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

Abstract

The present application provides an electrode assembly, a battery cell, a secondary battery, and an electric device. The electrode assembly comprises 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 comprises a modification layer, the modification layer is located between the negative electrode current collector and the separator, and the modification layer comprises a base material and an active material dispersed in the base material; the lithium metal nucleation overpotential of the base material is greater than or equal to 80 mV, and the lithium metal nucleation overpotential of the active material is less than that of the base material. The modification layer in the electrode assembly of the present application can reduce volume expansion during the deposition of metals such as lithium and sodium on the negative electrode current collector, so that the risk of piercing the separator caused by volume expansion is reduced, thereby improving the reliability and the cycle performance of batteries.

Description

Electrode assembly, battery cell, secondary battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410137192.4, filed on January 31, 2024, entitled “Electrode assembly, battery cell, secondary battery and electrical device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to an electrode assembly, a battery cell, a secondary battery, and an electrical device. Background Art

[0004] Compared to ionic battery cells, metal battery cells can have higher energy density. However, unlike the negative electrode of ionic battery cells, the surface of the negative electrode current collector commonly used in metal batteries usually adopts a localized nucleation mode. The localized crystal nuclei easily grow into a loose and porous structure, causing the negative electrode current collector to expand rapidly and produce violent side reactions. It may even cause dendrites to pierce the separator, and at the same time affect the cycle stability of the battery cell. Summary of the Invention

[0005] The embodiments of the present application provide an electrode assembly, a battery cell, a secondary battery, and an electrical device, so that the battery cell has good cycle stability.

[0006] In a first aspect, an embodiment of the present application provides an electrode assembly, comprising a positive electrode sheet, a negative electrode current collector, and an isolation membrane located between the positive electrode sheet and the negative electrode current collector, the electrode assembly further comprising a modification layer, the modification layer being located between the negative electrode current collector and the isolation membrane, the modification layer comprising 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.

[0007] In the embodiment of the present application, a modification layer is provided between the ancient book current collector and the isolation membrane. The active material in the modification layer has a high affinity with 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 make the deposited metal evenly distributed on the surface of the negative electrode current collector, thereby 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 no volume change occurs before and after metal deposition, and plays a role in limiting the volume change of the negative electrode current collector in the modification layer, which can reduce the volume expansion of metals such as lithium and sodium during the deposition process, thereby reducing the risk of puncturing the isolation membrane due to volume expansion, thereby 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. These alloys can increase the potential of the negative electrode of the battery, which is beneficial to improving the quality of the solid electrolyte interface (SEI) film on the negative electrode surface, thereby improving the cycle stability of the battery cell.

[0008] In some embodiments, the lithium metal nucleation overpotential of the substrate material is 100 mV-500 mV.

[0009] In some embodiments, the active material has a lithium metal nucleation overpotential of 10 mV to 50 mV.

[0010] In some embodiments, the substrate material includes one or more of a non-graphitizable carbon material and a non-lithiophilic metal.

[0011] In some embodiments, the non-graphitizable carbon material includes hard carbon, amorphous carbon, or a combination thereof.

[0012] In some embodiments, the non-lithiophilic metal includes one or more of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Ta, W, Pt, and Ir.

[0013] In some embodiments, the active material includes one or more of graphitized carbon, a lithiophilic metal, or a compound thereof.

[0014] In some embodiments, the graphitized carbon includes one or more of graphite, graphene, and graphyne.

[0015] In some embodiments, the lithiophilic metal includes one or more of Sn, Mg, Zn, Bi, Pb, Au, Ag, Al, Si, In, and Ga. The lithiophilic metal compound includes one or more of oxides, sulfides, fluorides, chlorides, nitrides, and carbides.

[0016] In some embodiments, based on the total weight of the modified layer, the weight content of the active material is 40%-95%, and the weight content of the base material is 5%-60%.

[0017] 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 base material is 30%-45%.

[0018] In some embodiments, the surface density of the active material is ≥ 0.5 g / m 2 .

