Polymer current collector, preparation method thereof, and related secondary battery, battery module, battery pack and device

Abstract

A polymer current collector includes a polymer film layer, wherein the polymer film layer includes a first polymer film layer and a second polymer film layer, the resistivity of the first polymer film layer is denoted as ρ1, the resistivity of the second polymer film layer is denoted as ρ2, and the current collector satisfies: ρ1>ρ2. The polymer current collector can induce lithium metal to deposit from a side with low conductivity to a side with high conductivity, thereby avoiding the risk of lithium ions depositing on the surface of the current collector, thereby improving the cycle life of a lithium metal battery.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a polymer current collector, a preparation method thereof, and related secondary batteries, battery modules, battery packs, and devices. Background Art

[0002] Lithium metal (Li) has a very high theoretical specific capacity (3860 mAh g -1 ), the lowest reduction potential (-3.04 V vs. standard hydrogen electrode), the smallest atomic radius, and the lowest density (0.534 g cm -3 ) and other advantages, and has been widely studied in the industry. However, during the deposition process of lithium metal, lithium dendrites are inevitably produced, which greatly affects the safety and electrochemical properties of lithium metal batteries, limiting the rapid popularization of lithium metal batteries.

[0003] Therefore, it is necessary to provide a technical solution to improve the safety and cycle life of lithium metal batteries. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the purpose of the present application is to provide a polymer current collector that can be used for lithium metal batteries, a method for preparing the polymer current collector, a secondary battery containing the polymer current collector, and related battery modules, battery packs and devices. The polymer current collector effectively avoids the risk of lithium ion deposition on the surface of the current collector and improves the cycle life of the lithium metal battery.

[0005] In order to achieve the above purpose, this application adopts the following technical solutions:

[0006] In a first aspect, the present application provides a polymer current collector, which includes a polymer film layer, and the polymer film layer includes a first polymer film layer and a second polymer film layer. The resistivity of the first polymer film layer is denoted as ρ1, the resistivity of the second polymer film layer is denoted as ρ2, and the current collector satisfies: ρ1>ρ2.

[0007] The second aspect of the present application provides a method for preparing the polymer current collector according to the first aspect, the method comprising the following steps:

[0008] S1, providing two or more polymer films having different resistivities;

[0009] S2, pressing the polymer films with different resistivities described in S1 in order of resistivity from high to low or from low to high to obtain the polymer current collector;

[0010] The polymer current collector includes a polymer film layer, the polymer film layer includes a first polymer film layer and a second polymer film layer, the resistivity of the first polymer film layer is denoted as ρ1, the resistivity of the second polymer film layer is denoted as ρ2, and the current collector satisfies: ρ1>ρ2.

[0011] A third aspect of the present application provides a secondary battery, the secondary battery comprising a negative electrode plate, the negative electrode plate comprising the polymer current collector described in the first aspect of the present application or the polymer current collector prepared by the method described in the second aspect of the present application.

[0012] A fourth aspect of the present application provides a battery module, which includes the secondary battery of the third aspect of the present application.

[0013] A fifth aspect of the present application provides a battery pack, which includes the battery module of the fourth aspect of the present application.

[0014] A sixth aspect of the present application provides a device comprising at least one of the secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application, or the battery pack of the fifth aspect of the present application.

[0015] The beneficial effects of this application are:

[0016] The polymer current collector of the present application has a conductive gradient, which can induce lithium metal to deposit from the side with low conductivity to the side with high conductivity, avoiding the risk of lithium ion deposition on the surface of the current collector, thereby improving the cycle life of the lithium metal battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic structural diagram of a polymer current collector according to one embodiment of the present application.

[0018] Figure 2 It is a schematic structural diagram of a polymer current collector according to another embodiment of the present application.

[0019] Figure 3 This is a schematic diagram of a pole piece according to an embodiment of the present application.

[0020] Figure 4 The cycling performance of the polymer current collector according to the embodiment of the present application applied to a lithium metal battery is shown.

[0021] Figure 5 It is a schematic diagram of one embodiment of the secondary battery of the present application.

[0022] Figure 6 It is an exploded schematic diagram of an embodiment of a secondary battery of the present application.

[0023] Figure 7is a schematic diagram of one embodiment of a battery module.

[0024] Figure 8 is a schematic diagram of one embodiment of a battery pack.

[0025] Fig. 9 yes Figure 8 Exploded diagram of .

[0026] Fig.10 Schematic diagram of one embodiment of a device using a secondary battery of the present application as a power source.

[0027] The following are the descriptions of the reference numerals:

[0028] 1 battery pack;

[0029] 2-Upper box;

[0030] 3-Lower box;

[0031] 4-Battery module;

[0032] 5- Secondary battery;

[0033] 51-housing;

[0034] 52-electrode assembly;

[0035] 53-Cover. DETAILED DESCRIPTION

[0036] The present application is further described below in conjunction with specific implementations. It should be understood that these specific implementations are only used to illustrate the present application and are not used to limit the scope of the present application.

