Polymer protective film, metal lithium negative electrode, lithium battery and vehicle

Abstract

The present application discloses a polymer protective film, a metal lithium negative electrode, a lithium battery and a vehicle. The polymer protective film is composed of a composition of polymer A and polymer B, wherein polymer B is a conductive polymer and the structural formula of polymer A is as follows: or the polymer A in the polymer protective film of the present application can effectively conduct lithium ions, promote lithium ion transmission, and inhibit the formation of lithium dendrites. At the same time, it can also improve the flexibility of the polymer protective film, which is conducive to adapting to the expansion of lithium metal; polymer B is conducive to the uniform distribution of lithium ions, thereby improving the safety performance and cycle performance of the battery.

Description

Technical Field

[0001] The present invention generally relates to the technical field of lithium batteries, and in particular to a polymer protective film, a metal lithium negative electrode, a lithium battery and a vehicle. Background Art

[0002] With the widespread application of smart electronic devices, electric vehicles, and large-scale energy storage devices, lithium secondary batteries with higher energy density and cycle life are urgently needed. Lithium metal has a high theoretical specific capacity (3860mAh / g) and a low electrochemical potential (-3.040V vs standard hydrogen electrode), and is considered to be the most ideal negative electrode material for the next generation of lithium secondary batteries.

[0003] Lithium metal has active chemical properties and is prone to side reactions with the electrolyte, resulting in a decrease in the coulombic efficiency of the battery, as well as uneven surface morphology and charge distribution of the metal lithium, which easily leads to the formation of lithium dendrites. As the lithium dendrites continue to grow, they pierce the battery separator and cause a short circuit in the battery, posing a safety hazard. At the same time, it reduces the battery cycle life, thereby limiting the application of metal lithium negative electrodes.

[0004] Currently, polymer protective films are used on lithium metal negative electrodes to prevent direct contact between the lithium metal and the electrolyte, thus preventing the formation of lithium dendrites. However, conventional protective films cannot effectively conduct lithium ions, affecting the transmission of lithium ions and causing uneven distribution of lithium ions. In addition, conventional polymer protective films have poor mechanical strength and are unable to inhibit the growth of lithium dendrites, resulting in poor battery cycle performance and safety. Summary of the Invention

[0005] In view of the above-mentioned defects or deficiencies in the prior art, it is desired to provide a polymer protective film, a metal lithium negative electrode, a lithium battery and a vehicle. The polymer protective film can not only effectively conduct lithium ions and improve the transmission efficiency of lithium ions, but also has high mechanical strength, inhibiting the formation and growth of lithium dendrites, thereby improving the cycle life and safety performance of the battery.

[0006] In a first aspect, the present invention provides a polymer protective film, which includes polymer A and polymer B, wherein polymer B is a conductive polymer, and the structural formula of polymer A is as follows:

[0007]

[0008] Wherein, R1 is selected from one of hydrogen, halogen, and a substituted or unsubstituted C1-C6 alkyl group;

[0009] R2 is selected from substituted or unsubstituted wherein z1, z2, z3, and z4 are each independently an integer from 2 to 100;

[0010] R3 and R9 are each independently selected from hydrogen or lithium atoms;

[0011] R4, R5, R6, and R7 are each independently selected from a hydrogen or fluorine atom;

[0012] R8, R 21 、R 22 、R 23 、R 24 are each independently selected from O, NH or S;

[0013] m and n are the molar ratios of the corresponding segments in the entire polymer, and m and n are each independently any decimal between 0 and 1, and m + n is equal to 1.0; x and y are the molar ratios of the corresponding segments in the entire polymer, and x and y are each independently any decimal between 0 and 1, and x + y is equal to 1.0.

[0014] As an optional solution, the molar ratio of polymer A to polymer B is 1:(0.025-1).

[0015] As an optional solution, 0.5≤m≤0.95, 0.05≤n≤0.5; 0.5≤x≤0.95, 0.05≤y≤0.5.

[0016] As an optional solution, 0.6≤m≤0.8, 0.2≤n≤0.4; 0.6≤x≤0.8, 0.2≤y≤0.4.

