Battery monomer, battery device and electric device

Abstract

The invention provides a battery monomer, a battery device and a power utilization device. The single battery comprises a shell and an electrode assembly located in the shell, the electrode assembly comprises a positive pole piece, a negative pole piece and an isolating membrane located between the positive pole piece and the negative pole piece, a positive active material comprises nickel-containing lithium transition metal oxide and lithium-containing phosphate, and a negative active material comprises nickel-containing lithium transition metal oxide and lithium-containing phosphate. The battery cell is configured to have a discharge gram capacity of 145 mAh / g to 210 mAh / g when discharged from 4.3 V to 2.5 V at a rate of 0.33 C; the shell is provided with two first side walls parallel in the first direction and two second side walls parallel in the second direction, the first direction is perpendicular to the second direction, the area of the first side walls is larger than that of the second side walls, and the thickness of the first side walls ranges from 0.1 mm to 0.8 mm.

Description

Technical Field

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

[0002] In recent years, the application of electric vehicles has experienced explosive growth. At the same time, it is also facing key issues such as range anxiety, long charging time, and safety performance, which put forward higher requirements for battery cell energy density, power, cycle stability, safety performance and other indicators. Among them, power batteries need to solve the pain point of range, and the solution mainly lies in improving energy density. Summary of the invention

[0003] The present application provides a battery cell, a battery device and an electrical device to improve the energy density of the battery device.

[0004] The first aspect of the present application provides a battery cell, which includes a shell and an electrode assembly located inside the shell, the electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator located between the positive electrode plate and the negative electrode plate, wherein the negative electrode plate includes a negative electrode collector and a negative electrode active layer arranged on at least one side of the negative electrode collector, the negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes graphite; the positive electrode plate includes a positive electrode collector and a positive electrode active layer arranged on at least one side of the positive electrode collector, the positive electrode active layer includes a positive electrode active material, and the positive electrode active material includes a nickel-containing lithium transition metal oxide and a lithium-containing phosphate, and the battery cell is configured to discharge from 4.3V to 2.5V at a rate of 0.33C with a discharge capacity of 145mAh / g-210mAh / g; the shell has two first side walls parallel to a first direction and two second side walls parallel to a second direction, the first direction and the second direction are perpendicularly arranged, the area of ​​the first side wall is greater than the area of ​​the second side wall, and the thickness of the first side wall is 0.1mm-0.8mm.

[0005] Nickel-containing lithium transition metal oxides generally have a higher energy density, and the energy density will increase accordingly with the increase of nickel content; lithium-containing phosphates have good structural stability and cycle performance and cost advantages. The two materials are used together as active materials with complementary advantages, which is conducive to obtaining battery cells with higher energy density, better safety performance and higher cycle stability at low cost.

[0006] In a battery cell including a nickel-containing lithium transition metal oxide and a lithium phosphate positive electrode active material, when the battery cell is discharged from 4.3V to 2.5V at a rate of 0.33C, the discharge gram capacity is 145mAh / g-210mAh / g, and the energy density of the battery cell is high. At this time, the mass content of the nickel-containing lithium transition metal oxide in the corresponding positive electrode active material is relatively high or the mass content of the nickel element in the positive electrode active material is relatively high. Correspondingly, at this time, the structural stability of the nickel lithium transition metal oxide is insufficient, and the problem of nickel dissolution is prone to occur, which leads to a side reaction between the positive electrode active material and the electrolyte, a greater risk of gas production, and an increased risk of swelling of the first side wall of the battery cell; at this time, by using the wall thickness of the first side wall within a reasonable thickness range, the risk of large-surface swelling of the battery cell can be effectively reduced, and the battery energy density will not be affected by excessive wall thickness. Therefore, by combining the above-mentioned discharge gram capacity and the thickness of the first side wall, the energy density can be improved as much as possible on the basis of low cost, and the safety of the high energy density battery cell can be improved.

[0007] In any embodiment of the first aspect, the battery cell is configured to have a discharge capacity of 150 mAh / g to 195 mAh / g when discharged from 4.3 V to 2.5 V at a rate of 0.33 C.

[0008] In any embodiment of the first aspect, in the above-mentioned positive electrode active material, the mass content of lithium phosphate is 50%-90%, and can be optionally 50%-70%, which can further improve the cycle life and maintain a higher discharge gram capacity.

[0009] In any embodiment of the first aspect, the above-mentioned nickel-containing lithium transition metal oxide includes manganese and cobalt elements. In the nickel-containing lithium transition metal oxide, the molar amount of nickel element accounts for 50%-95% of the total molar amount of nickel, cobalt and manganese elements, and can be optionally 70%-95%, and further optionally 80%-95%.

[0010] In any embodiment of the first aspect, the thickness of the first side wall of the battery cell is 0.4 mm-0.8 mm, and can be optionally 0.6 mm-0.8 mm.

[0011] In any embodiment of the first aspect, the nickel-containing lithium transition metal oxide includes one or more lithium-containing nickel-cobalt-manganese oxides.

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

[0013] In any embodiment of the first aspect, the lithium-containing nickel cobalt manganese oxide includes one or more of Zr, Al or B.

[0014] In any embodiment of the first aspect, the mass content of elements in the lithium-containing nickel-cobalt-manganese oxide satisfies at least one of the following: Zr content of 1000ppm to 3000ppm, Al content of 100ppm to 1000ppm, and B content of 50ppm to 300ppm. The above elements may be present in the lithium-containing nickel-cobalt-manganese oxide as dopants or coating materials.

[0015] In any embodiment of the first aspect, the lithium-containing phosphate includes Mn element and Fe element, and the molar amount of Mn element in the lithium-containing phosphate accounts for 20%-80% of the total molar amount of Mn element and Fe element, which can be optionally 30%-70%, and further optionally 50%-70%, which is beneficial to the improvement of volume energy density, and as the proportion of Mn molar amount increases, the platform voltage of the lithium-containing phosphate increases, thereby improving the energy density of the battery cell.

[0016] In any embodiment of the first aspect, the lithium-containing phosphate includes lithium iron manganese phosphate, and the lithium iron manganese phosphate includes one or more of Al, B, Ca, Cr, Cu, K, Mg, Na, P, Si, Ti, V or Zn elements.

[0017] In any embodiment of the first aspect, the lithium manganese iron phosphate contains one or more of Al, Ca, Na, Ti or V elements.

[0018] In any embodiment of the first aspect, the mass content of the elements in the lithium manganese iron phosphate satisfies at least one of the following: the mass content of Al is 100ppm to 1000ppm, the mass content of Ca is 50ppm to 300ppm, the mass content of Na is 50ppm to 300ppm, the mass content of Ti is 100ppm to 1000ppm, and the mass content of V is 1000ppm to 3000ppm. The above elements may be present in the lithium manganese iron phosphate as dopants or coating materials.

[0019] In any embodiment of the first aspect, the positive electrode active layer of the battery cell contains lithium iron manganese phosphate and lithium-containing nickel cobalt manganese oxide, and the positive electrode active material contains one or more of Al, B, Ca, Na, Sr, Ti, V, Y or Zr elements, and based on the total mass of the positive electrode active material, the mass content of each element satisfies: Al: 0.005%-0.1%; Ca: 0.0001%-0.02%; Na: 0.005%-0.06%; Ti: 0.005%-0.15%; V: 0.0001%-0.3%; Zr: 0.005%-0.2%; B: 0.01%-0.1%.

