Negative pole piece, preparation method thereof and battery

Abstract

The invention relates to the field of batteries, in particular to a negative pole piece, a preparation method thereof and a battery. The negative pole piece comprises a current collector and a polymer protective layer arranged on at least one side surface of the current collector, the polymer protection layer comprises a block copolymer and a lithium salt; the block copolymer comprises a rigid chain segment and a flexible chain segment; the polymer monomer of the rigid chain segment comprises an acrylamide compound containing a cyano group; the polymer monomer of the flexible chain segment comprises an acrylate compound; lithium ions in the lithium salt are connected with amide groups and / or cyano groups in the rigid chain segments through chemical bonds; and anions in the lithium salt are connected with imino groups in the rigid chain segments through hydrogen bonds. The negative electrode plate provided by the invention is provided with the polymer layer rich in lithium salt, the long-term maintenance of the protection effect of a solid electrolyte interface film can be promoted, and meanwhile, the polymer has a rigid and flexible protection layer, so that dendritic crystal growth can be inhibited, interface fluctuation in a metal lithium negative electrode deposition / dissolution process can be borne, and the cycle stability can be improved.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a negative electrode sheet, a preparation method thereof, and a battery. Background Art

[0002] Lithium metal anodes offer a theoretical capacity 10 times higher than graphite (3860 mAh / g) and the lowest electrode potential (-3.04 V), making lithium metal batteries considered the best choice for next-generation battery systems. However, the high reactivity of metallic lithium and the unstable solid electrolyte interface membrane easily lead to unbridled dendrite growth and drastic volume changes, ultimately resulting in poor lithium deposition / stripping reversibility and potential safety hazards, seriously hindering the application of lithium metal batteries.

[0003] Stabilizing the lithium metal interface is one of the necessary conditions for the practical application of lithium metal batteries, among which the design of the electrolyte is the most critical. Ether electrolytes show excellent compatibility with lithium metal. Lithium nitrate (LiNO3), as a commonly used additive in ether electrolytes, can promote the formation of a Li3N-rich SEI film, which significantly improves battery performance. However, as a "sacrificial electrolyte additive", when LiNO3 is exhausted, the electrochemical performance will deteriorate. At the same time, conventional ether electrolytes cannot be used in high-voltage battery systems due to their narrow electrochemical window, and the solubility of LiNO3 in carbonate-based electrolytes is poor (10 -5 g / mL), limiting the further application of lithium metal batteries. In addition, due to the unlimited volume expansion, the solid electrolyte interface (SEI) film formed by the reaction between lithium metal and organic electrolyte is extremely fragile during the cycle, resulting in continuous consumption of lithium metal and electrolyte, thereby shortening the cycle life of the battery. Summary of the Invention

[0004] In view of this, the present invention is dedicated to providing a negative electrode plate and a preparation method thereof and a battery to solve the problem of dendrite growth in existing lithium batteries.

[0005] In order to solve the above technical problems, this application is implemented as follows:

[0006] The present invention provides a negative electrode plate, comprising a current collector and a polymer protective layer provided on at least one side of the current collector;

[0007] The polymer protective layer includes a block copolymer and a lithium salt;

[0008] Wherein, the block copolymer comprises a rigid segment and a flexible segment; the polymer monomer of the rigid segment comprises a cyano group-containing acrylamide compound; the polymer monomer of the flexible segment comprises an acrylate compound;

[0009] The lithium ions in the lithium salt and the amide groups and / or cyano groups in the rigid segment are connected through chemical bonds; the anions in the lithium salt and the imino groups in the rigid segment are connected through hydrogen bonds.

[0010] Optionally, the mass ratio of the polymer monomer of the rigid segment to the polymer monomer of the flexible segment is (0.2-0.8):1, preferably (0.3-0.5):1.

[0011] Optionally, the mass ratio of the lithium salt to the polymer monomer of the rigid segment is (0.5-1.5):1, preferably (0.8-1):1.

[0012] Optionally, the lithium salt includes at least one of lithium nitrate, rubidium nitrate, lithium difluorophosphate and lithium tetrafluoroborate; Optionally, the cyano group-containing acrylamide compound includes At least one of; Optionally, the chemical formula of the acrylate compound is as shown in formula (1):

[0013]

[0014] wherein n is an integer from 1 to 10, preferably an integer from 1 to 5;

[0015] Optionally, the acrylate compound includes at least one of polyethylene glycol diacrylate, ethylene glycol diacrylate and diethylene glycol diacrylate.