[0017] As an optional scheme, the substituent is selected from halogen, hydroxyl, amino, carbonyl, cyano, C1-C6 alkoxy, C1-C6 alkyl, C6-C 12 Aryl or C6-C 12 of a cycloalkyl group.

[0018] As an optional scheme, the halogen is selected from one of fluorine, chlorine and bromine; the amine group is selected from a C1-C6 primary amine, a C1-C6 alkyl-substituted secondary amine or a tertiary amine; the C1-C6 alkoxy group is selected from a methoxy group or an ethoxy group; the C1-C6 alkyl group is selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group or a tert-butyl group; the C6-C 12 The aryl group is selected from phenyl, naphthyl, or biphenyl; C6-C 12 The cycloalkyl group is selected from cyclohexyl or bicyclohexyl.

[0019] As an optional solution, the molecular weight of polymer A is 1,000-2,000,000, preferably 10,000-500,000.

[0020] As an optional solution, polymer B is polyethylene dioxythiophene, and the structural formula is shown below:

[0021]

[0022] Wherein, z is an integer from 2 to 100,000.

[0023] In a second aspect, the present invention provides a metal lithium negative electrode, comprising a metal lithium sheet and the polymer protective film of the first aspect, wherein the polymer protective film is disposed on the metal lithium sheet.

[0024] In a third aspect, the present invention provides a lithium battery comprising the metallic lithium negative electrode of the second aspect.

[0025] In a fourth aspect, the present invention provides a vehicle comprising the lithium battery of the fourth aspect.

[0026] The polymer protective film of the present application contains chain segments that conduct lithium ions, which can form a strong interaction with lithium metal, reducing the interfacial impedance between the polymer protective film and lithium metal, while promoting lithium ion transmission and making lithium ions evenly distributed, reducing the generation of lithium dendrites; moreover, the polymer protective film has good flexibility and can adapt to the expansion of lithium metal. At the same time, the conductive polymer in the polymer protective film is rigid, which effectively improves the mechanical strength of the protective film, is beneficial to inhibiting the growth of lithium dendrites, and thereby effectively improves the safety performance and cycle performance of the battery. DETAILED DESCRIPTION

[0027] The present application will be further described in detail below with reference to the embodiments. It will be appreciated that the specific embodiments described herein are intended only to explain the invention and are not intended to limit the invention. Furthermore, it should be noted that, for ease of description, only portions relevant to the invention are shown in the embodiments.

[0028] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the embodiments.

[0029] An embodiment of the present invention provides a polymer protective film, which includes polymer A and polymer B, wherein polymer B is a conductive polymer, and the structural formula of polymer A is as follows:

[0030]

[0031] Wherein, R1 is selected from one of hydrogen, halogen, and a substituted or unsubstituted C1-C6 alkyl group;

[0032] R2 is selected from substituted or unsubstituted wherein z1, z2, z3, and z4 are each independently an integer from 2 to 100;

[0033] R3 and R9 are each independently selected from hydrogen or lithium atoms;

[0034] R4, R5, R6, and R7 are each independently selected from a hydrogen or fluorine atom;

[0035] R8, R 21 、R 22 、R 23 、R 24 are each independently selected from O, NH or S;

[0036] m and n are each independently any decimal between 0 and 1, and m+n is equal to 1.0; x and y are each independently any decimal between 0 and 1, and x+y is equal to 1.0.

[0037] The main active ingredients in the polymer protective film of this embodiment are polymer A and polymer B. The polymer protective film may contain only polymer A and polymer B, or may include other components in addition to polymer A and polymer B. For example, during the actual preparation process, the polymer protective film may include lithium salts, etc. The specific other components are not limited.

[0038] As can be seen from the structural formula of polymer A, the left part of the structural formula of polymer A is a lithium ion conductive segment, and the right part is a polystyrene sulfonate (lithium) segment; controlling the values ​​of m and n, or x and y, is beneficial to regulating the content of the lithium ion conductive segment and the polystyrene sulfonate (lithium) segment of the polymer protective film, and thus is beneficial to controlling the lithium ion conductive ability, conductivity, flexibility and mechanical strength of the polymer protective film.

