storage time, the better the high-temperature storage performance.

[0175] (4) Anode manganese dissolution content test after high-temperature storage:

[0176] After the above high-temperature storage was completed, the tested battery was rested at 25 °C for 2 h, and then charged at 0.5 C to an upper limit voltage of 4.4 V, and then charged at a constant voltage of 4.4 V until the current was less than or equal to 0.05 C, and then rested for 5 min (adjusted to 100% SOC).

[0177] Then the battery is disassembled, and 0.5 g of the center region of the negative electrode sheet is taken. The negative electrode sheet taken is placed in an appropriate amount of digestion solvent concentrated nitric acid solvent, and is digested by using a flat plate digestion method. Finally, 7% (volume fraction of hydrochloric acid) hydrochloric acid is used to dissolve the extraction solvent, and then the obtained solution is diluted to an appropriate volume. Then, the inductively coupled plasma emission spectrometer ICP-OES is used for testing, and the mass fraction of manganese element is calculated.

[0178] Example 2

[0179] Other than example 1, the only difference is that the positive active material of the upper layer slurry is LiNi 0.65 Co 0.07 Mn 0.28 O2, and the volume particle size Dv50 is 3.5 μm.

[0180] Example 3

[0181] Other than example 1, the only difference is that the positive active material of the lower layer slurry is LiNi 0.55 Co 0.07 Mn 0.377 Ti 0.003 O2, and the volume particle size Dv50 is 3.8 μm. The positive active material of the upper layer slurry is LiNi 0.55 Co 0.16 Mn 0.29 O2, and the volume particle size Dv50 is 3.3 μm.

[0182] Example 4

[0183] Other than example 1, the only difference is that the positive active material of the lower layer slurry is Li 0.988 Na 0.012 Ni 0.55 Co 0.07 Mn 0.38 O2, and the volume particle size Dv50 is 3.5 μm.

[0184] Example 5

[0185] Other than example 1, the only difference is that the positive active material of the lower layer slurry is Li 0.992 Na 0.008 Ni 0.55 Co 0.07 Mn 0.38 O2, and the volume particle size Dv50 is 3.3 μm.

[0186] Example 6

[0187] Other than example 1, the only difference is that the positive active material of the lower layer slurry is Li 0.997 Na 0.003 Ni 0.55 Co0.07 Mn 0.38 O2, the volume particle size Dv50 was 3.6 pm.

[0188] Comparative Example 1

[0189] Other than Example 1, the only difference is that the positive electrode is coated with a single layer of slurry, and the positive electrode slurry is specifically Li 0.995 Na 0.005 Ni 0.55 Co 0.07 Mn 0.38 O2 cathode active material (volume particle size Dv50 is 3.7 pm), LiNi 0.55 Co 0.16 Mn 0.29 O2 cathode active material (volume particle size Dv50 is 3.3 pm), acetylene black, positive electrode binder PVDF, carbon nanotubes are added in a certain amount of solvent NMP according to the mass ratio 48.5:48.5:0.5:2:0.5 to prepare a slurry, and the coating amount is 276 mg / 1540.25 mm 2 .

[0190] Comparative Example 2

[0191] Other than Example 1, the only difference is that the positive electrode active material in the lower layer slurry is LiNi 0.55 Co 0.16 Mn 0.29 O2 (volume particle size Dv50 is 3.3 pm), and the positive electrode active material in the upper layer slurry is Li 0.995 Na 0.005 Ni 0.55 Co 0.07 Mn 0.38 O2 (volume particle size Dv50 is 3.7 pm).

[0192] Comparative Example 3

[0193] Other than Example 1, the only difference is that the positive electrode active material in the lower layer slurry is LiNi 0.55 Co 0.07 Mn 0.38 O2 (volume particle size Dv50 is 3.3 pm), and does not contain other elements.

[0194] The data of b1, c1 in each example and comparative example are recorded in Table 1. The battery performance test results are also recorded in Table 1.