[0016] Optionally, the structural formula of the block copolymer is shown in formula (2):

[0017]

[0018]

[0019] Here, m1, m2, and m3 are each independently an integer from 1 to 20, preferably an integer from 5 to 10.

[0020] A second aspect of the present invention further provides a method for preparing a negative electrode sheet, comprising the following steps:

[0021] S1, heating and mixing a cyano group-containing acrylamide compound and a lithium salt to obtain a deep eutectic solvent;

[0022] S2, performing a first mixing process on a photoinitiator, an acrylate compound, and the deep eutectic solvent to obtain a precursor solution;

[0023] S3. Apply the precursor solution to at least one surface of the current collector and perform a photocuring polymerization reaction.

[0024] Optionally, the mass ratio of the cyano-containing acrylamide compound to the lithium salt is 1:(0.8-1);

[0025] The mass ratio of the acrylic acid ester compound to the deep eutectic solvent is 1:(4-6);

[0026] The mass ratio of the photoinitiator to the acrylate compound is (0.01-0.15):1.

[0027] Optionally, the photoinitiator includes at least one of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl-1-propanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and benzophenone.

[0028] Optionally, in step S1, the conditions for the heating and mixing treatment include: a temperature of 80-100°C and a time of 15-30 min; optionally, in step S2, the first mixing treatment is performed under light-proof conditions; optionally, in step S3, the conditions for the photocuring polymerization reaction include: a light source including ultraviolet light with a wavelength of 360-410 nm and an intensity of 4-8 mW / cm 2 , time is 1 to 5 minutes.

[0029] The third aspect of the present invention further provides a battery, which includes a negative electrode plate, wherein the negative electrode plate includes the above-mentioned negative electrode plate and / or the negative electrode plate prepared according to the above-mentioned preparation method.

[0030] Through the above technical solution, the beneficial technical effects of the present invention are:

[0031] (1) The negative electrode plate of the present invention includes a current collector and a polymer protective layer, wherein the polymer protective layer includes a block polymer composed of rigid segments and flexible segments and a lithium salt. Among them, the polymer layer rich in lithium salt can promote the formation of a large amount of Li3N inorganic interface layer on the surface of metallic lithium, guide the uniform and dense deposition of lithium metal particles, and promote the long-term maintenance of the protective effect of the solid electrolyte interface film. At the same time, the polymer has both rigid and flexible protective layers. The rigid component can improve the mechanical modulus of the protective layer, thereby inhibiting dendrite growth, while the flexible component can withstand the interface fluctuations during the deposition / dissolution process of the metallic lithium negative electrode, thereby significantly improving the cycle stability. In addition, the acrylic acid ester compound contains a large number of ether oxygen bonds, which can coordinate with the lithium ions in the lithium salt, thereby facilitating ion transport. At the same time, the acrylic acid ester compound contains two carbon-carbon double bonds, which can form a stable three-dimensional cross-linked network structure, which can further improve the mechanical strength of the polymer protective layer.

[0032] (2) The preparation method of the negative electrode plate of the present invention is as follows: first, the lithium ions in the lithium salt and the amide group and cyano group in the cyano-containing acrylamide compound interact to form a chemical bond, and the anions in the lithium salt and the imino group in the cyano-containing acrylamide compound form an intermolecular hydrogen bond, so that the lithium salt and the cyano-containing acrylamide compound form a deep eutectic solvent; under the action of a photoinitiator, the acrylate compound and the deep eutectic solvent undergo cross-linking polymerization to form a polymer protective layer on the surface of the current collector. By utilizing the strong interaction force in the deep eutectic molecules to introduce the lithium salt into the polymer protective layer, the concentration of the lithium salt in the system can be increased to the greatest extent, so that the polymer protective layer is rich in lithium salt. The lithium salt stored in the polymer protective layer can be continuously decomposed in the carbonate electrolyte and form a large amount of Li3N inorganic interface layer on the surface of the lithium metal, guiding the uniform and dense deposition of lithium metal particles and promoting the long-term maintenance of the protective effect of the solid electrolyte interface film. Acrylate compounds contain a large number of ether oxygen bonds, which can coordinate with lithium ions in lithium salts, thereby facilitating ion transport. At the same time, acrylate compounds contain two carbon-carbon double bonds. Cyano-containing acrylamide compounds and acrylate compounds can form a stable three-dimensional cross-linked network structure. In the three-dimensional cross-linked network structure, cyano-containing acrylamide compounds are rigid chain segments, which give the polymer protective layer mechanical strength and are more conducive to resisting the growth of lithium dendrites; in the cross-linked structure, acrylate compounds are flexible chain segments, which give the protective layer a certain elasticity, so that the protective layer can adapt to the infinite volume expansion during the cycle of lithium metal batteries and withstand the interface fluctuations during the deposition / dissolution of the metal lithium negative electrode, thereby significantly improving the cycle stability of the battery.

