Negative electrode protection layer, preparation method and negative electrode plate

Abstract

The invention provides a negative electrode protection layer, a preparation method and a negative electrode plate, which are used for solving the problems of insufficient cycle performance and stability when a current lithium battery takes high-reducibility metal such as lithium metal as a negative electrode. The negative protection layer is attached to the surface of one side, facing the positive plate, of the negative plate; and the negative electrode protection layer comprises a cross-linked polydimethylsiloxane polymer.

Description

Technical Field

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

[0002] Lithium metal is used as the negative electrode of lithium batteries because it has the following advantages: 1) High specific energy, with a gram capacity of 3860 mAh / g, which is ten times or even higher than that of graphite negative electrode. 2) Low potential, the low potential of the negative electrode material can make the lithium battery have a higher output voltage.

[0003] At the same time, when lithium metal is used as the negative electrode, due to its strong surface reducibility, it is easy to react with the electrolyte during the charge-discharge process, which leads to insufficient cycle performance of the lithium battery. In addition, during the charge-discharge process, with the deposition / stripping of lithium, the volume of the lithium metal negative electrode changes significantly (that is, the ratio of the volume after expansion during charging to the volume after contraction during discharge exceeds 100%). That is, the ratio between the volume after expansion of the lithium metal negative electrode and the volume after contraction of the lithium metal negative electrode during discharge is large. Such obvious and repeated volume changes, coupled with the lithium dendrites generated during charge-discharge, cause the SEI (Solid Electrolyte Interface, solid electrolyte interface (film)) on the surface of the negative electrode sheet to rupture, resulting in the lithium battery also having insufficient stability. Therefore, the current lithium battery with lithium metal as the negative electrode has problems of insufficient cycle performance and stability. Summary of the invention

[0004] The present application provides a negative electrode protective layer, a preparation method and a negative electrode sheet, which are used to improve the problems of insufficient cycle performance and stability existing in current lithium batteries when a strong reducing metal such as lithium metal is used as the negative electrode.

[0005] In a first aspect, an embodiment of the present application provides a negative electrode protection layer, which is attached to a surface of a negative electrode sheet facing a positive electrode sheet; the negative electrode protection layer includes a cross-linked polydimethylsiloxane polymer.

[0006] In a possible implementation manner, the content of the cross-linked polydimethylsiloxane polymer is 20%-80% by mass percentage based on the total mass of the negative electrode protection layer.

[0007] In a possible implementation manner, the negative electrode protective layer includes a soluble lithium salt and a pyrrolidine ionic liquid.

[0008] In a possible implementation manner, the content of the soluble lithium salt is 5%-40%, and the content of the pyrrolidine ionic liquid is 15%-40%, calculated as a mass percentage based on the total mass of the negative electrode protection layer.

[0009] In a possible implementation manner, the soluble lithium salt includes at least one of lithium tetrafluoroborate, lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0010] In a possible implementation manner, the pyrrolidine ionic liquid includes at least one of methylethylpyrrolidine bistrifluoromethanesulfonyl imide, methylpropylpyrrolidine bistrifluoromethanesulfonyl imide, methylbutylpyrrolidine bistrifluoromethanesulfonyl imide, methylethylpyrrolidine bisfluorosulfonyl imide, methylpropylpyrrolidine bisfluorosulfonyl imide, and methylbutylpyrrolidine bisfluorosulfonyl imide.

[0011] In a second aspect, the present application provides a method for preparing the negative electrode protective layer described in the first aspect and any possible implementation manner, comprising:

[0012] dissolving a mixture containing the negative electrode protective layer components in a solvent to obtain a component solution; wherein the negative electrode protective layer components include a cross-linked polydimethylsiloxane polymer;

[0013] The component solution is coated on the surface of the negative electrode sheet facing the positive electrode sheet, and allowed to stand to obtain the negative electrode protective layer.

[0014] In a possible implementation manner, the cross-linked polydimethylsiloxane polymer is obtained by the following method:

[0015] The prepolymer, the crosslinking agent and the initiator are subjected to an organic polymerization reaction at 50-80° C. to obtain the crosslinked polydimethylsiloxane polymer.