[0019] In some embodiments, the thickness of the modified layer is 10 nm-1000 nm.

[0020] In some embodiments, the modification layer has a thickness of 100 nm to 500 nm.

[0021] In some embodiments, the material of the negative electrode current collector includes one or more of copper, nickel, titanium, magnesium, aluminum, copper alloys, nickel alloys, titanium alloys, magnesium alloys, and aluminum alloys.

[0022] In a second aspect, an embodiment of the present application provides a battery cell, which includes the electrode assembly of the embodiment of the first aspect of the present application.

[0023] In some embodiments, the battery cell includes at least one of a negative electrode-free lithium metal battery cell and a negative electrode-free sodium metal battery cell.

[0024] In a third aspect, an embodiment of the present application provides a secondary battery, comprising the battery cell of the embodiment of the second aspect of the present application.

[0025] In a fourth aspect, an embodiment of the present application provides an electrical device, comprising the secondary battery of the embodiment of the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0027] FIG1 is a schematic diagram of a battery cell provided in some embodiments of the present application.

[0028] FIG2 is an exploded schematic diagram of a battery cell provided in some embodiments of the present application.

[0029] FIG3 is a schematic diagram of a battery module provided in some embodiments of the present application.

[0030] FIG4 is a schematic diagram of a battery pack provided in some embodiments of the present application.

[0031] FIG5 is an exploded schematic diagram of the battery pack shown in FIG4 .

[0032] FIG6 is a schematic structural diagram of an electrode assembly of a battery cell provided in some embodiments of the present application.

[0033] FIG7 is a schematic diagram of an electrical device provided in some embodiments of the present application.

[0034] In the accompanying drawings, the drawings are not necessarily drawn to scale.

[0035] The accompanying drawings are explained as follows: 1. battery pack; 2. upper box; 3. lower box; 4. battery module; 5. battery cell; 51. shell; 52. electrode assembly; 53. cover plate; 10. positive electrode sheet; 20. negative electrode current collector; 30. isolation membrane; 40. modification layer. DETAILED DESCRIPTION

[0036] Below, the embodiments of the electrode assembly, battery cell, battery and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0037] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this 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.

[0038] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0039] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0040] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating 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), indicating 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.

[0041] Unless otherwise specified, the terms "connected" and "connection" in this application should be understood broadly. For example, they can refer to fixed connection, detachable connection, or integral connection; they can refer to direct connection, indirect connection through an intermediate medium, or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0042] As used herein, the term "multiple" refers to more than two, including two. As used herein, the term "multiple" refers to more than two, including two.

[0043] The battery mentioned in the embodiments of the present application may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application may include a battery cell, a battery module, or a battery pack.

[0044] A battery cell is the smallest unit of a battery, independently capable of charging and discharging. A battery cell can be cylindrical, rectangular, or have other shapes, though this is not a limitation in the present invention. Figure 1 shows a battery cell 5 with a rectangular structure as an example.

[0045] When there are multiple battery cells, the multiple battery cells are connected in series, in parallel, or in mixed series via a busbar. In some embodiments, the battery may 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 may be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed in the housing. In some embodiments, the housing may serve as part of the vehicle's chassis structure. For example, a portion of the housing may form at least a portion of the vehicle's floor, or a portion of the housing may form at least a portion of the vehicle's crossbeam or longitudinal beam.

[0046] In some embodiments, battery cells can be assembled into a battery module. The number of battery cells contained in a battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 2 is a schematic diagram of a battery module 4 as an example. As shown in Figure 2, in the battery module 4, multiple battery cells 5 can be arranged in sequence along the length of the battery module 4. Of course, they can also be arranged in any other manner. The multiple battery cells 5 can further be fixed by fasteners.

[0047] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0048] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0049] Figures 3 and 4 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 3 and 4, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing comprises an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in any manner within the housing.

[0050] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0051] The battery cells provided in the embodiments of the present application are negative electrode-free battery cells, and may include, for example, at least one of negative electrode-free lithium metal battery cells and negative electrode-free sodium metal battery cells.

