Electrode, electrode preparation method and secondary battery

Abstract

The invention discloses an electrode, an electrode preparation method and a secondary battery, and the electrode comprises a current collector; the porous layer is arranged on at least one side of the current collector; the electrode layer is arranged on at least one side of the porous layer; wherein the porous layer is arranged between the current collector and the electrode layer; the porous layer comprises a porous material, a binding material and a conductive material, so that the porous layer is at least formed by combining the porous material, the binding material and the conductive material in a dry state. The electrode, the electrode preparation method and the secondary battery have the beneficial effects that the porous layer is improved through the dry-method membrane preparation process, so that the performance of the electrode is improved.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and in particular relates to an electrode, an electrode preparation method and a secondary battery. Background Art

[0002] Metal materials such as lithium metal have high theoretical specific capacity and extremely low redox potential, and can be used as ideal negative electrodes for all-solid-state batteries. However, when used as negative electrodes, metal materials such as lithium metal have problems with dendrite growth, volume expansion, and pulverization, which lead to rapid degradation of battery cycle performance and the risk of short circuit, thus limiting the large-scale commercial application of metal materials such as lithium metal as electrodes.

[0003] In the related art, a porous structure, such as a three-dimensional carbon skeleton material, can be added to the electrode to promote the uniform deposition of metal ions such as lithium ions and reduce the local current density, thereby inhibiting the growth of undesirable defects such as lithium dendrites.

[0004] However, porous materials such as three-dimensional carbon skeleton materials generally have a higher specific surface area and strong powder liquid absorption capacity, which makes it difficult to disperse them in the slurry and they are prone to agglomeration during the dispersion process. This also leads to the coating of porous materials such as three-dimensional carbon skeletons failing to improve the electrode cycling performance of lithium metal as expected. Summary of the invention

[0005] In view of this, the present application provides an electrode, an electrode preparation method and a secondary battery, aiming to improve the aforementioned volume problem.

[0006] In the first aspect, an embodiment of the present application provides an electrode comprising: a current collector; a porous layer, arranged on at least one side of the current collector; an electrode layer, arranged on at least one side of the porous layer; wherein the porous layer is arranged between the current collector and the electrode layer; the porous layer comprises: a porous material, a bonding material and a conductive material so that the porous layer is at least composed of the porous material, the bonding material and the conductive material combined in a dry state.

[0007] Optionally, in some embodiments of the present application, the porous material includes a three-dimensional carbon skeleton material.

[0008] Optionally, in some embodiments of the present application, the electrode layer includes lithium metal.

[0009] Optionally, in some embodiments of the present application, the current collector includes copper metal and / or aluminum metal.

[0010] Optionally, in some embodiments of the present application, the bonding material is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polyethylene oxide, polyphenylene ether or polydimethylsiloxane.

[0011] Optionally, in some embodiments of the present application, the conductive material is selected from one or more of conductive carbon black, conductive graphite, carbon nanotubes, and vapor-grown carbon fibers.

[0012] Optionally, in some embodiments of the present application, the weight average molecular weight of the conductive material ranges from 4 million to 12 million.

[0013] Optionally, in some embodiments of the present application, the porous layer density ranges from 21 g / m 2 Up to 25g / m 2 .

[0014] Optionally, in some embodiments of the present application, the thickness of the porous layer ranges from 30 μm to 60 μm.

[0015] Optionally, in some embodiments of the present application, the ratio of the thickness of the electrode layer to the thickness of the porous layer ranges from 0.50 to 0.67.

[0016] Optionally, in some embodiments of the present application, the porous layer and the electrode layer are provided on both sides of the current collector.

[0017] Optionally, in some embodiments of the present application, the porous layers on both sides of the current collector are symmetrically arranged; and / or the electrode layers on both sides of the current collector are symmetrically arranged.

[0018] Optionally, in some embodiments of the present application, the particle size of the porous material ranges from 30 μm to 50 μm.

[0019] Optionally, in some embodiments of the present application, the specific surface area of ​​the porous material is in the range of 40 m 2 / g to 100m 2 / g.

[0020] Optionally, in some embodiments of the present application, in the porous layer, the mass fraction of the porous material ranges from 89 to 93 parts, the mass fraction of the conductive material ranges from 4 to 6 parts; and the mass fraction of the bonding material ranges from 3 to 5 parts.

[0021] In a second aspect, an embodiment of the present application provides a secondary battery comprising the aforementioned electrode.

[0022] In the third aspect, an embodiment of the present application provides an electrode preparation method which also includes: providing a porous layer; attaching the porous layer to a current collector; attaching the electrode layer to the whole formed by the current collector and the porous layer; wherein the porous layer is arranged between the current collector and the electrode layer; the porous layer includes: a porous material, a bonding material and a conductive material so that the porous layer is at least composed of the porous material, the bonding material and the conductive material combined in a dry state.

