Electrode assembly, battery cell, secondary battery, and electric device

Abstract

The invention provides an electrode assembly, a battery monomer, a secondary battery and an electric device. The electrode assembly comprises a positive pole piece, a negative pole current collector and an isolating membrane positioned between the positive pole piece and the negative pole current collector, the electrode assembly further comprises a modification layer, the modification layer is located between the negative electrode current collector and the isolating membrane, and the modification layer comprises a substrate material and an active material dispersed in the substrate material; the lithium metal nucleation overpotential of the substrate material is greater than or equal to 80 mV, and the lithium metal nucleation overpotential of the active material is smaller than the lithium metal nucleation overpotential of the substrate material. The modification layer in the electrode assembly can reduce volume expansion of metals such as lithium, sodium and the like on the negative electrode current collector in the deposition process, so that the risk of puncturing the isolating membrane due to the volume expansion is reduced, and the reliability and the cycle performance of the battery are improved.

Description

Technical Field

[0001] This application relates to the field of battery technologies, and particularly to an electrode assembly, a battery cell, a secondary battery, and an electrical device. Background Art

[0002] Compared with ionic battery cells, metal battery cells can have a higher energy density. However, different from the negative electrode of ionic battery cells, the surface of the negative electrode current collector commonly used in metal battery cells usually has a local nucleation mode, and local crystal nuclei are prone to grow into a loose and porous structure, resulting in a rapid volume expansion of the negative electrode current collector and generating intense side reactions, and may even cause dendrites to pierce the separator, while affecting the cycle stability of the battery cell. Summary of the Invention

[0003] Embodiments of this application provide an electrode assembly, a battery cell, a secondary battery, and an electrical device, enabling the battery cell to have good cycle stability.

[0004] In a first aspect, embodiments of this application provide an electrode assembly. The electrode assembly includes a positive electrode sheet, a negative electrode current collector, and a separator located between the positive electrode sheet and the negative electrode current collector. The electrode assembly further includes a modification layer located between the negative electrode current collector and the separator. The modification layer includes a base material and an active material dispersed in the base material; the lithium metal nucleation overpotential of the base material is ≥80 mV, and the lithium metal nucleation overpotential of the active material is less than that of the base material.

[0005] In embodiments of this application, by providing a modification layer between the ancient collection current collector and the separator, the active material in the modification layer has a high affinity for metals such as lithium and sodium, which can increase the active sites on the surface of the negative electrode current collector, reduce the nucleation overpotential of the negative electrode current collector, and enable the deposited metal to be evenly distributed on the surface of the negative electrode current collector, reducing the local deposition of metals such as lithium and sodium on the surface of the negative electrode current collector; the base material in the modification layer hardly reacts with metals such as lithium and sodium, so there is no volume change before and after metal deposition, and it plays a role in restricting the volume change of the negative electrode current collector in the modification layer, reducing the volume expansion during the deposition of metals such as lithium and sodium, thereby reducing the risk of piercing the separator due to volume expansion, and thus improving the reliability and cycle performance of the battery. In addition, the active material in the modification layer can react with metals such as lithium and sodium to form alloys, and these alloys can increase the negative electrode potential of the battery, which is beneficial to improving the quality of the solid electrolyte interface (SEI) film on the negative electrode surface, and further enhancing the cycle stability of the battery cell.

[0006] In some embodiments, the lithium metal nucleation overpotential of the base material is 100 mV - 500 mV.

[0007] In some embodiments, the lithium metal nucleation overpotential of the active material is 10 mV - 50 mV.

[0008] In some embodiments, the substrate material includes one or more of non-graphitized carbon materials and non-lithophilic metals.

[0009] In some embodiments, the non-graphitized carbon material includes hard carbon, amorphous carbon, or a combination thereof.

[0010] In some embodiments, the non-lithophilic metal includes one or more of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Ta, W, Pt, Ir.

[0011] In some embodiments, the active material includes one or more of graphitized carbon, lithophilic metals, or their compounds.

[0012] In some embodiments, the graphitized carbon includes one or more of graphite, graphene, graphyne.

[0013] In some embodiments, the lithophilic metal includes one or more of Sn, Mg, Zn, Bi, Pb, Au, Ag, Al, Si, In, Ga. The compounds of the lithophilic metal include one or more of oxides, sulfides, fluorides, chlorides, nitrides, carbides.

[0014] In some embodiments, based on the total weight of the modification layer, the weight content of the active material is 40% - 95%, and the weight content of the substrate material is 5% - 60%.

[0015] In some embodiments, based on the total weight of the modification layer, the weight content of the active material is 55% - 70%, and the weight content of the substrate material is 30% - 45%.

[0016] In some embodiments, the areal density of the active material ≥ 0.5 g / m 2 。

[0017] In some embodiments, the thickness of the modification layer is 10 nm - 1000 nm.