[0052] A negative electrode-free battery cell generally refers to a battery cell constructed without the active negative electrode layer being applied during the manufacturing process. For example, a negative electrode active material layer is not applied to the negative electrode through coating or deposition, or a carbonaceous active material layer is used to form the negative electrode active material layer. During initial charging, ions on the negative electrode side gain electrons and deposit on the surface of the negative electrode current collector to form metal. During discharge, the metal can be converted back to ions and returned to the positive electrode, enabling cyclic charge and discharge. Compared to other battery cells, negative electrode-free battery cells can achieve higher energy density due to the lack of a negative electrode active material layer. In some embodiments, to improve battery cell performance, the negative electrode side of the negative electrode-free battery cell may also be provided with some conventional negative electrode active materials, such as carbon materials. Although these materials have a certain capacity, their content is relatively low and they are not used as the primary negative electrode active material in the battery cell. Therefore, the battery cell constructed in this manner can still be considered a negative electrode-free battery cell. The CB (Cell Balance) value of a battery cell without a negative electrode is typically very small. For example, in some embodiments, the CB value of a battery cell without a negative electrode can be less than or equal to 0.1. The CB value is the unit area capacity of the negative electrode in the battery cell divided by the unit area capacity of the positive electrode. Because a battery cell without a negative electrode contains no or only a small amount of negative electrode active material, the unit area capacity of the negative electrode is relatively small, and thus the CB value is very small, for example, typically less than or equal to 0.1.

[0053] The battery cell includes an electrode assembly, which may be a wound structure or a laminated structure, and the present invention is not limited thereto.

[0054] The battery cell may also include an outer packaging that can be used to encapsulate the electrode assembly. The outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging can also be a soft shell, such as a bag-type soft shell. The soft shell material can be a plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0055] In some embodiments, as shown in Figure 5, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, which together 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, thereby sealing the receiving cavity. The electrode assembly 52 is enclosed in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and can be adjusted according to needs.

[0056] [Electrode assembly]

[0057] An embodiment of the first aspect of the present application provides an electrode assembly, as shown in Figure 6, the electrode assembly 52 includes a positive electrode sheet 10, a negative electrode current collector 20, and an isolation membrane 30 located between the positive electrode sheet 10 and the negative electrode current collector 20; the electrode assembly 52 also includes a modification layer 40, the modification layer 40 is located between the negative electrode current collector 20 and the isolation membrane 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 ≥80mV, and the lithium metal nucleation overpotential of the active material is less than the lithium metal nucleation overpotential of the base material.

[0058] The negative electrode current collectors commonly used in metal battery cells currently have poor affinity for lithium and sodium, resulting in a high nucleation overpotential, which leads to insufficient active sites for lithium and sodium metal deposition. Lithium and sodium metals adopt a localized nucleation pattern on the untreated negative electrode current collector surface, resulting in loose metal deposition. This causes unlimited volume expansion of the lithium and sodium metals and produces violent side reactions, which can even cause dendrites to directly pierce the separator, posing a short circuit risk.

[0059] In the embodiment of the present application, a modification layer is provided between the negative electrode 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 a high affinity with 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 make the deposited metal uniformly distributed on the surface of the negative electrode current collector, which can reduce 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 plays a role in limiting the volume change of the negative electrode current collector in the modification layer, which can reduce the volume expansion of metals such as lithium and sodium during the deposition process, thereby reducing the risk of puncturing 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. These alloys can increase the potential of the negative electrode of the battery, which is beneficial to improving the quality of the solid electrolyte interface (SEI) film on the negative electrode surface, thereby improving the cycle stability of the battery cell.

[0060] In some embodiments, the lithium metal nucleation overpotential of the active material may be 10 mV to 50 mV, optionally 20 mV to 35 mV.

[0061] The lithium metal nucleation overpotential of the active material is within this range, and it has better affinity with metals such as lithium and sodium, thereby providing more active sites, inducing uniform deposition of the metal, and forming alloys with the deposited metal, thereby reducing the nucleation overpotential of the negative electrode current collector and reducing local nucleation.