[0039] Among them, regulating the structure of the R1, R2, R4, R5, R6, R7, and R8 groups is beneficial to controlling the ion conduction ability of polymer A and its interaction with metallic lithium. At the same time, it can also adjust the flexibility of polymer A, so that the polymer protective film can effectively conduct lithium ions, form a strong interaction with lithium metal, reduce the interface impedance between the polymer protective film and lithium metal, and at the same time, the polymer protective film can adapt to the expansion of lithium metal.

[0040] Polymer B can be any conductive polymer, such as polyaniline, polypyrrole, polyethylenedioxythiophene, or derivatives thereof. In a preferred embodiment, polymer B is polyethylenedioxythiophene. Conductive polymers are rigid, which can enhance the mechanical strength of the polymer protective film and inhibit the growth of lithium dendrites. Furthermore, conductive polymers can be combined with lithium metal anodes to form a negative electrode with a gradient of different conductivity properties. This gradient structure can induce uniform nucleation and deposition of lithium ions beneath the protective film, preventing battery short circuits and inhibiting the formation of lithium dendrites, thereby improving battery safety and cycle life.

[0041] The polymer protective film of this embodiment includes polymer A and polymer B. Polymer A contains a segment that can conduct lithium ions and a polystyrene sulfonate lithium segment, and polymer B is a conductive polymer. The combination of polymer A and polymer B can improve the processability of polymer B, making polymer B easy to disperse in the solvent and convenient for preparing the polymer protective film. At the same time, polymer B can also improve the conductivity of the polymer protective film. The segment that conducts lithium ions in polymer A can promote lithium ion transmission and make lithium ions evenly distributed, reducing the generation of lithium dendrites; the polystyrene sulfonate (lithium) segment can form an electrostatic effect with polymer B, so that polymer B is evenly dispersed, which is beneficial to the preparation of the polymer protective film. At the same time, due to the electrostatic effect between polymer B and the sulfonic acid group, it is beneficial to better fit closely with the metal lithium sheet and avoid the polymer protective film from falling off. The polymer B in the polymer protective film can be combined with the metal negative electrode to form a negative electrode with different conductivity gradients. That is, the conductive polymer with relatively poor conductivity covers the surface of the lithium metal negative electrode with excellent conductivity. The advantage of this gradient structure is that lithium ions can be easily distributed evenly due to the electric field when passing through the conductive polymer layer. However, since the metal layer has better conductivity and lower potential (the conductive polymer has resistance and higher potential), the evenly distributed lithium ions will uniformly nucleate and deposit in the metal layer under the protective film. Therefore, the lithium ions will not preferentially gather and deposit at the tip, which is beneficial to inhibiting the growth of lithium dendrites. In addition, the conductive polymer is rigid, which can improve the mechanical strength of the protective film and further inhibit the growth of lithium dendrites.

[0042] Furthermore, the molar ratio of polymer A to polymer B is 1:(0.025-1).

[0043] Furthermore, 0.5≤m≤0.95, 0.05≤n≤0.5; 0.5≤x≤0.95, 0.05≤y≤0.5. For example, m is 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.9, and 0.95; n is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.4, and 0.5; x is 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.9, and 0.95; y is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.4, and 0.5. The value ranges of m and n, or x and y disclosed in the embodiments of the present application are conducive to regulating the content of the conductive lithium ion segment and the polystyrene sulfonate lithium segment in polymer A, so that the conductive lithium ion segment and the polystyrene sulfonate lithium segment have a suitable ratio, thereby promoting the formation of a strong interaction between the polymer protective film and metallic lithium, effectively conducting lithium ions, and at the same time improving the flexibility of the polymer protective film so that it can adapt to the expansion of metallic lithium.