[0037] For simplicity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.

[0038] In the description of this article, it should be noted that, unless otherwise specified, "above" and "below" are inclusive of the number itself, and "several" in "one or several" means two or more.

[0039] Unless otherwise specified, the terms used in this application have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0040] The following describes in detail the polymer current collector of the first aspect of the present application, the method for preparing the polymer current collector of the first aspect of the present application, the secondary battery of the third aspect of the present application using the polymer current collector of the first aspect of the present application or the polymer current collector prepared by the preparation method of the second aspect of the present application, the battery module of the fourth aspect of the present application using the secondary battery of the third aspect of the present application, the battery pack of the fifth aspect of the present application using the battery module of the fourth aspect of the present application, and the device of the sixth aspect of the present application using the secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application or the battery pack of the fifth aspect of the present application.

[0041] Polymer current collector

[0042] According to the polymer current collector described in the first aspect of the present application, the polymer current collector includes a polymer film layer, the polymer film layer includes a first polymer film layer and a second polymer film layer, the resistivity of the first polymer film layer is denoted as ρ1, the resistivity of the second polymer film layer is denoted as ρ2, and the current collector satisfies: ρ1>ρ2.

[0043] The inventors of the present application discovered that when ρ1>ρ2, that is, when the polymer current collector has a conductivity gradient, it can induce lithium metal to deposit from the side with low conductivity to the side with high conductivity, which can effectively avoid the risk of lithium ion deposition on the surface of the current collector, thereby improving the cycle life of the lithium metal battery.

[0044] The ratio of ρ1 / ρ2 will affect the difference in conductivity between two adjacent polymer film layers. When ρ1 / ρ2≥40, it can induce lithium metal to deposit from the side with low conductivity to the side with high conductivity, thereby improving the cycle life of lithium metal batteries. The smaller the ratio, the smaller the conductivity difference. A small conductivity difference will make it difficult to induce lithium ions to spontaneously and evenly migrate from the first layer to the second layer, making it difficult to evenly and densely fill the entire polymer. When the difference in skeleton conductivity is too large, the first layer of the polymer skeleton will be basically non-conductive. When the non-conductive polymer skeleton removes lithium metal, it is easy to form a large amount of dead lithium inside the skeleton, which is not conducive to the uniform removal of lithium metal. Therefore, the ratio of ρ1 / ρ2 is controlled at 50-60000.

[0045] According to some embodiments of the present application, the ratio of ρ1 / ρ2 is 500-20000.

[0046] According to some embodiments of the present application, the ratio of ρ1 / ρ2 is 500-5000, 500-3000, 500-1000, 550-900, 550-800, 600-700, 640-850, 600-2000 or 600-4000.

[0047] According to some embodiments of the present application, ρ1 is 10 2 Ω·cm-10 9 Ω·cm.

[0048] According to some embodiments of the present application, ρ1 is 10 3 Ω·cm-10 6 Ω·cm.

[0049] According to some embodiments of the present application, ρ1 is 5000Ω·cm-10000Ω·cm, 15000Ω·cm-20000Ω·cm, 25000Ω·cm-30000Ω·cm, 35000Ω·cm-40000Ω·cm, 45000Ω·cm-50000Ω·cm or 55000Ω·cm-60000Ω·cm.

[0050] According to some embodiments of the present application, ρ2 is 10Ω·cm-10 4 Ω·cm.

[0051] According to some embodiments of the present application, ρ2 is 10Ω·cm-1000Ω·cm.

[0052] According to some embodiments of the present application, ρ2 is 10Ω·cm-50Ω·cm, 75-200Ω·cm, 250-400Ω·cm, 450-600Ω·cm, 650-700Ω·cm or 750-1000Ω·cm.

[0053] The inventors of the present application discovered that as the sintering (carbonization) temperature gradually increases, the N or O content in the polymer will gradually decrease, thereby improving the conductivity of the polymer. Therefore, measuring the change in C / N or C / O in the polymer film layer can indirectly determine the difference in conductivity of each layer of polymer.

[0054] The C / N or C / O variation mentioned in the present application refers to the difference between the C / N or C / O value of the polymer film before calcination and the C / N or C / O value after calcination.

[0055] According to some embodiments of the present application, in the first polymer film layer, the change in C / N is 0.1-10.

[0056] According to some embodiments of the present application, in the first polymer film layer, the change in C / N is 0.2-3.

[0057] According to some embodiments of the present application, in the first polymer film layer, the variation of C / O is 0.1-10.

