Lithium metal negative electrode polymer protection layer and preparation method and application thereof

Abstract

The invention discloses a lithium metal negative electrode polymer protection layer as well as a preparation method and application thereof. The lithium metal negative electrode polymer protection layer comprises an acrylate polymer; the lithium metal negative electrode polymer protection layer meets the following relational expression: 0 < = [(P-0.11) 2 + (E-0.45) 2] / T * 10000 < = 1, P is the tensile strength of the lithium metal negative electrode polymer protection layer, T is the glass transition temperature of the lithium metal negative electrode polymer protection layer, and E is the liquid retention coefficient of the lithium metal negative electrode polymer protection layer. According to the invention, the polymer protection layer is formed by using the acrylate polymer, and the comprehensive coefficient M of the polymer protection layer is controlled within the range of 0-1, so that the cycle performance of the battery cell can be improved, and the capacity retention ratio can be increased.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium metal anode interface protection, and relates to a polymer protective layer for lithium metal anode, a preparation method thereof and an application thereof. Background Art

[0002] Lithium metal anodes have advantages such as high specific capacity and low potential. However, during the charging and discharging processes, due to the absence of a protective layer on the surface of traditional lithium metal anodes, the lithium metal anodes will undergo side reactions with the electrolyte, resulting in capacity decay and safety problems of the lithium metal anodes. For example, in lithium-sulfur batteries, the lithium metal anodes will undergo side reactions with polysulfide electrolytes, resulting in capacity decay and safety problems of the lithium metal anodes.

[0003] Polymer protective layers can effectively prevent the direct contact between lithium metal anodes and electrolytes, thereby reducing the occurrence of side reactions and improving the cycling performance and safety of lithium metal anodes. For example, by coating a polymer protective layer on the surface of a lithium metal anode, the direct contact between the lithium metal anode and the polysulfide electrolyte can be effectively prevented, thereby reducing the occurrence of side reactions and improving the cycling performance and safety of lithium-sulfur batteries.

[0004] However, the research on polymer protective layers still has problems such as single composition and inability to balance various parameters, resulting in poor protection effects on lithium metal anodes. Therefore, providing a polymer protective layer for lithium metal anodes that can effectively protect lithium metal anodes is a technical problem that needs to be solved urgently at present. Summary of the Invention

[0005] Aiming at the above technical problems existing in the prior art, the purpose of the present invention is to provide a polymer protective layer for lithium metal anodes, a preparation method thereof and an application thereof.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a polymer protective layer for lithium metal anodes, and the polymer protective layer for lithium metal anodes includes acrylate polymers;

[0008] The polymer protective layer for lithium metal anodes satisfies the following relational expression:

[0009] 0≤[(P - 0.11)^2+(E - 0.45)^2] / T×10000≤1, where P is the tensile strength of the polymer protective layer for lithium metal anodes, T is the glass transition temperature of the polymer protective layer for lithium metal anodes, and E is the liquid retention coefficient of the polymer protective layer for lithium metal anodes.

[0010] In the present invention, (P - 0.11)^2 refers to the square of P - 0.11. (E - 0.45)^2 refers to the square of E - 0.45.

[0011] Preferably, 0 ≤ [(P - 0.11)^2 + (E - 0.45)^2] / T × 10000 ≤ 0.5.

[0012] Preferably, the tensile strength P of the polymer protective layer of the lithium metal negative electrode is 0.05 MPa to 0.15 MPa, preferably 0.07 MPa to 0.09 MPa.

[0013] Preferably, the glass transition temperature T of the polymer protective layer of the lithium metal negative electrode is 50 °C to 150 °C, preferably 70 °C to 88 °C.

[0014] Preferably, the liquid retention coefficient E of the polymer protective layer of the lithium metal negative electrode is 0.3 to 0.5, preferably 0.4 to 0.48.

[0015] Preferably, the acrylate polymer includes at least one of polyethyl methacrylate (PEMA), butyl α-cyanoacrylate (α-BCA), and polyethylene glycol diacrylate (PEGDA).