[0044] In a preferred embodiment, 0.6≤m≤0.8, 0.2≤n≤0.4; 0.6≤x≤0.8, 0.2≤y≤0.4. For example, m is 0.6, 0.65, 0.7, 0.75, and 0.8, etc.; n is 0.2, 0.25, 0.3, 0.35, and 0.4, etc.; x is 0.6, 0.65, 0.7, 0.75, and 0.8, etc.; y is 0.2, 0.25, 0.3, 0.35, and 0.4, etc.

[0045] Furthermore, the substituent is selected from halogen, hydroxyl, amino, carbonyl, cyano, C1-C6 alkoxy, C1-C6 alkyl, C6-C 12 Aryl or C6-C 12 The substituent is beneficial to improving the lithium ion conductivity of the polymer protective film, increasing the lithium ion migration number, making the lithium ions evenly distributed, thereby more effectively preventing the formation of lithium dendrites, and also improving the flexibility of the polymer protective film.

[0046] Furthermore, the halogen is selected from one of fluorine, chlorine and bromine; the amine group is selected from a C1-C6 primary amine, a C1-C6 alkyl-substituted secondary amine or a tertiary amine; the C1-C6 alkoxy group is selected from a methoxy group or an ethoxy group; the C1-C6 alkyl group is selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group or a tert-butyl group; the C6-C 12 The aryl group is selected from phenyl, naphthyl, or biphenyl; C6-C 12 The cycloalkyl group is selected from cyclohexyl or bicyclohexyl.

[0047] Furthermore, the molecular weight of polymer A is 1000 to 2000000. For example, the molecular weight of polymer A can be 1000, 3000, 5000, 7000, 9000, 10000, 15000, 20000, 30000, 50000, 100000, 180000, 250000, 30000, 360000, 400000, 430000, 480000, 500000, 800000, 1000000, 1500000, and 2000000, etc. In a preferred embodiment, the molecular weight of polymer A is 10000-500000. The embodiments of the present invention do not limit the specific molecular weight.

[0048] In a preferred embodiment, polymer B is polyethylene dioxythiophene, and its structural formula is shown below:

[0049]

[0050] Wherein, z is an integer from 2 to 100,000.

[0051] In summary, polymer A in the polymer protective film of the embodiment of the present application can effectively conduct lithium ions, promote lithium ion transmission, and inhibit the formation of lithium dendrites. At the same time, it can also improve the flexibility of the polymer protective film, which is conducive to adapting to the expansion of lithium metal; polymer B is beneficial to enhancing the mechanical strength of the polymer protective film, further inhibiting the growth of lithium dendrites, and thereby improving the safety performance and cycle performance of the battery.

[0052] Moreover, by regulating the content of each chain segment in the polymer, it is beneficial to control the ionic conductivity, interaction with lithium ions and flexibility of the polymer protective film to be optimal, thereby improving the cycle performance and safety performance of the battery.

[0053] In a second aspect, the present invention provides a lithium metal anode comprising a lithium metal sheet and the polymer protective film of the first aspect, the polymer protective film being disposed on the lithium metal sheet. Those skilled in the art will appreciate that this lithium battery anode possesses all the features and advantages of the polymer protective film described above, and further details will not be given here.

[0054] In a specific embodiment, the metallic lithium negative electrode is prepared by the following process:

[0055] Will Mix evenly in a solvent according to a certain proportion, add an initiator to initiate polymerization, and obtain a polymer

[0056] Will and Reaction preparation of macroinitiator Combine it with The mixture is mixed evenly in a solvent, and the ligand 2,2'-bipyridine and the catalyst cuprous bromide are added thereto to obtain a polymer by atom transfer radical polymerization (ATRP). Where i is an integer from 2 to 10000;

[0057] The conductive polymer monomer and polymer A are uniformly mixed in a solvent, and an initiator is added to polymerize the mixture. After removing the solvent, a composition of polymer A and polymer B is obtained, wherein the conductive polymer monomer can be one of aniline, pyrrole, ethylenedioxythiophene, or derivatives thereof, and the molar ratio of the conductive polymer monomer to the benzenesulfonic acid group in polymer A is 1:(0.5-2), preferably 1:1;

[0058] The composition of polymer A and polymer B is dissolved in a solvent to obtain a mixed solution, which is then coated on a metal lithium sheet, dried at room temperature, and then placed in a vacuum oven to obtain a metal lithium negative electrode.