[0058] According to some embodiments of the present application, in the first polymer film layer, the variation of C / O is 0.2-3.

[0059] According to some embodiments of the present application, in the second polymer film layer, the change in C / N is 0.1-15.

[0060] According to some embodiments of the present application, in the second polymer film layer, the change in C / N is 0.2-5.

[0061] According to some embodiments of the present application, in the second polymer film layer, the variation of C / O is 0.1-15.

[0062] According to some embodiments of the present application, in the second polymer film layer, the variation of C / O is 0.2-5.

[0063] The inventors of the present application have found that in the polymer current collector of the present application, the more layers of the polymer film layer with different resistivities, the better the performance of the final battery. On the premise of meeting the actual application thickness of the polymer current collector, the number of layers of the polymer film layer is greater than 2, preferably greater than or equal to 3, and more preferably 3-5.

[0064] According to some embodiments of the present application, the polymer current collector also includes a third polymer film layer, and the second polymer film layer is arranged between the third polymer film layer and the first polymer film layer, the resistivity of the third polymer film layer is denoted as ρ3, and the current collector also satisfies: ρ2>ρ3.

[0065] The inventors of the present application have discovered that when the polymer current collector includes three or more polymer film layers, a multi-level conductive gradient can be formed in the current collector, which can increase the driving force for the deposition of lithium metal from the inside out, thereby facilitating a more uniform and dense deposition of lithium metal.

[0066] According to some embodiments of the present application, the ratio of ρ2 / ρ3 is 20-1000. The smaller the ratio, the smaller the conductivity difference. The small conductivity difference will make it difficult to induce lithium ions to migrate spontaneously and evenly from the second layer to the third layer, so that it is difficult to fill the entire polymer evenly and densely. When the difference in skeleton conductivity is too large, the second layer polymer skeleton will be basically non-conductive. When the non-conductive polymer skeleton is released from lithium metal, a large amount of dead lithium is easily formed inside the skeleton, which is not conducive to the uniform release of lithium metal.

[0067] According to some embodiments of the present application, the ratio of ρ2 / ρ3 is 20-500.

[0068] According to some embodiments of the present application, the ratio of ρ2 / ρ3 is 20-40, 23-40, 25-35, 25-30, 26-50 or 26-100.

[0069] According to some embodiments of the present application, ρ3 is 1Ω·cm-500Ω·cm.

[0070] According to some embodiments of the present application, ρ3 is 10Ω·cm-100Ω·cm.

[0071] According to some embodiments of the present application, in the third polymer film layer, the variation of C / N is 0.3-20.

[0072] According to some embodiments of the present application, in the third polymer film layer, the variation of C / N is 1-5.

[0073] According to some embodiments of the present application, in the third polymer film layer, the variation of C / O is 0.3-20.

[0074] According to some embodiments of the present application, in the third polymer film layer, the variation of C / O is 0.3-2.

[0075] According to some embodiments of the present application, each polymer film layer of the polymer current collector includes the same polymer.

[0076] According to some embodiments of the present application, the polymer current collector has a porous structure. Using a polymer current collector with a porous structure, on the one hand, the porous structure can provide a deposition skeleton for lithium metal, which is beneficial to reducing the volume expansion of lithium metal; on the other hand, the porous structure can increase the deposition sites of lithium metal, which is beneficial to the uniform deposition of lithium metal.

[0077] The inventors of the present application have found that the thickness of the polymer film layer will directly affect the strength of the current collector and the energy density of the subsequent battery. If the film layer is too thin, it will affect the strength of the current collector and will easily break during the assembly and later cycles of the battery; if the film layer is too thick, on the one hand, it will increase the weight of the current collector, and on the other hand, it will require more electrolyte to infiltrate the current collector, which is not conducive to the overall energy density of the battery. Not only that, if the film is too thick, it will greatly increase the diffusion distance of lithium ions, which is not conducive to the uniform deposition of lithium metal. Therefore, the thickness of the polymer film layer is controlled to be greater than or equal to 1μm, preferably 5-100μm.

[0078] According to some embodiments of the present application, the thickness of the first polymer film layer is ≥1 μm.

[0079] According to some embodiments of the present application, the thickness of the first polymer film layer is 5-100 μm.

[0080] According to some embodiments of the present application, the thickness of the first polymer film layer is 10-50 μm.

[0081] According to some embodiments of the present application, the thickness of the second polymer film layer is ≥1 μm.

[0082] According to some embodiments of the present application, the thickness of the second polymer film layer is 5-100 μm.

[0083] According to some embodiments of the present application, the thickness of the second polymer film layer is 10-50 μm.

[0084] According to some embodiments of the present application, the thickness of the third polymer film layer is ≥1 μm.

[0085] According to some embodiments of the present application, the thickness of the third polymer film layer is 5-100 μm.