[0062] In some embodiments, the lithium metal nucleation overpotential of the substrate material may be 100 mV-500 mV, optionally 150 mV-350 mV.

[0063] 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. It hardly reacts with the substrate material during the metal deposition process, thereby further reducing the volume expansion after metal deposition and improving the reliability of the battery cell.

[0064] The nucleation overpotential of the active material and substrate material can be measured as follows: In an argon-protected glove box, a button cell is assembled with a lithium metal sheet as the counter electrode and a sheet (8 μm thick) of the active material or substrate corresponding material. The electrolyte salt is LiFSI at a concentration of 1 mol / L, and the electrolyte solvent is a mixed solvent of ethylene glycol dimethyl ether (DME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a weight ratio of 1:1. The separator is a 12 μm thick PE film.

[0065] At 25°C, the assembled button cell was left to stand for 12 hours and the current was measured at 1 mA / cm2 The current density is constant current discharge to 1 mAh / cm 2 At the beginning of the lithium metal deposition process, there will be a significant voltage drop, followed by a flat voltage platform. The difference between the voltage at the lowest point of the discharge curve and the flat part of the voltage platform (here expressed as the absolute value) is used as the lithium metal nucleation overpotential of the active material or substrate material.

[0066] It should be noted that the specific numerical value of the lithium metal nucleation overpotential of the above-mentioned active material or substrate material is used to indicate the physicochemical properties of the active material or substrate material, as well as the affinity between the active material or substrate material and the deposited metal. It does not mean that the negative electrode current collector provided in the embodiment of the present application can only be used in a negative electrode-free lithium metal battery cell. The negative electrode current collector provided in the embodiment of the present application can also be used in a negative electrode-free sodium metal battery cell.

[0067] In some embodiments, the substrate material includes one or more of a non-graphitizable carbon material and a non-lithiophilic metal.

[0068] In some embodiments, the non-graphitizable carbon material includes hard carbon, amorphous carbon, or a combination thereof.

[0069] In some embodiments, the non-lithiophilic 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, and Ir; optionally, the non-lithiophilic metal includes one or more of Fe, Cu, and Mo.

[0070] In some embodiments, the active material includes one or more of graphitized carbon, a lithiophilic metal, or a compound thereof.

[0071] In some embodiments, the graphitized carbon includes one or more of graphite, graphene, and graphyne.

[0072] In some embodiments, the lithiophilic metal includes one or more of Sn, Mg, Zn, Bi, Pb, Au, Ag, Al, Si, In, and Ga; optionally, the lithiophilic metal includes one or more of Sn, Mg, Zn, and Bi.

[0073] In some embodiments, the lithiophilic metal compound includes one or more of an oxide, a sulfide, a fluoride, a chloride, a nitride, and a carbide.

[0074] In some embodiments, based on the total weight of the modified layer, the weight content of the active material is 40%-95%, and the weight content of the base material is 5%-60%.

[0075] By adjusting the weight content of the active material and the base material in the modified layer within the above range, the synergistic effect of the base material and the active material can be better exerted, the volume expansion caused by metal deposition can be reduced, and the nucleation overpotential can be reduced, thereby reducing local nucleation and slowing down dendrite growth.

[0076] When the content of active material in the modification layer is low and the content of base material is high, the active material in the modification layer can provide fewer active sites, which makes it difficult to effectively reduce local nucleation and slow down dendrite growth, and the cycle stability and reliability of the battery cell will be reduced.

[0077] When the content of active material in the modification layer is high and the content of base material is low, the base material cannot effectively limit the volume expansion caused by the deposition of metals such as lithium and sodium. As a result, there is a risk of puncturing the isolation membrane during the long-term cycle charge and discharge of the battery, resulting in reduced reliability of the battery cell; at the same time, excessive volume expansion will lead to reduced internal porosity of the battery, poor electrolyte wettability and other problems, which will lead to reduced cycle stability of the battery.