[0059] Among them, the solvent can be selected from any one of toluene, xylene, trimethylbenzene, n-pentane, n-hexane, n-heptane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, ethyl ether, propyl ether, butyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, acetone, butanone, ethyl acetate, butyl acetate, ethyl propionate, butyl propionate, water, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, N,N-dimethylformamide, sulfolane or dimethyl sulfoxide.

[0060] The initiator is selected from any one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, benzoyl peroxide, tert-butyl benzoyl peroxide, benzophenone, benzophenone, methyl o-benzoylbenzoate, potassium persulfate, ammonium persulfate, potassium dichromate, hydrogen peroxide, and ferric chloride.

[0061] The coating method includes drip coating, blade coating, spin coating or spray coating, as long as it can ensure that the polymer protective film is evenly coated on the metal lithium sheet. This embodiment does not make any specific restrictions on this.

[0062] The thickness of the protective film is 1 μm to 10 μm. For example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. The thickness of the protective film in this embodiment helps ensure that the metal lithium negative electrode has high activity, while preventing direct contact between the metal lithium and the electrolyte, thereby preventing the formation of lithium dendrites, and improving the cycle performance and safety performance of the battery.

[0063] To ensure that the polymer protective film is firmly bonded to the lithium metal sheet, the drying temperature is 25°C-50°C and the drying time is 0.5h-4h. The embodiments of the present invention do not limit the specific reaction temperature and time. The temperature and time range disclosed in the embodiments of the present invention are conducive to ensuring that the polymer protective film is firmly bonded to the lithium metal sheet while avoiding affecting the activity of the lithium metal negative electrode and causing decomposition of the polymer protective film.

[0064] In a third aspect, the present invention provides a lithium battery comprising the lithium metal anode of the second aspect. Those skilled in the art will appreciate that this lithium secondary battery possesses all the features and advantages of the polymer protective film described above, and further details will not be given here. In summary, the lithium battery of the present invention has excellent cycle performance and safety.

[0065] In a specific embodiment, the lithium battery further includes: a positive electrode, a separator, and an electrolyte. Among them, the positive electrode includes a positive electrode current collector and an active material layer located on the positive electrode current collector. The active material layer includes a positive electrode active material, a binder, and a conductive agent. The positive electrode active material can be selected from lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium iron phosphate (LiFePO4), lithium cobalt phosphate (LiCoPO4), lithium manganese phosphate (LiMnPO4), lithium nickel phosphate (LiNiPO4), lithium manganate (LiMnO2), binary material LiNi x A (1-x) O2 (where A is selected from one of Co and Mn, 0 < x < 1), ternary material LiNimBnC (1-m-n) O2 (where B and C are independently selected from at least one of Co, Al, and Mn, and B and C are different, 0 < m < 1, 0 < n < 1).

[0066] The separator can be any separator material used in existing lithium secondary batteries. Specifically, it can be polyethylene, polypropylene, polyvinylidene fluoride, and their multilayer composite films.

[0067] The electrolyte includes an organic solvent, a lithium salt, and an additive. Among them, the organic solvent can be selected from at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, ethyl acetate, acid anhydride, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, acetonitrile, sulfolane, dimethyl sulfoxide, ethylene sulfite, propylene sulfite, methyl sulfide, diethyl sulfite, dimethyl sulfite, fluorinated cyclic organic ester, sulfur-containing cyclic organic ester; the lithium salt is selected from at least one of organic lithium salts and inorganic lithium salts, such as LiPF6, LiBF4, LiTFSI, LiFSI, LiClO4, LiAsF6, LiBOB, LiDFOB, LiTFOP; the additive can be selected from at least one of vinylene carbonate, fluorinated carbonate, difluorinated ethylene carbonate, fluorinated ethylene carbonate, ethylene vinylene carbonate, ethylene sulfite, methylene methane disulfonate, 1,3-propane sultone, 1,3-propylene sultone, ethylene sulfate, lithium difluorophosphate, lithium difluorobis(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate.