[0195] Table 1

[0196] From the comparison of the data of Examples 1 to 6 and Comparative Examples 1 and 2 in Table 1, it can be seen that when the manganese content of the lithium-containing first transition metal oxide in the upper film layer is lower than the manganese content of the lithium-containing first transition metal oxide in the lower film layer, the cycle performance and high-temperature storage performance of the battery cell can be improved.

[0197] From the comparison of the data of Example 1, Examples 4 to 6 and Comparative Example 3, it can be seen that when the manganese element content of the first transition metal oxide in the first film layer of the lower layer of Comparative Example 3 is high and no sodium element is doped, the structural stability is insufficient, resulting in insufficient cycle performance and storage performance of the battery cell, and the doping of sodium element in the lithium-containing first transition metal oxide in the first film layer is beneficial to improve the cycle performance and storage performance of the battery cell, but the sodium element doping amount exceeding a certain degree will cause the increase of the internal resistance of the battery.

[0198] The technical effects of the transition metal doping in the first transition metal oxide in the first film layer are investigated as follows.

[0199] Example 7

[0200] Other than Example 1, the only difference is that the positive active material of the lower layer slurry is Li 0.995 Na 0.005 Ni 0.55 Co 0.07 Mn 0.372 Ti 0.008 O2, the volume particle size Dv50 is 4.0 μm.

[0201] Example 8

[0202] Other than Example 1, the only difference is that the positive active material of the lower layer slurry is Li 0.995 Na 0.005 Ni 0.55 Co 0.07 Mn 0.376 Ti 0.004 O2, the volume particle size Dv50 is 3.9 μm.

[0203] Example 9

[0204] Other than Example 1, the only difference is that the positive active material of the lower layer slurry is Li 0.995 Na 0.005 Ni 0.55 Co 0.07 Mn 0.378 Ti 0.002 O2, the volume particle size Dv50 is 3.7 μm.

[0205] The content of the doping elements in the first transition metal oxides of Example 1, Examples 7 to 9 is recorded in Table 2, and the battery performance test results are also recorded in Table 2.

[0206] Table 2

[0207] Comparing the data of Example 1, Examples 7 to 9, it can be seen that the doping of transition metals is beneficial to improve the cycle performance of the battery, but the doping amount exceeding a certain degree will also cause the increase of the internal resistance of the battery.

[0208] The following investigates the effect of the addition of lithium-containing phosphate on the battery monomer.

[0209] Example 10

[0210] Other than Example 1, the only difference is that the positive active material Li 0.995 Na 0.005 Ni 0.55 Co 0.07 Mn 0.38 O2, acetylene black, positive electrode binder PVDF, carbon nanotubes, the mass ratio is 97:0.5:2:0.5.

[0211] Example 11

[0212] Other than Example 1, the only difference is that in the lower layer slurry, the positive active material Li 0.995 Na 0.005 Ni 0.55 Co 0.07 Mn 0.38 O2, LiFePO4 positive electrode additive, acetylene black, positive electrode binder PVDF, carbon nanotubes, the mass ratio is 92:5:0.5:2:0.5.

[0213] Example 12

[0214] Other than Example 1, the only difference is that:

[0215] The positive active material Li 0.995 Na 0.005 Ni 0.55 Co 0.07 Mn 0.38 O2, acetylene black, positive electrode binder PVDF, carbon nanotubes, the mass ratio is 97:0.5:2:0.5;

[0216] The positive active material LiNi 0.55 Co 0.16 Mn0.29 O2, acetylene black, positive electrode binder PVDF, carbon nanotubes, and the mass ratio is 97:0.5:2:0.5.

[0217] The lithium-containing phosphate content and battery performance test results are recorded in Table 3.

