A negative electrode sheet treatment liquid, a surface-modified negative electrode sheet, and a lithium-ion battery

Abstract

The present application provides a negative electrode sheet treatment liquid, which includes an organic solvent and an additive. The additive includes a first additive shown by the structural formula as formula (I) or a second additive shown by formula (II): #imgabs0##imgabs1# wherein, R1 and R2 are each independently selected from any one of alkylene, alkenylene, alkynylene, arylene or methylene silyl; X1 is selected from O or S; R3 is selected from any one of sub-alkylene, sub-alkenylene, sub-alkynylene, sub-arylene or sub-methylene silyl; R4 and R5 are each independently selected from any one of alkylene, alkenylene, alkynylene or arylene; X2 and X3 are each independently selected from O or S. This negative electrode sheet treatment liquid can reduce the loss of lithium ions during the first charge of the battery; and can also remove the moisture in the negative electrode sheet, thereby improving the safety performance of the lithium battery. The present application also provides a surface-modified negative electrode sheet and a lithium ion battery.

Description

Technical Field

[0001] The present application relates to the technical field of lithium - ion batteries, and particularly relates to a negative electrode sheet treatment liquid, a surface - modified negative electrode sheet, and a lithium - ion battery. Background Art

[0002] During the first charge - discharge process of a lithium - ion battery, part of the electrolyte reacts at the negative electrode of the battery and combines with the lithium ions released from the positive electrode to form a solid electrolyte interface (SEI) film. The formation of the SEI film consumes lithium in the battery, converting lithium into inactive lithium - containing compounds, thereby causing a loss of reversible lithium, reducing the first - cycle efficiency and discharge capacity of the battery.

[0003] To compensate for the lithium loss caused by the formation of the SEI film during the first charge, the existing method is to add inert lithium powder to the negative electrode sheet of the battery to make up for the lithium loss during the first charge. However, this method cannot ensure the uniform distribution of lithium powder in the electrode sheet, resulting in local lithium residues in the electrode sheet, which is likely to cause a short - circuit of the battery, posing a serious safety hazard to the manufactured lithium battery; and using inert lithium powder for lithium compensation will cause inert substances to remain on the electrode surface, increasing the battery impedance and degrading the battery performance. Therefore, it is necessary to provide a new negative electrode treatment method to reduce the lithium loss caused by the formation of the SEI film in the battery. Summary of the Invention

[0004] In view of this, the present application provides a negative electrode sheet treatment liquid, which can form a protective layer on the surface of the negative electrode sheet. This protective layer can pre - form an SEI film with the electrolyte, thereby reducing the loss of lithium ions in the positive electrode sheet during the first charge of the battery; and this negative electrode sheet treatment liquid can also remove moisture in the negative electrode sheet, thereby improving the safety performance of the lithium battery. The present application also provides a surface - modified negative electrode sheet and a lithium - ion battery.

[0005] The first aspect of the present application provides a negative electrode sheet treatment liquid, which includes an organic solvent and an additive. The additive includes a first additive shown by the structural formula of formula (I) or a second additive shown by formula (II):

[0006]

[0007] In formula (I), R1 and R2 are each independently selected from any one of alkylene, alkenylene, alkynylene, arylene, or methylene silyl; X1 is selected from O or S;

[0008] In formula (II), R3 is selected from any one of sub - alkylene, sub - alkenylene, sub - alkynylene, sub - arylene, or sub - methylene silyl; R4 and R5 are each independently selected from any one of alkylene, alkenylene, alkynylene, or arylene; X2 and X3 are each independently selected from O or S.