[0016] In a possible implementation manner, the crosslinking agent is an unsaturated polydimethylsiloxane polymer, and the prepolymer is a saturated polydimethylsiloxane polymer; wherein,

[0017] The mass ratio of the prepolymer to the cross-linking agent is (1-20):1, the molecular weight of the saturated polydimethylsiloxane polymer is 500-100000, and the molecular weight of the unsaturated polydimethylsiloxane polymer is 500-100000.

[0018] In a possible implementation manner, the crosslinking agent is a polyethylene glycol acrylate monomer, and the prepolymer is an unsaturated polydimethylsiloxane polymer and / or a saturated polydimethylsiloxane polymer; wherein,

[0019] The molecular weight of the saturated polydimethylsiloxane polymer is 500-100000, and the molecular weight of the unsaturated polydimethylsiloxane polymer is 500-100000.

[0020] In a possible implementation manner, the negative electrode protective layer components include a soluble lithium salt and a pyrrolidine ionic liquid.

[0021] In a possible implementation manner, the content of the cross-linked polydimethylsiloxane polymer in the negative electrode protection layer component is 20%-80% by mass percentage based on the total mass of the negative electrode protection layer component.

[0022] In a possible implementation manner, in the negative electrode protection layer components, the content of the soluble lithium salt is 5%-40%, and the content of the pyrrolidine ionic liquid is 15%-40%, calculated as mass percentage based on the total mass of the negative electrode protection layer components.

[0023] In a possible implementation manner, the soluble lithium salt includes at least one of lithium tetrafluoroborate, lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0024] In a possible implementation manner, the pyrrolidine ionic liquid includes at least one of methylethylpyrrolidine bistrifluoromethanesulfonyl imide, methylpropylpyrrolidine bistrifluoromethanesulfonyl imide, methylbutylpyrrolidine bistrifluoromethanesulfonyl imide, methylethylpyrrolidine bisfluorosulfonyl imide, methylpropylpyrrolidine bisfluorosulfonyl imide, and methylbutylpyrrolidine bisfluorosulfonyl imide.

[0025] In a third aspect, an embodiment of the present application provides a negative electrode sheet, comprising:

[0026] The negative electrode protective layer described in the first aspect and any possible implementation manner.

[0027] One or more technical solutions provided in the embodiments of the present application have at least the following beneficial effects:

[0028] The embodiment of the present application provides a negative electrode protective layer attached to the surface of the negative electrode sheet facing the positive electrode sheet. The cross-linked polydimethylsiloxane polymer therein has good reduction resistance, so the cycle performance of the lithium battery is not affected by the strongly reducing negative electrode sheet (lithium metal). In addition, the side reaction between the negative electrode sheet and the lithium metal can be significantly alleviated by isolating the negative electrode sheet (lithium metal) from the electrolyte, thereby further improving the cycle performance of the lithium battery.

[0029] At the same time, because cross-linked polydimethylsiloxane has the advantages of excellent elasticity and toughness, it can effectively avoid the problem in existing technologies, such as polyethylene oxide as a protective layer, which is easily damaged when a significant volume change occurs due to the deposition / stripping of lithium on a strongly reducing negative electrode (lithium metal), thereby improving the stability of the lithium battery.

[0030] In addition, when the above-mentioned negative electrode protective layer includes a soluble lithium salt and a pyrrolidine-type ionic liquid, a cross-linked polydimethylsiloxane polymer can be used as a framework structure to accommodate the soluble lithium salt and the pyrrolidine-type ionic liquid used for dissociation and acting as a dispersant, thereby effectively improving the ionic conductivity of the negative electrode protective layer, thereby improving the ionic conduction performance of the lithium battery during the charge-discharge process.