[0018] In some embodiments, the thickness of the modification layer is 100 nm - 500 nm.

[0019] In some embodiments, the material of the negative electrode current collector includes one or more of copper, nickel, titanium, magnesium, aluminum, copper alloy, nickel alloy, titanium alloy, magnesium alloy, aluminum alloy.

[0020] Second aspect, an embodiment of the present application provides a battery cell, and the battery cell includes the electrode assembly of the embodiment of the first aspect of the present application.

[0021] In some embodiments, the battery cell includes at least one of a lithium metal battery cell without a negative electrode and a sodium metal battery cell without a negative electrode.

[0022] Third aspect, an embodiment of the present application provides a secondary battery, including the battery cell of the embodiment of the second aspect of the present application.

[0023] Fourth aspect, an embodiment of the present application provides an electrical device, including the secondary battery of the embodiment of the third aspect of the present application. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments of the present application. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0025] Figure 1 It is a schematic diagram of a battery cell provided by some embodiments of the present application.

[0026] Figure 2 It is an exploded schematic diagram of a battery cell provided by some embodiments of the present application.

[0027] Figure 3 It is a schematic diagram of a battery module provided by some embodiments of the present application.

[0028] Figure 4 It is a schematic diagram of a battery pack provided by some embodiments of the present application.

[0029] Figure 5 is Figure 4 an exploded schematic diagram of the shown battery pack.

[0030] Figure 6 It is a schematic structural diagram of an electrode assembly of a battery cell provided by some embodiments of the present application.

[0031] Figure 7 It is a schematic diagram of an electrical device provided by some embodiments of the present application.

[0032] In the drawings, the drawings are not necessarily drawn to actual scale.

[0033] The description of the reference numerals is as follows: 1, battery pack; 2, upper box body; 3, lower box body; 4, battery module; 5, battery cell; 51, housing; 52, electrode assembly; 53, cover plate; 10, positive electrode plate; 20, negative current collector; 30, separator; 40, modification layer. Detailed Embodiments

[0034] Hereinafter, embodiments of the electrode assembly, battery cell, battery, and electrical device of the present application will be specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary details are omitted. For example, there are cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0035] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The range defined in this way can include or exclude the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" represents that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution, and such a technical solution should be considered to be included in the disclosure of the present application.

[0037] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution, and such a technical solution should be considered to be included in the disclosure of the present application.

[0038] Unless otherwise specified, all steps of this application can be carried out 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) carried out sequentially, or may include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can 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.

[0039] Unless otherwise specified, in this application, the terms "connected" and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, and can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0040] In this application, "a plurality of" refers to more than two, including two. "A variety of" in this application refers to more than two, including two.

[0041] The battery mentioned in the embodiments of this application can be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, battery packs, etc.

[0042] A battery cell is the smallest unit that makes up a battery and can independently perform the functions of charging and discharging. The battery cell can be in the shape of a cylinder, a cuboid, or other shapes, which is not limited in the embodiments of this application. As Figure 1 is a battery cell 5 in the shape of a cuboid as an example.

[0043] When there are multiple battery cells, the multiple battery cells are connected in series, parallel, or in a hybrid connection through a busbar component. In some embodiments, the battery can be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, and the battery pack includes a box body and battery cells, and the battery cells or battery modules are accommodated in the box body. In some embodiments, the box body can be a part of the chassis structure of a vehicle. For example, a part of the box body can be at least a part of the vehicle floor, or a part of the box body can be at least a part of the crossbeam and longitudinal beam of the vehicle.

[0044] In some embodiments, the battery cells can be assembled into a battery module, and the number of battery cells included in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 2It is a schematic diagram of a battery module 4 as an example. As Figure 2 shown, in the battery module 4, multiple battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the multiple battery cells 5 can be fixed by fasteners.

[0045] Optionally, the battery module 4 can further include a housing having an accommodation space, and the multiple battery cells 5 are accommodated in the accommodation space.

[0046] In some embodiments, the above battery module can also be assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0047] Figure 3 and Figure 4 are schematic diagrams of a battery pack 1 as an example. As Figure 3 and Figure 4 shown, the battery pack 1 can include a box body and multiple battery modules 4 arranged in the box body. The box body includes an upper box body 2 and a lower box body 3. The upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in the box body in any way.

[0048] In some embodiments, the battery can be an energy storage device. The energy storage device includes an energy storage container, an energy storage cabinet, etc.

[0049] The battery cell provided by the embodiment of the present application is a non-negative electrode battery cell, and for example, it can include at least one of a non-negative electrode lithium metal battery cell and a non-negative electrode sodium metal battery cell.