[0023] Optionally, in some embodiments of the present application, providing the porous layer includes: fiberizing the mixed porous material, bonding material and conductive material at a preset temperature and a preset shear speed to obtain a fiberized powder; and rolling the fiberized powder to obtain the porous layer.

[0024] Optionally, in some embodiments of the present application, the preset temperature ranges from 185°C to 220°C; and / or the preset shear speed ranges from 15m / s to 25m / s.

[0025] The beneficial effects of the present application are as follows: an electrode, an electrode preparation method and a secondary battery are provided, which improve the porous layer through a dry film-making process and thus improve the electrode performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1A A schematic diagram of the structure of a lithium metal negative electrode provided in some embodiments of the present application;

[0028] Figure 1B A schematic diagram of the structure of a battery provided in some embodiments of the present application;

[0029] Figure 2 A schematic diagram of the main steps of the electrode preparation method provided in some embodiments of the present application;

[0030] Figure 3 This is a scanning electron microscope image of the electrode provided in Example 3 of the present application;

[0031] Figure 4 This is a physical picture of the sample of Example 1 after the cycle performance test;

[0032] Figure 5 This is a scanning electron microscope image of the sample of Example 1 after the cycle performance test;

[0033] Figure 6 This is a physical picture of the sample of Example 6 after the cycle performance test;

[0034] Figure 7 This is a scanning electron microscope image of the sample of Example 6 after the cycle performance test;

[0035] Figure 8 A physical picture of the electrodes provided in some embodiments of the present application undergoing a peel strength test.

[0036] In the figure: 10, electrode; 11, current collector; 12, porous layer; 13, electrode layer; 20, separator; 30, positive electrode. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application. In addition, it should be understood that the specific implementation methods described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0039] In this application, unless otherwise stated, directional words such as "upper" and "lower" generally refer to the upper and lower parts of the device in actual use or working state, specifically the drawing direction in the accompanying drawings; while "inner" and "outer" refer to the outline of the device. In addition, in the description of this application, the term "including" means "including but not limited to". The terms first, second, third, etc. are used only as labels and do not impose numerical requirements or establish an order.

[0040] In this application, "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0041] In the present application, "at least one" means one or more, and "plurality" means two or more. "One or more", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0042] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0043] According to the first aspect of the present application, reference Figure 1A As shown, an electrode 10 is provided, comprising: a current collector 11, a porous layer 12 and an electrode layer 13.

[0044] The current collector 11 may be made of metal foil, such as copper foil or aluminum foil. The porous layer 12 is disposed on at least one side of the current collector 11; the electrode layer 13 is disposed on at least one side of the porous layer 12;

[0045] The porous layer 12 is disposed between the current collector 11 and the electrode layer 13; the porous layer 12 comprises: a porous material, a bonding material and a conductive material so that the electrode layer 13 is at least formed by combining the porous material, the bonding material and the conductive material in a dry state.

[0046] It should be noted that the dry state in the present application refers to the state in which the ambient temperature is 25°C ± 3°C and the ambient humidity is 0.1% to 5%, and the electrolyte material, the first conductive material and the first adhesive material are all in a dry powder state, that is, a state without any solvent.

[0047] By using bonding materials and a dry membrane making process, the porous material, bonding material and conductive material form a self-supporting membrane, and a three-dimensional porous structure is provided in the membrane layer. Since there is no slurry mixing process, the porous material is more evenly distributed in the porous layer 12, thereby solving the problem of agglomeration of the porous material in the porous layer 12 under the wet process, thereby improving the performance of the electrode 10 and the secondary battery constituted by it.

[0048] In some embodiments of the present application, the porous layer 12 material includes a three-dimensional carbon skeleton material.

[0049] In some embodiments of the present application, the electrode layer 13 includes lithium metal.

[0050] In some embodiments of the present application, the current collector 11 includes copper metal and / or aluminum metal.

[0051] In some embodiments of the present application, the bonding material is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polyethylene oxide, polyphenylene ether or polydimethylsiloxane.

[0052] In some embodiments of the present application, the conductive material is selected from one or more of conductive carbon black, conductive graphite, carbon nanotubes, and vapor-grown carbon fibers.

[0053] In some embodiments of the present application, the weight average molecular weight of the conductive material ranges from 4 million to 12 million.

[0054] In some embodiments of the present application, the surface density of the porous layer 12 is in the range of 21 g / m 2 Up to 25g / m 2 .

[0055] More specifically, the surface density of the porous layer 12 is in the range of 21 g / m 2 Up to 25g / m 2 For example, the surface density of the porous layer 12 is 21 g / m 2 , 22g / m 2 , 23g / m 2 , 24g / m 2 , 25g / m 2 Or any one of them or a range between any two of them.