[0031] Other features and advantages of the present application will be described in the subsequent description, and partly become apparent from the description, or be understood by practicing the present application. The purpose and other advantages of the present application can be achieved and obtained by the structures or compositions specifically pointed out in the written description, claims, and drawings. It should be understood that the above general description and the detailed description below are only exemplary and explanatory and cannot limit the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0033] Figure 1 A schematic flow chart of a method for preparing a negative electrode protective layer provided in an embodiment of the present application. DETAILED DESCRIPTION

[0034] In view of the problems of insufficient cycle performance and stability of lithium batteries with lithium metal as negative electrodes, the present application provides a negative electrode protective layer, which is attached to the surface of the negative electrode sheet facing the positive electrode sheet, so that the cross-linked polydimethylsiloxane polymer in the negative electrode protective layer can be attached to the surface of the negative electrode sheet. The negative electrode protective layer can form an internal circuit together with the negative electrode sheet, the positive electrode sheet, and the electrolyte, thereby providing a transmission channel for lithium ions during the charge-discharge process of the lithium battery.

[0035] When the negative electrode sheet is a material with strong reducing properties such as lithium metal, the cross-linked polydimethylsiloxane has excellent chemical stability, so it can resist the strong reducing properties of lithium metal and exist stably (that is, it does not undergo continuous chemical reactions with lithium metal or electrolyte). On this basis, the negative electrode protective layer attached to the negative electrode sheet can play a role in reducing the surface activity of lithium metal, which significantly reduces the interface side reactions between the negative electrode sheet and the electrolyte, thereby improving the cycle performance of the lithium battery.

[0036] At the same time, since cross-linked polydimethylsiloxane has good toughness and elasticity, it will not be damaged due to the obvious volume change of the negative electrode (the ratio of the volume after expansion during charging to the volume after contraction during discharge), and it is not easy to be penetrated by lithium dendrites to cause positive and negative electrode contact. Therefore, the negative electrode protective layer can significantly improve the stability of the lithium battery where the negative electrode is located.

[0037] The following is a detailed description of a negative electrode protective layer, a preparation method and a negative electrode sheet provided in the embodiments of the present application. It should be noted that the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The invention provides a negative electrode protection layer, which is attached to a surface of a negative electrode sheet facing a positive electrode sheet. The negative electrode protection layer comprises cross-linked polydimethylsiloxane.

[0039] The cross-linked polydimethylsiloxane polymer can be obtained by curing through an organic polymerization reaction between a prepolymer and a cross-linking agent under the conditions of an initiator and 50-80° C. The initiator can be an initiator of a free radical polymerization reaction.

[0040] In some embodiments, the crosslinking agent is an unsaturated polydimethylsiloxane polymer, and the prepolymer is a saturated polydimethylsiloxane polymer. In this case, the organic polymerization reaction is actually a self-crosslinking reaction.

[0041] In other embodiments, the cross-linking agent is a polyethylene glycol acrylate monomer, and the prepolymer is a saturated polydimethylsiloxane polymer, an unsaturated polydimethylsiloxane polymer and / or a saturated polydimethylsiloxane polymer.

[0042] Since the cross-linked polydimethylsiloxane obtained by the aforementioned self-cross-linking reaction has better chemical stability, the embodiment of the present application preferably uses a cross-linked polydimethylsiloxane polymer obtained by a self-cross-linking reaction using an unsaturated polydimethylsiloxane polymer as a cross-linking agent.

[0043] Furthermore, the content of the cross-linked polydimethylsiloxane polymer is 20%-80% by mass percentage based on the total mass of the negative electrode protection layer.

[0044] Furthermore, the cross-linked polydimethylsiloxane can be used as a framework of the negative electrode protection layer. In order to further improve the ionic conductivity of the negative electrode protection layer so that the lithium battery maintains a low internal resistance and thus achieves the purpose of reducing power loss, the negative electrode protection layer can also include a soluble lithium salt and a pyrrolidine ionic liquid.

[0045] Among them, pyrrolidine ionic liquids can dissociate lithium salts and then disperse soluble lithium salts, so that the dissociated lithium salts can promote the conduction of lithium ions and improve the ionic conductivity of lithium batteries.