[0086] According to some embodiments of the present application, the thickness of the third polymer film layer is 10-50 μm.

[0087] Preparation method of polymer current collector

[0088] In a second aspect, the present application provides a method for preparing the polymer current collector according to the first aspect, the method comprising the following steps:

[0089] S1, providing two or more polymer films having different resistivities;

[0090] S2, pressing the polymer films with different resistivities described in S1 in the order of resistivity from high to low or from low to high to obtain the polymer current collector.

[0091] According to some embodiments of the present application, the method for preparing the polymer film comprises the following steps:

[0092] (1) providing two or more polymer film precursors comprising the same polymer raw material;

[0093] (2) Sintering the polymer film precursors in (1), wherein the sintering temperatures of the polymer film precursors are different, to obtain polymer films with different resistivities.

[0094] According to some embodiments of the present application, the polymer membrane is selected from at least one of a membrane formed by a porous polymer raw material and a membrane formed by electrostatic spinning of a polymer raw material solution.

[0095] According to some embodiments of the present application, the method for preparing the polymer film precursor comprises the following steps:

[0096] (a) preparing a polymer raw material solution;

[0097] (b) The polymer raw material solution in (a) is electrospinned to form two or more polymer membrane precursors.

[0098] The inventors of the present application have found that electrospinning has a wide range of choices for polymer raw materials and can control the porosity and strength of the skeleton. Therefore, the present application preferably adopts electrospinning to prepare the polymer membrane precursor.

[0099] According to some embodiments of the present application, the polymer raw material may include one or more of nitrile polymers, alcohol polymers, cellulose polymers, sulfone polymers, amine polymers, ester polymers, ketone polymers, melamine foam and cotton fiber.

[0100] According to some embodiments of the present application, the polymer raw material may include one or more of polyacrylonitrile, polyvinyl alcohol, carboxymethyl cellulose and polysulfoneamide.

[0101] According to some embodiments of the present application, the molecular weight of the polymer raw material is 500,000-2,000,000.

[0102] According to some embodiments of the present application, the electrospinning includes spraying a polymer raw material solution onto a metal foil at a uniform speed under high pressure to form a polymer film precursor.

[0103] According to some embodiments of the present application, the sintering is performed under an inert atmosphere. Preferably, the inert atmosphere is formed by a commonly used inert gas, such as nitrogen or argon.

[0104] The inventors of the present application have found that the sintering temperature can control the conductivity of the current collector. As the sintering (carbonization) temperature gradually increases, the N or O content in the polymer will gradually decrease, thereby improving the conductivity of the polymer.

[0105] According to some embodiments of the present application, the sintering temperature is 200-2000°C, preferably 300-1000°C, and more preferably 400-800°C.

[0106] According to some embodiments of the present application, the sintering time is 0.5-5 h, preferably 1-3 h.

[0107] According to some embodiments of the present application, the pressing is selected from one or more of rolling, flat pressing, hot pressing and cold pressing.

[0108] The inventors of the present application have found that adding a surfactant such as polyvinyl pyrrolidone during the preparation of the polymer film allows the polymer to be fully dispersed, which is conducive to forming a polymer film with uniform pore size, thereby allowing lithium metal to be uniformly transported within the polymer film, avoiding the problem of uneven deposition concentration, thereby further avoiding the generation of lithium dendrites. Preferably, the molecular weight of the polyvinyl pyrrolidone is 50,000-250,000, for example, 100,000-150,000. Preferably, the amount of polyvinyl pyrrolidone added is 5-15wt% of the polymer solution.

[0109] Secondary battery

[0110] The third aspect of the present application provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.

[0111] [Negative electrode]

[0112] In the secondary battery of the present application, the negative electrode plate includes the polymer current collector described in the first aspect or the polymer current collector prepared by the method described in the second aspect.

[0113] In the secondary battery of the present application, when a polymer current collector is selected for the negative electrode plate, the first polymer film layer is closer to the separator in the battery than the second polymer film layer.

[0114] According to some embodiments of the present application, the negative electrode plate only includes the above-mentioned polymer current collector.

[0115] According to some embodiments of the present application, the negative electrode plate is a polymer current collector-lithium composite negative electrode, wherein lithium metal is deposited in the polymer current collector.

[0116] According to some embodiments of the present application, the negative electrode plate is a polymer current collector-lithium composite negative electrode, wherein the polymer current collector is placed on the surface of the lithium metal.

[0117] In the secondary battery of the present application, the negative electrode plate does not exclude other additional functional layers besides the above-mentioned polymer current collector.

[0118] [Positive electrode]

[0119] In the secondary battery of the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector and including a positive electrode active material.