[0056] In some embodiments of the present application, the thickness of the porous layer 12 ranges from 30 μm to 60 μm.

[0057] In some embodiments of the present application, the thickness of the porous layer 12 ranges from 20 μm to 50 μm.

[0058] In some embodiments of the present application, the thickness of the porous layer 12 ranges from 30 μm to 40 μm.

[0059] Exemplarily, the thickness of the porous layer 12 is 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, 32 μm, 35 μm, 38 μm, 40 μm, 43 μm, 45 μm, 47 μm, 50 μm or any range therebetween or any two thereof.

[0060] In some embodiments of the present application, the ratio of the thickness of the electrode layer 13 to the thickness of the porous layer 12 ranges from 0.50 to 0.67.

[0061] For example, the ratio of the thickness of the electrode layer 13 to the thickness of the porous layer 12 can also be 1 / 2, 13 / 24, 7 / 12, 5 / 8, 2 / 3, or a value between any two of the above values. The above ratio can balance the embedding of the electrode layer 13 and the porous layer 12 and the inhibition provided by the porous layer 12 itself.

[0062] The surface density of the porous layer 12 is positively correlated with the thickness of the porous layer 12. The greater the surface density of the porous layer 12, the greater the thickness of the porous layer 12, which is conducive to the embedding of the porous material into the electrode layer 13. The greater the volume change of the metal in the electrode layer 13 during the battery cycle, the smaller the volume change of the metal in the electrode layer 13, thereby ensuring that the battery has good cycle performance.

[0063] Reference Figure 1A As shown, in some embodiments of the present application, the porous layer and the electrode layer are provided on both sides of the current collector.

[0064] In some embodiments of the present application, the porous layers on both sides of the current collector are symmetrically arranged; and / or the electrode layers on both sides of the current collector are symmetrically arranged.

[0065] In some embodiments of the present application, the particle size of the porous material ranges from 30 μm to 50 μm. More specifically, the D50 particle size of the porous material ranges from 30 μm to 50 μm.

[0066] As a more specific solution, the D50 of the porous material may range from 30 μm to 50 μm. For example, the particle size D50 of the three-dimensional carbon skeleton material is 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or any one or any two thereof.

[0067] In some embodiments of the present application, the specific surface area of ​​the porous material ranges from 40 m 2 / g to 100m 2 / g.

[0068] In some embodiments of the present application, in the porous layer, the mass fraction of the porous material ranges from 89 to 93 parts, the mass fraction of the conductive material ranges from 4 to 6 parts; and the mass fraction of the bonding material ranges from 3 to 5 parts.

[0069] Reference Figure 2 As shown, according to the second aspect of the present application, a method for preparing an electrode is provided, which specifically comprises the following steps:

[0070] S100: providing a porous layer;

[0071] S200: attaching the porous layer to a current collector;

[0072] S300: attaching an electrode layer to the whole body consisting of the current collector and the porous layer.

[0073] Wherein, the porous layer is arranged between the current collector and the electrode layer; the porous layer comprises: a porous material, a bonding material and a conductive material so that the porous layer is at least formed by combining the porous material, the bonding material and the conductive material in a dry state.

[0074] In some implementations of the present application, step S100 specifically includes the following steps:

[0075] S101: performing a fiberization treatment on the mixed porous material, bonding material and conductive material at a preset temperature and a preset shear speed to obtain a fiberized powder;

[0076] S102: Roll-pressing the fiberized powder to obtain the porous layer.

[0077] In some embodiments of the present application, the preset temperature ranges from 185° C. to 220° C.; the preset shear speed ranges from 15 m / s to 25 m / s.

[0078] The particle size of the porous material is related to the uniformity of lithium ion deposition. The larger the particle size of the porous material, the more conducive it is for lithium ions to deposit in the porous structure inside it. The smaller the particle size of the porous material, the less conducive it is for lithium ions to enter the porous structure inside it.

[0079] In some embodiments of the present application, the specific surface area of ​​the porous material may range from 40 m 2 / g to 100m 2 / g. For example, the specific surface area of ​​the three-dimensional carbon skeleton material is 40m 2 / g, 50m 2 / g, 60m 2 / g, 70m 2 / g, 80m 2 / g, 90m 2 / g、100m 2 / g or any one of them or a range between any two of them.

[0080] The specific surface area of ​​the porous material is related to the lithium ion deposition rate. The larger the specific surface area of ​​the porous material, the more conducive it is to increasing the lithium ion deposition rate. The higher the deposition rate, the more likely it is to pass through the diaphragm and cause a short circuit in the battery, which in turn causes the battery capacity to decay rapidly. The specific surface area of ​​the porous material in the embodiment of the present application is not more than 100m 2 / g is appropriate.