[0218] The battery cells of Examples 1, 10 to 12 were subjected to low-temperature 0°C 10% SOC DCR testing: in a constant-temperature environment at 25°C, the battery cell was charged at 0.5C constant current to the upper limit voltage 4.4V, and then charged at constant voltage at the upper limit voltage 4.4V to the current ≤0.05C, and rested for 5min; the battery was discharged at 1C constant current to the lower limit voltage 2.5V and the discharge capacity Cn was recorded, and rested for 5min; 0.9Cn capacity was discharged at 0.33C to adjust the battery to 10% SOC, and rested for 5min; the battery was placed in a 0°C environment and rested for 2h, and the voltage V3 at the end of the resting period was recorded, then discharged at 0.36C for 30s, and the voltage at the end of the discharge was recorded as V4, and the 0°C discharge DCR=(V3-V4) / 0.36C. The smaller the DCR value, the stronger the low-temperature low-SOC discharge capability.

[0219] Table 3

[0220] According to the data in Table 3, it can be seen that the low-temperature low-SOC discharge capability is poor without lithium-containing phosphate, and the low-temperature SOC discharge capability can be significantly improved after adding lithium-containing phosphate; and adjusting the distribution of lithium-containing phosphate in the two film layers can further improve the discharge capability, for example, comparing Example 1 and Example 10, it can be found that when the lithium-containing phosphate is arranged more in the second film layer, the low-temperature 0°C 10% SOC discharge DCR can be better reduced, and the low-temperature SOC discharge capability can be improved.

[0221] In addition, however, when the lithium-containing phosphate content is too high, the cycle performance will be affected, as shown by the comparison between Example 1 and Example 11, because the lithium-containing phosphate material has poor high-pressure resistance, resulting in deterioration of the cycle performance of the battery cell.

[0222] Example 13

[0223] The other aspects are the same as Example 1, except that in the preparation process of the positive electrode sheet, the lower layer slurry and the upper layer slurry are uniformly coated on the positive electrode current collector at the same time, wherein the coating amount of the lower layer slurry is 40mg / 1540.25mm 2 , and the coating amount of the upper layer slurry is 160mg / 1540.25mm 2 .f1 / f2=0.25.

[0224] Example 14

[0225] The other is the same as Example 1, except that the positive electrode sheet is prepared by simultaneously uniformly coating the positive current collector with the lower slurry and the upper slurry, wherein the coating amount of the lower slurry is 320 mg / 1540.25 mm 2 The coating amount of the upper slurry is 80 mg / 1540.25 mm 2 f1 / f2 = 4.

[0226] Example 15

[0227] The other is the same as Example 1, except that the positive electrode sheet is prepared by simultaneously uniformly coating the positive current collector with the lower slurry and the upper slurry, wherein the coating amount of the lower slurry is 48 mg / 1540.25 mm 2 The coating amount of the upper slurry is 136 mg / 1540.25 mm 2 f1 / f2 = 1 / 3.

[0228] The test results of the battery performance of the battery cells of the above examples are recorded in Table 4.

[0229] Table 4

[0230] The coating amount of the second film layer in Example 15 is too small to approach the separator side high Mn material, which deteriorates Mn elution and cycle performance.

[0231] The following examines the effects of the doping elements in the first film layer and the second film layer on the battery performance.

[0232] Example 16

[0233] The other is the same as Example 1, except that the positive active material of the upper slurry is Li 0.998 Na 0.002 Ni 0.55 Co 0.16 Mn 0.29 O2.

[0234] Example 17

[0235] The other is the same as Example 1, except that the positive active material of the upper slurry is Li 0.992 Na 0.008 Ni 0.55 Co 0.16 Mn 0.29 O2.

[0236] Example 18

[0237] The other is the same as Example 3, except that the positive active material of the lower slurry is LiNi 0.55 Co 0.07 Mn 0.377 Ti 0.003O2, the positive active material of the upper slurry is Li 0.995 Na 0.005 Ni 0.72 Co 0.07 Mn 0.208 Ti 0.002 O2, the volume particle size Dv50 is 3.2 μm.