[0078] Therefore, by adjusting the weight contents of the active material and the base material in the modification layer within the above range, the active material of the base material can play a better synergistic role, thereby enabling the battery cell to have both high reliability and long cycle life.

[0079] Optionally, the weight content of the active material is 55%-70%, and the weight content of the base material is 30%-45%.

[0080] Further adjusting the weight contents of the active material and the base material in the modified layer within the above range can further improve the cycle stability and reliability of the battery cell.

[0081] In some embodiments, the surface density of the active material is ≥ 0.5 g / m 2 .

[0082] In the examples of this application, the surface density refers to the weight of the active material per unit area. The active material in the modified layer primarily serves to provide active sites, reduce the nucleation overpotential, and minimize localized nucleation. By regulating the surface density of the active material in the modified layer within the above range, the active material can be dispersed more uniformly and densely in the modified layer, thereby providing more active sites, reducing the nucleation overpotential, reducing localized nucleation, and slowing dendrite growth, thereby improving the cycling stability and reliability of the battery cell.

[0083] Optionally, the surface density of the active material in the modified layer is 0.6 g / m 2 -60g / m 2 , further optional 5g / m 2 -50g / m2 , 10g / m2 is optional 2 -25g / m 2 .

[0084] By limiting the surface density of the active material in the modified layer to within the above range, it is possible to further provide more active sites, reduce the nucleation overpotential, reduce localized nucleation, and slow down dendrite growth, thereby further improving the cycling stability and reliability of the battery cell. The surface density of the active material is related to the thickness of the modified layer and the content of the active material in the modified layer. It is understandable that when the thickness of the modified layer remains unchanged, the higher the proportion of active material, the higher its surface density; when the proportion of active material in the modified layer remains unchanged, the thicker the modified layer, the higher its surface density.

[0085] In some embodiments, the thickness of the modification layer is 10 nm to 1000 nm.

[0086] The thickness of the modified layer is limited to the above range, which 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.

[0087] Optionally, the thickness of the modification layer is 100 nm-500 nm.

[0088] The thickness of the modified layer is limited to the above range, which can further reduce the nucleation overpotential and limit the volume expansion during the metal deposition process, thereby further improving the reliability and cycle stability of the battery.

[0089] In some embodiments, the modification layer can be disposed on the surface of the negative electrode current collector by magnetron sputtering, chemical plating, electroplating, or spraying.

[0090] Alternatively, the modified layer can be deposited on the negative electrode current collector surface using magnetron sputtering. Compared to other methods, magnetron sputtering is simpler, faster, and more convenient to operate. Furthermore, the modified layer formed by magnetron sputtering has a stronger bond with the negative electrode current collector and better stability.

[0091] In some embodiments, the material of the negative electrode current collector includes one or more of copper, nickel, titanium, magnesium, aluminum, copper alloys, nickel alloys, titanium alloys, magnesium alloys, and aluminum alloys.

[0092] Alternatively, the negative electrode current collector may include copper foil or nickel foil, more preferably copper foil.

[0093] [Positive electrode]

[0094] In some embodiments, the positive electrode sheet 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 comprising a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0095] In some embodiments, the positive electrode active material includes a material capable of extracting and inserting lithium.

[0096] 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. Lithium transition metal oxides may include, but are not limited to, layered structures and spinel structures. Examples of lithium-containing phosphates may include, but are not limited to, one or more of 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 iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds.

[0097] 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 f One 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.

[0098] 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.

[0099] As an example, the positive electrode active material may include but is not limited to LiCoO2, LiNiO2, LiMnO2, LiNi 1 / 2 Mn 1 / 2 O2、LiMn2O4、Li 4 / 3 Ti 5 / 3 O4、LiNi 1 / 2 Mn1 / 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.

[0100] 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.

[0101] In some embodiments, as examples, the positive electrode active material may include but is not limited to NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, Na 0.67 MO2 (M includes at least two of Fe, Co, Cr, Mn, Ni, V, Ti, Mo), NaMO2 (M includes at least two of Fe, Co, Ni, V, Ti, 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.