[0020] In any embodiment of the first aspect, the thickness of the second side wall of the shell is 0.8 mm-1.2 mm, and the thickness of the bottom wall of the shell is 1 mm-1.5 mm.

[0021] In any embodiment of the first aspect, the positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer, the first positive electrode active layer is arranged close to the positive electrode current collector, the second positive electrode active layer is arranged on the side of the first positive electrode active layer away from the positive electrode current collector, and the nickel-containing lithium transition metal oxide and the lithium-containing phosphate are independently arranged in the first positive electrode active layer and / or in the second positive electrode active layer. The use of a multi-layer coating method can further improve the electrical performance, reduce the side reaction of the electrolyte and the positive electrode material, or improve the power performance of the battery cell by reducing the internal resistance.

[0022] In any embodiment of the first aspect, the mass ratio of the positive electrode active layer per unit area of ​​the single layer to the positive electrode current collector is (0.15-10): 1, and can be optionally (4.5-5.6): 1. The positive electrode sheet with a mass ratio within the above range has good processability and a lightweight positive electrode sheet setting, thereby fully improving the energy density.

[0023] In any embodiment of the first aspect, the negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer, the first negative electrode active layer is arranged close to the negative electrode current collector, the second negative electrode active layer is arranged on the side of the first negative electrode active layer away from the negative electrode current collector, and the average particle size of the graphite particles arranged in the first negative electrode active layer is greater than the average particle size of the graphite particles arranged in the second negative electrode active layer; optionally, the average particle size of the graphite particles arranged in the first negative electrode active layer is 12μm-25μm, and the average particle size of the graphite particles arranged in the second negative electrode active layer is 5μm-12μm.

[0024] In any embodiment of the first aspect, an explosion-proof valve is provided on the second side wall of the shell, and the area of ​​the explosion-proof valve is 8%-20% of the area of ​​the second side wall, and can be optionally 12%-16%, which is conducive to rapid pressure release and thus can improve the safety of high energy density battery cells. In any embodiment of the first aspect, the battery cell includes at least one top cover assembly, the top cover assembly is connected to the first side wall and the second side wall by welding; each top cover assembly includes a positive terminal and a negative terminal, the electrode assembly includes a stacked positive electrode ear and a negative electrode ear, the positive electrode ear is welded to the positive terminal, and the negative electrode ear is welded to the negative terminal, wherein: The weld area between the positive electrode ear and the single positive terminal is set to 0.5mm 2 / Ah-1mm 2 / Ah, and / or, the weld area between the negative electrode ear and the single negative terminal is set to 0.5mm2 / Ah-1mm 2 / Ah.

[0026] In any embodiment of the first aspect, the liquid injection coefficient of the battery cell is 1.8g / Ah-3.5g / Ah, and can be 1.9g / Ah-3.1g / Ah. The liquid injection coefficient within the above range can improve the wettability of the battery cell while inhibiting side reactions and reducing cycle gas production, thereby increasing the cycle life of the battery cell.

[0027] A second aspect of the present application provides a battery device, including a battery cell, wherein the battery cell includes any one of the battery cells of the first aspect, and the battery device includes a battery module, a battery pack or an energy storage device.

[0028] A third aspect of the present application provides an electrical device, comprising any one of the battery cells of the first aspect, or the battery device of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0030] Figure 1 It is a schematic diagram of a battery assembly according to one embodiment of the present application.

[0031] Figure 2 It is a schematic diagram of a shell according to one embodiment of the present application.

[0032] Figure 3 It is an exploded view of a battery cell according to one embodiment of the present application.

[0033] Figure 4 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0034] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0035] Figure 6 Schematic diagram of an electrical device using a battery pack according to an embodiment of the present application as a power source.

[0036] In the drawings, the drawings are not drawn to scale.

[0037] Description of reference numerals:

[0038] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly; 11 first side wall; 12 second side wall; 13 explosion-proof valve. DETAILED DESCRIPTION

[0039] The following detailed description and drawings of the embodiments of the present application are used to illustrate the principles of the present application, but cannot be used to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0040] Hereinafter, the battery cells, battery devices and power devices of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0041] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, 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 the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0043] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0044] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0045] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or comprised.

[0046] If not otherwise specified, in this application, the term "or" is inclusive. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0047] [Battery Cell]

[0048] The structural design of a battery cell and the physical and chemical properties of its electrode assembly have an important influence on the key performance indicators of the battery cell. In order to improve the energy density of a battery cell, the first embodiment of the present application provides a battery cell, which includes a shell and an electrode assembly located inside the shell, the electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator located between the positive electrode plate and the negative electrode plate, wherein the negative electrode plate includes a negative electrode current collector and a negative electrode active layer disposed on at least one side of the negative electrode current collector, the negative electrode active layer includes a negative electrode active material, the negative electrode active material includes graphite, the positive electrode plate includes a positive electrode current collector and a positive electrode active layer disposed on at least one side of the positive electrode current collector, and the positive electrode current collector includes a positive electrode active layer disposed on at least one side of the positive electrode current collector. The active layer includes a positive electrode active material, which includes a nickel-containing lithium transition metal oxide and a lithium-containing phosphate. The battery cell is configured to have a discharge capacity of 145mAh / g-210mAh / g when discharged from 4.3V to 2.5V at a rate of 0.33C; the shell has two first side walls 11 parallel to a first direction and two second side walls 12 parallel to a second direction, the first direction and the second direction are vertically arranged, the area of ​​the first side wall 11 is greater than the area of ​​the second side wall 12, and the thickness of the first side wall 11 is 0.1mm-0.8mm.

[0049] During the battery charging and discharging process, active ions (such as lithium ions) are inserted and removed back and forth between the positive electrode and the negative electrode. The separator is set between the positive electrode and the negative electrode, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing the active ions to pass through. For example, Figure 1 The electrode assembly 52 is a rectangular parallelepiped structure as an example.

[0050] Nickel-containing lithium transition metal oxides generally have a higher energy density, and the energy density will increase accordingly with the increase of nickel content; lithium-containing phosphates have good structural stability and cycle performance and cost advantages. The two materials are used together as active materials with complementary advantages, which is conducive to obtaining battery cells with higher energy density, better safety performance and higher cycle stability at low cost.

[0051] In a battery cell including a nickel-containing lithium transition metal oxide and a lithium phosphate positive electrode active material, when the battery cell is configured to discharge from 4.3V to 2.5V at a rate of 0.33C, the discharge gram capacity is 145mAh / g-210mAh / g, and the energy density of the battery cell is high. At this time, the mass content of the nickel-containing lithium transition metal oxide in the corresponding positive electrode active material is relatively high or the mass content of the nickel element in the positive electrode active material is relatively high. Correspondingly, the structural stability of the nickel lithium transition metal oxide is insufficient, and the problem of nickel dissolution is prone to occur, which leads to a side reaction between the positive electrode active material and the electrolyte, a greater risk of gas production, and an increased risk of swelling of the first side wall of the battery cell; at this time, by using the wall thickness of the first side wall in a reasonable thickness range, the risk of swelling of the large surface (i.e., the first side wall) of the battery cell can be effectively reduced, and the battery energy density will not be affected by excessive wall thickness. Therefore, by combining the above-mentioned discharge gram capacity and the thickness of the first side wall, the energy density can be improved as much as possible on the basis of low cost, and the safety of the high energy density battery cell can be improved.