[0033] Other features and advantages of the present invention will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0034] The present invention discloses a negative electrode sheet, a method for preparing the same, and a battery. Those skilled in the art may refer to the contents herein and appropriately modify the process parameters to achieve the desired results. It is particularly important to note that all similar substitutions and modifications apparent to those skilled in the art are considered encompassed by the present invention. The methods and applications of the present invention have been described through preferred embodiments. It is apparent that those skilled in the art can modify or appropriately alter and combine the methods and applications described herein to implement and apply the technology of the present invention without departing from the content, spirit, and scope of the present invention.

[0035] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0036] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0037] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0038] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0039] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0040] In order to solve the problem of dendrite growth in lithium batteries in the prior art, the present invention adopts the following technical solutions:

[0041] The present invention provides a negative electrode plate, which includes a current collector and a polymer protective layer provided on at least one side of the current collector;

[0042] The polymer protective layer includes a block copolymer and a lithium salt;

[0043] The block copolymer includes a rigid segment and a flexible segment; the polymer monomer of the rigid segment includes a cyano group-containing acrylamide compound; the polymer monomer of the flexible segment includes an acrylate compound;

[0044] The lithium ions in the lithium salt and the amide groups and / or cyano groups in the rigid chain segments are connected through chemical bonds; the anions in the lithium salt and the imino groups in the rigid chain segments are connected through hydrogen bonds.

[0045] In this negative electrode sheet, the polymer protective layer disposed on at least one surface of the current collector means that the polymer protective layer can be disposed on one surface of the current collector along its thickness direction, or on both surfaces of the current collector along its thickness direction. The "surface" herein can refer to the entire area of ​​the current collector or a portion of the current collector, and this is not particularly limited in the present invention, as long as the objectives of this application can be achieved.

[0046] The negative electrode plate of the present invention includes a current collector and a polymer protective layer, wherein the polymer protective layer includes a block polymer composed of rigid segments and flexible segments and a lithium salt. Among them, the polymer layer rich in lithium salt can promote the formation of a large amount of Li3N inorganic interface layer on the surface of metallic lithium, guide the uniform and dense deposition of lithium metal particles, and promote the long-term maintenance of the protective effect of the solid electrolyte interface membrane. At the same time, the polymer has both rigid and flexible protective layers. The rigid component can increase the mechanical modulus of the protective layer, thereby inhibiting dendrite growth, while the flexible component can withstand the interface fluctuations during the deposition / dissolution process of the metallic lithium negative electrode, thereby significantly improving the cycle stability. In addition, the acrylic acid ester compound contains a large number of ether oxygen bonds, which can coordinate with the lithium ions in the lithium salt, thereby facilitating ion transport. At the same time, the acrylic acid ester compound contains two carbon-carbon double bonds, which can form a stable three-dimensional cross-linked network structure, which can further improve the mechanical strength of the polymer protective layer.

[0047] According to the present invention, the mass ratio of the polymer monomer of the rigid segment to the polymer monomer of the flexible segment is (0.2 to 0.8): 1. In the present invention, the appropriate mass ratio of the polymer monomer of the rigid segment to the polymer monomer of the flexible segment can not only make the block copolymer have a certain elasticity, make the polymer protective layer suitable for the volume expansion during the cycle of the lithium metal battery to improve the cycle stability, but also make the block copolymer have a higher mechanical strength and inhibit the growth of dendrites. As an example, the mass ratio of the polymer monomer of the rigid segment to the polymer monomer of the flexible segment can be any value among 0.2: 1, 0.3: 1, 0.4: 1, 0.5: 1, 0.6: 1, 0.7: 1 and 0.8: 1 or any value within the range of any two of the above values. In the present invention, if the content of the rigid segment polymer monomer is too high, the flexibility of the block polymer will be reduced, and the cycle performance of the battery will not be improved. If the content of the flexible segment polymer monomer is too high, the mechanical strength of the block copolymer will be low, and the growth of dendrites will not be inhibited. Preferably, the mass ratio of the polymer monomer of the rigid segment to the polymer monomer of the flexible segment is (0.3-0.5):1.