[0016] Preferably, the acrylate polymer is a mixture, the mixture includes polyethyl methacrylate and butyl α-cyanoacrylate, and the mass ratio of polyethyl methacrylate to butyl α-cyanoacrylate is (80 - 40):(20 - 60).

[0017] Preferably, the thickness of the polymer protective layer of the lithium metal negative electrode is 2 μm to 10 μm, preferably 4 μm to 7 μm.

[0018] In a second aspect, the present invention provides a method for preparing a polymer protective layer of a lithium metal negative electrode as described in the first aspect, and the preparation method includes the following steps:

[0019] Dissolve the acrylate polymer in an organic solvent to obtain a polymer solution;

[0020] Coat the polymer solution on the surface of the substrate, and after drying, form the polymer protective layer of the lithium metal negative electrode on the surface of the substrate.

[0021] Preferably, the organic solvent includes at least one of ethanol, dichloromethane, acetone, and dimethylformamide (DMF).

[0022] Preferably, the solid content of the polymer solution is 15 wt% to 35 wt%.

[0023] In a third aspect, the present invention provides a lithium metal anode, which comprises a substrate and a protective layer disposed on the surface of the substrate. The substrate is a lithium strip, and the protective layer is the lithium metal anode polymer protective layer described in the first aspect or the lithium metal anode polymer protective layer prepared by the method described in the second aspect.

[0024] In a fourth aspect, the present invention provides a method for preparing a lithium metal anode as described in the third aspect, which is prepared by the method described in the second aspect, and the substrate is a lithium strip.

[0025] In a fifth aspect, the present invention provides a lithium battery, which comprises the lithium metal anode described in the fourth aspect, or the lithium metal anode prepared by the method described in the fourth aspect.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The lithium metal anode polymer protective layer provided by the present invention includes acrylate polymers. By regulating the tensile strength P, glass transition temperature T, and liquid retention coefficient E of the lithium metal anode polymer protective layer, it can be ensured that the lithium metal anode polymer protective layer can significantly improve the cycle attenuation of the battery assembled with the lithium metal anode. Specific Embodiments

[0028] The technical solutions of the present invention will be further described below through specific embodiments.

[0029] In one embodiment of the present invention, a lithium metal anode polymer protective layer is provided, and the lithium metal anode polymer protective layer includes acrylate polymers;

[0030] The lithium metal anode polymer protective layer satisfies the following relational expression:

[0031] 0 ≤ [(P - 0.11)^2 + (E - 0.45)^2] / T × 10000 ≤ 1, where P is the tensile strength of the lithium metal anode polymer protective layer, T is the glass transition temperature of the lithium metal anode polymer protective layer, and E is the liquid retention coefficient of the lithium metal anode polymer protective layer.

[0032] Through a large number of studies, the present invention discovers that for a polymer protective layer containing acrylate polymers, the higher the tensile strength P of the polymer protective layer of the lithium metal anode, the better the mechanical properties of the polymer protective layer of the lithium metal anode, and the stronger the protective effect on the lithium metal anode. However, at the same time, the impedance to lithium ion transmission is also greater. The higher the glass transition temperature T of the polymer protective layer of the lithium metal anode, the more regular the molecular chain segments, which is more conducive to the transmission of ions and electrons. At the same time, the greater the tensile strength P of the polymer protective layer of the lithium metal anode, the more it can inhibit the generation and uneven deposition of lithium dendrites, which is beneficial to the capacity retention rate during the cycling process of the battery. The higher the liquid retention coefficient E of the polymer protective layer of the lithium metal anode, the lower the mechanical strength of the polymer protective layer of the lithium metal anode; the lower the liquid retention coefficient E, the lower the electrolyte porosity, and the worse the electrolyte and lithium ion transmission ability.