[0052] For ease of understanding, Figure 2 A schematic structural diagram of a shell 51 of an embodiment is shown. The shell is rectangular. The shell 51 may include a bottom plate and two pairs of side plates arranged perpendicular to the bottom plate. A pair of side plates with a larger area constitutes a first side wall 11, and another pair of side plates with a smaller area perpendicular to the side plates constitute a second side wall 12. The thickness of the first side wall 11 with a larger area is 0.1mm-0.8mm (for example, 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm or 0.8mm). When the wall thickness is large, the capacity of the battery cell under low temperature conditions can be improved; in addition, as the wall thickness decreases, the volume energy density of the battery cell can be effectively improved. Moreover, the thickness of the first side wall 11 can meet the safety requirements of battery cells with high energy density.

[0053] In some embodiments, the battery cell is configured to have a discharge capacity of 150 mAh / g to 195 mAh / g when discharged from 4.3 V to 2.5 V at a rate of 0.33 C, which can further improve the cycle stability while maintaining a high energy density.

[0054] The method for determining the elements contained in the above positive electrode active material is as follows:

[0055] The positive electrode sheet of the battery cell was fully cleaned with dimethyl carbonate (DMC), and the positive electrode sheet was dried and calcined to collect the positive electrode active material in the positive electrode active layer. The positive electrode active material was tested by inductively coupled plasma atomic emission spectrometry (ICP-OES).

[0056] The above discharge gram capacity is determined as follows:

[0057] Place the battery cell at room temperature, charge it to 4.3V at a constant current of 0.33C, and then charge it to 0.05C at a constant voltage. Record the discharge capacity C0 (unit: mAh) of the battery cell when it is discharged from 4.3V to 2.5V at a constant current of 0.33C, where C is the nominal capacity of the battery cell.

[0058] The positive electrode plates of the battery cells were fully cleaned with dimethyl carbonate (DMC), and the positive electrode plates were dried and calcined, and the positive electrode materials in the positive electrode active layer were collected and weighed, and recorded as m (unit: g); discharge gram capacity = C0 / m.

[0059] In some embodiments, the mass content of lithium-containing phosphate in the positive electrode active material of the battery cell is 50%-90%, and can be optionally 50%-70%. The lithium-containing phosphate is combined with the nickel-containing lithium transition metal oxide within the above mass content range, and the advantages of the two are fully utilized, so that the energy density and cycle performance of the battery cell are fully improved. In some embodiments, the nickel-containing lithium transition metal oxide includes manganese and cobalt elements. In the nickel-containing lithium transition metal oxide, the molar amount of nickel element accounts for 50%-95% of the total molar amount of nickel, cobalt and manganese elements, which can be optionally 70%-95%, and further optionally 80%-95%. The nickel element helps to increase the gram capacity of the positive electrode active material and plays a role in improving the energy density of the battery cell. In some embodiments, when the molar amount of the nickel element accounts for 80%-95%, the wall thickness of the first side wall can be selected to be 0.6mm-0.8mm to improve the safety performance of the battery cell.

[0060] In some embodiments, the nickel-containing lithium transition metal oxide includes one or more of lithium-containing nickel cobalt manganese oxides.

[0061] Examples of nickel-containing lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) and at least one of its modified compounds, etc. Examples of lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0062] In some embodiments, the nickel-containing lithium transition metal oxide includes a lithium-containing nickel-cobalt-manganese oxide, and the lithium-containing nickel-cobalt-manganese oxide includes one or more of the elements Zr, Al, B, Fe, Ca, Sr, Ti, V or Y, and the above elements may be present in the lithium-containing nickel-cobalt-manganese oxide as dopants or coating materials.

[0063] In some embodiments, the lithium-containing nickel-cobalt-manganese oxide includes one or more of Zr, Al, B, or Fe. 4+ Can occupy Ni 2+ Bit and Li + The strong chemical bond between Zr-O is conducive to stabilizing the crystal structure of layered materials and plays a supporting role in the process of lithium extraction / insertion. 3+The transition metal layer dissolved in the lithium-containing nickel cobalt manganese oxide in the form of a solid solution can effectively improve the capacity retention during the cycle process. Boron anion doping can relieve the strain of the lithium-containing nickel cobalt manganese oxide during the lithiation / delithiation process and improve the cycle stability and life.

[0064] In order to give full play to the role of each element, in some embodiments, the mass content of elements in the lithium-containing nickel-cobalt-manganese oxide satisfies at least one of the following: Zr content 1000ppm~3000ppm, Al content 100ppm~1000ppm, B element 50ppm~300ppm.

[0065] In some embodiments, the lithium-containing phosphate includes Mn and Fe, and the molar amount of the Mn element in the lithium-containing phosphate is 20%-80% of the total molar amount of the Mn and Fe elements, optionally 30%-70%, and further optionally 50%-70%. The molar ratio of the Mn element is within the above range, and as the molar ratio of Mn increases, the platform voltage of the lithium-containing phosphate increases, thereby improving the energy density of the battery cell.

[0066] In some embodiments, the lithium-containing phosphate includes lithium iron manganese phosphate, which includes one or more of Al, B, Ca, Cr, Cu, K, Mg, Na, P, Si, Ti, V or Zn elements. Optionally, the lithium iron manganese phosphate includes one or more of Al, Ca, Na, Ti or V elements, and the above elements can be present in the lithium iron manganese phosphate as dopants or coating materials.

[0067] Doping one or more of the above elements into the lithium manganese iron phosphate cathode material promotes Li by introducing lattice vacancies or changing the atomic bond length. + The lattice migration can improve the conductivity of the material. For example, Mg doping can improve the conductivity and improve the structural stability; Al doping can improve the conductivity of the material and help suppress the phase change under high voltage or deep discharge; Ca doping can improve the cycle stability; Na doping can promote the ion diffusion rate and improve the specific capacity; Ti doping can provide additional Li + sites, improve the specific capacity, and help reduce the dissolution of Mn during the cycle; V doping can improve the conductivity and electrochemical activity, and improve the charge and discharge performance.

[0068] In order to give full play to the role of each element, further optionally, in the lithium manganese iron phosphate, the mass content of the elements satisfies at least one of the following: the mass content of Al is 100ppm~1000ppm, the mass content of Ca is 50ppm~300ppm, the mass content of Na is 50ppm~300ppm, the mass content of Ti is 100ppm~1000ppm, and the mass content of V is 1000ppm~3000ppm.

[0069] In some embodiments, the positive electrode active layer contains lithium manganese iron phosphate and lithium-containing nickel cobalt manganese oxide, and the positive electrode active material contains one or more of Al, B, Ca, Na, Sr, Ti, V, Y or Zr elements, and in order to give full play to the role of each element, based on the total mass of the positive electrode active material, the mass content of each element satisfies: Al: 0.005%-0.1%; Ca: 0.0001%-0.02%; Na: 0.005%-0.06%; Ti: 0.005%-0.15%; V: 0.0001%-0.3%; Zr: 0.005%-0.2%; B: 0.01%-0.1%.

[0070] The content of the above elements can refer to the determination method of the elements contained in the above positive electrode active material.

[0071] In some embodiments, the positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer, the first positive electrode active layer is arranged close to the positive electrode current collector, the second positive electrode active layer is arranged on the side of the first positive electrode active layer away from the positive electrode current collector, and the nickel-containing lithium transition metal oxide and the lithium-containing phosphate are each independently arranged in the first positive electrode active layer and / or in the second positive electrode active layer.