[0048] According to the present invention, the mass ratio of the lithium salt and the polymer monomer of the rigid segment is (0.5-1.5):1. In the present invention, the appropriate mass ratio of the lithium salt and the polymer monomer of the rigid segment is conducive to the formation of a clear and transparent deep eutectic solvent. As an example, the mass ratio of the lithium salt and the polymer monomer of the rigid segment is any value among 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 and 1.5:1 or any value within the range of values ​​composed of any two of the above values. In the present invention, if the content of the lithium salt is too high, it will result in the formation of only an opaque sol; if the content of the polymer monomer of the rigid segment is too high, it will result in the protective effect of the formed polymer layer being weak. Preferably, the mass ratio of the lithium salt and the polymer monomer of the rigid segment is (0.8-1):1.

[0049] Exemplarily, the lithium salt includes at least one of lithium nitrate, rubidium nitrate, lithium difluorophosphate, and lithium tetrafluoroborate. Preferably, the lithium salt includes lithium nitrate. In the present invention, the nitrate in the lithium nitrate can promote the formation of a Li3N-rich SEI film.

[0050] Exemplarily, cyano-containing acrylamide compounds include At least one of .

[0051] For example, the chemical formula of the acrylate compound is shown in formula (1):

[0052]

[0053] Wherein, n is an integer from 1 to 10. For example, n can be 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10. Preferably, n is an integer from 1 to 5.

[0054] Illustratively, the acrylate compound includes at least one of polyethylene glycol diacrylate, ethylene glycol diacrylate, and diethylene glycol diacrylate.

[0055] For example, the structural formula of the block copolymer is shown in formula (2):

[0056]

[0057] Wherein, m1, m2, and m3 are each independently an integer from 1 to 20. For example, m1, m2, and m3 are each independently 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. Preferably, m1, m2, and m3 are each independently an integer from 5 to 10.

[0058] A second aspect of the present invention further provides a method for preparing a negative electrode sheet, comprising the following steps:

[0059] S1, heating and mixing a cyano group-containing acrylamide compound and a lithium salt to obtain a deep eutectic solvent;

[0060] S2, performing a first mixing process on a photoinitiator, an acrylate compound, and a deep eutectic solvent to obtain a precursor solution;

[0061] S3. Apply the precursor solution to at least one surface of the current collector and perform a photocuring polymerization reaction.

[0062] The method for preparing the negative electrode plate of the present invention is as follows: first, the lithium ions in the lithium salt and the amide group and cyano group in the cyano-containing acrylamide compound interact to form a chemical bond, and the anions in the lithium salt and the imino group in the cyano-containing acrylamide compound form an intermolecular hydrogen bond, so that the lithium salt and the cyano-containing acrylamide compound form a deep eutectic solvent; under the action of a photoinitiator, the acrylate compound and the deep eutectic solvent undergo cross-linking polymerization to form a polymer protective layer on the surface of the current collector. By utilizing the strong interaction force in the deep eutectic molecules to introduce the lithium salt into the polymer protective layer, the concentration of the lithium salt in the system can be increased to the greatest extent, so that the polymer protective layer is rich in lithium salt. The lithium salt stored in the polymer protective layer can be continuously decomposed in the carbonate electrolyte and form a large amount of Li3N inorganic interface layer on the surface of the lithium metal, guiding the uniform and dense deposition of lithium metal particles, and promoting the long-term maintenance of the protective effect of the solid electrolyte interface film. Acrylate compounds contain a large number of ether oxygen bonds, which can coordinate with lithium ions in lithium salts, thereby facilitating ion transport. At the same time, acrylate compounds contain two carbon-carbon double bonds. Cyano-containing acrylamide compounds and acrylate compounds can form a stable three-dimensional cross-linked network structure. In the three-dimensional cross-linked network structure, cyano-containing acrylamide compounds are rigid chain segments, which give the polymer protective layer mechanical strength and are more conducive to resisting the growth of lithium dendrites; in the cross-linked structure, acrylate compounds are flexible chain segments, which give the protective layer a certain elasticity, so that the protective layer can adapt to the infinite volume expansion during the cycle of lithium metal batteries and withstand the interface fluctuations during the deposition / dissolution of the metal lithium negative electrode, thereby significantly improving the cycle stability of the battery.