[0120] It can be understood that the positive electrode current collector has two surfaces opposite to each other in the thickness direction thereof, and the positive electrode film can be laminated on any one or both of the two opposite surfaces of the positive electrode current collector.

[0121] In the secondary battery of the present application, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0122] In the secondary battery of the present application, the positive electrode active material may adopt the positive electrode active material for secondary batteries known in the art. For example, the positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates with olivine structures 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 and their modified compounds. Examples of lithium-containing phosphates with olivine structures 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 modified compounds. The present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries may also be used.

[0123] In some preferred embodiments, in order to further improve the energy density of the battery, the positive electrode active material may include one or more of the lithium transition metal oxides and modified compounds thereof as shown in Formula 1,

[0124] Li a Ni b Co c M d O e A f Formula 1,

[0125] In Formula 1, 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from one or more of N, F, S and Cl.

[0126] In the present application, the modified compounds of the above materials may be the materials subjected to doping modification and / or surface coating modification.

[0127] [Electrolytes]

[0128] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte).

[0129] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0130] In some embodiments, the electrolyte salt can be selected from one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium dioxalatoborate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalatophosphate) and LiTFOP (lithium tetrafluorooxalatophosphate).

[0131] In some embodiments, the solvent can be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), 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), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0132] In some embodiments, the electrolyte may optionally include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, and additives that improve battery low temperature performance.

[0133] [Isolation film]

[0134] Secondary batteries using electrolytes and some secondary batteries using solid electrolytes also include a separator. The separator is arranged between the positive electrode and the negative electrode to isolate the positive electrode. The present application has no particular restrictions on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.

[0135] In some embodiments, the material of the isolation membrane can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different.

[0136] In some embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly by a winding process or a lamination process.

[0137] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0138] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0139] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 5 A secondary battery 5 of a square structure is shown as an example.

[0140] In some embodiments, reference Figure 6 , the outer package may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a accommodating cavity. The shell 51 has an opening connected to the accommodating cavity, and the cover plate 53 can be covered on the opening to close the accommodating cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the accommodating cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to needs.

[0141] Method for preparing secondary battery

[0142] The present application also provides a method for preparing a secondary battery, comprising preparing a negative electrode sheet of the battery by the following steps:

[0143] The obtained polymer current collector and lithium metal are assembled into a half-cell, wherein the polymer fiber film with the lowest resistivity is placed close to the negative electrode, and lithium metal is pre-deposited into the porous current collector cavity. Finally, the current collector-lithium composite negative electrode is removed from the half-cell.

[0144] According to some embodiments of the present application, the polymer current collector can be directly used as a negative electrode and matched with a positive electrode sheet.

[0145] According to some embodiments of the present application, lithium metal is deposited into the polymer current collector to obtain a negative electrode sheet.

[0146] According to some embodiments of the present application, a polymer current collector is placed on a lithium metal surface to obtain a negative electrode sheet.

[0147] In addition to the preparation method of the negative electrode sheet of the present application, the other structures and preparation methods of the secondary battery of the present application are well known in themselves. For example, the positive electrode sheet of the present application can be prepared as follows: the positive electrode active material and the optional conductive agent (such as carbon black and other carbon materials), the binder (such as PVDF), etc. are mixed and dispersed in a solvent (such as NMP), stirred evenly and coated on the positive electrode collector, and the positive electrode sheet is obtained after drying. Metal foils such as aluminum foil or porous metal plates can be used as positive current collectors. When preparing the positive electrode sheet, the positive electrode sheet can be prepared by punching or laser die cutting in the uncoated area of ​​the positive current collector.

[0148] Finally, the positive electrode sheet, the isolation film, and the negative electrode sheet can be stacked in order, so that the isolation film is placed between the positive and negative electrode sheets to play an isolating role, and then the electrode assembly is obtained through a winding (or lamination) process; the electrode assembly is placed in an outer package, and after drying, the electrolyte is injected, and after vacuum packaging, standing, formation, shaping and other processes, a secondary battery is obtained.

[0149] Battery Module

[0150] The fourth aspect of the present application provides a battery module. The battery module includes the secondary battery of the third aspect of the present application. The battery module of the present application uses the secondary battery provided by the present application, and therefore has at least the same advantages as the secondary battery.

[0151] The battery module of the present application may contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0152] Figure 7 4 is an example of a battery module. Figure 7 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0153] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0154] Battery Pack

[0155] The fifth aspect of the present application provides a battery pack. The battery pack includes the battery pack of the fourth aspect of the present application. The number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0156] Figure 8 and Fig. 9 1 is a battery pack 1 as an example. Figure 8 and Fig. 9 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0157] Device

[0158] The sixth aspect of the present application provides a device. The device includes at least one of the secondary battery of the third aspect of the present application, the battery module of the fourth aspect, or the battery pack of the fifth aspect. The secondary battery can be used as a power source for the device or as an energy storage unit for the device. The device of the present application uses the secondary battery provided by the present application, and therefore has at least the same advantages as the secondary battery.