[0009] In the negative electrode sheet treatment liquid of the present application, the additive is an organolithium compound. This organolithium compound can not only react with the water in the negative electrode sheet, but also react with the hydroxyl groups on the surface of the graphite negative electrode to form an interfacial film similar to the SEI film, which covers the surface of the negative electrode sheet. After drying the negative electrode sheet treated with the negative electrode sheet treatment liquid, the unreacted additive can be evenly distributed on the surface of the negative electrode sheet. The additive can also react with the electrolyte to form an interfacial film similar to SEI, which covers the surface of the negative electrode sheet. This interfacial film similar to SEI can be used as a protective layer to inhibit the reaction between the electrolyte and lithium ions on the negative electrode sheet, reduce the loss of active lithium in the battery during formation, and improve the energy density and cycling performance of the battery.

[0010] Optionally, the number of carbon atoms of the R1, the R2, the R3, the R4, and the R5 is 1-20.

[0011] Optionally, the organic solvent includes an ether solvent and an amine solvent.

[0012] Optionally, the volume ratio of the ether solvent to the amine solvent is 1∶(0.3-3).

[0013] Optionally, the ether solvent includes one or more of non-fluorinated ethers and fluorinated ethers.

[0014] Optionally, the amine solvent includes one or more of non-fluorinated tertiary amines and fluorinated tertiary amines.

[0015] Optionally, the number of carbon atoms of the non-fluorinated ether, the fluorinated ether, the non-fluorinated tertiary amine, and the fluorinated tertiary amine is 1-8.

[0016] Optionally, the non-fluorinated ether includes one or more of diethyl ether, dimethoxymethane, 1,2-dimethoxyethane, 1,4-dioxane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether.

[0017] Optionally, the fluorinated ether includes one or more of 2,2,2-trifluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis-2,2,2-trifluoroethyl ether, and nonafluorobutyl methyl ether.

[0018] Optionally, the non-fluorinated tertiary amine includes one or more of triethylamine, tripropylamine, and triisopropylamine.

[0019] Optionally, the fluorinated tertiary amine includes one or more of tris(trifluoroethyl)amine and tris(hexafluoroisopropyl)amine.

[0020] Optionally, the molar concentration of the additive in the negative electrode sheet treatment liquid is less than or equal to 3 mol / L. Further, the molar concentration of the additive in the negative electrode sheet treatment liquid is 0.02 mol / L - 0.5 mol / L.

[0021] Optionally, the method for using the negative electrode sheet treatment liquid includes: coating the negative electrode sheet treatment liquid on the surface of the negative electrode sheet, or immersing the negative electrode sheet in the negative electrode sheet treatment liquid.

[0022] Optionally, the immersion time is 5 h - 20 h.

[0023] The negative electrode sheet treatment liquid provided in the first aspect of the present application can form a uniform protective layer on the surface of the negative electrode sheet, thereby inhibiting the reduction of the electrolyte on the negative electrode surface, reducing the loss of active lithium in the battery, and ensuring that the battery has a high energy density and cycle life.

[0024] In the second aspect, the present application provides a surface-modified negative electrode sheet, which is obtained by treating with the above-mentioned negative electrode sheet treatment liquid. The surface-modified negative electrode sheet includes a negative electrode sheet body and a protective layer provided on the negative electrode sheet body. The protective layer includes one or more of a third protective agent represented by the structural formula (Ⅲ) and a fourth protective agent represented by the structural formula (Ⅳ);

[0025]

[0026] In the formula (Ⅲ), R6 is selected from any one of alkyl, alkenyl, alkynyl, aryl or methylsilyl; R7 is selected from any one of alkylene, alkenylene, alkynylene, arylene or methylenesilyl; X4 is selected from O or S;

[0027] In the formula (Ⅳ), R8, R9, R 10 are respectively selected from any one of alkylene, alkenylene, alkynylene or arylene; X5 and X6 are respectively selected from O or S.

[0028] Optionally, the negative electrode sheet body includes one or more of a carbon-based negative electrode, a silicon-based negative electrode, a tin-based negative electrode, a lithium negative electrode, a sodium negative electrode, a potassium negative electrode, a magnesium negative electrode, a zinc negative electrode and an aluminum negative electrode. Further, the negative electrode sheet body includes a graphite negative electrode.