[0068] In a fourth aspect, the present invention provides a vehicle, which includes the lithium battery of the fourth aspect. For example, it may include a plurality of battery packs composed of the aforementioned lithium batteries. Thus, the vehicle has all the features and advantages of the aforementioned lithium battery, which will not be elaborated here.

[0069] The present invention is described below by means of specific examples. It should be noted that the following specific examples are only for illustrative purposes and are not intended to limit the scope of the present invention in any way.

[0070] Example 1

[0071] (1) Preparation of metallic lithium negative electrode:

[0072] A composition of polymer A and polymer B polyethylene dioxythiophene is dissolved in tetrahydrofuran to obtain a mixed solution. The structural formula of polymer A is as follows:

[0073]

[0074] The mixed liquid was coated on a metal lithium sheet, dried at room temperature, and then placed in a vacuum oven at 50°C for 2 hours to obtain a lithium metal negative electrode with a protective film having a thickness of 3 μm.

[0075] (2) Half-cell preparation

[0076] CR2025 button cells were assembled in an argon-filled glove box (content O2≤0.5ppm, H2O≤0.5ppm), wherein the positive electrode was a lithium iron phosphate electrode, the negative electrode was the above-mentioned lithium metal negative electrode with a protective film, the electrolyte was a 1 mol / L solution of lithium bis(fluorosulfonyl)imide in 1,3-dioxolane and ethylene glycol dimethyl ether (DOL / DME, v / v 1:1), and the separator was a 14 μm PE separator.

[0077] Example 2

[0078] The difference between this embodiment and embodiment 1 is that the structural formula of polymer A is:

[0079]

[0080] Example 3

[0081] The difference between this embodiment and embodiment 1 is that the structural formula of polymer A is:

[0082]

[0083] Example 4

[0084] The difference between this embodiment and embodiment 1 is that the structural formula of polymer A is:

[0085]

[0086] Example 5

[0087] The difference between this embodiment and embodiment 1 is that the structural formula of polymer A is:

[0088]

[0089] Example 6

[0090] The difference between this embodiment and embodiment 1 is that the structural formula of polymer A is:

[0091]

[0092] Example 7

[0093] The difference between this embodiment and embodiment 1 is that the structural formula of polymer A is:

[0094]

[0095] Example 8

[0096] The difference between this embodiment and embodiment 1 is that the structural formula of polymer A is:

[0097]

[0098] Example 9

[0099] The difference between this embodiment and embodiment 1 is that the structural formula of polymer A is:

[0100]

[0101] Example 10

[0102] The difference between this embodiment and embodiment 1 is that the structural formula of polymer A is:

[0103]

[0104] Example 11

[0105] The difference between this embodiment and embodiment 1 is that the structural formula of polymer A is:

[0106]

[0107] Example 12

[0108] The difference between this embodiment and embodiment 1 is that the structural formula of polymer A is:

[0109]

[0110] Example 13

[0111] The difference between this embodiment and embodiment 1 is that the structural formula of polymer A is:

[0112]

[0113] Example 14

[0114] The difference between this embodiment and embodiment 1 is that the structural formula of polymer A is:

[0115]

[0116] Example 15

[0117] The difference between this embodiment and embodiment 1 is that the structural formula of polymer A is:

[0118]

[0119] Example 16

[0120] The difference between this embodiment and embodiment 1 is that polymer B is polyaniline.

[0121] Example 17

[0122] The difference between this embodiment and embodiment 1 is that polymer B is polypyrrole.

[0123] Comparative Example 1

[0124] The difference between this comparative example and Example 1 is that the polymer is PEO (polyethylene oxide) with a molecular weight of 600,000;

[0125] Comparative Example 2

[0126] The difference between this comparative example and Example 1 is that the protective film contains only polymer

[0127] Comparative Example 3

[0128] The difference between this comparative example and Example 1 is that the protective film contains only polymer B polyethylenedioxythiophene.