[0159] The device may be, but is not limited to, a mobile device (such as a mobile phone, 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 and a satellite, an energy storage system, etc.

[0160] The device can select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0161] Fig.10 The device is used as an example. The device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0162] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0163] The beneficial effects of the present application are further illustrated below in conjunction with embodiments.

[0164] Example

[0165] In order to make the invention purpose, technical scheme and beneficial technical effect of the present application clearer, the present application is further described in detail below in conjunction with the examples. However, it should be understood that the examples of the present application are only for explaining the present application, not for limiting the present application, and the examples of the present application are not limited to the examples given in the specification. The specific experimental conditions or operating conditions not specified in the examples are made under conventional conditions, or are made under the conditions recommended by the material supplier.

[0166] Polymers used in the examples and comparative examples:

[0167] Polyacrylonitrile: molecular weight 1 million, purchased from Sigma Aldrich;

[0168] Polyvinyl pyrrolidone: molecular weight 130,000, purchased from Sigma Aldrich;

[0169] Polyvinyl alcohol: molecular weight 900,000, purchased from Sigma Aldrich;

[0170] Carboxymethyl cellulose: molecular weight 1 million, purchased from Sigma Aldrich;

[0171] Polysulfoneamide: molecular weight 1 million, purchased from Sigma Aldrich.

[0172] Resistivity test method:

[0173] In this application, the resistivity of the polymer film layer is a well-known meaning in the art and can be tested by methods known in the art. The test steps are as follows: placing the compacted polymer film layer in the four-probe tester, making the four probes contact the polymer film layer, and reading the data after the resistivity data is stable.

[0174] Test method for the change of C / N and C / O in polymer film layer:

[0175] In this application, the changes of C / N and C / O have well-known meanings in the art and can be tested by methods known in the art. The polymer film layer was subjected to EDX analysis using a Zeiss Gemini500 scanning electron microscope to determine the content of each element in the polymer film layer before and after calcination. The difference between the C / N value in the polymer film layer before calcination and the C / N value in the polymer film layer after calcination was the change of C / N, and the difference between the C / O value in the polymer film layer before calcination and the C / O value in the polymer film layer after calcination was the change of C / O.

[0176] Test method for polymer film thickness:

[0177] In this application, the thickness of the polymer film layer has a well-known meaning in the art and can be measured by methods known in the art. A Zeiss Gemini500 scanning electron microscope is used to perform SEM analysis on the cross section of the polymer film layer to measure the thickness of the cross section of the polymer film layer. A micrometer can also be used to directly measure the thickness of the film layer.

[0178] Test method for polymer current collector thickness:

[0179] In this application, the thickness of the polymer current collector has a well-known meaning in the art and can be tested by methods known in the art. A Zeiss Gemini500 scanning electron microscope is used to perform SEM analysis on the cross section of the polymer film layer to measure the thickness of the cross section of the polymer film layer. A micrometer can also be used to directly measure the thickness of the film layer.

[0180] Example 1

[0181] 1) Preparation of polymer current collector

[0182] 5g of polyacrylonitrile and 1g of polyvinyl pyrrolidone were dissolved in 5mL DMF to prepare an electrospinning solution mainly composed of polyacrylonitrile polymer. The electrospinning solution was then uniformly sprayed on aluminum foil under a high voltage of 15KV. After solidification, polymer nanofibers were formed. The polymer nanofibers were peeled off from the aluminum foil to obtain a polymer fiber membrane mainly composed of polyacrylonitrile, with a thickness of 10μm. Two polymer fiber membranes were prepared using the same method as above. The two membranes were sintered at 400℃ and 500℃ for 2h respectively. The two membranes were then pressed together by rolling to form a polymer current collector with a conductive gradient.

[0183] 2) Preparation of batteries

[0184] The obtained polymer current collector with conductive gradient is assembled with lithium metal into a half-cell, in which the polymer fiber film with the lowest resistivity is placed close to the negative electrode, and lithium metal is pre-deposited into the cavity of the polymer current collector. Finally, the current collector-lithium composite negative electrode is removed from the half-cell and re-matched with NCM811 to assemble a lithium metal full cell.

[0185] Examples 2-33 and Comparative Examples 1-5

[0186] The preparation methods of the polymer current collectors and batteries of Examples 2-33 and Comparative Examples 1-5 are similar to the preparation method of the battery of the polymer current collector of Example 1, but the composition and product parameters of the polymer current collector are adjusted. The different product parameters are detailed in Table 1.