[0072] The use of multi-layer coating can further improve the electrical performance:

[0073] On the one hand, there is relatively more lattice water in lithium-containing phosphates, and direct contact with the electrolyte may cause side reactions and affect the cycle life of the battery cells. Therefore, when the positive electrode active material in the first positive electrode active layer is mainly lithium-containing phosphate and the positive electrode active material in the second positive electrode active layer is mainly nickel-containing lithium transition metal oxide, the second positive electrode active layer establishes physical isolation between the lithium-containing phosphate and the electrolyte, which can effectively reduce the probability of side reactions of the electrolyte.

[0074] For example, the positive electrode active material in the first positive electrode active layer is a lithium-containing phosphate, and the positive electrode active material in the second positive electrode active layer is a nickel-containing lithium transition metal oxide; or the positive electrode active material in the first positive electrode active layer is a lithium-containing phosphate, and the positive electrode active material in the second positive electrode active layer is a nickel-containing lithium transition metal oxide and a small amount of lithium-containing phosphate; or the positive electrode active material in the first positive electrode active layer is a lithium-containing phosphate and a small amount of nickel-containing lithium transition metal oxide.

[0075] On the other hand, the ion mobility and electronic conductivity of lithium-containing phosphates are lower than those of transition metal oxides. When the positive electrode active material of the first positive electrode active layer is mainly nickel-containing lithium transition metal oxide and the positive electrode active material of the second positive electrode active layer is mainly lithium-containing phosphate, the lithium-containing phosphate contacts the electrolyte faster, shortening the ion transmission distance, thereby reducing the internal resistance, which is beneficial to the power increase of the battery cell.

[0076] For example, the positive electrode active material in the first positive electrode active layer is a nickel-containing lithium transition metal oxide, and the positive electrode active material in the second positive electrode active layer is a lithium-containing phosphate; or the positive electrode active material in the first positive electrode active layer is a nickel-containing lithium transition metal oxide and a small amount of lithium-containing phosphate, and the positive electrode active material in the second positive electrode active layer is a lithium-containing phosphate; or the positive electrode active material in the first positive electrode active layer is a nickel-containing lithium transition metal oxide, and the positive electrode active material in the second positive electrode active layer is a lithium-containing phosphate and a small amount of nickel-containing lithium transition metal oxide; or the positive electrode active material in the first positive electrode active layer is a nickel-containing lithium transition metal oxide and a small amount of lithium-containing phosphate, and the positive electrode active material in the second positive electrode active layer is a lithium-containing phosphate and a small amount of nickel-containing lithium transition metal oxide.

[0077] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0078] In some embodiments, the mass ratio of the positive electrode active layer per unit area of ​​a single layer to the positive electrode current collector is (0.15-10): 1, and can be optionally (4.5-5.6): 1. The higher the mass ratio, the more conducive it is to lightweighting the battery cell and improving the energy density; however, if the mass ratio is too high, the mechanical strength of the positive electrode sheet will be affected, making it difficult to process.

[0079] In some embodiments, the positive electrode active layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

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

[0081] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0082] [Negative electrode]

[0083] In some embodiments, the negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer, the first negative electrode active layer is arranged close to the negative electrode current collector, the second negative electrode active layer is arranged on the side of the first negative electrode active layer away from the negative electrode current collector, and the average particle size of the graphite particles arranged in the first negative electrode active layer is greater than the average particle size of the graphite particles arranged in the second negative electrode active layer; optionally, the average particle size of the graphite particles arranged in the first negative electrode active layer is 12μm-25μm, and the average particle size of the graphite particles arranged in the second negative electrode active layer is 5μm-12μm. The small-particle graphite transmission path of the second negative electrode active layer is relatively short, and has excellent kinetics, which can make the internal resistance lower and thus obtain better power performance. However, the small-particle graphite has a large contact area with the electrolyte, which is easy to cause side reactions and affect the cycle life. Therefore, the first negative electrode active layer uses large-particle graphite, which is conducive to delaying the cycle life and further optimizing the cycle life.

[0084] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0085] In some embodiments, the negative electrode film layer may further include a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0086] In some embodiments, the negative electrode film layer may further include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose CMC-Na).

[0088] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0089] [Electrolytes]

[0090] In some embodiments, the battery cell includes an electrolyte, which acts as a conductor of ions between the positive electrode and the negative electrode. The present application does not specifically limit the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0091] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0092] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0093] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0094] In some embodiments, the electrolyte may further include additives. As examples, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0095] [Isolation film]

[0096] In some embodiments, the battery cell further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0097] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0098] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0099] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. For example, Figure 1 The electrode assembly 52 is an example of a battery cell having a square structure.

[0100] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a top cover assembly 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs. The second embodiment of the present application also provides a battery device, including any one of the battery cells provided in the first embodiment above, and the battery device includes a battery module, a battery pack or an energy storage device.

[0101] Since the energy density of the battery cells of the present application is relatively high, in order to further improve the safety of the battery cells during long-term use and to control the effect of wall thickness on the energy density of the battery cells as much as possible, in some embodiments, the thickness of the first side wall 11 of the shell is 0.4mm~0.8mm, and can be optionally 0.6mm~0.8mm.

[0102] The area of ​​the second side wall 12 and the bottom wall of the battery cell shell is relatively small, so the thickness change has little effect on the energy density of the battery cell, but can improve the safety of the battery cell. In some embodiments, the thickness of the second side wall 12 is 0.8mm~1.2mm, and / or the bottom wall thickness of the shell is 1mm~1.5mm.

[0103] In some embodiments, the battery cell housing may be a steel housing, such as a stainless steel housing. The structural strength of the steel housing is relatively high, and the wall thickness may be reduced accordingly. In some embodiments, the wall thickness of the steel housing is 0.1 mm to 0.5 mm. In some embodiments, the battery cell housing may be an aluminum alloy housing. Aluminum alloy has the characteristics of low density and corrosion resistance. Therefore, the aluminum alloy housing has the advantages of light weight, strong corrosion resistance, good heat dissipation, and easy processing. In some embodiments, the wall thickness of the aluminum alloy housing is 0.6 mm to 1.0 mm.

[0104] In some embodiments, Figure 2 As shown, the second side wall of the battery cell housing is provided with an explosion-proof valve 13. Since the battery cell of the present application has a high energy density, in order to further improve the safety of the battery cell, in some embodiments, the area of ​​the explosion-proof valve 13 is 8%-20%, and optionally 12%-16% of the area of ​​the second side wall 12. The area of ​​the explosion-proof valve in the present application is increased relative to the area of ​​the explosion-proof valve of a conventional battery cell, so it is conducive to rapid pressure relief, thereby improving the safety of the battery cell with a high energy density. In some embodiments, the battery cell includes at least one top cover assembly, which is connected to the first side wall and the second side wall by welding; each top cover assembly includes a positive terminal and a negative terminal, and the electrode assembly includes a stacked positive electrode ear and a negative electrode ear, the positive electrode ear is welded to the positive terminal, and the negative electrode ear is welded to the negative terminal, wherein the weld print area between the positive electrode ear and the positive terminal is set to 0.5mm 2 / Ah-1mm 2 / Ah, and / or, the weld area between the negative electrode ear and the negative terminal is set to 0.5mm 2 / Ah-1mm 2 / Ah. Each top cover assembly includes a positive terminal and a negative terminal, which is beneficial to improving the current capacity of the battery cell and reducing the internal temperature rise of the battery cell; The weld print area is designed according to the capacity of the battery cell, so as to better control the internal temperature rise of the battery cell and improve the current carrying capacity of the battery cell; and because the discharge gram capacity of the battery cell of the present application is relatively high, the energy density of the battery cell is relatively high at the same weight, and the corresponding weld print area is relatively large, thereby reducing the internal resistance of the battery and improving the power capacity of the battery cell.