[0081] In some embodiments of the present application, in the porous layer, the mass percentage of the porous material is 89% to 93%, the mass percentage of the conductive agent is 4% to 6%, and the mass percentage of the binder is 3% to 5%. That is, when preparing the porous layer, when the total mass of the raw materials of the porous layer is 100%, the mass percentage of each component is taken according to the above values.

[0082] The porous layer of the embodiment of the present application contains a higher mass percentage of porous material. The higher the content of porous material, the more conducive it is to providing a stronger lithium deposition induction effect, which is beneficial to reducing the surface lithium precipitation phenomenon, thereby further improving the problems of dendrites and volume expansion of the lithium metal negative electrode during the cycle process.

[0083] In some embodiments of the present application, the porous material may be a three-dimensional carbon skeleton material, which may be prepared by the following method:

[0084] Add 16g of melamine and 600ml of water into a container, stir until dissolved, then add 30g of formaldehyde, and then add 5g of zinc oxide and stir until evenly dispersed, then add a certain amount of hydrochloric acid to adjust the pH to 2, and after stirring the mixed solution evenly, let it stand, filter, wash until neutral, and dry to obtain a polymer skeleton material doped with zinc oxide.

[0085] That is, in some embodiments of the present application, the porous material can also be prepared by the following method:

[0086] Phenol and formaldehyde are added to conductive carbon black according to a certain ratio of substances, and a porous material is obtained through a heating polycondensation reaction.

[0087] The porous material prepared by the embodiment of the present application has a three-dimensional porous structure, the outside of the skeleton material is macropores, and the inside of the skeleton material is mainly mesopores and micropores. Since the surface and the inside of the three-dimensional carbon skeleton have a porous structure, it helps to improve the deposition induction effect on lithium, thereby improving the problems of dendrites and volume expansion of lithium metal negative electrodes during the cycle process.

[0088] In some embodiments of the present application, the conductive agent includes but is not limited to conductive carbon black, conductive graphite, carbon nanotubes, vapor-grown carbon fibers, and the like.

[0089] In some embodiments of the present application, the weight average molecular weight of PTFE ranges from 6 million to 8 million. The higher the molecular weight of PTFE, the stronger its ability to undergo fiberization in the porous layer.

[0090] In some embodiments of the present application, the preset shearing speed may be in the range of 15 m / s to 25 m / s. Further, the preset shearing speed may be in the range of 18 m / s to 22 m / s.

[0091] It is understandable that the preset shear rate in the embodiment of the present application should not be too large, because a larger preset shear rate may break up the porous structure of the porous material, which is not conducive to the deposition induction of lithium ions inside the porous material.

[0092] In some embodiments of the present application, the preset temperature may range from 185°C to 220°C.

[0093] Specifically, the preset temperature may be 185°C, 188°C, 190°C, 192°C, 195°C, 198°C, 200°C, 205°C, 210°C, 215°C or 220°C.

[0094] It can be understood that the preset temperature of the embodiment of the present application is relatively high, which is conducive to the sufficient softening of the binder to ensure that a high degree of fiberization can still be achieved at a relatively low shear rate; since the binder is fully softened, it is conducive to improving the peel strength of the porous layer, thereby ensuring that the porous layer is not easy to fall off during the battery cycle.

[0095] In some embodiments of the present application, rolling the fiberized powder includes: rolling the fiberized powder into an initial membrane sheet of a porous layer, and then rolling the initial membrane sheet at a temperature of 140° C. to 180° C. to obtain a porous layer.

[0096] It should be noted that the rolling process helps to make the density of the porous layer more uniform, reduce the porosity, lower the impedance of the battery, and increase the ionic conductivity, which is crucial to improving the performance of the battery.

[0097] According to the second aspect of the present application, a secondary battery is provided, comprising the aforementioned lithium metal negative electrode. Since the aforementioned electrode is conducive to solving the problems of dendrites and volume expansion during the cycle of the battery, the battery of the embodiment of the present application is not prone to problems such as dendrites and volume expansion during the cycle.

[0098] In some embodiments of the present application, reference Figure 1BThe secondary battery may include a lithium metal negative electrode 10, a separator 20, a positive electrode 30, a separator 20, and a lithium metal negative electrode 10 stacked in sequence, wherein the lithium metal negative electrode 10 may adopt the aforementioned electrode.

[0099] The present application is described in detail below by means of specific examples, which are only partial examples of the present application and are not intended to limit the present application. The raw materials used in the following examples are all commercially available products unless otherwise specified.