[0102] The modified compounds of the above-mentioned positive electrode active materials may be used to perform doping modification and / or surface coating modification on the positive electrode active materials.

[0103] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. As an example, the positive electrode 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.

[0104] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, fluorinated acrylic 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 one or more of carboxymethyl chitosan (CMCS).

[0105] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may 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).

[0106] The positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional positive electrode conductive agent, optional positive electrode binder, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0107] [Isolation film]

[0108] The separator is located between the positive and negative electrodes and mainly serves to prevent internal short circuits.

[0109] The present application has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0110] In some embodiments, the material of the isolation membrane may include, but is not limited to, one or more of fiberglass, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different.

[0111] [Electrolytes]

[0112] The battery cells include an electrolyte.

[0113] In some embodiments, the electrolyte is an electrolyte solution including an electrolyte salt and an organic solvent.

[0114] In some embodiments, the electrolyte includes anions, which may include bis(fluorosulfonyl)imide anions (FSI - ), bis(trifluoromethanesulfonyl)imide anion (TFSI - ), dioxalatoborate anion (BOB - ), difluorooxalatoborate anion (DFOB - ), difluorobis(oxaloyl)phosphate anion (DFOP - ), tetrafluorooxalophosphate anion (TFOP - ), difluorophosphate anion (PO2F2 - ), hexafluorophosphate anion (PF6 - ), tetrafluoroborate anion (BF4 - ), hexafluoroarsenate anion (AsF6 - ), trifluoromethanesulfonate anion (CF3SO3 - )

[0115] In some embodiments, the electrolyte includes cations, which may include one or more of lithium ions and sodium ions.

[0116] In some embodiments, the concentration of the electrolyte salt may be greater than 0.3 mol / L, and may be greater than 0.7 mol / L. The concentration of the electrolyte salt may further be less than 4 mol / L, and may be less than 2.5 mol / L or less than 1.7 mol / L. When the concentration of the electrolyte salt is within the above range, the electrolyte solution can have suitable ionic conductivity.

[0117] Organic solvent can include but not limited to one or more in esters, ethers, sulfones, nitrile etc.Ester can include but not limited to one or more in carbonate, phosphate, carboxylate, sulfate, sulfonate etc.Carbonate can comprise cyclic carbonate and / or chain carbonate, alternatively, carbonate can comprise cyclic carbonate and chain carbonate simultaneously.Chain carbonate can comprise low-viscosity polar chain carbonate, aliphatic branched-chain carbonate etc.

[0118] As an example, the organic solvent may include, but is not limited to, 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, C4F9O CH3, 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-trifluoromethyl One or more of trifluoromethyl decafluoropentyl methyl ether, 4-trifluoromethyl decafluoropentyl ethyl ether, 4-trifluoromethyl decafluoropentyl propyl ether, 5-trifluoromethyl dodecafluorohexyl methyl ether, 5-trifluoromethyl dodecafluorohexyl ethyl ether, 5-trifluoromethyl dodecafluorohexyl propyl ether, 6-trifluoromethyl tetradecafluoroheptyl methyl ether, 6-trifluoromethyl tetradecafluoroheptyl ethyl ether, 6-trifluoromethyl tetradecafluoroheptyl propyl ether, 7-trifluoromethyl hexafluorooctyl methyl ether, 7-trifluoromethyl hexafluorooctyl ethyl ether, and 7-trifluoromethyl hexafluorooctyl propyl ether.

[0119] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0120] The preparation method of battery cells 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 lamination process. The electrode assembly is placed in an outer package, dried, and then injected with the above-mentioned electrolyte. After vacuum packaging, standing, formation and other processes, a battery cell is obtained. Multiple battery cells can also be further connected in series, in parallel, or in a mixed manner to form a battery module. Multiple battery modules can also be connected in series, in parallel, or in a mixed manner to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0121] The present application also provides an electrical device, which includes a battery provided in the present application. The battery can be used as a power source for the electrical device or as an energy storage unit for 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.