[0046] The soluble lithium salt includes at least one of lithium tetrafluoroborate LiBF4, lithium hexafluorophosphate LiPF6, lithium perchlorate LiClO4, lithium bis(oxalatoborate) LiBOB, lithium difluorooxalatoborate LiDFOB, lithium bis(fluorosulfonyl)imide LiFSI, and lithium bis(trifluoromethanesulfonyl)imide LiTFSI.

[0047] The above-mentioned pyrrolidine ionic liquids include methyl ethyl pyrrolidine bis trifluoromethanesulfonimide (PYR 1,2 TFSI), methylpropylpyrrolidine bis(trifluoromethanesulfonimide) (PYR 1,3 TFSI), methylbutylpyrrolidine bis(trifluoromethanesulfonimide) (PYR 1, 4TFSI), methylethylpyrrolidine bis(fluorosulfonyl)imide (PYR 1,2 FSI), methylpropylpyrrolidine bis(fluorosulfonyl)imide (PYR 1, 3FSI), and methylbutylpyrrolidine bis(fluorosulfonyl)imide (PYR 1,4 At least one of FSI).

[0048] Furthermore, in terms of mass percentage based on the total mass of the negative electrode protection layer, the content of the soluble lithium salt is 5%-40%, and the content of the pyrrolidine ionic liquid is 15%-40%.

[0049] Based on the same inventive concept, the present application also provides a method for preparing the aforementioned negative electrode protective layer, which includes the following implementation steps, please refer to Figure 1 .

[0050] Step 101: dissolving a mixture containing negative electrode protective layer components in a solvent to obtain a component solution.

[0051] Wherein, the negative electrode protection layer component includes cross-linked polydimethylsiloxane.

[0052] The concentration of the component solution is 5%-20%. Here, concentration refers to the ratio between the mass of the component and the mass of the component, the solvent and the solute.

[0053] The solvent may be an ether material such as 1,3-dioxolane (DOL) or ethylene glycol dimethyl ether (DME) or tetrahydrofuran (THF).

[0054] In some embodiments, the negative electrode protection layer composition may further include soluble lithium salts and pyrrolidine ionic liquids to enhance ion conductivity.

[0055] The soluble lithium salt includes at least one of lithium tetrafluoroborate LiBF4, lithium hexafluorophosphate LiPF6, lithium perchlorate LiClO4, lithium bis(oxalatoborate) LiBOB, lithium difluorooxalatoborate LiDFOB, lithium bis(fluorosulfonyl)imide LiFSI, and lithium bis(trifluoromethanesulfonyl)imide LiTFSI.

[0056] Pyrrolidine ionic liquids include methylethylpyrrolidine bis(trifluoromethanesulfonyl)imide (PYR 1,2 TFSI), methylpropylpyrrolidine bis(trifluoromethanesulfonimide) (PYR 1,3 TFSI), methylbutylpyrrolidine bis(trifluoromethanesulfonimide) (PYR 1, 4TFSI), methylethylpyrrolidine bis(fluorosulfonyl)imide (PYR 1,2 FSI), methylpropylpyrrolidine bis(fluorosulfonyl)imide (PYR 1, 3FSI), and methylbutylpyrrolidine bis(fluorosulfonyl)imide (PYR 1,4 At least one of FSI).

[0057] In some embodiments, the content of the cross-linked polydimethylsiloxane polymer is 20%-80% by weight based on the total weight of the negative electrode protection layer (ie, the total weight of the aforementioned mixture).

[0058] In some embodiments, the content of the soluble lithium salt is 5%-40%, and the content of the pyrrolidine ionic liquid is 15%-40%, calculated as a percentage by mass based on the total mass of the negative electrode protection layer (ie, the total mass of the aforementioned mixture).

[0059] Furthermore, the cross-linked polydimethylsiloxane polymer can be obtained by an organic polymerization reaction of a prepolymer and a cross-linking agent under the action of an initiator at 50-80° C. The initiator of the free radical polymerization reaction includes but is not limited to at least one of azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (AIHN), benzoyl peroxide (BPO), and methyl ethyl ketone peroxide (MEKP).