[0029] Optionally, the thickness of the protective layer is less than or equal to 50 nm.

[0030] The surface-modified negative electrode sheet provided in the second aspect of the present application can form a protective layer on the surface of the negative electrode sheet body by treating the negative electrode sheet. The protective layer can inhibit the reduction of the electrolyte on the negative electrode surface, reduce the loss of active lithium, and ensure that the battery has a high energy density and cycle life.

[0031] In a third aspect, the present application provides a lithium secondary battery, including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. Among them, the negative electrode sheet includes the negative electrode sheet as described in the second aspect of the present application.

[0032] For the lithium secondary battery provided in the third aspect of the present application, since its negative electrode sheet is treated with the negative electrode sheet treatment liquid of the present application, it can have a relatively high energy density and cycle life. Description of the Drawings

[0033] Figure 1 It is a scanning electron microscope image of the surface-modified negative electrode sheet prepared in Example 1 of the present application;

[0034] Figure 2 It is a scanning electron microscope image of the negative electrode sheet prepared in Comparative Example 1 of the present application. Detailed Description of the Embodiments

[0035] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present application.

[0036] The core components of a lithium secondary battery include a positive electrode sheet, a negative electrode sheet, an electrolyte, a separator, and corresponding connecting accessories and circuits. During charging, lithium ions escape from the lattice of the positive electrode sheet, pass through the electrolyte, and deposit on the negative electrode sheet; during discharging, lithium ions escape from the negative electrode sheet, pass through the electrolyte, and are inserted into the lattice of the positive electrode sheet. However, during the first charging process of the lithium secondary battery, part of the electrolyte will undergo a reduction reaction on the surface of the negative electrode sheet, and at the same time combine with the lithium ions escaping from the positive electrode sheet to form a solid electrolyte interface film (SEI film). The formation of the SEI film will consume the active lithium in the battery, convert the active lithium into an inactive lithium-containing compound, thereby causing a loss of reversible lithium and reducing the first efficiency and discharge capacity of the battery. To reduce the side reaction between the electrolyte and the negative electrode sheet, reduce the lithium loss caused by the formation of the SEI film in the battery, and improve the battery capacity and Coulomb efficiency, the embodiments of the present application provide a negative electrode sheet treatment liquid. Treating the negative electrode sheet with this negative electrode sheet treatment liquid can form a protective layer on the surface of the negative electrode sheet. This protective layer can react with the electrolyte to form an interface film similar to the SEI film, thereby isolating the electrolyte from the negative electrode sheet, and reducing the amount of SEI film generated during the first charging of the battery, thereby reducing the loss of active lithium in the battery and improving the comprehensive performance of the battery.

[0037] The negative electrode sheet treatment liquid provided by the present application includes an organic solvent and an additive. In some embodiments of the present application, the additive includes a first additive with a structural formula as shown in formula (I): Formula (I), in formula (I), R1 and R2 are each independently selected from any one of alkylene, alkenylene, alkynylene, arylene or methylene silyl, and X1 is selected from O or S. In the embodiments of the present application, R1 and R2 can be the same or different groups. In some embodiments of the present application, R1 and / or R2 is arylene. When R1 and / or R2 is arylene, the interfacial film similar to the SEI film formed by the first additive is thinner and has lower impedance. In the embodiments of the present application, the carbon atom numbers of R1 and R2 are 1-20. Further, the carbon atom numbers of R1 and R2 can be 1-10. The carbon atom numbers of R1 and R2 can specifically be, but are not limited to, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 15 or 20.