[0050] An anode-free battery cell generally refers to a battery cell that is constructed without actively disposing an anode active material layer on the anode side during the manufacturing process of the battery cell. For example, during the manufacturing process of the battery cell, a layer is not disposed at the anode through processes such as coating or deposition, or an anode active material layer is formed by a carbonaceous active material layer. During the first charging, ions gain electrons on the anode side and are deposited on the surface of the anode current collector to form a metal. During discharging, the metal can be converted into ions and return to the cathode to achieve cyclic charge and discharge. Compared with other battery cells, the anode-free battery cell can obtain a higher energy density because it does not have an anode active material layer. In some embodiments, in order to improve the performance of the battery cell, some substances that can be used as anode active materials, such as carbon materials, can also be disposed on the anode side of the anode-free battery cell. Although these substances have a certain capacity, since their content is small and they are not used as the main anode active material in the battery cell, the battery cell thus constituted can still be regarded as an anode-free battery cell. The CB (Cell Balance) value of the anode-free battery cell is usually very small. For example, in some embodiments, the CB value of the anode-free battery cell can be less than or equal to 0.1. The CB value is the unit area capacity of the anode in the battery cell divided by the unit area capacity of the cathode. Since the anode-free battery cell does not contain or only contains a small amount of anode active material, the unit area capacity of the anode is small, and thus the CB value is very small, for example, usually less than or equal to 0.1.

[0051] The battery cell includes an electrode assembly. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of the present application do not limit this.

[0052] The battery cell may further include an outer package, and the outer package can be used to encapsulate the electrode assembly. The outer package can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0053] In some embodiments, as Figure 5 shown, the outer package may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The electrode assembly 52 is encapsulated in the receiving cavity. The number of electrode assemblies 52 included in the battery cell 5 can be one or more, and can be adjusted according to requirements.

[0054] [Electrode Assembly]

[0055] An embodiment of the first aspect of the present application provides an electrode assembly, as Figure 6As shown, the electrode assembly 52 includes a positive electrode tab 10, a negative current collector 20, and a separator 30 located between the positive electrode tab 10 and the negative current collector 20; the electrode assembly 52 further includes a modification layer 40, the modification layer 40 is located between the negative current collector 20 and the separator 30, and the modification layer 40 includes a base material and an active material dispersed in the base material; the lithium metal nucleation overpotential of the base material is ≥80 mV, and the lithium metal nucleation overpotential of the active material is less than that of the base material.

[0056] The negative current collectors of currently commonly used metal battery monomers have poor affinity with lithium and sodium, and large nucleation overpotentials, resulting in insufficient active sites for metal deposition such as lithium and sodium. Metals such as lithium and sodium adopt a local nucleation mode on the surface of the untreated negative current collector, causing loose metal deposition. Metals such as lithium and sodium exhibit infinite volume expansion and generate intense side reactions, and may even cause dendrites to directly pierce the separator, posing a risk of short circuit.

[0057] In the embodiments of the present application, a modification layer is provided between the negative current collector and the separator. The modification layer includes an active material and a base material, and the active material is uniformly dispersed in the base material. The active material in the modification layer has high affinity with metals such as lithium and sodium, which can increase the active sites on the surface of the negative current collector, reduce the nucleation overpotential of the negative current collector, and enable the deposited metal to be evenly distributed on the surface of the negative current collector, reducing local deposition of metals such as lithium and sodium on the surface of the negative current collector; the base material in the modification layer hardly reacts with metals such as lithium and sodium, so there is no volume change before and after metal deposition, and it plays a role in restricting the volume change of the negative current collector in the modification layer, reducing the volume expansion during the deposition of metals such as lithium and sodium, and thus reducing the risk of piercing the separator due to volume expansion, thereby improving the reliability of the battery. In addition, the active material in the modification layer can react with metals such as lithium and sodium to form alloys, and these alloys can increase the negative electrode potential of the battery, which is beneficial to improving the quality of the solid electrolyte interface (SEI) film on the negative electrode surface, and further enhancing the cycle stability of the battery monomer.

[0058] In some embodiments, the lithium metal nucleation overpotential of the active material can be 10 mV - 50 mV, and can be optionally 20 mV - 35 mV.

[0059] When the lithium metal nucleation overpotential of the active material is within this range, it has better affinity with metals such as lithium and sodium, thereby providing more active sites, inducing uniform metal deposition, and forming alloys with the deposited metal, thus reducing the nucleation overpotential of the negative current collector and reducing local nucleation. [[ID=~]]

[0060] In some embodiments, the lithium metal nucleation overpotential of the base material can be 100 mV - 500 mV, and can be optionally 150 mV - 350 mV.

[0061] The lithium metal nucleation overpotential of the substrate material is within this range, and its affinity with metals such as lithium and sodium is worse. During the metal deposition process, it hardly reacts with the substrate material, thereby further reducing the volume expansion after metal deposition and improving the reliability of the battery cell.