[0063] As an example, N-cyanomethyl acrylamide is selected as the cyano group-containing acrylamide compound, and lithium carbonate is selected as the lithium salt. The structural formula of the formed deep eutectic solvent is shown in the following formula (3):

[0064]

[0065] According to the present invention, the mass ratio of the cyano-containing acrylamide compound and the lithium salt is 1:(0.8-1). In the present invention, the appropriate mass ratio of the cyano-containing acrylamide compound and the lithium salt is conducive to the formation of a clear and transparent deep eutectic solvent. As an example, the mass ratio of the cyano-containing acrylamide compound and the lithium salt can be any of 1:0.8, 1:0.85, 1:0.9, 1:0.95 and 1:1, or any value within the range of any two of the above values. In the present invention, if the content of the cyano-containing acrylamide compound is too much, the protective effect of the formed polymer layer will be weak; if the content of the lithium salt is too much, only an opaque sol will be formed.

[0066] According to the present invention, the mass ratio of the acrylate compound and the deep eutectic solvent is 1:(4-6). In the present invention, a suitable mass ratio of the acrylate compound and the deep eutectic solvent is helpful to form a polymer protective layer with certain mechanical strength and elasticity. As an example, the mass ratio of the acrylate compound and the deep eutectic solvent can be any of 1:4, 1:4.5, 1:5, 1:5.5 and 1:6 or any value within the range of any two of the above values. In the present invention, if the content of the acrylate compound is too much, the mechanical strength of the polymer protective layer will be weak, which is not enough to resist the growth of lithium dendrites; if the content of the deep eutectic solvent is too much, the polymer protective layer will be brittle and unable to adapt to the volume expansion during the cycle.

[0067] According to the present invention, the mass ratio of the photoinitiator to the acrylate compound is (0.01-0.15): 1. As an example, the mass ratio of the photoinitiator to the acrylate compound can be any value among 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.11:1, 0.12:1, 0.13:1, 0.14:1 and 0.15:1, or any value within the range consisting of any two of the above values.

[0068] Illustratively, the photoinitiator includes at least one of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl-1-propanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and benzophenone.

[0069] According to the present invention, in step S1, the conditions for the heating and mixing treatment include: a temperature of 80 to 100°C and a time of 15 to 30 minutes. As an example, in step S1, the conditions for the heating and mixing treatment include: a temperature of 80°C, 82°C, 85°C, 86°C, 88°C, 90°C, 92°C, 94°C, 95°C, 98°C and 100°C or any value within a range consisting of any two of the above values, and a time of 15 minutes, 17 minutes, 20 minutes, 22 minutes, 24 minutes, 25 minutes, 28 minutes and 30 minutes or any value within a range consisting of any two of the above values.

[0070] According to the present invention, in step S2, the first mixing process is performed under light-proof conditions.

[0071] According to the present invention, in step S3, the conditions for the photocuring polymerization reaction are: the light source includes ultraviolet light with a wavelength of 360 to 410 nm and an intensity of 4 to 8 mW / cm 2 As an example, in step S3, the conditions for the photocuring polymerization reaction are as follows: the light source includes ultraviolet light, the wavelength can be any value among 360nm, 370nm, 380nm, 390nm, 400nm and 410nm or any value within the range of any two of the above values, and the intensity can be 4mW / cm 2 , 5mW / cm 2 , 6mW / cm 2 , 7mW / cm 2 and 8mW / cm 2 The time can be any value among 1min, 2min, 3min, 4min and 5min or any value within the range composed of any two of the above values.

[0072] The third aspect of the present invention further provides a battery, which includes a negative electrode plate, wherein the negative electrode plate includes the above-mentioned negative electrode plate and / or the negative electrode plate prepared according to the above-mentioned preparation method.

[0073] The present invention is further described in detail below by way of examples. The raw materials used in the examples can all be obtained through commercial sources.