[0038] In some embodiments of the present application, the additive includes a second additive with a structural formula as shown in formula (II): Formula (II), in formula (II), R3 is selected from any one of sub-alkyl, sub-alkenyl, sub-alkynyl, sub-arylene or sub-methylene silyl, R4 and R5 are each independently selected from any one of alkylene, alkenylene, alkynylene or arylene, and X2 and X3 are each independently selected from O or S. In the embodiments of the present application, R4 and R5 can be the same or different groups. In some embodiments of the present application, R4 and / or R5 is arylene. When R4 and / or R5 is arylene, the interfacial film similar to the SEI film formed by the second additive is thinner and has lower impedance. In the embodiments of the present application, the carbon atom numbers of R3, R4 and R5 are 1-20. Further, the carbon atom numbers of R3, R4 and R5 can be 1-10. The carbon atom numbers of R3, R4 and R5 can specifically be, but are not limited to, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 15 or 20.

[0039] In a lithium secondary battery, the content of moisture will affect the comprehensive performance of the lithium secondary battery. For example, water will react with the electrolyte (LiPF6) of the lithium secondary battery to generate hydrofluoric acid (HF). The reaction equation is H2O + LiPF6 → LiF + 2HF↑ + POF3. Since HF has strong corrosiveness, hydrofluoric acid will dissolve the positive electrode material of the battery and form deposits on the surface of the negative electrode sheet of the battery, thereby affecting the formation of the SEI film on the negative electrode sheet or damaging the SEI film formed on the negative electrode sheet, increasing the interfacial impedance and reducing the safety performance of the battery. However, in the existing lithium secondary battery production process, the negative electrode sheet of the battery always contains a certain amount of moisture, which in turn affects the comprehensive performance of the battery. The negative electrode sheet treatment liquid provided by the present application can remove the moisture in the negative electrode sheet and improve the battery performance.

[0040] In this application, the additive in the negative electrode sheet treatment liquid can react with the residual water in the negative electrode sheet. When the additive is the first additive, the reaction between the first additive and water is as follows:

[0041]

[0042] As can be seen from the above reaction formula, the first additive can react with water to generate the first lithium alkoxide (lithium mercaptide) compound and lithium hydroxide, thereby removing the water in the negative electrode sheet. And when assembling the negative electrode sheet into a battery, the first lithium alkoxide (lithium mercaptide) compound can also react further with the electrolyte. Taking a lithium secondary battery with an electrolyte containing ethylene carbonate (EC) as an example, the reaction between the first lithium alkoxide (lithium mercaptide) compound of the embodiment of the present application and the electrolyte is as follows:

[0043]

[0044] As can be seen from the above reaction formula, in a lithium secondary battery system with an electrolyte containing ethylene carbonate (EC), the first lithium alkoxide (lithium mercaptide) compound of the embodiment of the present application can react with ethylene carbonate to form lithium glycolate alkoxide. Among them, lithium glycolate alkoxide can be used as a protective layer to cover the surface of the negative electrode sheet, thereby inhibiting the reduction of the electrolyte on the negative electrode surface and reducing the loss of active lithium.

[0045] Taking a lithium secondary battery with an electrolyte containing fluoroethylene carbonate (FEC) as an example, the reaction between the first lithium alkoxide (lithium mercaptide) compound of the embodiment of the present application and the electrolyte is as follows:

[0046]

[0047] As can be seen from the above reaction formula, in a lithium secondary battery system with an electrolyte containing fluoroethylene carbonate (FEC), the first lithium alkoxide (lithium mercaptide) compound of the embodiment of the present application can react with fluoroethylene carbonate to form alkyl (thio) etherified carbonate and lithium fluoride. Among them, both alkyl (thio) etherified carbonate and lithium fluoride can be used as protective layers to cover the surface of the negative electrode sheet, thereby inhibiting the reduction of the electrolyte on the negative electrode surface and reducing the loss of active lithium.