[0062] The nucleation overpotentials of the active material and the substrate material can be measured as follows: In a glove box protected by argon, a lithium metal sheet is used as the counter electrode and assembled into a coin cell with a sheet of the corresponding material (thickness: 8 μm) of the active material or the substrate material. The electrolyte salt of the electrolyte is LiFSI with a concentration of 1 mol / L, and the solvent of the electrolyte uses a mixed solvent of ethylene glycol dimethyl ether (DME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) with a weight ratio of 1:1. The separator uses a PE membrane with a thickness of 12 μm.

[0063] At 25°C, after the assembled coin cell is left standing for 12 h, it is discharged at a constant current density of 1 mA / cm 2 to 1 mAh / cm 2 . At the beginning of the lithium metal deposition process, there will first be an obvious voltage drop, and then a flat voltage plateau. The difference (here representing the absolute value) between the voltage at the lowest point of the discharge curve and the flat part of the voltage plateau is used as the lithium metal nucleation overpotential of the active material or the substrate material.

[0064] It should be noted that the specific values of the lithium metal nucleation overpotentials of the above-mentioned active material or substrate material are used to represent the physical and chemical properties of the active material or substrate material, as well as the affinity degree between the active material or substrate material and the deposited metal. It does not mean that the negative current collector provided by the embodiments of the present application can only be used in the non-aqueous lithium metal battery cell. The negative current collector provided by the embodiments of the present application can also be used in the non-aqueous sodium metal battery cell.

[0065] In some embodiments, the substrate material includes one or more of non-graphitized carbon materials and non-lithophilic metals.

[0066] In some embodiments, the non-graphitized carbon material includes hard carbon, amorphous carbon, or a combination thereof.

[0067] In some embodiments, the non-lithophilic metal refers to a metal that hardly reacts with lithium and may include one or more of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Ta, W, Pt, Ir; optionally, the non-lithophilic metal includes one or more of Fe, Cu, Mo.

[0068] In some embodiments, the active material includes one or more of graphitized carbon, lithophilic metals, or their compounds.

[0069] In some embodiments, the graphitized carbon includes one or more of graphite, graphene, and graphyne.

[0070] In some embodiments, the lithiumophilic metal includes one or more of Sn, Mg, Zn, Bi, Pb, Au, Ag, Al, Si, In, and Ga; optionally, the lithiumophilic metal includes one or more of Sn, Mg, Zn, and Bi.

[0071] In some embodiments, the compounds of the lithiumophilic metal include one or more of oxides, sulfides, fluorides, chlorides, nitrides, and carbides.

[0072] In some embodiments, based on the total weight of the modification layer, the weight content of the active material is 40%-95%, and the weight content of the substrate material is 5%-60%.

[0073] By adjusting the weight contents of the active material and the substrate material in the modification layer within the above ranges, the synergistic effect of the substrate material and the active material can be better exerted, the volume expansion caused by metal deposition can be reduced, the nucleation overpotential can be lowered, local nucleation can be reduced, and dendrite growth can be slowed down.

[0074] When the content of the active material in the modification layer is low and the content of the substrate material is high, the active sites provided by the active material in the modification layer are few, so it is difficult to play a good role in reducing local nucleation and slowing down dendrite growth, and the cycle stability and reliability of the battery cell will be reduced.

[0075] When the content of the active material in the modification layer is high and the content of the substrate material is low, the substrate material cannot well limit the volume expansion caused by the deposition of metals such as lithium and sodium. Therefore, during the long-term cyclic charge and discharge process of the battery, there is a risk of piercing the separator, resulting in a reduction in the reliability of the battery cell; at the same time, excessive volume expansion will lead to problems such as a decrease in the internal porosity of the battery and poor wettability of the electrolyte, which will reduce the cycle stability of the battery.

[0076] Therefore, by adjusting the weight contents of the active material and the substrate material in the modification layer within the above ranges, the synergistic effect of the substrate material and the active material can be better exerted, so that the battery cell can have both high reliability and long cycle life.

[0077] Optionally, the weight content of the active material is 55%-70%, and the weight content of the substrate material is 30%-45%.

[0078] Further adjusting the weight contents of the active material and the substrate material in the modification layer within the above ranges can further improve the cycle stability and reliability of the battery cell.

[0079] In some embodiments, the areal density of the active material ≥0.5 g / m 2 .

[0080] In the embodiments of the present application, the areal density refers to the weight of the active material per unit area. The active material mainly plays the role of providing active sites, reducing the nucleation overpotential, and reducing local nucleation in the modification layer. By controlling the areal density of the active material in the modification layer within the above range, the active material can have a high dispersion uniformity and dispersion density in the modification layer, thereby providing more active sites, reducing the nucleation overpotential, playing the role of reducing local nucleation and slowing down dendrite growth, and thus improving the cycle stability and reliability of the battery cell.

[0081] Optionally, the areal density of the active material in the modification layer is 0.6 g / m 2 -60 g / m 2 , and further optionally 5 g / m 2 -50 g / m 2 , and more optionally 10 g / m 2 -25 g / m 2 .