[0074] Example 1

[0075] The preparation of the negative electrode sheet includes the following steps:

[0076] S1. Heat N-cyanomethylacrylamide at 80°C for 25 min in a glove box, then add an equal amount of LiNO3 and stir at room temperature in a magnetic stirrer for 1 h to form a homogeneous solution deep eutectic solvent (DES).

[0077] S2. In a glove box, polyethylene glycol diacrylate (PEGDA) containing 1% photoinitiator 2-hydroxy-2-methyl-1-phenylpropanone (HMPP) was added to the DES obtained in S1 and stirred in the dark to form a precursor solution, wherein the mass ratio of PEGDA to DES was 1:4;

[0078] S3. Smooth the surface of the lithium copper composite strip in a glove box, pour the precursor solution on the surface of the lithium copper composite strip, and use a scraper with a scraper gap of 3 μm to evenly coat the precursor solution on the surface of the lithium copper composite strip. Then place it under a wavelength of 365 nm and an intensity of 5 mW / cm 2 Irradiate under ultraviolet light for 2 minutes to obtain the negative electrode.

[0079] Example 2

[0080] The preparation of the negative electrode sheet includes the following steps:

[0081] S1. In a glove box, heat N-cyanomethyl acrylamide at 80°C for 25 minutes, then add LiNO3 (80% by mass of N-cyanomethyl acrylamide) and stir in a magnetic stirrer at room temperature for 1 hour to form a homogeneous solution deep eutectic solvent (DES);

[0082] S2. In a glove box, polyethylene glycol diacrylate (PEGDA) containing 1% photoinitiator 2-hydroxy-2-methyl-1-phenylpropanone (HMPP) was added to the DES obtained in S1 and stirred in the dark to form a precursor solution, wherein the mass ratio of PEGDA to DES was 1:5;

[0083] S3. Smooth the surface of the lithium copper composite strip in a glove box, pour the precursor solution on the surface of the lithium copper composite strip, and use a scraper with a scraper gap of 3 μm to evenly coat the precursor solution on the surface of the lithium copper composite strip. Then place it under a wavelength of 365 nm and an intensity of 5 mW / cm 2 Irradiate under ultraviolet light for 2 minutes to obtain the negative electrode.

[0084] Example 3

[0085] The preparation of the negative electrode sheet is different from that of Example 1 in that:

[0086] In step S1, N-cyanomethyl acrylamide is replaced by

[0087] The rest are the same as in Example 1.

[0088] Example 4

[0089] The preparation of the negative electrode sheet is different from that of Example 1 in that:

[0090] In step S1, the mass ratio of N-cyanomethyl acrylamide to LiNO3 is 1:0.9.

[0091] The rest are the same as in Example 1.

[0092] Example 5

[0093] The preparation of the negative electrode sheet is different from that of Example 1 in that:

[0094] In step S2, the mass ratio of PEGDA to DES is 1:6.

[0095] The rest are the same as in Example 1.

[0096] Comparative Example 1

[0097] The preparation of the negative electrode sheet is different from that of Example 1 in that:

[0098] There is no polymer protective layer.

[0099] The rest are the same as in Example 1.

[0100] Comparative Example 2

[0101] The preparation of the negative electrode sheet includes the following steps:

[0102] S1. Add N-cyanomethyl acrylamide and polyethylene glycol diacrylate (PEGDA) in a mass ratio of 1:1 to dimethyl sulfoxide (DMSO) solution, and the mass ratio of DMSO to PEGDA is 2:1. Stir at 45°C for 1 hour, then add 1% of the mass of PEGDA as the photoinitiator 2-hydroxy-2-methyl-1-phenylpropanone (HMPP) and stir evenly to form a precursor solution.

[0103] S2. Smooth the surface of the lithium copper composite tape in a glove box, pour the precursor solution on the surface of the lithium copper composite tape, and use a scraper with a scraper gap of 3 μm to evenly coat the precursor solution on the surface of the lithium copper composite tape; then place it under a wavelength of 365 nm and an intensity of 5 mW / cm 2 After irradiation under ultraviolet light for 2 minutes, a lithium metal negative electrode with a polymer protective layer was obtained.

[0104] Battery assembly and performance testing

[0105] 1. Battery assembly

[0106] A Li||Li symmetric battery was assembled, where the electrodes on both sides were the negative electrode sheets prepared in the embodiments and comparative examples, and the electrolyte was 1.2 M LiPF6-EC:EMC:FEC (volume ratio 10:10:1).