[0122] 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.

[0123] Figure 7 is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module may be used.

[0124] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0125] Example

[0126] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0127] Example 1

[0128] negative electrode current collector

[0129] Commercially available two-dimensional copper foil with a thickness of 8 μm.

[0130] S10, wipe the copper foil surface with 1 mol / L acetic acid solution, let it stand for 20 minutes, continue to wipe the copper foil surface with anhydrous ethanol, ultrasonically clean it with deionized water for 5 minutes, and vacuum dry it at 80°C for 30 minutes;

[0131] S20, installing a Cu-Sn target (Cu and Sn are evenly dispersed in the target, and the mass ratio of Cu to Sn is 1:1), placing the copper foil in a magnetron sputtering instrument, and evacuating the device (vacuum degree <1 Pa);

[0132] S30, after injecting argon gas into the magnetron sputtering instrument cabin to 1 bar, evacuate the chamber again (vacuum degree < 1 Pa);

[0133] S40, setting the magnetron sputtering current to 30 mA and the magnetron sputtering time to 438 s, to form a modified layer on the copper foil, the modified layer having a thickness of 200 nm.

[0134] Positive electrode

[0135] Lithium iron phosphate, conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in an appropriate amount of solvent N-methylpyrrolidone (NMP) at a weight ratio of 8:1:1 to obtain a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector aluminum foil and dried to obtain a positive electrode sheet.

[0136] Isolation film

[0137] The isolation film is a PE film with a thickness of 12 μm.

[0138] Examples 2 to 14

[0139] The preparation process is consistent with that of Example 1, and the differences are detailed in Table 1.

[0140] Comparative Example 1

[0141] Commercially available two-dimensional copper foil with a thickness of 8 μm was used as the negative electrode current collector.

[0142] Comparative Examples 2 to 3

[0143] The preparation process is the same as that of Example 1, and the differences are shown in Table 1

[0144] Comparative Example 4

[0145] Commercially available two-dimensional copper foil with a thickness of 8 μm.

[0146] S10, wipe the copper foil surface with 1 mol / L acetic acid solution, let it stand for 20 minutes, continue to wipe the copper foil surface with anhydrous ethanol, ultrasonically clean it with deionized water for 5 minutes, and vacuum dry it at 80°C for 30 minutes;

[0147] S20, after installing the Cu target, place the copper foil in the magnetron sputtering instrument and evacuate the chamber (vacuum degree < 1 Pa);

[0148] S30, after injecting argon gas into the magnetron sputtering instrument cabin to 1 bar, evacuate the chamber again (vacuum degree < 1 Pa);

[0149] S40, setting the magnetron sputtering current to 30 mA and the magnetron sputtering time to 119 s;

[0150] S50, replace the Sn target, and evacuate the chamber (vacuum degree <1Pa), inject argon gas into the chamber to 1bar, and evacuate the chamber again (vacuum degree <1Pa);

[0151] S60, setting the magnetron sputtering current to 30 mA and the magnetron sputtering time to 438 s.

[0152] Test section

[0153] In an argon-protected glove box, the positive electrode sheet, negative electrode current collector, and separator were assembled into a button cell. The electrolyte salt was LiFSI at a concentration of 1 mol / L, and the solvent was ethylene glycol dimethyl ether (DME).

[0154] (1) Thickness expansion rate of negative electrode current collector after lithium deposition

[0155] Before charging the button cell, the total thickness of the modified layer is recorded as H0. After standing for 12 hours at 25°C, the assembled button cell is charged at a constant current of 0.1C to 3.65V. Then, it is charged at a constant voltage of 3.65V to 0.05C. The button cell is disassembled and the total thickness of the modified layer is measured and recorded as H1. The thickness expansion ratio of the negative electrode current collector after lithium deposition is expressed as H1 / H0. Six or more button cell samples can be used, and the test results are averaged.