[0100] Example 1

[0101] A battery comprising a lithium metal negative electrode, a separator, a lithium-rich manganese-based wet positive electrode (double-sided coating, surface density of 320g / m 2 , compaction density is 2.80g / cc, capacity is 220mAh / g, the proportion of lithium-rich manganese base is 95%), and they are stacked and assembled into soft-pack batteries in the order of double-sided lithium metal negative electrode-diaphragm-double-sided positive electrode-diaphragm-double-sided lithium metal negative electrode for testing.

[0102] Wherein, the lithium metal negative electrode is prepared by the following method:

[0103] ST100, the porous material, conductive carbon black SP (manufacturer: Swiss Termeco, brand name: Super P Li) and polytetrafluoroethylene PTFE are mixed in a mass ratio of 91:5:4 to obtain a mixture; wherein the porous material adopts the three-dimensional carbon skeleton material prepared in the above-mentioned embodiment.

[0104] The particle size D50 of the three-dimensional carbon skeleton material is 42 μm to 45 μm, and the specific surface area of ​​the three-dimensional carbon skeleton material is 80 m 2 / g, the tap density of the three-dimensional carbon skeleton material is 0.2g / cm 3 Up to 0.4g / cm 3 , true density is 1.3g / cm 3 Up to 1.7g / cm 3 , the compacted density of the powder is 1g / cm 3 Up to 1.5g / cm 3 , porosity is 60% to 90%. The above value range takes into account the measurement deviation that may be caused by the raw materials.

[0105] ST 200, then fiberize it at 200°C and a shear speed of 22 m / s to obtain a fiberized powder;

[0106] ST 300, the fiberized powder was pressed into an initial film of a porous layer at 80°C by a hot roller press, and then the initial film was thinned by roller pressing at 150°C to obtain a porous layer with a thickness of 60 μm and a surface density of 23 g / m 2 ;

[0107] ST 400, placing a copper foil with a thickness of 8 μm between two porous layers, and compounding them at a temperature of 150° C. using a hot roller press to obtain a composite copper foil;

[0108] ST 500, two lithium foils with a thickness of 10 μm were placed on both sides of the composite copper foil, and a layer of PET film was placed on the outside of the lithium foil, and the composite was performed by a hot roller press at a temperature of 65° C. Then the PET film was torn off to obtain a lithium metal negative electrode.

[0109] Example 2

[0110] The difference from Example 1 is that the thickness of the lithium foil is 20 μm.

[0111] Example 3

[0112] The difference from Example 1 is that the thickness of the lithium foil is 30 μm.

[0113] Example 4

[0114] The difference from Example 1 is that the thickness of the lithium foil is 40 μm.

[0115] Example 5

[0116] The difference from Example 1 is that the thickness of the lithium foil is 50 μm.

[0117] Example 6

[0118] The difference from Example 1 is that the thickness of the lithium foil is 60 μm.

[0119] Example 7

[0120] The difference from Example 1 is that the thickness of the porous layer is 30 μm.

[0121] Example 8

[0122] A battery, which is different from Example 7 in that the thickness of the lithium foil is 15 μm.

[0123] Example 9

[0124] The difference from Example 7 is that the thickness of the lithium foil is 20 μm.

[0125] Example 10

[0126] The difference from Example 7 is that the thickness of the lithium foil is 25 μm.

[0127] Embodiment 11

[0128] The difference from Example 7 is that the thickness of the lithium foil is 30 μm.

[0129] Comparative Example 1

[0130] The difference from Example 3 is that the primer layer is changed to SP:PTFE=96:4, and the thickness of the primer layer is also controlled at 60 μm. At this time, the surface density is about 12 g / m 2 .

[0131] Comparative Example 2

[0132] The difference from Example 3 is that the porous layer is wet-coated, and the specific steps include: adding the three-dimensional carbon skeleton material and the conductive carbon black SP, the dispersant, and the SBR in a mass ratio of 80.7:10:1.3:8.0 into deionized water and mixing them evenly to obtain a slurry; coating the slurry on both sides of a copper foil with a thickness of 8 μm by a coating machine, and drying to obtain a composite copper foil; placing a lithium foil with a thickness of 30 μm on both sides of the above-mentioned composite copper foil, and placing a layer of PET film on the outside of the lithium foil, and compounding the above-mentioned film layers at a temperature of 80°C by a hot roller press to obtain a double-sided composite lithium metal negative electrode.

[0133] Preparation of lithium metal full battery:

[0134] The lithium metal negative electrode prepared in the above examples and comparative examples was combined with a separator (thickness 12 μm), a lithium-rich manganese-based wet-process positive electrode (double-sided coating, surface density 320 g / m 2 , compaction density 2.80g / cc, design gram capacity 220mAh / g, active material ratio 95%) in the order of "double-sided negative electrode sheet-diaphragm-double-sided positive electrode sheet-diaphragm-double-sided negative electrode sheet" (such as Figure 1B The batteries were stacked and assembled into soft-pack batteries for testing.