[0238] Example 19

[0239] Other than Example 3, the only difference is that the positive active material of the lower slurry is LiNi 0.55 Co 0.07 Mn 0.377 Ti 0.003 O2, the positive active material of the upper slurry is Li 0.995 Na 0.005 Ni 0.60 Co 0.16 Mn 0.236 Ti 0.004 O2, the volume particle size Dv50 is 2.9 μm.

[0240] The doping element content in the first and second film layers and the battery performance test results are recorded in Table 5.

[0241] Table 5

[0242] Comparing the data of Examples 16 to 19, it can be seen that when the doping element content at the lithium site in the positive active material in the first film layer located in the lower layer is greater than the doping element content at the lithium site in the positive active material in the second film layer located in the upper layer, or when the doping element content at the transition metal site in the positive active material in the first film layer located in the lower layer is greater than the doping element content at the transition metal site in the positive active material in the second film layer located in the upper layer, it is more beneficial to improve the cycle performance of the battery monomer and control the battery internal resistance. This is because in the first film layer located in the lower layer, the manganese element content in the first transition metal oxide containing lithium is high, and more lithium site doping or transition metal site doping can improve the structural stability thereof, thereby reducing the dissolution of manganese element therein, so as to better improve the cycle performance of the battery monomer and control the growth of the battery internal resistance.

[0243] Although the present application has been described with reference to the preferred embodiments, various modifications can be made to it without departing from the scope of the application, and equivalent parts can be substituted for the parts thereof. In particular, the technical features mentioned in each embodiment can be combined in any manner as long as there is no structural conflict. 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 comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive film layer disposed on at least one side of the positive current collector, wherein, The positive electrode film layer comprises: a first film layer disposed on at least one side of the positive electrode current collector, the first film layer comprising a first positive electrode active material, the first positive electrode active material comprising a lithium-containing first transition metal oxide, the lithium-containing first transition metal oxide comprising lithium elements, nickel elements, cobalt elements, manganese elements, and first doping elements, the mass content of manganese elements in the lithium-containing first transition metal oxide being a1; a second film layer disposed on a side of the first film layer away from the positive electrode current collector, the second film layer comprising a second positive electrode active material, the second positive electrode active material comprising a lithium-containing second transition metal oxide, the lithium-containing second transition metal oxide comprising lithium elements, nickel elements, cobalt elements, manganese elements, and optional second doping elements, the mass content of manganese elements in the lithium-containing second transition metal oxide being a2, a1>a2; The first doping elements and the second doping elements each independently comprise one or more elements of Na, K, Be, Mg, Ca, Group IIIA, Group IB, Group IIB, Group IIIB, Group IVB, Group VB, Group VIB, and Group VIII.

2. The battery cell of claim 1, wherein, The first doping elements and the second doping elements each independently comprise first metal doping elements, the first metal doping elements each independently comprising one or more elements of Na, K, Be, Mg, and Ca.

3. The battery cell of claim 2, wherein, The first metal doping elements each independently comprise one or more elements of Na, K, and Mg, further optionally comprising Na and / or Mg.

4. The battery cell of claim 2 or 3, wherein, In the lithium-containing first transition metal oxide, the mass ratio of the first metal doping elements to the lithium elements is b1; in the lithium-containing second transition metal oxide, the mass ratio of the first metal doping elements to the lithium elements is b2, b1>b2.

5. The battery cell of claim 4, wherein, 39300 ppm≥b1>0 ppm, optionally 26300 ppm≥b1≥9900 ppm.

6. The battery cell of claim 4 or 5, wherein, 26300 ppm≥b2≥0 ppm.

7. The battery cell of any one of claims 1 to 6, wherein, The first doping elements and the second doping elements each independently further comprise second metal doping elements, the second metal doping elements each independently comprising one or more elements of Group IIIA, Group IB, Group IIB, Group IIIB, Group IVB, Group VB, Group VIB, and Group VIII.