[0082] By limiting the areal density of the active material in the modification layer within the above range, it can further provide more active sites, reduce the nucleation overpotential, play the role of reducing local nucleation and slowing down dendrite growth, and thus further improve the cycle stability and reliability of the battery cell. The areal density of the active material is related to the thickness of the modification layer and the content of the active material in the modification layer. It can be understood that when the thickness of the modification layer remains unchanged, the higher the proportion of the active material, the higher its areal density; when the proportion of the active material in the modification layer remains unchanged, the thicker the modification layer, the higher its areal density.

[0083] In some embodiments, the thickness of the modification layer is 10 nm - 1000 nm.

[0084] Limiting the thickness of the modification layer within the above range can provide more active sites for the deposited metal, reduce the nucleation overpotential, reduce local nucleation, and at the same time limit the volume expansion during the metal deposition process, thereby improving the cycle stability and reliability of the battery cell.

[0085] Optionally, the thickness of the modification layer is 100 nm - 500 nm.

[0086] Limiting the thickness of the modification layer within the above range can play the role of further reducing the nucleation overpotential and at the same time limiting the volume expansion during the metal deposition process, thereby further improving the reliability and cycle stability of the battery.

[0087] In some embodiments, the modification layer can be disposed on the surface of the negative electrode current collector by magnetron sputtering, electroless plating, electroplating, or spraying.

[0088] Optionally, the modification layer can be disposed on the surface of the negative electrode current collector by magnetron sputtering. Compared with other methods, magnetron sputtering is simpler, faster, and more convenient to operate. At the same time, the bonding force between the modification layer formed by magnetron sputtering and the negative electrode current collector is higher, and the stability of the modification layer is better.

[0089] In some embodiments, the material of the negative electrode current collector includes one or more of copper, nickel, titanium, magnesium, aluminum, copper alloy, nickel alloy, titanium alloy, magnesium alloy, and aluminum alloy.

[0090] Optionally, the negative electrode current collector may include copper foil or nickel foil, and may alternatively be copper foil.

[0091] [Positive electrode plate]

[0092] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0093] In some embodiments, the positive electrode active material includes a material capable of deintercalating and intercalating lithium.

[0094] As an example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, metal chalcogenides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium titanium oxide, and their respective modified compounds. The lithium transition metal oxides may include, but are not limited to, a layered structure and a spinel structure. Examples of lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds.

[0095] In some embodiments, in order to further improve the energy density of the battery cell, the positive electrode active material may include a general formula of Li a Ni b Co c M d O e D fOne or more lithium transition metal oxides and modified compounds thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M may include but is not limited to one or more of Ge, Mo, Sn, Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and D may include but is not limited to one or more of N, F, S and Cl.

[0096] In some embodiments, the positive electrode active material may include both a lithium transition metal oxide and a lithium-containing phosphate, thereby facilitating the production of a battery cell having both high capacity and high reliability.

[0097] As an example, the positive electrode active material may include but is not limited to LiCoO2, LiNiO2, LiMnO2, LiNi 1 / 2 Mn 1 / 2O2、LiMn2O4、Li 4 / 3 Ti 5 / 3 O4、LiNi 1 / 2 Mn 1 / 2 O2、LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523),LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.80 Co 0.15 Al 0.05 O2, LiFePO4, LiMnPO4, Li 1.13 Ti 0.57 Fe 0.3 One or more of S2.

[0098] In some embodiments, the positive electrode active material includes a material capable of extracting and inserting sodium. For example, the positive electrode active material may include, but is not limited to, one or more of layered transition metal oxides (including but not limited to P2 type, O3 type, etc.), polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian materials.

[0099] In some embodiments, as examples, the positive electrode active material may include but is not limited to NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, Na0.67 MO₂ (M includes at least two of Fe, Co, Cr, Mn, Ni, V, Ti, and Mo), NaMO₂ (M includes at least two of Fe, Co, Ni, V, Ti, and Mo), NaFePO₄, NaMnPO₄, NaCoPO₄, Na₄Fe₃(PO₄)₂O₇, Na₃V₂(PO₄)₂F₃, Na₃V₂(PO₄)₃, Prussian blue, Prussian white, and one or more of their respective modified compounds.

[0100] The modified compounds of the above-mentioned cathode active materials can be doping modification and / or surface coating modification of the cathode active materials.

[0101] In some embodiments, the cathode film layer may optionally further include a cathode conductive agent. As an example, the cathode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0102] In some embodiments, the cathode film layer may optionally further include a cathode binder. As an example, the cathode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, fluorinated acrylate resin, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0103] In some embodiments, the cathode current collector can be a metal foil or a composite current collector. As an example of the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0104] The positive electrode film layer is usually formed by coating a positive electrode slurry on a positive electrode current collector and then drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional positive electrode conductive agent, an optional positive electrode binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0105] [Separator membrane]

[0106] The separator membrane is located between the positive electrode and the negative electrode and mainly functions to prevent internal short circuit.