[0129] Comparative Example 4

[0130] The difference between this comparative example and Example 1 is that the structural formula of polymer A is:

[0131]

[0132] The value of a is chosen so that the molecular weight of the polymer is 10,000-500,000.

[0133] Comparative Example 5

[0134] The difference between this comparative example and Example 1 is that the structural formula of polymer A is:

[0135]

[0136] The value of b is such that the molecular weight of the polymer is 10,000-500,000.

[0137] Comparative Example 6

[0138] The difference between this comparative example and Example 1 is that the structural formula of polymer A is:

[0139]

[0140] The value of c is chosen so that the molecular weight of the polymer is 10,000-500,000.

[0141] Comparative Example 7

[0142] The difference between this comparative example and Example 1 is that there is no protective film on the surface of the lithium metal negative electrode.

[0143] The lithium batteries prepared in the above examples and comparative examples were subjected to the following performance tests to characterize the electrochemical properties of the polymer protective films.

[0144] The test procedure was as follows: 10 batteries prepared in each example and comparative example were subjected to charge-discharge cycling at 0.5C on a LAND CT 2001C secondary battery performance tester at 25±1°C. The procedure was as follows: 1 cycle was defined as: 5 minutes of rest; constant current charging to 3.8V; 5 minutes of rest; and constant current discharge to 2.7V. This cycle was repeated until the battery capacity fell below 80% of the initial discharge capacity. This number of cycles was considered the battery's cycle life. The test results are shown in Table 1.

[0145] Table 1 Performance test results of half-cells prepared in Examples 1-17 and Comparative Examples 1-7

[0146]

[0147]

[0148] From the results shown in Table 1, we can get:

[0149] The test results of Examples 1-17 and Comparative Example 7 indicate that the half-cells assembled with the polymer protective films of Examples 1-17 outperformed the half-cell of Comparative Example 7 in terms of initial charge and discharge capacity, initial coulombic efficiency, and cycle life. The metallic lithium negative electrode in the half-cell of Comparative Example 7 was not coated with a polymer protective film. Therefore, the polymer protective films of the present invention are beneficial for improving battery performance.

[0150] According to the test results of Examples 1-17 and Comparative Example 1, it can be concluded that the half-cells assembled with the polymer protective films of Examples 1-17 are superior to the half-cell of Comparative Example 1 in terms of the initial charge and discharge capacity, initial coulombic efficiency, and cycle life, indicating that the polymer protective films prepared in the embodiments of the present invention are more conducive to improving the performance of lithium batteries than conventional polymer protective films.

[0151] According to the test results of Examples 1-3 and Examples 7-9, it can be concluded that the half-cells of Examples 1-3 and Examples 7-9 all have high initial charge and discharge capacity, initial coulombic efficiency and excellent cycle performance. Therefore, the value range of the conductive lithium ion segment and the polystyrene sulfonate lithium segment in the polymer A of the embodiment of the present application is conducive to promoting a strong interaction between the polymer protective film and metallic lithium, effectively conducting lithium ions, and at the same time improving the flexibility of the polymer protective film so that it can adapt to the expansion of metallic lithium.

[0152] According to the test results of Examples 4-6 and Examples 10-15, it can be concluded that different R groups have little effect on the performance of the polymer, and the polymer structures disclosed in the examples of this application can effectively improve the performance of the battery.

[0153] According to the test results of Example 1 and Examples 16-17, it can be concluded that different conductive polymers have little effect on the performance of the polymer protective film, and the half-cells prepared with the polymer protective film disclosed in the examples of this application all have high capacity and good cycle performance.

[0154] According to the test results of Example 1 and Comparative Examples 2-6, the half-cell of Example 1 is superior to the half-cells of Comparative Examples 2-6 in terms of the initial charge and discharge capacity, initial coulombic efficiency, and cycle life. Among them, the polymer in Comparative Example 2 contains only polymer A, the polymer in Comparative Example 3 contains only polymer B, and the polymer A in Comparative Examples 4-6 contains only one of the segments. Therefore, it can be seen that the reason why the polymer disclosed in the present application can improve the performance of the battery is that the synergistic effect of polymer A and polymer B enables the polymer protective film to effectively conduct lithium ions, and to be tightly combined with the metal lithium sheet, while effectively inhibiting the growth of lithium dendrites; and polymer A must contain both conductive lithium ion segments and polystyrene sulfonate lithium segments, which can effectively conduct lithium ions while forming an electrostatic effect with polymer B, thereby improving the performance of the battery.