[0135] 1. Test method of electrode resistance:

[0136] The electrode resistance meter BER2500 produced by Yuanneng Technology was used for testing. Double-sided electrodes were used for testing. The size of the electrode was 50mm*150mm. If the electrode to be tested was positive, the pressure was set to 25MPa; if the electrode to be tested was negative, the pressure was set to 5MPa. Ten points were tested at equal intervals along the long side of the electrode. The pressure holding time for each test point was 10s. Finally, the data of 10 test points were obtained. The average of these data was taken to obtain the electrode resistance of the electrode.

[0137] 2. Pole peel strength test method:

[0138] The Japanese Shimadzu electronic universal testing machine, model AGX-10KNVD, was used. Before the test, the electrode was cut into 25mm*200mm rectangular strips, and the rectangular strips were attached to the mirror steel plate using 3M double-sided tape. During the gluing process, the adhesive tape and the steel plate were ensured to be firmly bonded and free of bubbles in the middle. The surface of the electrode to be tested was then attached to the double-sided tape on the steel plate. At this time, the electrode protruded 100mm beyond the adhesive tape. The electrode was parallel to the steel plate and rolled back and forth 3 times with an automatic roller to ensure that the bonding surface between the electrode and the double-sided tape was flat and free of bubbles. The lower end of the steel plate with the electrode attached was fixed in the lower fixture of the equipment, and the portion of the electrode that protruded beyond the adhesive tape was manually peeled back by about 2mm in length, and the portion was clamped in the fixture of the equipment, such as Figure 8 During the test, the upper fixture starts to move upward and peels off the dressing on the electrode. The total length of the upper fixture displacement stroke is 100mm. The final test result takes the value of the stroke from 20mm to 90mm. The peel strength (unit: mN / mm) of three samples of each electrode is tested and the average value is taken.

[0139] 3. Test method for full battery electrical performance:

[0140] The following test was conducted using a CT3001A blue power test cabinet: the battery was charged to 4.55V at 0.3C constant current and constant voltage, the cut-off current was 0.05C during the constant voltage stage, and the battery was left for 5 minutes, then discharged to 2.5V at 0.5C constant current and left for 5 minutes. The above steps were repeated until the battery capacity dropped to 80% of the initial capacity.

[0141] Test results:

[0142] 1. Test results of the electrode performance and batteries of Example 3 and Comparative Examples 1-2:

[0143] Table 1 shows the test results of the battery electrical performance of Example 3 and Comparative Examples 1-2:

[0144]

[0145] Combining the test results of Example 3, Comparative Example 1 and Table 1, it can be seen that the peel strength of Comparative Example 1 is significantly lower than that of Example 3. This is because the main component of the primer layer of Comparative Example 1 is SP (accounting for 96%). It is well known that the particle size of SP is only 30-40nm and the specific surface area is 60-70g / m 2The extremely small particle size and high specific surface area make it require a higher bonding ability of the binder, so the bonding effect of the binder of Comparative Example 1 on the main part SP in the bottom coating layer at a similar degree of fiberization is weaker, which will also make the bonding force between the bottom coating layer and the current collector (i.e., peel strength) weaker. It can also be seen that the pole sheet resistance of Comparative Example 1 is significantly lower than that of Example 1. This is because SP itself is a material with excellent electronic conductivity. Generally speaking, the higher the proportion of SP in the bottom coating layer, the lower the pole sheet resistance. Finally, by comparing the cycle performance of Example 3 with that of Comparative Example 1, it can be seen that the number of cycles of Comparative Example 1 is significantly less than that of Example 3, which is mainly attributed to two factors: (1) In Comparative Example 1, the main component of the base coating is SP, which does not contain any three-dimensional carbon skeleton material, and SP itself does not have the function of inducing lithium ion deposition / dissolution and improving the volume expansion of lithium metal. Therefore, during the cycle process, the lithium metal will quickly experience volume expansion, pulverization, dendrites and other problems, resulting in rapid decay of the battery capacity; (2) Since the peel strength of the base coating is significantly low, it is more likely to fall off during the cycle process due to the repeated volume changes of lithium metal, which makes the electronic contact between lithium metal and the current collector worse, which also leads to rapid decay of capacity.