[0048] When the additive of the embodiment of the present application is the second additive, the reaction between the second additive and water is as follows:

[0049]

[0050] As can be seen from the above reaction formula, the second additive can react with water to generate the second lithium alkoxide (lithium mercaptide) compound and lithium hydroxide, and the second lithium alkoxide (lithium mercaptide) compound can also react further with the electrolyte. Taking a lithium secondary battery with an electrolyte containing ethylene carbonate (EC) as an example, the reaction between the second lithium alkoxide (lithium mercaptide) compound of the embodiment of the present application and the electrolyte is as follows:

[0051]

[0052] As can be seen from the above reaction formula, in a lithium secondary battery system where the electrolyte contains ethylene carbonate (EC), the lithium dialcoholate (lithium mercaptide) compound of the embodiments of the present application can react with ethylene carbonate to form lithium glycolate. Among them, lithium glycolate can be used as a protective layer to cover the surface of the negative electrode plate, thereby inhibiting the reduction of the electrolyte on the negative electrode surface and reducing the loss of active lithium.

[0053] Taking a lithium secondary battery with an electrolyte containing fluoroethylene carbonate (FEC) as an example, the reaction of the lithium dialcoholate (lithium mercaptide) compound of the embodiments of the present application with the electrolyte is as follows:

[0054]

[0055] As can be seen from the above reaction formula, in a lithium secondary battery system where the electrolyte contains fluoroethylene carbonate (FEC), the lithium dialcoholate (lithium mercaptide) compound of the embodiments of the present application can react with fluorinated ethylene carbonate to form alkyl (thio) etherified carbonate and lithium fluoride. Among them, alkyl (thio) etherified carbonate and lithium fluoride can be used as the SEI film to cover the surface of the negative electrode plate, thereby inhibiting the reaction of the electrolyte on the negative electrode plate.

[0056] In a lithium secondary battery, when the negative electrode material is graphite, the active hydrogen on the surface of the graphite negative electrode will form an SEI film and generate gas during battery formation, which will cause the loss of active lithium in the battery and the decline of the battery safety performance. The additive in the present application can also react with the active hydrogen on the surface of graphite, thereby removing the active hydrogen on the surface of graphite and improving the battery performance. Specifically, when the additive is the first additive, the reaction of the first additive with active hydrogen is as follows:

[0057]

[0058] Among them, G in the reaction formula refers to graphite. As can be seen from the above reaction formula, the first additive can react with active hydrogen to form a lithium dialcoholate (lithium mercaptide) compound and graphite with a lithium alcoholate group on the surface, and the lithium dialcoholate (lithium mercaptide) compound can further react with the electrolyte to form an SEI film.

[0059] When the additive is the second additive, the reaction of the second additive with active hydrogen is as follows:

[0060]

[0061] As can be seen from the above reaction formula, the second additive can react with active hydrogen to form a second lithium alkoxide (lithium mercaptide) compound and graphite with lithium alkoxide groups on its surface, and the second lithium alkoxide (lithium mercaptide) compound can further react with the electrolyte to form a SEI film.

[0062] In a lithium secondary battery, a carbonate solvent is often used as the solvent of the electrolyte, and the carbonate solvent has good electrochemical stability. The additive of the present application can react with the carbonate solvent. The reaction product can not only cover the surface of the negative electrode to form a protective layer, but also further react with the electrolyte to form an interfacial film similar to the SEI film, thereby inhibiting the reaction of the electrolyte on the surface of the negative electrode sheet in subsequent cycles and reducing the loss of lithium. Among them, taking a lithium secondary battery with an electrolyte containing ethylene carbonate (EC) as an example, when the additive in the embodiment of the present application is the first additive, the reaction of the first additive with the electrolyte is:

[0063]

[0064] The reaction product of the first additive and the electrolyte can further react with the electrolyte to form an interfacial film similar to the SEI film. The reaction of the reaction product with the electrolyte is:

[0065]

[0066] When the additive in the embodiment of the present application is the second additive, the reaction of the second additive with the electrolyte is:

[0067]

[0068] The reaction product of the second additive and the electrolyte can further react with the electrolyte to form an interfacial film similar to the SEI film. The reaction of the reaction product with the electrolyte is:

[0069]

[0070] As can be seen from the above reaction formula, in a lithium secondary battery system with an electrolyte containing ethylene carbonate (EC), the additive in the embodiment of the present application can react with ethylene carbonate to form lithium glycolate carboxylate or lithium ethylene carbonate alkoxide. Among them, both lithium glycolate carboxylate and lithium ethylene carbonate alkoxide can inhibit the reaction of the electrolyte on the surface of the negative electrode sheet, thereby reducing the loss of active lithium.