[0107] This application does not particularly limit the type of the separator membrane, and any well-known porous structure separator membrane with good chemical stability and mechanical stability can be selected.

[0108] In some embodiments, the material of the separator membrane may include, but is not limited to, one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane can be a single-layer film or a multi-layer composite film. When the separator membrane is a multi-layer composite film, the materials of each layer are the same or different.

[0109] [Electrolyte]

[0110] The battery cell includes an electrolyte.

[0111] In some embodiments, the electrolyte uses an electrolytic solution, and the electrolytic solution includes an electrolyte salt and an organic solvent.

[0112] In some embodiments, the electrolytic solution includes anions, and the anions can include bis(fluorosulfonyl)imide anion (FSI - ), bis(trifluoromethanesulfonyl)imide anion (TFSI - ), bis(oxalato)borate anion (BOB - ), difluoro(oxalato)borate anion (DFOB - ), difluoro(dioxalato)phosphate anion (DFOP - ), tetrafluoro(oxalato)phosphate anion (TFOP - ), difluorophosphate anion (PO2F2[[ID=3)7]] - ), hexafluorophosphate anion (PF6 - ), tetrafluoroborate anion (BF4 - ), hexafluoroarsenate anion (AsF6 - ), trifluoromethanesulfonate anion (CF3SO3 - ) or one or more of them.

[0113] In some embodiments, the electrolytic solution includes cations, and the cations can include one or more of lithium ions and sodium ions.

[0114] In some embodiments, the concentration of the electrolyte salt may be 0.3 mol / L or more, optionally 0.7 mol / L or more, and further may be 4 mol / L or less, optionally 2.5 mol / L or less, 1.7 mol / L or less. When the concentration of the electrolyte salt is within the above range, the electrolyte solution can have appropriate ionic conductivity.

[0115] The organic solvent may include, but is not limited to, one or more of esters, ethers, sulfones, nitriles, etc. The esters may include, but are not limited to, one or more of carbonates, phosphates, carboxylates, sulfates, sulfonates, etc. The carbonates may include cyclic carbonates and / or chain carbonates. Optionally, the carbonates may include both cyclic carbonates and chain carbonates. The chain carbonates may include low-viscosity polar chain carbonates, aliphatic branched carbonates, etc.

[0116] As an example, the organic solvent may include, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), tetraethylene glycol dimethyl ether (TEGDME), ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), trimethyl phosphate, 3-methoxypropionitrile, H(CF2)2OCH3, C4F9OCH3, H(CF2)2OCH2CH3, H(CF2)2OCH2CF3, H(CF2)2CH2O(CF2)2H, CF3CHFCF2OCH3, CF3CHFCF2OCH2CH3, 2-trifluoromethylhexafluoropropyl methyl ether, 2-trifluoromethylhexafluoropropyl ethyl ether, 2-trifluoromethylhexafluoropropyl propyl ether, 3-trifluoromethyloctafluorobutyl methyl ether, 3-trifluoromethyloctafluorobutyl ethyl ether, 3-trifluoromethyloctafluorobutyl propyl ether, 4-trifluoromethyldecafluoropentyl methyl ether, 4-trifluoromethyldecafluoropentyl ethyl ether, 4-trifluoromethyldecafluoropentyl propyl ether, 5-trifluoromethyldodecafluorohexyl methyl ether, 5-trifluoromethyldodecafluorohexyl ethyl ether, 5-trifluoromethyldodecafluorohexyl propyl ether, 6-trifluoromethyltetradecafluoroheptyl methyl ether, 6-trifluoromethyltetradecafluoroheptyl ethyl ether, 6-trifluoromethyltetradecafluoroheptyl propyl ether, 7-trifluoromethylhexadecafluorooctyl methyl ether, 7-trifluoromethylhexadecafluorooctyl ethyl ether, 7-trifluoromethylhexadecafluorooctyl propyl ether.

[0117] In some embodiments, the electrolyte may also optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature performance of the battery, additives for improving the low-temperature power performance of the battery, and the like.

[0118] The preparation method of the battery cell is well-known. In some embodiments, the positive electrode, separator, negative electrode, and electrolyte can be assembled to form a battery cell. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process, the electrode assembly is placed in an outer package, dried, and then the above-mentioned electrolyte is injected. After processes such as vacuum packaging, standing, and formation, a battery cell is obtained. Multiple battery cells can further be connected in series, parallel, or in a hybrid connection to form a battery module. Multiple battery modules can also be connected in series, parallel, or in a hybrid connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0119] The embodiments of the present application also provide an electrical device, and the electrical device includes the battery provided by the embodiments of the present application. The battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0120] The electrical device can select the type of battery according to its usage requirements, such as a battery cell, a battery module, or a battery pack.