[0146] Combined with Example 3, Comparative Example 2, Table 1 and Figure 3 It can be seen from the test results that the battery includes a porous layer made by a dry process, which helps to improve the cycle performance of the battery. This is because in the dry process, the content of the three-dimensional carbon skeleton material is 91%, while the content of the three-dimensional carbon skeleton material in the wet process is 80.7%. Obviously, the content of the three-dimensional carbon skeleton material in the dry process is higher than that in the wet process, which helps the three-dimensional carbon skeleton material in the dry process to have a stronger lithium deposition induction effect, which helps to improve the battery cycle performance. Secondly, during the cycle of the battery, the porous layer will fall off due to the continuous expansion and contraction of lithium metal, resulting in a significant weakening of the lithium deposition / dissolution ability on the lithium metal negative electrode, causing the battery cycle performance to decay rapidly, and the peeling strength of the porous layer in the dry process of the present application is higher, making it difficult for the porous layer and the copper foil to fall off, which is beneficial to improve the battery cycle performance. In addition, the porous layer of Example 3 has a lower electrode sheet resistance, which also makes the lithium metal negative electrode of Example 3 less likely to have surface lithium precipitation, which helps to improve the battery cycle performance.

[0147] 2. Comparison of battery cycle performance and sheet resistance of lithium metal negative electrode in Examples 1 to 6:

[0148] Table 2 Test results of battery cycle performance and sheet resistance of lithium metal negative electrode of Examples 1-6

[0149]

[0150]

[0151] Combining the test results of Examples 1 to 6 and Table 2, it can be seen that as the thickness of the lithium foil increases, the cycle number of the battery shows a trend of first increasing and then decreasing. When the thickness of the lithium foil increases from 20 μm to 30 μm, the cycle number increases sharply by 76 weeks. When the thickness of the lithium foil increases from 40 μm to 50 μm, the cycle number decreases sharply by 69 weeks. Therefore, when the thickness of the lithium foil is between 30 μm and 40 μm, the cycle performance of the battery is relatively optimal.

[0152] As the thickness of lithium foil increases, the electrode sheet resistance of the lithium metal negative electrode continues to decrease. When the thickness of lithium foil increases from 20μm to 30μm, the electrode sheet resistance drops sharply from 38.3mΩ to 16.3mΩ, a decrease of 57.4%. This further confirms that the number of cycles will increase sharply when the thickness of lithium foil increases from 20μm to 30μm.

[0153] In this way, considering the use of less lithium foil and obtaining better performance, the ratio of the thickness of the electrode layer to the thickness of the porous layer can be limited to a range of 0.500 to 0.667. When the amount of lithium foil is not considered, the ratio of the thickness of the electrode layer to the thickness of the porous layer can be any one of 0.333, 0.500, 0.667, 0.833 or any two thereof.

[0154] Combined with Example 1, Table 1 and Figure 4-5 It can be seen that the sample of Example 1 has a surface lithium deposition phenomenon, and its scanning electron microscope image shows a porous, loose, and uneven amorphous lithium deposition structure. This is because the thickness of the lithium foil embedded in the porous layer is relatively small, and most of the porous layer is still not filled with lithium metal. The part that is not filled with lithium metal has a highly porous structure, so the electrons passing through are relatively scarce, resulting in a higher electrode sheet resistance in the sample. The high electrode sheet resistance causes the sample of Example 1 to produce a larger polarization during the lithium deposition process, resulting in lithium ions being deposited on the surface of the porous layer, rather than entering the porous layer and being induced to deposit, which ultimately leads to the occurrence of surface lithium deposition.

[0155] Combined with Example 6, Table 1 and Figure 6-7 It can be seen that after the cycle performance and electrode resistance tests of the sample of Example 6, the porous layer of the lithium metal negative electrode fell off, exposing a large area of ​​copper foil. This is because the thickness of the lithium foil is too large. After compounding, the lithium foil is completely filled in the porous layer, and there is no "buffer space" to accommodate the volume change of the lithium metal during the deposition / dissolution process. The repeated expansion / contraction of the huge volume of lithium metal destroys the structure of the porous layer, weakening the bonding force between the porous layer and the copper foil, and eventually leading to the shedding of the porous layer and the copper foil. In Table 1, when the thickness of the lithium foil increases from 40μm to 50μm, the number of cycles of the battery drops sharply, which may also be caused by the shedding of the porous layer. In addition, Figure 7 and Figure 5compared to, Figure 7 The surface of the sample is smoother and denser, but the lithium metal deposition morphology in different areas is less uniform, indicating that the carbon skeleton cannot evenly control the deposition of lithium metal, and excessive volume changes lead to the shedding of the porous layer.

[0156] In summary, when the thickness of the porous layer is 60μm, the optimal thickness range of the lithium foil is 30μm to 40μm, that is, the thickness of the lithium foil is 1 / 2 to 2 / 3 of the thickness of the porous layer. At this time, the lithium metal negative electrode has a lower electrode sheet resistance, and the battery has better cycle performance.