[0071] Taking a lithium secondary battery with an electrolyte containing fluoroethylene carbonate (FEC) as an example, when the additive in the embodiment of the present application is the first additive, the reaction of the first additive with the electrolyte is:

[0072]

[0073] The reaction product of the first additive and the electrolyte can further react with the electrolyte to form an interfacial film similar to the SEI film. The reaction of the reaction product and the electrolyte is as follows:

[0074]

[0075] When the additive in the embodiment of the present application is the second additive, the reaction of the second additive and the electrolyte is as follows:

[0076]

[0077] The reaction product of the second additive and the electrolyte can further react with the electrolyte to form an interfacial film similar to the SEI film. The reaction of the reaction product and the electrolyte is as follows:

[0078]

[0079] It can be seen from the above reaction formulas that in a lithium secondary battery system where the electrolyte contains fluoroethylene carbonate (FEC), the additive in the embodiment of the present application can react with fluoroethylene carbonate to generate lithium fluoroethylene glycol carboxylate and lithium fluoride. Among them, lithium fluoroethylene glycol carboxylate and lithium fluoride can act as a protective layer covering the surface of the negative electrode sheet, thereby inhibiting the reaction of the electrolyte on the surface of the negative electrode sheet and reducing the loss of active lithium.

[0080] In some specific embodiments of the present application, the additive can be any one or more compounds shown in Table 1:

[0081] Table 1 Structural formulas and names of additives in some embodiments of the present application

[0082]

[0083]

[0084] In the embodiments of the present application, the molar concentration of the additive in the negative electrode sheet treatment liquid is less than or equal to 3 mol / L. In some embodiments of the present application, the molar concentration of the additive in the negative electrode sheet treatment liquid is 0.02 mol / L - 0.5 mol / L. The molar concentration of the additive in the negative electrode sheet treatment liquid may specifically be, but is not limited to, 0.01 mol / L, 0.02 mol / L, 0.05 mol / L, 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L or 3 mol / L. Within the above molar concentration range, the negative electrode sheet treatment liquid can sufficiently remove the moisture in the negative electrode sheet, and form a complete protective layer on the surface of the negative electrode sheet, inhibit the reaction of the electrolyte on the surface of the negative electrode sheet, and reduce the loss of active lithium. If the concentration of the additive is too high, it will cause the thickness of the formed protective layer to be too large, resulting in a large interfacial impedance, hindering the transmission of lithium ions, and reducing the discharge capacity.

[0085] In the embodiments of the present application, the organic solvents in the negative electrode sheet treatment liquid include ether solvents and amine solvents. Ether solvents have good solubility for alkyl lithium compounds, but have low solubility for strongly polar lithium alcohol compounds; while amine solvents have good solubility for lithium alcohol compounds. The organic solvents obtained by compounding ether solvents and amine solvents can well dissolve the additive, thereby obtaining a homogeneous negative electrode sheet treatment liquid. In the embodiments of the present application, the number of carbon atoms of the ether solvent and the amine solvent is 1 - 8. Solvents with fewer carbon atoms have low boiling points and are easy to remove. Using organic solvents with low boiling points can more easily remove the organic solvents on the surface of the negative electrode sheet, thereby forming a protective layer.

[0086] In some embodiments of the present application, the ether solvent includes one or more of non-fluorinated ethers and fluorinated ethers. In some embodiments of the present application, the non-fluorinated ethers include one or more of diethyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, diethylene glycol dimethyl ether and triethylene glycol dimethyl ether. In some embodiments of the present application, the fluorinated ethers include one or more of 2,2,2-trifluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis-2,2,2-trifluoroethyl ether and nonafluoro-n-butyl methyl ether.