[0121] Figure 7 FIG. is a schematic diagram of an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device for high power and high energy density, a battery pack or a battery module can be used.

[0122] Another example of an electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. This electrical device usually requires thin and light design, and a battery cell can be used as the power source.

[0123] Embodiment

[0124] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those technologies or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For the reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchase.

[0125] Example 1

[0126] Negative current collector

[0127] A commercially available two-dimensional copper foil with a thickness of 8 μm was used.

[0128] S10: Wipe the surface of the copper foil with 1 mol / L acetic acid solution, let it stand for 20 min, then continue to wipe the surface of the copper foil with absolute ethanol, ultrasonically clean it with deionized water for 5 min, and dry it in vacuum at 80 °C for 30 min;

[0129] S20: Install a Cu-Sn target (Cu and Sn are evenly dispersed in the target, and the mass ratio of Cu to Sn is 1:1), place the copper foil in a magnetron sputtering instrument, and evacuate (vacuum degree < 1 Pa);

[0130] S30: Inject argon into the magnetron sputtering instrument chamber until it reaches 1 bar, and then evacuate again (vacuum degree < 1 Pa);

[0131] S40: Set the magnetron sputtering current to 30 mA and the magnetron sputtering time to 438 s to obtain a modified layer on the copper foil, and the thickness of the modified layer is 200 nm.

[0132] Positive electrode sheet

[0133] Lithium iron phosphate, conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were mixed evenly in an appropriate amount of solvent N-methylpyrrolidone (NMP) according to a weight ratio of 8:1:1 to obtain a positive electrode slurry; the positive electrode slurry was coated on a positive electrode current collector aluminum foil, and after drying, a positive electrode plate was obtained.

[0134] Separator

[0135] The separator membrane used was a PE membrane with a thickness of 12 μm.

[0136] Examples 2 to 14

[0137] 9] The preparation process is the same as that of Example 1, and the differences are shown in Table 1 in detail.

[0138] Comparative Example 1

[0139] A commercially available two-dimensional copper foil with a thickness of 8 μm was used as the negative electrode current collector.

[0140] Comparative Examples 2 to 3

[0141] The preparation process is the same as that of Example 1, and the differences are shown in Table 1 in detail.

[0142] Comparative Example 4

[0143] Commercially available two-dimensional copper foil with a thickness of 8 μm.

[0144] S10. Wipe the surface of the copper foil with 1 mol / L acetic acid solution, let it stand for 20 min, then continue to wipe the surface of the copper foil with anhydrous ethanol, ultrasonically clean it with deionized water for 5 min, and dry it in vacuum at 80 °C for 30 min;

[0145] S20. After installing the Cu target, place the copper foil in the magnetron sputtering instrument and evacuate (vacuum degree < 1 Pa);

[0146] S30. Inject argon into the magnetron sputtering instrument chamber to 1 bar, and then evacuate again (vacuum degree < 1 Pa);

[0147] S40. Set the magnetron sputtering current to 30 mA and the magnetron sputtering time to 119 s;

[0148] S50. Replace the Sn target and evacuate (vacuum degree < 1 Pa), inject argon into the chamber to 1 bar, and then evacuate again (vacuum degree < 1 Pa);

[0149] S60. Set the magnetron sputtering current to 30 mA and the magnetron sputtering time to 438 s.

[0150] Test part

[0151] In a glove box under argon protection, assemble the positive electrode plate, negative electrode current collector and separator into a button cell. The electrolyte salt of the electrolyte is LiFSI with a concentration of 1 mol / L, and the solvent of the electrolyte uses ethylene glycol dimethyl ether (DME).

[0152] (1) Thickness expansion rate of the negative electrode current collector after lithium deposition

[0153] Before charging the button cell, record the total thickness of the modified layer as H0; at 25 °C, after standing the assembled button cell for 12 h, charge it at a constant current of 0.1C to 3.65 V, and then charge it at a constant voltage of 3.65 V to 0.05C; disassemble the button cell, measure the total thickness of the modified layer and record it as H1. Use H1 / H0 to represent the thickness expansion rate of the negative electrode current collector after lithium deposition. The number of button cell samples can be more than 6, and the test results are averaged.

[0154] (2) Cycle stability

[0155] At 25 °C, after the assembled coin cell is left standing for 12 h, it is charged at a constant current of 0.2C to 3.65 V, and then charged at a constant voltage of 3.65 V to 0.05C; after the coin cell is left standing for 10 min, it is discharged at a constant current of 0.5C to 2 V. The coin cell is cycled for charge and discharge according to the above method until the discharge capacity decays to 50% of the first-cycle discharge capacity, and the number of cycles is recorded. During testing, the number of coin cell samples can be more than 6, and the test results are averaged.