[0155] The above description is merely a preferred embodiment of the present application and an illustration of the technical principles employed. Those skilled in the art should understand that the scope of the invention herein is not limited to the technical solutions formed by the specific combination of the above-mentioned technical features, but also encompasses other technical solutions formed by any combination of the above-mentioned technical features or their equivalents without departing from the inventive concept. For example, a technical solution formed by replacing the above-mentioned features with (but not limited to) technical features having similar functions disclosed in this application.

Claims

1. A polymer protective film, characterized in that The polymer protective film includes polymer A and polymer B, wherein the polymer B is a conductive polymer, and the structural formula of the polymer A is as follows: ,or Wherein, R1 is selected from one of hydrogen, halogen, and a substituted or unsubstituted C1-C6 alkyl group; R2 is selected from the group consisting of 、 、 、 ; Wherein, z1, z2, z3, z4 are each independently an integer of 2-100; R3 and R9 are each independently selected from hydrogen or lithium atoms; R4, R5, R6, and R7 are each independently selected from a hydrogen or fluorine atom; R8, R 21 、R 22 、R 23 、R 24 are each independently selected from O, NH or S; m and n are the molar ratios of the corresponding segments in the entire polymer, and m and n are each independently any decimal between 0 and 1, and m + n is equal to 1.0; x and y are the molar ratios of the corresponding segments in the entire polymer, and x and y are each independently any decimal between 0 and 1, and x + y is equal to 1.

0.

2. The polymer protective film according to claim 1, characterized in that The molar ratio of polymer A to polymer B is 1:(0.025~1).

3. The polymer protective film according to claim 1, characterized in that 0.5≤m≤0.95, 0.05≤n≤0.5; 0.5≤x≤0.95, 0.05≤y≤0.

5.

4. The polymer protective film according to claim 3, characterized in that 0.6≤m≤0.8, 0.2≤n≤0.4; 0.6≤x≤0.8, 0.2≤y≤0.

4.

5. The polymer protective film according to any one of claims 1 to 4, characterized in that: The substituent is selected from halogen, hydroxyl, amino, carbonyl, cyano, C1-C6 alkoxy, C1-C6 alkyl, C6-C 12 Aryl or C6-C 12 of a cycloalkyl group.

6. The polymer protective film according to claim 5, characterized in that The halogen is selected from one of fluorine, chlorine and bromine; the amino group is selected from C1-C6 primary amine, C1-C6 alkyl-substituted secondary amine or tertiary amine; the C1-C6 alkoxy group is selected from methoxy or ethoxy; the C1-C6 alkyl group is selected from methyl, ethyl, propyl, isopropyl, butyl or tert-butyl; the C6-C 12 The aryl group is selected from phenyl, naphthyl, or biphenyl; the C6-C 12 The cycloalkyl group is selected from cyclohexyl or bicyclohexyl.

7. The polymer protective film according to any one of claims 1 to 4, characterized in that: The molecular weight of the polymer A is 1,000 to 2,000,000.

8. The polymer protective film according to claim 7, characterized in that The molecular weight of the polymer A is 10,000-500,000.

9. The polymer protective film according to any one of claims 1 to 4, characterized in that: The polymer B is polyethylene dioxythiophene, and its structural formula is shown below: Where z is an integer from 2 to 100,000.

10. A metallic lithium negative electrode, characterized in that: The invention comprises a metal lithium sheet and a polymer protective film according to any one of claims 1 to 9, wherein the polymer protective film is arranged on the metal lithium sheet.

11. A lithium battery, characterized in that: Including the metal lithium negative electrode according to claim 10.

12. A vehicle, characterized in that: Including the lithium battery according to claim 11.

Images