[0033] In one embodiment provided by the present invention, the polymer protective layer of the lithium metal anode includes acrylate polymers. By regulating the relationship among the tensile strength P, glass transition temperature T, and liquid retention coefficient E of the polymer protective layer of the lithium metal anode, the value calculated according to the formula [(P - 0.11)^2 + (E - 0.45)^2] / T×10000 is within the range of 0 to 1. The lower this value, the closer P, T, and E are to the optimal values, indicating that the quality of the polymer protective layer of the lithium metal anode is better, the protective effect on the lithium metal anode is better, and the improvement effect on the cycle capacity attenuation of the battery assembled with this lithium metal anode is greater; the higher this ratio value, the more P, T, and E deviate from the optimal values, indicating that the quality of the polymer protective layer of the lithium metal anode is worse, the protective effect on the lithium metal anode is worse, and the improvement effect on the cycle capacity attenuation of the battery assembled with this lithium metal anode is smaller.

[0034] It can ensure that the polymer protective layer of the lithium metal anode significantly improves the cycle attenuation of the battery assembled with the lithium metal anode.

[0035] In the present invention, the quality of the polymer protective layer of the lithium metal anode can be quickly evaluated through the above-mentioned relational formula. If this relational formula is satisfied, the quality of the polymer protective layer of the lithium metal anode meets the requirements; if this relational formula is not satisfied, the quality of the polymer protective layer of the lithium metal anode does not meet the requirements.

[0036] In one embodiment, 0≤[(P - 0.11)^2 + (E - 0.45)^2] / T×10000≤0.5.

[0037] In one embodiment, the tensile strength P of the polymer protective layer of the lithium metal negative electrode is 0.05 MPa to 0.15 MPa. For example, it can be 0.05 MPa, 0.06 MPa, 0.07 MPa, 0.08 MPa, 0.09 MPa, 0.1 MPa, 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa or 0.15 MPa, etc. Preferably, it is 0.07 MPa to 0.09 MPa. Within the preferred range, good mechanical properties and low impedance can be better balanced.

[0038] The tensile strength is related to the composition of the polymer protective layer of the lithium metal negative electrode. The tensile strength can be changed by regulating the composition, or can be achieved by adjusting the solid substance (i.e., the solid content of the polymer solution) during the preparation process. Among them, if the composition of the polymer is a single type of polymer, the tensile strength can be regulated by replacing the type of polymer; if it is a combination of multiple polymers, the tensile strength can be regulated by regulating the ratio of different polymers.

[0039] In one embodiment, the glass transition temperature T of the polymer protective layer of the lithium metal negative electrode is 50 °C to 150 °C. For example, it can be 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, 115 °C, 120 °C, 125 °C, 130 °C, 135 °C, 140 °C, 145 °C or 150 °C, etc. Preferably, it is 70 °C to 88 °C.

[0040] The glass transition temperature T can be determined by the turning of the baseline on the DSC spectrum. The glass transition temperature T is related to the composition of the polymer. Among them, if the composition of the polymer is a single type of polymer, the glass transition temperature can be regulated by replacing the type of polymer; if it is a combination of multiple polymers, the glass transition temperature can be regulated by regulating the ratio of different polymers.

[0041] In one embodiment, the liquid retention coefficient E of the polymer protective layer of the lithium metal negative electrode is 0.3 to 0.5. For example, it can be 0.3, 0.32, 0.35, 0.37, 0.4, 0.45 or 0.5, etc. Preferably, it is 0.4 to 0.48.

[0042] In one embodiment, the density ρ of the electrolyte ranges from 1.05 g / mL to 1.25 g / mL. For example, it can be 1.05 g / mL, 1.07 g / mL, 1.09 g / mL, 1.10 g / mL, 1.12 g / mL, 1.14 g / mL, 1.15 g / mL, 1.17 g / mL, 1.18 g / mL, 1.20 g / mL, 1.23 g / mL or 1.25 g / mL, etc.