[0156] (3) Initial Coulombic efficiency

[0157] At 25 °C, after the assembled coin cell is left standing for 12 h, it is charged at a constant current of 0.1C to 3.65 V, and then charged at a constant voltage of 3.65 V to 0.05C to obtain the charge capacity; after the coin cell is left standing for 10 min, it is discharged at a constant current of 0.2C to 2 V to obtain the discharge capacity. The initial Coulombic efficiency of the coin cell = discharge capacity / charge capacity × 100%. During testing, the number of coin cell samples can be more than 6, and the test results are averaged.

[0158] The test results are shown in Table 1.

[0159]

[0160] It can be seen from Examples 1 to 5 and Comparative Examples 1 to 3 that the modified layer obtained from the active material and the substrate material as raw materials can better achieve the purpose of improving the comprehensive performance of the battery. The increase of the active material in the modified layer within a certain range will improve the cycling performance, but the volume expansion of the current collector will also increase significantly.

[0161] It can be seen from the comparison between Example 1 and Comparative Example 4 that the modified layer formed by sputtering after the active material and the substrate material are uniformly mixed has better performance than the modified layer obtained by sputter-depositing the substrate material and the active material in layers. This may be because in the modified layer formed by sputtering after uniform mixing, the binding force between the active material and the substrate material is higher, the binding stability of the modified layer on the current collector during the charge and discharge process of the battery is better, the risk of the modified layer falling off is smaller, and it has better cycling performance.

[0162] It can be seen from the data of Examples 6 to 9 that the increase in the thickness of the modified layer can reduce the volume expansion of the negative current collector, but if the thickness of the modified layer is too thick, the initial Coulombic efficiency of the battery will decrease.

[0163] Although the present application has been described with reference to preferred embodiments, various modifications can be made thereto and components thereof can be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any manner. 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. An electrode assembly, comprising a positive electrode plate, a negative current collector, and a separator located between the positive electrode plate and the negative current collector, characterized in that, the electrode assembly further includes a modification layer, the modification layer is located between the negative current collector and the separator, and the modification layer includes a base material and an active material dispersed in the base material; the lithium metal nucleation overpotential of the base material is ≥80 mV, and the lithium metal nucleation overpotential of the active material is less than the lithium metal nucleation overpotential of the base material.

2. The electrode assembly according to claim 1, wherein, The lithium metal nucleation overpotential of the base material is 100 mV - 500 mV; and / or, the lithium metal nucleation overpotential of the active material is 10 mV - 50 mV.

3. The electrode assembly according to claim 1 or 2, characterized in that, The base material includes one or more of non-graphitized carbon materials and non-lithophilic metals.

4. The electrode assembly according to claim 3, characterized in that, The non-graphitized carbon materials include hard carbon, amorphous carbon or a combination thereof; and / or, The non-lithophilic metals include one or more of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Ta, W, Pt, Ir.

5. The electrode assembly according to any one of claims 1 to 4, characterized in that The active material includes one or more of graphitized carbon, lithophilic metals or their compounds.

6. The electrode assembly according to claim 5, characterized in that, The graphitized carbon includes one or more of graphite, graphene, graphyne; and / or The lithophilic metals include one or more of Sn, Mg, Zn, Bi, Pb, Au, Ag, Al, Si, In, Ga; and / or The compounds of the lithophilic metals include one or more of oxides, sulfides, fluorides, chlorides, nitrides, carbides.

7. The electrode assembly according to any one of claims 1 to 6, characterized in that Based on the total weight of the modification layer, the weight content of the active material is 50% - 95%, and the weight content of the base material is 5% - 50%.

8. The electrode assembly according to any one of claims 1 to 7, characterized in that, Based on the total weight of the modification layer, the weight content of the active material is 55% - 70%, and the weight content of the base material is 30% - 45%.

9. The electrode assembly according to any one of claims 1 to 8, characterized in that, The areal density of the active material ≥ 0.5 g / m 2 .

10. The electrode assembly according to any one of claims 1 to 9, characterized in that, The thickness of the modification layer is 10 nm - 1000 nm.

11. The electrode assembly according to any one of claims 1 to 10, characterized in that, The thickness of the modification layer is 100 nm - 500 nm.

12. The electrode assembly according to any one of claims 1 to 11, characterized in that, The material of the negative current collector includes one or more of copper, nickel, titanium, magnesium, aluminum, copper alloy, nickel alloy, titanium alloy, magnesium alloy, aluminum alloy.

13. A battery cell, characterized in that, An electrode assembly according to any one of claims 1 to 12.

14. The battery cell according to claim 13, wherein The battery cell includes at least one of a lithium metal-free battery cell and a sodium metal-free battery cell.

15. A secondary battery, characterized in that, A battery cell according to claim 13 or 14.

16. An electrical device, characterized in that, A secondary battery according to claim 15.

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