[0105] In some embodiments, the liquid filling coefficient of the battery cell is 1.8 g / Ah-3.5 g / Ah, and can be optionally 1.9 g / Ah-3.1 g / Ah.

[0106] The higher the injection coefficient of the battery cell, the greater the amount of electrolyte. By controlling the injection coefficient, on the one hand, the content of unstable components in the electrolyte (such as cyclic esters and carboxylic acid esters that are not resistant to oxidation solvents) is controlled, thereby inhibiting side reactions, reducing cycle gas production, and improving cycle life; on the other hand, the wettability of the battery cell is improved, so that the electrolyte maintains a high wetting effect on the electrode even after the battery cell has been cycled for a long time, thereby improving the cycle life of the battery cell.

[0107] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0108] In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the thickness direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells may be fixed by fasteners.

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

[0110] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0111] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0112] In addition, the present application also provides an electric device, which includes a battery cell or a battery device provided in the present application. The battery cell or the battery device can be used as a power source for the electric device, or as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

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

[0114] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the power consumption device's requirements for high power and high energy density of battery cells, a battery pack or a battery module can be used.

[0115] [Example]

[0116] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0117] Example 1

[0118] The battery cell preparation process is as follows.

[0119] Positive electrode:

[0120] The positive electrode active layer includes a positive electrode active material, a binder polyvinylidene fluoride, and a conductive agent acetylene black (mass ratio is 96.7:2.3:1). In the positive electrode active material, the mass ratio of the nickel-containing lithium transition metal oxide to the lithium-containing phosphate is 3:7. The chemical formula of the nickel-containing lithium transition metal oxide is Li(Ni 0.9 Co 0.05 Mn 0.05 )O2, the chemical formula of lithium phosphate is Li(Fe 0.5 Mn 0.5 )PO4.

[0121] The other elements in the positive electrode active material are all from lithium transition metal oxides containing nickel. The subscripts of Ni, Co and Mn in the chemical formula are rounded data. Because the content of other elements M is trace or even lower, these elements and their molar numbers are not reflected in the chemical formula. It does not mean that element M has no effect on the performance of the battery cell. In the chemical formula of Li(Ni 0.90 Co 0.05 Mn 0.05 )O2 nickel-containing lithium transition metal oxide, the mass content of each element in element M is: Al: 0.081%, B: 0.091%, Na: 0.0093%, S: 0.082%, Sb: 0.014%, Sr: 0.025%, W: 0.035%; Zr: 0.143%.

[0122] The thickness of the positive electrode current collector aluminum foil is 13 μm, the positive electrode active layer is located on both sides of the aluminum foil, and the mass ratio of the positive electrode active material to the current collector in the positive electrode active layer is 5.19:1.

[0123] There is a conductive primer layer between the positive electrode active layer and the aluminum foil. The conductive primer layer is a film layer formed by mixing the positive electrode conductive agent superconducting carbon, the positive electrode binder polyacrylate and the solvent evenly and then coating it on the surface of the positive electrode current collector and drying it. The thickness is 1μm, the mass content of the positive electrode conductive agent in the positive electrode conductive layer is 50%, and the mass content of the positive electrode binder in the positive electrode conductive layer is 50%. The length of the positive electrode sheet is 592mm.

[0124] The surface density of the positive electrode is 315mg / 1540.25mm 2 .

[0125] Negative electrode:

[0126] The negative electrode active layer includes a negative electrode active material graphite, a conductive agent acetylene black, a binder styrene butadiene rubber and a thickener sodium carboxymethyl cellulose in a ratio of 96:1:2:1. The negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer. The average particle size of the graphite particles arranged in the first negative electrode active layer is 25 μm, and the average particle size of the graphite particles arranged in the second negative electrode active layer is 12 μm.

[0127] The negative electrode current collector is a copper foil of 5 μm, there is a negative electrode conductive layer between the copper foil and the negative electrode active layer, and the conductive primer layer is a film layer formed by mixing the negative electrode conductive agent superconducting carbon, the negative electrode binder styrene-butadiene rubber SBR, the thickener sodium carboxymethyl cellulose (CMC-Na) and the solvent water evenly and then coating it on the surface of the negative electrode current collector and drying it. The thickness is 1 μm, the mass content of the negative electrode conductive agent in the negative electrode conductive layer is 35%, the mass content of the negative electrode binder in the negative electrode conductive layer is 60%, and the mass content of the thickener in the negative electrode conductive layer is 5%.

[0128] The surface density of the negative electrode is 165mg / 1540.25mm 2 .

[0129] The electrolyte includes an organic solvent, a lithium salt and an additive, wherein:

[0130] The organic solvent is a mixture of cyclic carbonate and linear carbonate, the cyclic carbonate is ethylene carbonate (EC), the linear carbonate is dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) mixed in a mass ratio of 13:40:12, and the remaining solvent is EC;

[0131] The lithium salt is lithium hexafluorophosphate (LiPF6) with a concentration of 1.2 mol / L;

[0132] The additive composition is as follows: 2.5 wt% of vinylene carbonate (VC), 1 wt% of fluoroethylene carbonate (FEC), 0.5 wt% of 1,3-propylene sultone (PS), 0.5 wt% of diethylene sulfite (DTD), and 0.5 wt% of lithium difluorophosphate (LiPO2F2).

[0133] Isolation film:

[0134] A polyethylene (PE) film coated with an alumina inorganic coating and a PVDF organic coating was used as the isolation film. The thickness of the polyethylene film was 7 μm. The isolation film was purchased from Zhuogao Technology Co., Ltd.

[0135] Battery cell assembly:

[0136] The electrode assembly includes a stacked positive electrode sheet, a separator, and a negative electrode sheet, wherein the top cover assembly of the electrode assembly includes a positive terminal and a negative terminal, the positive terminal is welded to the positive electrode ear, and the negative terminal is welded to the negative electrode ear, and the weld print area between the positive electrode ear and the positive terminal per unit discharge capacity is 0.8 mm 2 ·Ah -1 ; The weld area between the negative pole ear and the negative terminal per unit discharge capacity is 0.8mm 2 ·Ah -1 .

[0137] The electrode assembly is added to the shell, and the electrolyte is injected after drying. The injection coefficient is 2.9g / Ah. The shell is a square aluminum shell with the following size parameters: length is 600mm, thickness is 19mm, height is 105mm, first side wall thickness is 0.6mm, second side wall thickness is 1mm, bottom wall thickness is 1.2mm, and the explosion-proof valve area on the second side wall accounts for 16%;

[0138] After the processes of packaging, high temperature standing, formation, secondary liquid injection, aging, capacity and the like, a battery cell is obtained.

[0139] [Battery cell performance test]

[0140] Test method for discharge gram capacity:

[0141] The battery cell was placed at room temperature, charged to 4.3V at a constant current of 0.33C, and then charged to 0.05C at a constant voltage, and the discharge capacity C0 (unit: mAh) of the battery cell at a constant current of 0.33C from 4.3V to 2.5V was recorded, where C is the nominal capacity of the battery cell; the positive electrode sheet of the battery cell was fully cleaned with dimethyl carbonate (DMC), and the positive electrode sheet was dried and calcined, and the positive electrode material in the positive active layer was collected and weighed, and recorded as m (unit: g); discharge gram capacity = C0 / m.