[0060] The following provides two implementation methods for preparing the cross-linked polydimethylsiloxane polymer according to the different cross-linking agents in the organic polymerization reaction:

[0061] (I) Using unsaturated polydimethylsiloxane polymer as crosslinking agent

[0062] In order to ensure the ionic conductivity of the negative electrode protective layer, the prepolymer is a saturated polydimethylsiloxane polymer, and the two undergo a self-crosslinking reaction.

[0063] The mass ratio of the prepolymer to the crosslinking agent is (1-20): 1. The molecular weight of the saturated polydimethylsiloxane polymer is 500-100000. The molecular weight of the unsaturated polydimethylsiloxane polymer is 500-100000.

[0064] (ii) Cross-linking reaction using polyethylene glycol acrylate monomer as cross-linking agent under the action of initiator

[0065] The prepolymer is an unsaturated polydimethylsiloxane polymer and / or a saturated polydimethylsiloxane polymer; wherein,

[0066] The molecular weight of the saturated polydimethylsiloxane polymer is 500-100000, and the molecular weight of the unsaturated polydimethylsiloxane polymer is 500-100000.

[0067] The polyethylene glycol acrylate monomers include, but are not limited to, one or more of polyethylene glycol acrylate, polyethylene glycol methacrylate, polyethylene glycol ethyl acrylate, polyethylene glycol dimethacrylate, polyethylene glycol diethyl acrylate, polyethylene glycol methylethyl acrylate, polyglycidyl acrylate, polyglycidyl methacrylate, and polyglycidyl ethyl acrylate.

[0068] Since the cross-linked polydimethylsiloxane polymer obtained in embodiment (I) exhibits more excellent (electro)chemical stability, embodiment (I) is preferred in the examples of the present application.

[0069] Based on the same inventive concept, an embodiment of the present application further provides a negative electrode sheet, which includes the negative electrode protective layer mentioned above.

[0070] The negative electrode sheet may be a metal with strong reducing properties, such as lithium metal.

[0071] The following is a detailed description through specific embodiments:

[0072] Example 1

[0073] S1. Methoxy-terminated polydimethylsiloxane (PDMS, molecular weight of about 1000, 40% by mass based on the total mass of the negative electrode protective layer) is used as a saturated polymer, vinyl-terminated polydimethylsiloxane (PDMS, molecular weight of about 1000, 10% by mass) is used as an unsaturated polymer as a cross-linking agent, lithium hexafluorophosphate (LiPF6, 20% by mass based on the total mass of the negative electrode protective layer) is used as a lithium salt, and methylbutylpyrrolidine bistrifluoromethanesulfonimide (PYR1,4TFSI, 30% by mass based on the total mass of the negative electrode protective layer) is used as an ionic liquid dispersant to obtain a component mixture.

[0074] S2. Add tetrahydrofuran solvent to the component mixture, seal it at room temperature, and stir it evenly to make the component mixture fully dissolved in tetrahydrofuran to prepare a component solution with a concentration of 10%.

[0075] S3. The above component solutions are evenly coated on the surface of the lithium metal negative electrode plate, and allowed to stand in vacuum for 24 hours to form a polymer protective layer with a thickness of 20 μm.

[0076] Comparative Example 1

[0077] S1. Polyvinylidene fluoride (molecular weight 150,000) is selected as a component of the negative electrode protective layer.

[0078] S2. Add tetrahydrofuran solvent to the components of the negative electrode protective layer, seal at 60° C., and stir evenly to promote the dissolution of polyvinylidene fluoride to prepare a component solution with a concentration of 10%.

[0079] S3. The above component solutions are evenly coated on the surface of the lithium metal negative electrode plate, and allowed to stand in vacuum for 24 hours to form a polymer protective layer with a thickness of 20 μm.

[0080] The lithium metal containing the negative electrode protective layer in Example 1 and Comparative Example 1 was used as the negative electrode, and the lithium metal without the negative electrode protective layer was used as Comparative Example 2 to prepare a button-type symmetrical battery.

[0081] The positive electrode of the button-type symmetrical battery has a capacity of 2 mAh / cm 2 .

[0082] For the above-mentioned embodiments, the button-type symmetrical battery of Comparative Example 1-2 was tested at a current density of 0.4 mA / cm2 for its over-voltage and cycle stability time, and the results are shown in Table 1.