[0187] Battery performance test

[0188] Cycle number test

[0189] Specific test method:

[0190] The active area of ​​the soft pack battery is 40cm 2 The design capacity is 140mAh, the test rate is 0.2C charge and discharge, and the number of cycles is based on the capacity decay to 80% of the initial capacity. The test results are detailed in Table 1.

[0191] Table 1-1

[0192]

[0193] According to the data in Table 1-1, it can be seen that when the type of polymer and the thickness of each polymer film layer remain unchanged, by controlling the sintering temperature of the polymer, polymer film layers with different resistivities can be obtained. The C / N change also increases with the increase of the sintering temperature. When the difference in sintering temperature is greater, the larger ρ1 / ρ2 is, the greater the C / N change is, and the better the battery cycle performance is. However, when ρ1 / ρ2>60000, since the resistivity of the first layer is too high relative to the second layer, it is easy to cause the lithium metal to form dead lithium during the extraction process, and the battery performance is reduced.

[0194] Table 1-2

[0195]

[0196] According to the data in Table 1-2, when the polymer type and sintering temperature remain unchanged, the thickness of the polymer is preferably 10-100 μm, which has relatively good cycle performance. If the film layer is too thin, it will affect the strength of the current collector and easily break during the assembly and later cycles of the battery; if the film layer is too thick, on the one hand, it will increase the weight of the current collector, and on the other hand, it will require more electrolyte to infiltrate the current collector, which is not conducive to the overall energy density of the battery. In addition, if the film is too thick, it will greatly increase the diffusion distance of lithium ions, which is not conducive to the uniform deposition of lithium metal.

[0197] Table 1-3

[0198]

[0199] According to the data in Tables 1-3, it can be seen that when the sintering temperature and the thickness of the polymer film layer remain unchanged, the polymer film layer prepared by electrospinning using different types of polymers can achieve the same effect. This shows that the method of preparing a current collector with a conductive gradient by controlling the sintering temperature is universal in lithium metal batteries.

[0200] Table 1-4

[0201]

[0202] According to the data in Tables 1-4, it can be seen that when the polymer current collector has three polymer film layers, the battery performance is further improved compared to the polymer current collector with two polymer film layers when the polymer type and the polymer film layer thickness remain unchanged. The reason is that increasing the number of polymer layers can form a multi-level conductive gradient in the current collector, which can increase the driving force for lithium metal deposition from the inside out, thereby facilitating a more uniform and dense deposition of lithium metal.

[0203] Table 1-5

[0204] Code current collector Sintering temperature / ℃ Thickness / μm Resistivity ρ1 / Ω·cm C / N ratio (quality) Cycle number (capacity decay to 80%) Comparative Example 1 Polyacrylonitrile 800 30 32 5.2 125 Comparative Example 2 Polyacrylonitrile 600 30 860 4.1 76 Comparative Example 3 Polyacrylonitrile 400 30 560000 3.6 32 Comparative Example 4 Cu / Li NO 8 NO NO 49 Comparative Example 5 Cufoil NO 8 NO NO 10

[0205] -NO means it does not exist

[0206] It should be noted that, according to the disclosure and guidance of the above description, the technical personnel in the field to which the present application belongs can also make appropriate changes and modifications to the above implementation. Therefore, the present application is not limited to the specific implementation methods disclosed and described above, and some modifications and changes to the present application also fall within the scope of protection of the claims of the present application. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present application.

Claims

1. A polymer current collector, comprising a polymer film layer, wherein the polymer film layer comprises a first polymer film layer and a second polymer film layer, the resistivity of the first polymer film layer is denoted as ρ1, the resistivity of the second polymer film layer is denoted as ρ2, and the current collector satisfies: ρ1>ρ2; in the first polymer film layer, the change in C / N is 0.1-10; and / or, in the first polymer film layer, the change in C / O is 0.1-10.

2. The polymer current collector according to claim 1, wherein: In the first polymer film layer, the change in C / N is 0.2-3; and / or, in the first polymer film layer, the change in C / O is 0.2-3.

3. The polymer current collector according to claim 1, wherein: ρ1 / ρ2≥40.

4. The polymer current collector according to claim 1, wherein: 50≤ρ1 / ρ2≤60000.

5. The polymer current collector according to claim 1, wherein: 500≤ρ1 / ρ2≤20000.

6. The polymer current collector according to claim 1, wherein: 10 2 Ω·cm≤ρ1≤10 9 Ω·cm; and / or, 10Ω·cm≤ρ2≤10 4 Ohm cm.

7. The polymer current collector according to claim 1, wherein: 10 3 Ω·cm ≤ ρ1 ≤ 10 6 Ω·cm; and / or, 10 Ω·cm ≤ ρ2 ≤ 1000 Ω·cm.

8. The polymer current collector according to claim 1, wherein: In the second polymer film layer, the variation of C / N is 0.1-15; and / or, In the second polymer film layer, the variation of C / O is 0.1-15.