[0043] The liquid retention coefficient is related to the composition of the polymer. The liquid retention coefficient can be changed by regulating the composition, or can be achieved by adjusting the solid substance (i.e., the solid content of the polymer solution) during the preparation process. Among them, if the composition of the polymer is a single type of polymer, the liquid retention coefficient can be regulated by replacing the type of polymer; if it is a combination of multiple polymers, the liquid retention coefficient can be regulated by regulating the ratio of different polymers.

[0044] In one embodiment, the acrylate polymer includes at least one of polyethyl methacrylate, butyl α-cyanoacrylate, and polyethylene glycol diacrylate. The acrylate polymer is a polymer material that forms a cross-linked structure through covalent bonds, ionic bonds, etc., and can provide better mechanical properties, liquid absorption capacity, liquid retention capacity, and good thermal stability, so that the battery can simultaneously obtain better electrochemical performance and safety performance, and can reduce the self-discharge rate of lithium batteries, prevent oxidation, inhibit electrochemical reactions, etc.

[0045] In one embodiment, the acrylate polymer is a mixture.

[0046] The mixture includes polyethyl methacrylate and butyl α-cyanoacrylate, and the mass ratio of polyethyl methacrylate to butyl α-cyanoacrylate is (80 - 40):(20 - 60). Among them, the selection range of polyethyl methacrylate is "80 - 40", for example, it can be 80, 75, 70, 65, 60, 55, 50, 45 or 40, etc.; the selection range of butyl α-cyanoacrylate is "20 - 60", for example, it can be 20, 25, 30, 35, 40, 45, 50, 55 or 60, etc. By adjusting the mass ratio of polyethyl methacrylate and butyl α-cyanoacrylate, the cycle performance of the battery assembled with the lithium metal negative electrode can be greatly improved, thus facilitating the practical application of the lithium metal negative electrode.

[0047] In one embodiment, the thickness of the polymer protective layer of the lithium metal negative electrode is 2 μm to 10 μm, for example, it can be 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm or 10 μm, etc., and preferably 4 μm to 7 μm. If the thickness of the polymer protective layer of the lithium metal negative electrode is too large, the impedance to lithium ion transmission is greater, deteriorating the performance of the battery cell; if the thickness of the polymer protective layer of the lithium metal negative electrode is too small, the tensile strength is smaller, the protection effect on the lithium metal negative electrode becomes lower, and the effect on performance improvement also becomes smaller.

[0048] In another embodiment of the present invention, a method for preparing the polymer protective layer of the lithium metal negative electrode as described above is provided, and the preparation method includes the following steps:

[0049] Dissolve the acrylate polymer in an organic solvent to obtain a polymer solution;

[0050] Coat the polymer solution on the surface of the substrate, and after drying, form the lithium metal negative electrode polymer protective layer on the surface of the substrate.

[0051] In one embodiment, the organic solvent includes at least one of ethanol, dichloromethane, acetone, and dimethylformamide.

[0052] In one embodiment, the solid content of the polymer solution is 15 wt% - 35 wt%, for example, it can be 15 wt%, 16 wt%, 17 wt%, 18 wt%, 20 wt%, 21.5 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 33 wt%, 34 wt%, or 35 wt%, etc. If the solid content is too low, during the polymer coating process, due to surface tension, it will cause accumulation at the edges of the film area, resulting in uneven film thickness; if the solid content is too high, it will lead to uneven mixing of the polymer solution, resulting in inconsistent film area performance.

[0053] In yet another embodiment of the present invention, a lithium metal negative electrode is provided. The lithium metal negative electrode includes a substrate and a protective layer provided on the surface of the substrate. The substrate is a lithium strip, and the protective layer is the above-mentioned lithium metal negative electrode polymer protective layer or the lithium metal negative electrode polymer protective layer prepared by the above method. In yet another embodiment of the present invention, a method for preparing a lithium metal negative electrode as described above is provided. The method is used for preparation, and the substrate is a lithium strip.

[0054] In yet another embodiment of the present invention, a lithium battery is provided. The lithium battery includes the above-mentioned lithium metal negative electrode or the lithium metal negative electrode prepared by the above method.

[0055] The numerical ranges described in the present invention not only include the above-listed point values, but also include any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the range.