8. The battery cell of claim 7, wherein, The second metal doping elements each independently comprise one or more elements of Al, Ti, W, Zr, Sr, Cr, Fe, Zn, Cu, Mo, V, Ce, Nb, Sb, Ta, Ge, Nb, Sc, and Y, optionally one or more elements of Ti, W, Zr, Sr, Cr, Fe, Zn, Cu, Mo, V, Nb, Sb, Ta, Y, further optionally one or more elements of Ti, Mo, Nb, Sb, Ta.

9. The battery cell of claim 7 or 8, wherein, The mass of the second metal doping element in the lithium-containing first transition metal oxide accounts for c1 in the total mass of nickel element, cobalt element, manganese element and the second metal doping element; the mass of the second metal doping element in the lithium-containing second transition metal oxide accounts for c2 in the total mass of nickel element, cobalt element, manganese element and the second metal doping element, and c1>c2.

10. The battery cell of any one of claims 7-9, wherein, The mass content of the second metal doping element in the lithium-containing first transition metal oxide is 1700 ppm to 6700 ppm, and optionally 1700 ppm to 3400 ppm; the mass content of the second metal doping element in the lithium-containing second transition metal oxide is 0 ppm to 3400 ppm.

11. The battery cell of any one of claims 1 to 9, wherein, In the lithium-containing first transition metal oxide, the molar content of the manganese element in the nickel element, the cobalt element and the manganese element is 0.05:1-0.4:1; in the lithium-containing second transition metal oxide, the molar content of the manganese element in the nickel element, the cobalt element and the manganese element is 0.02:1-0.3:

1.

12. The battery cell of any one of claims 1-11, wherein, In the same cross section, the cross-sectional area of the first positive electrode active material in the first film layer accounts for d1, and the cross-sectional area of the second positive electrode active material in the second film layer accounts for d2, and d1 13. The battery cell of any one of claims 1-12, wherein, The first positive electrode active material further comprises a first lithium-containing phosphate, and / or the second positive electrode active material further comprises a second lithium-containing phosphate, and the first lithium-containing phosphate and the second lithium-containing phosphate each independently comprise one or more of lithium iron phosphate and its modified material, lithium manganese iron phosphate and its modified material.

14. The battery cell of claim 13, wherein, The mass content of the first lithium-containing phosphate in the first positive electrode active material is e1, the mass content of the second lithium-containing phosphate in the second positive electrode active material is e2, and e1≤e2, and optionally 0≤(e1+e2)≤8.

15. The battery cell of claim 14, wherein, 0≤e1≤4wt%; 0≤e2≤5wt%.

16. The battery cell of any one of claims 1-15, wherein, The thickness of the first film layer is f1, and the thickness of the second film layer is f2, and 0.25≤f1 / f2≤4.

17. The battery cell of any one of claims 1-16, wherein, The first film layer further comprises a first conductive agent, and the second film layer further comprises a second conductive agent, the mass content of the first conductive agent in the first film layer is g1, and the mass content of the second conductive agent in the second film layer is g2, and g1>g2.

18. The battery cell of claim 17, wherein, The first conductive agent and the second conductive agent each independently comprise one or more of super-conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers, and optionally the first conductive agent and the second conductive agent each independently comprise carbon nanotubes.

19. The battery cell of any one of claims 1-18, wherein, The charging voltage of the battery cell is 4.25V to 4.5V.

20. The battery cell of any one of claims 1-19, wherein, The coating weight CW of the positive electrode film layer satisfies: 100 mg / 1540.25 mm 2 ≤ CW≤ 500 mg / 1540.25 mm 2 .

21. A battery device comprising a plurality of battery cells, wherein, The battery cell comprises the battery cell of any one of claims 1 to 20.

22. An electrically powered device comprising a battery cell or battery device, wherein, The battery cell comprises the battery cell of any one of claims 1 to 20, and the battery device comprises the battery device of claim 21.

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