[0142] Test method for volume energy density:

[0143] Place the battery cell at room temperature, charge it to 4.3V at a constant current of 0.33C, and then charge it to 0.05C at a constant voltage. Record the discharge capacity A0 (unit: Ah) of the battery cell when it is discharged from 4.3V to 2.5V at a constant current of 0.33C, where C is the nominal capacity of the battery cell. Use a caliper to measure the length, width, and height of the battery cell (generally calculated based on the outer shell size of the battery, excluding the height of the electrode terminals and the insulating film outside the outer shell), and calculate the volume of the single battery V0, in L. The volume energy density of the battery cell VED = (A0 × discharge platform voltage) / V0, in Wh / L.

[0144] Cycle performance test method:

[0145] At room temperature, the battery cell is charged and discharged between 2.5V and 4.3V in a cycle. The specific operation is as follows: charge to 4.3V at 0.33C, then charge at a constant voltage at 4.3V until the current is no higher than 0.05C, let stand for 5 minutes, and then discharge to 2.5V at 1C. The capacity is recorded as C. m (m=1,2,3……), repeat the above operation, the capacity retention rate is expressed as C m / C3 ratio. m When / C3×100%=80%, the corresponding number of cycles is recorded as an examination indicator of the cycle capacity. The more cycles, the better the cycle performance of the battery cell.

[0146] The nickel-containing lithium transition metal oxides and lithium-containing phosphates used in the examples and comparative examples are all conventional materials in the art or are prepared using conventional methods.

[0147] On the basis of Example 1, only the composition of the positive electrode active material is adjusted in Comparative Examples 1 to 3. The rest of the configuration of the positive electrode plate is the same as that in Example 1. The negative electrode plate, isolation membrane, electrolyte and outer packaging shell of the battery cell are the same as those in Example 1. This is to examine the effects of different positive electrode material design schemes on the discharge capacity of the positive electrode plate.

[0148] The specific adjustment conditions are shown in Table 1. The battery cell performance test results of each embodiment are recorded in Table 1.

[0149] Table 1

[0150] It can be seen from the data in Table 1 that the positive electrode active material design of Example 1 can keep the energy density and cycle performance at a high level, making the overall performance of the battery cell more balanced. When the positive electrode active material is basically a lithium-containing phosphate, the discharge gram capacity of the positive electrode plate is low, the energy density of the battery cell is limited, and the cycle performance is not as good as Example 1. Comparative Examples 1 and 3 belong to this type of situation. The discharge gram capacity of the positive electrode plate in the above two comparative examples is less than 145 mAh / g. When the positive electrode active material is basically a high-nickel lithium transition metal oxide, such as Comparative Example 2, the energy density can reach a very high level (for example, higher than 210 mAh / g), which will increase the risk of thermal runaway in the working state of the battery cell. In addition, it will cause the cycle performance of the battery cell to decrease significantly, which is related to the inherent structural instability of the high-nickel lithium transition metal oxide system.

[0151] Considering the safety performance of battery cells, it is necessary to reasonably design the shell of the battery cells while improving the energy density. The following examples and comparative examples adjust the shell thickness of the battery cells according to the characteristics of the respective positive electrode active materials. In the positive electrode active materials of each example and comparative example, the composition of the nickel-containing lithium transition metal oxide is different, and the composition of the lithium-containing phosphate is Li(Fe 0.5 Mn 0.5 )PO4, the mass content of lithium phosphate in the positive electrode active material is 70%, the other settings of the positive electrode plate and the settings of the negative electrode plate, electrolyte, and separator are consistent, and the ear welding area per unit discharge capacity is 0.8mm 2 ·Ah -1 .

[0152] Specifically, the composition of the nickel-containing lithium transition metal oxide and the adjustment of the shell size parameters in each embodiment and comparative example are shown in Table 2, and the performance test results of the corresponding positive electrode plates and battery cells are also presented in Table 2.

[0153] Table 2 Note: Comparative Example 5 has severe swelling on the first side wall after charge and discharge cycles.

[0154] The chemical formula in Table 2 is Li(Ni 0.93 Co 0.06 Mn 0.01 )O2、Li(Ni 0.95 Co 0.03 Mn 0.02)O2-containing nickel-based lithium transition metal oxide, the mass contents of the elements in the element M are: Al: 0.081%, B: 0.091%, Na: 0.0093%, S: 0.082%, Sb: 0.014%, Sr: 0.025%, W: 0.035%; Zr: 0.143%.

[0155] The chemical formula is Li(Ni 0.50 Co 0.20 Mn 0.30 )O2-containing nickel-containing lithium transition metal oxide, the mass content of each element in the element M is: Al: 0.0054%, B: 0.0024%, Ca: 0.0032%, Cr: 0.0001%, Cu: 0.0003%, Mg: 0.0037%, Na: 0.010%, S: 0.063%, Sr: 0.085%, Ti: 0.175%, W: 0.059%, Y: 0.0001%, Zn: 0.0002%, Zr: 0.125%.

[0156] In Table 2, the shell with the first side wall having a thickness of 0.4 mm or 0.08 mm is a stainless steel shell to enhance the shell strength.

[0157] In Example 1 and Example 2, the molar ratio of nickel in nickel, cobalt and manganese in the nickel-containing lithium transition metal oxide system is more than 90%, which can provide a higher energy density. At the same time, in order to enhance the safety of the battery cell, a relatively thick shell is used, and the volume and weight of the battery cell will increase, which will reduce the energy density of the battery cell to a certain extent. Setting an overly thick shell will seriously affect the comprehensive performance of the battery cell. For example, the thickness of the first side wall of Comparative Example 4 is as high as 1.2 mm, and the volume energy density of the battery cell is significantly reduced.

[0158] In Example 3 and Comparative Example 5, the nickel element molar ratio of the nickel-containing lithium transition metal oxide system is 50%, which cannot provide as high an energy density as Example 1, but has excellent cycle performance, and does not need to enhance the safety properties of the battery cell by thickening the shell. However, the thickness of the first side wall of the shell in Comparative Example 5 is only 0.08 mm, and a more serious bulging problem of the first side wall of the battery occurs during the cycle. The overly thin shell increases the risk of thermal runaway of the battery cell. Once thermal runaway occurs, the shell may burst, resulting in a very high risk of runaway.

[0159] On the basis of Example 1, by adjusting the composition of the nickel-containing lithium transition metal oxide in the positive electrode active material, the effect of the molar ratio of nickel element in nickel, cobalt and manganese elements in the nickel-containing lithium transition metal oxide on the positive electrode sheet and battery performance was investigated.

[0160] In Examples 2 to 6, different nickel-containing lithium transition metal oxides from those in Example 1 were used. To reduce safety risks, the shell thickness of the battery cell was adjusted accordingly. The specific adjustment data are presented in Table 3. The contents not listed in Table 3 indicate that each example has the same settings as Example 1. In addition, the performance parameter test results of the positive electrode sheets and battery cells of Examples 1 to 6 are shown in Table 3.