[0056] The following are typical but non-limiting examples:

[0057] Example 1

[0058] Provide a lithium metal negative electrode, including a lithium strip and a lithium metal negative electrode polymer protective layer (with a thickness of 5 μm) provided on the surface of the lithium strip. The lithium metal negative electrode polymer protective layer includes polyethyl methacrylate (PEMA).

[0059] The preparation method of the above lithium metal negative electrode is as follows:

[0060] Dissolve 5 g of polymer PEMA in 20 g of acetone to obtain a polymer solution with a solid content of 20 wt%. Coat this polymer solution on a lithium strip to form a polymer film with a thickness of 5 μm. After drying at 45 °C, a lithium metal anode is obtained.

[0061] Example 2

[0062] Provide a lithium metal anode, including a lithium strip and a lithium metal anode polymer protective layer (with a thickness of 5 μm) provided on the surface of the lithium strip. The lithium metal anode polymer protective layer includes butyl α-cyanoacrylate (α-BCA).

[0063] The preparation method of the above lithium metal anode is as follows:

[0064] Take 5 g of polymer α-BCA and dissolve it in 20 g of acetone to obtain a polymer solution with a solid content of 20 wt%. Coat this polymer solution on a lithium strip to form a polymer film with a thickness of 5 μm. After drying at 45 °C, a lithium metal anode is obtained.

[0065] Examples 3-6

[0066] Provide a lithium metal anode. The difference in its preparation method from that of Example 1 lies in the type of polymer and the solid content of the polymer solution. Specifically:

[0067] The types of polymers in Examples 3-6 are mixtures of PEMA and α-BCA. The mass ratio of PEMA to α-BCA in Examples 3-5 is 50:50. By changing the different dosages of acetone, the solid contents of the prepared polymer solutions are different; the mass ratio of PEMA to α-BCA in Example 6 is 90:10. See Table 1 for polymers.

[0068] Examples 7-10

[0069] Provide a lithium metal anode. The difference in its preparation method from that of Example 1 lies in the type of polymer. Specifically:

[0070] The types of polymers in Examples 7-10 are mixtures of PEMA and α-BCA. The mass ratios of PEMA to α-BCA in Examples 7-10 are different. See Table 1.

[0071] Examples 11-12

[0072] Provide a lithium metal anode. The difference in its preparation method from that of Example 8 lies in the thickness of the protective layer. See Table 1.

[0073] Example 13

[0074] A lithium metal anode is provided. The difference between its preparation method and that of Example 8 lies in the type of polymer. Specifically:

[0075] The polymer type in Example 13 is a mixture of PEMA and PEGDA.

[0076] Reference group

[0077] A lithium metal anode is provided. The lithium metal anode is a lithium strip, and no protective layer is provided on the surface of the lithium strip.

[0078] Physical property parameters of the polymer protective layers of the lithium metal anodes in Examples 1 - 13 were tested:

[0079] (1) Tear off the polymer protective layer of the lithium metal anode in Examples 1 - 13 and cut it into a size of 75 mm × 10 mm. At 25 °C, use a tensile testing machine to conduct mechanical property tests on the cut polymer film. The test condition is 1 mm / 2 min to obtain the tensile strength P of the polymer protective layer of the lithium metal anode.

[0080] (2) Take 10 mg of the polymer protective layer of the lithium metal anode and conduct differential scanning calorimetry tests under a nitrogen atmosphere. The test conditions are: heat from room temperature to 300 °C at a rate of 10 °C / min, isotherm for 5 min to remove the thermal history, then cool to 0 °C at a rate of 20 °C / min, hold for 2 min, and then heat to 300 °C for the second time at a rate of 10 °C / min. Determine the glass transition temperature by the turning of the baseline on the DSC spectrum to obtain the glass transition temperature T of the polymer protective layer of the lithium metal anode.