[0156] (2) Cyclic stability

[0157] After the assembled button cell was allowed to rest for 12 hours at 25°C, it was charged at a constant current of 0.2C to 3.65V. Then, it was charged at a constant voltage of 3.65V to 0.05C. After the button cell was allowed to rest for 10 minutes, it was discharged at a constant current of 0.5C to 2V. The button cell was cycled according to the above method until the discharge capacity decayed to 50% of the initial discharge capacity. The number of cycles was recorded. The number of button cell samples can be more than 6 during testing, and the test results are averaged.

[0158] (3) First Coulomb efficiency

[0159] After the assembled button cell was allowed to rest for 12 hours at 25°C, it was charged at a constant current of 0.1C to 3.65V. Then, it was charged at a constant voltage of 3.65V to 0.05C to obtain the charge capacity. After the button cell was allowed to rest for 10 minutes, it was discharged at a constant current of 0.2C to 2V to obtain the discharge capacity. The initial coulombic efficiency of the button cell = discharge capacity / charge capacity × 100%. The number of button cell samples can be more than 6, and the test results are averaged.

[0160] The test results are shown in Table 1.

[0161] Examples 1 to 5 and Comparative Examples 1 to 3 demonstrate that modified layers made from active materials and substrate materials can effectively enhance overall battery performance. Increasing the amount of active material in the modified layer within a certain range improves cycle performance, but also significantly increases the volume expansion of the current collector.

[0162] By comparing Example 1 and Comparative Example 4, it can be seen that the modified layer formed by sputtering after uniformly mixing the active material and the base material has better performance than the modified layer obtained by layered sputtering of the base material and the active material. This may be because in the modified layer formed by sputtering after uniform mixing, the binding force between the active material and the base material is higher, the binding stability of the modified layer on the current collector during battery charging and discharging is better, the risk of the modified layer falling off is smaller, and it has better cycle performance.

[0163] It can be seen from the data of Examples 6 to 9 that an increase in the thickness of the modified layer can reduce the volume expansion of the negative electrode current collector, but an excessively thick modified layer will result in a decrease in the first-cycle coulombic efficiency of the battery.

[0164] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described 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 encompasses all technical solutions within the scope of the claims.

Claims

1. An electrode assembly comprising 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, the modification layer being located between the negative electrode current collector and the separator, the modification layer including 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, wherein: The substrate material includes one or more of a non-graphitizable carbon material and a non-lithium-philic metal.

4. The electrode assembly according to claim 3, wherein: The non-graphitizable carbon material comprises hard carbon, amorphous carbon or a combination thereof; and / or, The non-lithium-philic metal includes one or more of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Ta, W, Pt, and Ir.

5. The electrode assembly according to any one of claims 1 to 4, wherein: The active material includes one or more of graphitized carbon, lithiophilic metals or compounds thereof.

6. The electrode assembly according to claim 5, wherein: The graphitized carbon includes one or more of graphite, graphene, and graphyne; and / or The lithiophilic metal includes one or more of Sn, Mg, Zn, Bi, Pb, Au, Ag, Al, Si, In, and Ga; and / or The lithium-philic metal compound includes one or more of oxides, sulfides, fluorides, chlorides, nitrides, and carbides.

7. The electrode assembly according to any one of claims 1 to 6, wherein: Based on the total weight of the modified 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, wherein: Based on the total weight of the modified 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, wherein: The surface density of the active material is ≥0.5 g / m 2 .

10. The electrode assembly according to any one of claims 1 to 9, wherein: The thickness of the modified layer is 10 nm to 1000 nm.

11. The electrode assembly according to any one of claims 1 to 10, wherein: The thickness of the modified layer is 100nm-500nm.

12. The electrode assembly according to any one of claims 1 to 11, wherein: 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. 13 . A battery cell comprising the electrode assembly according to claim 1 .

14. The battery cell according to claim 13, wherein: The battery cell includes at least one of a negative electrode-free lithium metal battery cell and a negative electrode-free sodium metal battery cell. 15 . A secondary battery comprising the battery cell according to claim 13 .

16. An electrical device comprising the secondary battery according to claim 15.

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