[0161] Adjustment of the shell size parameters only affects some properties of the battery cell and has no effect on the performance of the positive electrode. For the embodiments in Table 3, the higher the molar proportion of nickel element in nickel-cobalt-manganese in the nickel-containing lithium transition metal oxide, the greater the discharge gram capacity and energy density of the positive electrode, and the fewer the number of cycles of the battery cell.

[0162] The energy density of the battery cell needs to take the shell thickness into consideration. Taking Examples 3 and 6 as examples, even a relatively thin shell can be used to achieve a battery cell with a high volume energy density. For example, the molar content of Ni in the positive electrode active material of Example 6 is lower than that of Example 3, and the energy density of its positive electrode sheet is lower than that of Example 3. However, because the first side wall of the shell is thin, the volume energy density of its battery cell is higher than that of Example 3.

[0163] The shells with the first side wall thickness of 0.4 mm or 0.1 mm in Table 3 and Table 4 are stainless steel shells to enhance the shell strength.

[0164] Furthermore, the positive electrode active material composition of Examples 7 and 8 is set to be the same as that of Example 5, that is, the positive electrode active material contains nickel-containing lithium transition metal oxide Li (Ni 0.8 Co 0.1 Mn 0.1 )O2 and lithium phosphate Li(Fe 0.5 Mn 0.5 )PO4 has a mass ratio of 3:7, and the settings of the rest of the positive electrode plate, the negative electrode plate, the isolation membrane, and the electrolyte are the same as those in Example 5. The shell only changes the size of the first side wall. The specific settings and test results are shown in Table 4, which more clearly illustrate the effect of increasing the thickness of the first side wall on the energy density of the battery cell.

[0167] The lithium-containing phosphate has good cycle stability, and the nickel-containing lithium transition metal oxide can provide a higher discharge capacity. The combination of the two positive electrode active materials can give full play to the advantages of both. In order to investigate the impact of the change in the mass content of the lithium-containing phosphate in the positive electrode active material, based on the setting of Example 1, the mass content of the lithium-containing phosphate in the positive electrode active material of Examples 9 to 13 is set to different values ​​of 40% to 90%, and the lithium-containing phosphate Li(Fe 0.5 Mn 0.5)PO4 and nickel-containing lithium transition metal oxides Li(Ni 0.9 Co 0.05 Mn 0.05 )O2 is consistent with Example 1, and the settings of the rest of the positive electrode sheet, the negative electrode sheet, the isolation membrane, the electrolyte, and the battery cell shell are also the same as in Example 1.

[0168] The variable settings and performance test results are listed in Table 5.

[0169] Table 5

[0170] According to the data in Table 5, by comparing Comparative Example 3 with the embodiments, it can be found that, under the premise that other conditions remain the same, the nickel-containing lithium transition metal oxide and the lithium-containing phosphate are combined in a certain proportion as the positive electrode active material, and the energy density and cycle performance of the battery monomer are better than those of the battery monomer using only the lithium-containing phosphate as the positive electrode active material. The mass content of the lithium-containing phosphate in the positive electrode active material is in the range of 50% to 90%, which can make the energy density and cycle life of the battery monomer at a relatively balanced level. In the range of 50% to 70%, the discharge gram capacity of the positive electrode sheet can be maintained at more than 160mAh / g, the volume energy density of the battery monomer is maintained at more than 450Wh / L, and the number of cycles is maintained at more than 1700 cycles, and the battery monomer has obtained more excellent comprehensive performance.

[0171] Furthermore, the influence of the molar ratio of Mn element in Mn element and Fe element in lithium-containing phosphate on the performance of positive electrode sheet and battery cell was investigated. To this end, based on Example 1, the composition of lithium-containing phosphate in the positive electrode active material of Examples 14 to 17 was adjusted, and the mass content of lithium-containing phosphate in the positive electrode active material was 70%, and the mass content of nickel-containing lithium transition metal oxide Li (Ni 0.9 Co 0.05 Mn 0.05 )O2 is consistent with Example 1, and the rest of the positive electrode sheet, the negative electrode sheet, the separator, the electrolyte, and the battery cell housing are also arranged in the same manner as in Example 1. The variable settings and performance test results are listed in Table 6.

[0172] Table 6

[0173] By comparing the performance of each embodiment in Table 6, it can be learned that when the molar amount of the Mn element in the lithium-containing phosphate is 20% to 80% of the total molar amount of the Mn element and the Fe element, a positive electrode sheet discharge gram capacity greater than 145 mAh / g can be obtained. However, when the Mn element content is 80%, not only the volume energy density of the battery cell is significantly reduced, but also the cycle performance is also deteriorated due to the serious dissolution of the Mn element. When the molar amount of the Mn element in the lithium-containing phosphate is 30% to 70% of the total molar amount of the Mn element and the Fe element, the energy density of the positive electrode sheet and the battery cell is improved. When the molar proportion of the Mn element is 50% to 70%, the positive electrode sheet discharge gram capacity and the energy density of the battery cell are further improved.

[0174] The positive electrode current collector plays the role of carrying active materials, collecting and outputting current in the electrode sheet, which is very important for maintaining structural stability. At the same time, reducing the thickness and mass of the positive electrode current collector as much as possible is conducive to lightweighting the battery cell and improving the energy density of the battery cell. The following embodiments are set up to investigate the effect of the mass ratio of the single-layer positive electrode active layer to the current collector on the performance of the battery cell. Examples 18 to 20 adjust the mass of the current collector on the basis of Example 5. The rest of the positive electrode sheet, the negative electrode sheet, the separator, the electrolyte, and the shell are set in accordance with Example 5. The specific settings and test results are shown in Table 7. In Table 7, Ma / Mc represents the mass ratio of the single-layer positive active layer (active material layer) to the positive electrode current collector (collector).

[0175] Table 7

[0176] Because the mass of the positive electrode active material in each embodiment is the same, if the mass ratio Ma / Mc of the single-layer positive electrode active layer to the positive electrode current collector is larger, it means that the coating amount of the positive electrode active material relative to the positive electrode current collector is larger. From the data in Table 7, it can be seen that the mass ratio Ma / Mc of the single-layer positive electrode active layer to the positive electrode current collector is positively correlated with the volume energy density of the battery cell and negatively correlated with the cycle performance.

[0177] By adjusting the graphite particle size in the two negative electrode active layers, how the particle size of the negative electrode active particles affects the performance of the battery cell is investigated. The adjustment of the graphite particle size of the first and second negative electrode active layers in Examples 21 and 22 is shown in Table 8, and the rest of the negative electrode sheet, the positive electrode sheet, the separator, the electrolyte, and the shell are all the same as in Example 1.

[0178] Table 8

[0179] The first negative electrode active layer is arranged close to the negative electrode current collector. The graphite particles with larger particle size can reduce the contact area between the graphite particles and the electrolyte, and the negative electrode structure is more stable, which is conducive to improving the cycle life.

[0180] The selection of the injection coefficient involves the degree of wetting of the electrode plate and the internal pressure of the battery cell, and is closely related to the internal resistance and structural stability of the battery cell. In order to investigate the impact of the change in the injection coefficient on the performance of the battery cell, the injection coefficients of Examples 23 to 26 are set differently, and the settings of the positive electrode plate, negative electrode plate, separator, electrolyte composition, and battery shell are consistent with those of Example 1.

[0181] The specific variable settings and battery cell performance test results are listed in Table 9.

[0182] Table 9

[0183] From the data in Table 9, we can know that the filling coefficient mainly affects the cycle performance of the battery cell. A moderate filling coefficient can fully wet the electrode, which is beneficial to the improvement of active ion dynamics, and is not prone to excessive free electrolyte, which aggravates the degree of side reactions.