[0081] (3) Weigh the weight m of the polymer protective layer with a size of 75 mm × 10 mm 1 , then immerse the polymer protective layer of the lithium metal anode in the electrolyte for 12 h, take it out and weigh the total weight m 2 , calculate the volume V of the electrolyte adsorbed by the protective layer according to the electrolyte density ρ, V = (m 2 - m 1 ) / ρ. The liquid retention coefficient E is defined as the volume of the electrolyte adsorbed per unit volume of the polymer protective layer, E = V / (75 mm × 10 mm × d), where d is the thickness of the polymer protective layer. The electrolyte in this experiment includes a solvent and a solute. The solute is 1 mol / L LiPF 6 , and the solvent is a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1.

[0082] The tensile strength P, glass transition temperature T, and liquid retention coefficient E of the polymer protective layer of the lithium metal anode obtained by testing are used to calculate the comprehensive index M. M = [(P - 0.11)^2 + (E - 0.45)^2] / T × 10000. The data are shown in Table 1.

[0083] Soft-pack batteries were fabricated using the lithium metal anodes of Examples 1-13 and the control group, and tested.

[0084] The process of fabricating the soft-pack battery includes:

[0085] Positive electrode plate: Using ternary positive electrode material LiNi 0.8 Co 0.1 Mn 0.1 O 2 as the active material, 95 wt% of the active material, 3 wt% of the conductive agent (Super P), and 2 wt% of the binder (PVDF) were fully stirred and mixed evenly in N-methylpyrrolidone to form a positive electrode slurry. Then, the obtained positive electrode slurry was evenly coated on both the front and back surfaces of the positive electrode current collector aluminum foil, and then dried at 90 °C to obtain a positive electrode active material layer. After that, it was cold-pressed, slit, cut into pieces, and the positive electrode tab was welded to obtain the positive electrode plate.

[0086] Separator: The separator used is a ceramic-coated polyethylene (PE) material separator.

[0087] Assembly: The positive electrode plate, separator, and lithium metal anode were stacked in sequence, with the separator placed in the middle between the positive electrode plate and the lithium metal anode to play an isolation role. The electrode assembly was placed in an aluminum-plastic film packaging shell, injected with electrolyte and encapsulated, and then formed into the final lithium-ion battery.

[0088] The soft-pack battery was tested for cyclic performance under the conditions of a voltage range of 2.8 - 4.25 V and 0.5C / 1C, and the 200-cycle retention rate was obtained, denoted as the capacity retention rate @200 cycles. The results are shown in Table 1.

[0089] Table 1

[0090]

[0091] Combined with Table 1, by comparing Examples 1-13 with the reference group, it can be seen that using acrylate polymers to form a polymer protective layer and controlling the comprehensive coefficient M of the polymer protective layer within the range of 0 - 1 can improve the cyclic performance of the battery cell and increase the capacity retention rate. Moreover, when M is preferably within the range of 0 - 0.5, the improvement effect on the cyclic performance is better, and the 200-cycle retention rate can reach more than 90.0%.

[0092] From the comparison of Examples 1-3, it can be seen that the combined use of PEMA and α-BCA can make the comprehensive coefficient M of the polymer protective layer smaller and the improvement effect on cycling better compared to the polymer protective layer formed by a single type.

[0093] In Examples 3-5, the solid content of the polymer solution was changed during the preparation process, and polymer protective layers with different liquid retention coefficients were prepared. There is a certain correlation between the liquid retention coefficient E and the tensile strength P, and the glass transition temperatures are also different. The comprehensive index M of the polymer protective layer prepared from the polymer solution with a solid content of 20% in Example 3 is the lowest, and the capacity retention rate is the highest.

[0094] In Examples 3, 6 and 7-10, the mass ratio of PEMA and α-BCA was changed during the preparation process. The results show that when the mass ratio is between (80-40):(20-60), the comprehensive index M is lower and the improvement of the capacity is greater.