[0107] 2. Performance Testing

[0108] The battery is at 1mA / cm 2 The current density and 1mAh / cm 2 Cycling performance test was conducted at the surface capacity of 1mA / cm 2 The current density was 1mA / cm 2 The discharge overpotential of each Li||Li symmetrical battery was recorded as a function of the number of cycles. The results are shown in Table 1.

[0109] Table 1

[0110] 10 laps 100 cycles 500 cycles Example 1 85mV 88mV 97mV Example 2 88mV 90mV 102mV Example 3 93mV 96mV 102mV Example 4 89mV 92mV 106mV Example 5 91mV 93mV 105mV Comparative Example 1 78mV 145mV 569mV Comparative Example 2 82mV 128mV 497mV

[0111] As can be seen from Table 1, the cycle performance of the lithium metal battery of the present invention is significantly improved, and the overpotential does not increase significantly after 500 cycles.

[0112] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A negative electrode plate, characterized in that: The negative electrode plate includes a current collector and a polymer protective layer provided on at least one side of the current collector; The polymer protective layer includes a block copolymer and a lithium salt; Wherein, the block copolymer comprises a rigid segment and a flexible segment; the polymer monomer of the rigid segment comprises a cyano group-containing acrylamide compound; the polymer monomer of the flexible segment comprises an acrylate compound; The lithium ions in the lithium salt and the amide groups and / or cyano groups in the rigid segment are connected through chemical bonds; the anions in the lithium salt and the imino groups in the rigid segment are connected through hydrogen bonds.

2. The negative electrode sheet according to claim 1, characterized in that: The mass ratio of the polymer monomer of the rigid segment to the polymer monomer of the flexible segment is (0.2-0.8):1, preferably (0.3-0.5):

1.

3. The negative electrode sheet according to claim 1, characterized in that: The mass ratio of the lithium salt to the polymer monomer of the rigid segment is (0.5-1.5):1, preferably (0.8-1):

1.

4. The negative electrode sheet according to claim 1, characterized in that: The lithium salt includes at least one of lithium nitrate, rubidium nitrate, lithium difluorophosphate and lithium tetrafluoroborate; And / or, the cyano-containing acrylamide compound includes At least one of; And / or, the chemical formula of the acrylic acid ester compound is as shown in formula (1): wherein n is an integer from 1 to 10, preferably an integer from 1 to 5; Optionally, the acrylate compound includes at least one of polyethylene glycol diacrylate, ethylene glycol diacrylate and diethylene glycol diacrylate.

5. The negative electrode sheet according to claim 4, characterized in that: The structural formula of the block copolymer is shown in formula (2): Here, m1, m2, and m3 are each independently an integer from 1 to 20, preferably an integer from 5 to 10.

6. A method for preparing a negative electrode sheet according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, heating and mixing a cyano group-containing acrylamide compound and a lithium salt to obtain a deep eutectic solvent; S2, performing a first mixing process on a photoinitiator, an acrylate compound, and the deep eutectic solvent to obtain a precursor solution; S3. Apply the precursor solution to at least one surface of the current collector and perform a photocuring polymerization reaction.

7. The method for preparing a negative electrode sheet according to claim 6, wherein: The mass ratio of the cyano-containing acrylamide compound to the lithium salt is 1:(0.8-1); The mass ratio of the acrylic acid ester compound to the deep eutectic solvent is 1:(4-6); The mass ratio of the photoinitiator to the acrylate compound is (0.01-0.15):

1.

8. The method for preparing a negative electrode sheet according to claim 6, wherein: The photoinitiator includes at least one of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl-1-propanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and benzophenone.

9. The method for preparing a negative electrode sheet according to claim 6, wherein: In step S1, the conditions of the heating and mixing treatment include: a temperature of 80 to 100° C. and a time of 15 to 30 minutes; and / or, In step S2, the first mixing process is performed under light-proof conditions; and / or, In step S3, the conditions for the photocuring polymerization reaction are: the light source includes ultraviolet light with a wavelength of 360 to 410 nm and an intensity of 4 to 8 mW / cm 2 , time is 1 to 5 minutes.

10. A battery, characterized in that: The battery includes a negative electrode sheet, wherein the negative electrode sheet includes the negative electrode sheet according to any one of claims 1 to 5 and / or the negative electrode sheet prepared by the preparation method according to any one of claims 6 to 9.

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