9. The polymer current collector according to claim 1, wherein: In the second polymer film layer, the change in C / N is 0.2-5; and / or, in the second polymer film layer, the change in C / O is 0.2-5.

10. The polymer current collector according to any one of claims 1 to 9, wherein: The number of the polymer film layers is greater than 2.

11. The polymer current collector according to any one of claims 1 to 9, wherein: The number of the polymer film layers is 3-5.

12. The polymer current collector according to any one of claims 1 to 9, wherein: The polymer current collector further includes a third polymer film layer, and the second polymer film layer is arranged between the third polymer film layer and the first polymer film layer, the resistivity of the third polymer film layer is denoted as ρ3, and the current collector also satisfies: ρ2>ρ3.

13. The polymer current collector according to claim 12, wherein: The polymer current collector also satisfies one or more of the following conditions (1)-(4): (1)20≤ρ2 / ρ3≤1000; (2)1≤ρ3≤500Ω·cm; (3) In the third polymer film layer, the variation of C / N is 0.3-20; (4) In the third polymer film layer, the variation of C / O is 0.3-20.

14. The polymer current collector according to claim 12, wherein: 20≤ρ2 / ρ3≤500.

15. The polymer current collector according to claim 12, wherein: In the third polymer film layer, a change in C / N is 1-5; and / or, in the third polymer film layer, a change in C / O is 0.3-2.

16. The polymer current collector according to any one of claims 12 to 15, wherein: The thickness of the first polymer film layer is ≥1 μm; and / or, The thickness of the second polymer film layer is ≥1 μm; and / or, The thickness of the third polymer film layer is ≥1 μm.

17. The polymer current collector according to any one of claims 12 to 15, wherein: The thickness of the first polymer film layer is 5-100 μm; and / or, The thickness of the second polymer film layer is 5-100 μm; and / or, The thickness of the third polymer film layer is 5-100 μm.

18. The polymer current collector according to any one of claims 12 to 15, wherein: The thickness of the first polymer film layer is 10-50 μm; and / or, The thickness of the second polymer film layer is 10-50 μm; and / or, The thickness of the third polymer film layer is 10-50 μm.

19. The polymer current collector according to any one of claims 1 to 15, wherein: The polymer current collector has a porous structure.

20. A method for preparing a polymer current collector according to any one of claims 1 to 19, comprising the following steps: S1, providing two or more polymer films having different resistivities; S2, pressing the polymer films described in S1 in order of resistivity from high to low or from low to high to obtain the polymer current collector; The polymer current collector includes a polymer film layer, the polymer film layer includes a first polymer film layer and a second polymer film layer, the resistivity of the first polymer film layer is denoted as ρ1, the resistivity of the second polymer film layer is denoted as ρ2, and the current collector satisfies: ρ1>ρ2.

21. The preparation method according to claim 20, wherein: The method for preparing the polymer film comprises the following steps: (1) providing two or more polymer film precursors comprising the same polymer raw material; (2) Sintering the polymer film precursors in (1), wherein the sintering temperatures of the polymer film precursors are different, to obtain polymer films with different resistivities.

22. The preparation method according to claim 21, wherein The sintering temperature is 200-2000°C.

23. The preparation method according to claim 21, wherein The sintering temperature is 300-1000°C.

24. The preparation method according to claim 21, wherein The sintering temperature is 400-800°C.

25. The preparation method according to any one of claims 21 to 24, wherein: The polymer raw material includes one or more of nitrile polymers, alcohol polymers, cellulose polymers, sulfone polymers, amine polymers, ester polymers, ketone polymers, melamine foam and cotton fiber.

26. The preparation method according to any one of claims 21 to 24, wherein: The polymer raw material includes one or more of polyacrylonitrile, polyvinyl alcohol, carboxymethyl cellulose and polysulfone amide.

27. A secondary battery comprising a negative electrode plate, wherein the negative electrode plate comprises a polymer current collector according to any one of claims 1 to 19 or a polymer current collector prepared according to the method according to any one of claims 20 to 26.

28. The secondary battery according to claim 27, wherein The secondary battery further includes a separator, and the first polymer film layer is closer to the separator than the second polymer film layer.

29. The secondary battery according to claim 27 or 28, wherein The secondary battery is an alkali metal secondary battery.

30. The secondary battery according to claim 27 or 28, wherein The secondary battery is a lithium metal secondary battery, a potassium metal secondary battery or a sodium metal secondary battery.

31. A battery module comprising the secondary battery according to any one of claims 27 to 30.

32. A battery pack comprising the battery module according to claim 31.

33. A device comprising at least one of the secondary battery of any one of claims 27 to 30, the battery module of claim 31, or the battery pack of claim 32.

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