[0095] From the comparison of Example 8 with Examples 11-12, it can be seen that there is a preferred range for the thickness of the polymer protective layer on the lithium metal anode. If the protective layer thickness is too low (the thickness in Example 11 is 2 μm), the tensile strength is too low; if the protective layer thickness is too high (the thickness in Example 12 is 10 μm), the tensile strength is too high, both of which will lead to too high comprehensive index M and a decrease in the improvement effect on cycling compared to Example 8.

[0096] From the comparison of Example 8 with Example 13, it can be seen that the change in the type of polymer has a certain impact on the final cycling improvement effect. The mixture of PEMA and α-BCA used in Example 8 has a better effect.

[0097] The above is only a preferred specific embodiment of the present application; however, the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application, according to the technical solution and its improvement concept of the present application, makes equivalent substitutions or changes, and should be covered within the protection scope of the present application.

[0098] The applicant declares that the present invention uses the above examples to illustrate the detailed method of the present invention, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of each raw material of the product of the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A lithium metal negative electrode polymer protective layer, characterized in that: The lithium metal negative electrode polymer protective layer includes an acrylic polymer; The lithium metal negative electrode polymer protective layer satisfies the following relationship: 0≤[(P-0.11)^2+(E-0.45)^2] / T×10000≤1, wherein P is the tensile strength of the lithium metal negative electrode polymer protective layer, T is the glass transition temperature of the lithium metal negative electrode polymer protective layer, and E is the liquid retention coefficient of the lithium metal negative electrode polymer protective layer.

2. The lithium metal negative electrode polymer protective layer according to claim 1, characterized in that: 0≤[(P-0.11)^2+(E-0.45)^2] / T×10000≤0.

5.

3. The lithium metal negative electrode polymer protective layer according to claim 1, characterized in that: The tensile strength P of the lithium metal negative electrode polymer protective layer is 0.05Pa to 0.15MPa, preferably 0.07MPa to 0.09MPa; and / or, The glass transition temperature T of the lithium metal negative electrode polymer protective layer is 50° C. to 150° C., preferably 70° C. to 88° C.; and / or, The liquid retention coefficient E of the lithium metal negative electrode polymer protective layer is 0.3 to 0.5, preferably 0.4 to 0.

48.

4. The lithium metal negative electrode polymer protective layer according to claim 1, characterized in that: The acrylic polymer comprises at least one of polyethyl methacrylate, α-butyl cyanoacrylate and polyethylene glycol diacrylate; and / or, The acrylic polymer is a mixture, which includes polyethyl methacrylate and α-butyl cyanoacrylate, and the mass ratio of the polyethyl methacrylate to the α-butyl cyanoacrylate is (80-40):(20-60).

5. The lithium metal negative electrode polymer protective layer according to claim 1, characterized in that: The thickness of the lithium metal negative electrode polymer protective layer is 2 μm to 10 μm, preferably 4 μm to 7 μm.

6. A method for preparing a lithium metal negative electrode polymer protective layer according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: dissolving an acrylic acid ester polymer in an organic solvent to obtain a polymer solution; The polymer solution is coated on the surface of a substrate, and after drying, the lithium metal negative electrode polymer protective layer is formed on the surface of the substrate.

7. The preparation method according to claim 6, characterized in that: The organic solvent comprises at least one of ethanol, dichloromethane, acetone and dimethylformamide; and / or, The solid content of the polymer solution is 15 wt% to 35 wt%.

8. A lithium metal negative electrode, characterized in that The lithium metal negative electrode comprises a substrate and a protective layer arranged on the surface of the substrate, the substrate is a lithium strip, and the protective layer is the lithium metal negative electrode polymer protective layer according to any one of claims 1 to 5 or the lithium metal negative electrode polymer protective layer prepared by the method according to claim 6 or 7.

9. A method for preparing a lithium metal negative electrode as claimed in claim 8, characterized in that: The method according to claim 6 or 7 is used for preparation, and the substrate is a lithium strip.

10. A lithium battery, characterized in that: The lithium battery comprises the lithium metal negative electrode as described in claim 8, or the lithium metal negative electrode prepared by the method as described in claim 9.

Images