[0184] In summary, the present application can obtain a battery cell with both high energy density and cycle stability, while enhancing the safety of the battery cell, through the multi-faceted design of the battery cell, especially the adjustment and exploration of the positive electrode active material.

[0185] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, comprising a housing and an electrode assembly located inside the housing, wherein the electrode assembly comprises a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet, wherein: The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active layer comprises a negative electrode active material, and the negative electrode active material comprises graphite. The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on at least one side of the positive electrode current collector, the positive electrode active layer includes a positive electrode active material, the positive electrode active material includes a nickel-containing lithium transition metal oxide and a lithium-containing phosphate, and the battery cell is configured to have a discharge capacity of 145 mAh / g to 210 mAh / g when discharged from 4.3 V to 2.5 V at a rate of 0.33 C; The shell has two first side walls parallel to a first direction and two second side walls parallel to a second direction, the first direction is perpendicular to the second direction, the area of ​​the first side wall is greater than the area of ​​the second side wall, and the thickness of the first side wall is 0.1 mm-0.8 mm.

2. The battery cell according to claim 1, wherein: The battery cell is configured to have a discharge capacity of 150 mAh / g to 195 mAh / g when discharged from 4.3 V to 2.5 V at a rate of 0.33 C.

3. The battery cell according to claim 1 or 2, wherein: In the positive electrode active material, the mass content of the lithium-containing phosphate is 50%-90%, and optionally, the mass content of the lithium-containing phosphate is 50%-70%.

4. The battery cell according to any one of claims 1 to 3, wherein: The nickel-containing lithium transition metal oxide includes manganese and cobalt. In the nickel-containing lithium transition metal oxide, the molar amount of the nickel element accounts for 50%-95% of the total molar amount of the nickel, cobalt and manganese elements, and can be optionally 70%-95%, and further optionally 80%-95%.

5. The battery cell according to any one of claims 1 to 4, wherein: The thickness of the first side wall is 0.4 mm-0.8 mm, and can be optionally 0.6 mm-0.8 mm.

6. The battery cell according to any one of claims 1 to 5, wherein: The nickel-containing lithium transition metal oxide includes lithium-containing nickel-cobalt-manganese oxide, and the lithium-containing nickel-cobalt-manganese oxide includes one or more of Zr, Al, B, Fe, Ca, Sr, Ti, V or Y elements.

7. The battery cell according to any one of claims 1 to 6, wherein: The lithium-containing nickel-cobalt-manganese oxide includes one or more of Zr, Al or B; optionally, in the lithium-containing nickel-cobalt-manganese oxide, the mass content of the elements satisfies at least one of the following: the content of Zr is 1000ppm-300ppm, the content of Al is 100ppm-1000ppm, and the content of B is 50ppm-300ppm.

8. The battery cell according to any one of claims 1 to 7, wherein: The lithium-containing phosphate includes Mn and Fe elements, and the molar amount of the Mn element in the lithium-containing phosphate accounts for 20%-80% of the total molar amount of the Mn and Fe elements, optionally 30%-70%, and further optionally 50%-70%.

9. The battery cell according to any one of claims 1 to 8, wherein: The lithium-containing phosphate includes lithium iron manganese phosphate, and the lithium iron manganese phosphate includes one or more elements of Al, B, Ca, Cr, Cu, K, Mg, Na, P, Si, Ti, V or Zn; Optionally, the lithium manganese iron phosphate includes one or more of Al, Ca, Na, Ti or V elements; Further optionally, in the lithium manganese iron phosphate, the mass content of the elements satisfies at least one of the following: the mass content of Al is 100ppm to 1000ppm, the mass content of Ca is 50ppm to 300ppm, the mass content of Na is 50ppm to 300ppm, the mass content of Ti is 100ppm to 1000ppm, and the mass content of V is 1000ppm to 3000ppm.

10. The battery cell according to any one of claims 1 to 9, wherein: The positive electrode active layer contains lithium manganese iron phosphate and lithium-containing nickel cobalt manganese oxide, and the positive electrode active material contains one or more of Al, B, Ca, Na, Sr, Ti, V, Y or Zr elements, and based on the total mass of the positive electrode active material, the mass content of each element satisfies: Al:0.005％-0.1％； Ca: 0.0001%-0.02%; Na: 0.005%-0.06%; Ti: 0.005%-0.15%; V:0.0001％-0.3％； Zr:0.005％-0.2％； B:0.01％-0.1％。 11. The battery cell according to any one of claims 1 to 10, wherein: The thickness of the second side wall is 0.8 mm-1.2 mm, and the thickness of the bottom wall of the shell is 1 mm-1.5 mm.

12. The battery cell according to any one of claims 1 to 11, wherein: The positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer, the first positive electrode active layer is arranged close to the positive electrode current collector, the second positive electrode active layer is arranged on a side of the first positive electrode active layer away from the positive electrode current collector, and the nickel-containing lithium transition metal oxide and the lithium-containing phosphate are each independently arranged in the first positive electrode active layer and / or in the second positive electrode active layer.

13. The battery cell according to any one of claims 1 to 12, wherein: The ratio of the mass of the positive electrode active layer per unit area of ​​a single layer to the mass of the positive electrode current collector is (0.15-10):1, and can be optionally (4.5-5.6):

1.

14. The battery cell according to any one of claims 1 to 13, wherein: The negative electrode active layer comprises a first negative electrode active layer and a second negative electrode active layer, the first negative electrode active layer is arranged close to the negative electrode current collector, the second negative electrode active layer is arranged on a side of the first negative electrode active layer away from the negative electrode current collector, and the average particle size of the graphite particles arranged in the first negative electrode active layer is greater than the average particle size of the graphite particles arranged in the second negative electrode active layer; Optionally, the average particle size of the graphite particles disposed in the first negative electrode active layer is 12 μm-25 μm, and the average particle size of the graphite particles disposed in the second negative electrode active layer is 5 μm-12 μm.

15. The battery cell according to any one of claims 1 to 14, wherein: The second side wall of the shell is provided with an explosion-proof valve, and the area of ​​the explosion-proof valve is 8%-20% of the area of ​​the second side wall, and can be 12%-16%.

16. The battery cell according to any one of claims 1 to 15, wherein: The battery cell includes at least one top cover assembly, and the top cover assembly is connected to the first side wall and the second side wall by welding; each of the top cover assemblies includes a positive terminal and a negative terminal, and the electrode assembly includes a stacked positive electrode ear and a negative electrode ear, and the positive electrode ear is welded to the positive terminal, and the negative electrode ear is welded to the negative terminal, wherein: The weld area between the positive electrode ear and the single positive electrode terminal is set to 0.5mm 2 / Ah-1mm 2 / Ah, and / or, the weld area between the negative electrode ear and the single negative electrode terminal is set to 0.5mm 2 / Ah-1mm 2 / Ah.

17. The battery cell according to any one of claims 1 to 16, wherein: The liquid injection coefficient of the battery cell is 1.8g / Ah-3.5g / Ah, and can be optionally 1.9g / Ah-3.1g / Ah.

18. A battery device comprising a battery cell, wherein the battery cell comprises the battery cell according to any one of claims 1 to 17, and the battery device comprises a battery module, a battery pack or an energy storage device.

19. An electrical device comprising the battery cell according to any one of claims 1 to 17, or the battery device according to claim 18.

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