[0083] Table 1

[0084] Experimental Group Example 1 Comparative Example 1 Comparative Example 2 Steady overpotential(mV) 20 20 20 Stable cycle time (h) 1580 1300 800

[0085] Note: The stable cycle time in the table refers to the time when the overpotential suddenly increases to more than 200mV during the cycle process.

[0086] It can be seen from Table 1 that the stable overpotential in Example 1 is consistent with that in Comparative Examples 1-2, so the addition of the negative electrode protective layer in Example 1 has little effect on the impedance of the lithium battery, and thus its ion conductivity is comparable to that of a conventional lithium battery, especially a lithium battery with a lithium metal negative electrode without a negative electrode protective layer.

[0087] In addition, the cycle performance and stability in Example 1 are also significantly improved.

[0088] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A negative electrode protective layer, characterized in that: The negative electrode protection layer is attached to the surface of the negative electrode sheet facing the positive electrode sheet; the negative electrode protection layer includes a cross-linked polydimethylsiloxane polymer.

2. The negative electrode protective layer according to claim 1, characterized in that Calculated by mass percentage based on the total mass of the negative electrode protection layer, the content of the cross-linked polydimethylsiloxane polymer is 20%-80%.

3. The negative electrode protective layer according to claim 1 or 2, characterized in that: The negative electrode protection layer comprises a soluble lithium salt and a pyrrolidine ionic liquid.

4. The negative electrode protective layer according to claim 3, characterized in that: Calculated by mass percentage based on the total mass of the negative electrode protection layer, the content of the soluble lithium salt is 5%-40%, and the content of the pyrrolidine ionic liquid is 15%-40%.

5. The negative electrode protective layer according to claim 3, characterized in that: The soluble lithium salt includes at least one of lithium tetrafluoroborate, lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

6. The negative electrode protective layer according to claim 3, characterized in that: The pyrrolidine ionic liquid includes at least one of methylethylpyrrolidine bistrifluoromethanesulfonyl imide, methylpropylpyrrolidine bistrifluoromethanesulfonyl imide, methylbutylpyrrolidine bistrifluoromethanesulfonyl imide, methylethylpyrrolidine bisfluorosulfonyl imide, methylpropylpyrrolidine bisfluorosulfonyl imide, and methylbutylpyrrolidine bisfluorosulfonyl imide.

7. A method for preparing the negative electrode protective layer according to any one of claims 1 to 6, characterized in that: include: Dissolving a mixture containing negative electrode protection layer components in a solvent to obtain a component solution; wherein the negative electrode protection layer components include a cross-linked polydimethylsiloxane polymer; The component solution is coated on the surface of the negative electrode sheet facing the positive electrode sheet, and allowed to stand to obtain the negative electrode protective layer.

8. The method according to claim 7, characterized in that The cross-linked polydimethylsiloxane polymer is obtained by the following method: The prepolymer, the crosslinking agent and the initiator are subjected to an organic polymerization reaction at 50-80° C. to obtain the crosslinked polydimethylsiloxane polymer.

9. The method according to claim 8, characterized in that The crosslinking agent is an unsaturated polydimethylsiloxane polymer, and the prepolymer is a saturated polydimethylsiloxane polymer; wherein, The mass ratio of the prepolymer to the cross-linking agent is (1-20):1, the molecular weight of the saturated polydimethylsiloxane polymer is 500-100000, and the molecular weight of the unsaturated polydimethylsiloxane polymer is 500-100000.

10. The method according to claim 7, characterized in that The crosslinking agent is a polyethylene glycol acrylate monomer, and the prepolymer is an unsaturated polydimethylsiloxane polymer and / or a saturated polydimethylsiloxane polymer; wherein, The molecular weight of the saturated polydimethylsiloxane polymer is 500-100000, and the molecular weight of the unsaturated polydimethylsiloxane polymer is 500-100000.

11. A negative electrode sheet, characterized in that: include: The negative electrode protective layer according to any one of claims 1 to 6.

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