[0157] III. Test results of battery cycle performance and sheet resistance of lithium metal negative electrode of Examples 7 to 11:

[0158] Table 3 Test results of battery cycle performance and sheet resistance of lithium metal negative electrode of Examples 7-11

[0159]

[0160]

[0161] In combination with Examples 7-11 and Table 3, it can be seen that, taking the thickness of the porous layer as 30 μm as a benchmark, lithium foils with thicknesses of 10 μm, 15 μm, 20 μm, 25 μm, and 30 μm are used for compounding, respectively. As the thickness of the lithium foil increases, the number of cycles of the battery shows a trend of first increasing and then decreasing. When the thickness of the lithium foil increases from 10 μm to 15 μm, the number of cycles increases sharply by 50 weeks, and when the thickness of the lithium foil increases from 20 μm to 25 μm, the number of cycles decreases sharply by 50 weeks. Therefore, when the thickness of the self-supporting skeleton is 30 μm and the thickness of the lithium foil is between 15 μm and 20 μm, the cycle performance of the battery is relatively optimal. At this time, the ratio of the thickness of the lithium foil to the thickness of the porous layer is 1 / 2 to 2 / 3.

[0162] As the thickness of lithium foil increases, the electrode sheet resistance of the lithium metal negative electrode continues to decrease. When the thickness of lithium foil increases from 10μm to 15μm, the electrode sheet resistance drops sharply from 17.7mΩ to 7.3mΩ, a decrease of 58.8%. This further confirms that the number of cycles will increase sharply when the thickness of lithium foil increases from 10μm to 15μm.

[0163] From Tables 2 and 3, it can be seen that for lithium metal negative electrodes with a porous layer thickness of 30 μm to 60 μm, when the ratio of the thickness of the lithium foil to the thickness of the porous layer is 1 / 2 to 2 / 3, the battery has the best room temperature cycle performance.

[0164] The technical solutions provided by the embodiments of the present application are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for technical personnel in this field, according to the idea of ​​the present application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. An electrode, characterized in that: The electrode comprises: current collector; A porous layer, disposed on at least one side of the current collector; An electrode layer, disposed on at least one side of the porous layer; Wherein, the porous layer is arranged between the current collector and the electrode layer; the porous layer comprises: a porous material, a bonding material and a conductive material; the porous layer is at least formed by combining the porous material, the bonding material and the conductive material in a dry state.

2. The electrode according to claim 1, characterized in that: The porous material comprises a three-dimensional carbon skeleton material; and / or The electrode layer comprises lithium metal; and / or The current collector comprises copper metal and / or aluminum metal; and / or The bonding material is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polyethylene oxide, polyphenylene ether or polydimethylsiloxane; and / or The conductive material is selected from one or more of conductive carbon black, conductive graphite, carbon nanotubes, and vapor-grown carbon fibers.

3. The electrode according to claim 1, characterized in that: The weight average molecular weight of the conductive material ranges from 4 million to 12 million.

4. The electrode according to claim 1, characterized in that: The porous surface density ranges from 21 g / m 2 Up to 25g / m 2 ; and / or The thickness of the porous layer ranges from 30 μm to 60 μm; and / or The ratio of the thickness of the electrode layer to the thickness of the porous layer is in the range of 0.50 to 0.67; and / or The particle size of the porous material ranges from 30 μm to 50 μm; and / or The specific surface area of ​​the porous material ranges from 40 m 2 / g to 100m 2 / g; and / or In the porous layer, the mass fraction of the porous material ranges from 89 to 93 parts, the mass fraction of the conductive material ranges from 4 to 6 parts; and the mass fraction of the bonding material ranges from 3 to 5 parts.

5. The electrode according to any one of claims 1 to 4, characterized in that: The porous layer and the electrode layer are disposed on both sides of the current collector.

6. The electrode according to claim 5, characterized in that: The porous layers on both sides of the current collector are arranged symmetrically; and / or The electrode layers on both sides of the current collector are symmetrically arranged.

7. A secondary battery, characterized in that: The secondary battery comprises the electrode according to any one of claims 1 to 6.

8. A method for preparing an electrode, characterized in that: The electrode preparation method further comprises: providing a porous layer; attaching the porous layer to a current collector; attaching an electrode layer to the whole body consisting of the current collector and the porous layer; Wherein, the porous layer is arranged between the current collector and the electrode layer; the porous layer comprises: a porous material, a bonding material and a conductive material so that the porous layer is at least formed by combining the porous material, the bonding material and the conductive material in a dry state.

9. The electrode preparation method according to claim 8, Features: Wherein, providing a porous layer comprises: The mixed porous material, bonding material and conductive material are subjected to a fiberization treatment at a preset temperature and a preset shear speed to obtain a fiberized powder; The fiberized powder is rolled to obtain the porous layer.

10. The electrode preparation method according to claim 9, characterized in that: The preset temperature ranges from 185°C to 220°C; and / or The preset shear speed ranges from 15 m / s to 25 m / s.

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