[0087] In some embodiments of the present application, the amine solvent includes one or more of non-fluorinated tertiary amines and fluorinated tertiary amines. In some embodiments of the present application, the non-fluorinated tertiary amines include one or more of triethylamine, tripropylamine and triisopropylamine. In some embodiments of the present application, the fluorinated tertiary amines include one or more of tris(trifluoroethyl)amine and tris(hexafluoroisopropyl)amine.

[0088] In the embodiments of the present application, in the organic solvent, the volume ratio of the ether solvent to the amine solvent is 1∶(0.3 - 3). The volume ratio of the ether solvent to the amine solvent can specifically but is not limited to 1∶0.3, 1∶0.5, 1∶0.7, 1∶1, 1∶1.5, 1∶2, or 1∶3. Within the above volume ratio range, the organic solvent can fully dissolve the additive, ensuring the formation of a uniformly composed negative electrode sheet treatment solution, thereby forming a uniform protective layer on the electrode surface.

[0089] The negative electrode sheet treatment solution provided by the present application can form a uniform protective layer on the surface of the negative electrode sheet, thereby inhibiting the reaction between the electrolyte and active lithium on the negative electrode surface, reducing the loss of active lithium, and ensuring that the battery has a high energy density and cycle life.

[0090] The present application also provides a method for pre-treating a negative electrode sheet, including: coating the negative electrode sheet treatment solution of the present application on the surface of the negative electrode sheet body, or immersing the negative electrode sheet body in the negative electrode sheet treatment solution, and performing vacuum drying on the negative electrode sheet after coating or immersion to obtain the negative electrode sheet.

[0091] In some embodiments of the present application, the negative electrode sheet is pre-treated by coating, and the coating method includes any one of brush coating, roll coating, spray coating, knife coating, dip coating, or spin coating. In some embodiments of the present application, the negative electrode sheet is pre-treated by immersion, and the immersion time is 1h - 20h. Further, the immersion time of the negative electrode sheet is 10h - 20h. The immersion time of the negative electrode sheet can specifically but is not limited to 1h, 3h, 5h, 8h, 10h, 13h, 15h, 17h, or 20h. In the embodiments of the present application, the immersion temperature of the negative electrode sheet is -10℃ - 50℃. The immersion temperature of the negative electrode sheet can specifically but is not limited to -10℃, 0℃, 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 40℃, or 50℃. In the embodiments of the present application, the pre-treatment is carried out in a drying room, and the dew point of the drying room is greater than or equal to -50℃ and less than or equal to -30℃. The dew point of the drying room can specifically but is not limited to -50℃, -45℃, -40℃, or -30℃.

[0092] The method for pre-treating a negative electrode sheet provided by the present application is simple to operate, can efficiently and quickly form a protective layer on the surface of the negative electrode sheet, thereby inhibiting the occurrence of side reactions on the surface of the negative electrode sheet, reducing the loss of active lithium in the battery, and improving the battery capacity.

[0093] The present application also provides a surface-modified negative electrode sheet, including a negative electrode sheet body and a protective layer provided on the negative electrode sheet body. The protective layer includes one or more of a third protective agent shown in the structural formula (Ⅲ) and a fourth protective agent shown in the structural formula (Ⅳ):

[0094]

[0095] In formula (III), R6 is selected from any one of alkyl, alkenyl, alkynyl, aryl or methylsilyl; R7 is selected from any one of alkylene, alkenylene, alkynylene, arylene or methylenesilyl; X4 is selected from O or S;

[0096] In formula (IV), R8, R9, R 10 are each independently selected from any one of alkylene, alkenylene, alkynylene or arylene; X5 and X6 are each independently selected from O or S.

[0097] In the present application, after the negative electrode sheet is pretreated with the negative electrode sheet treatment liquid, the additives in the negative electrode sheet can be coated on the surface of the negative electrode sheet to form a protective layer. Among them, the first additive is the first protective agent of the protective layer, and the second additive is the second protective agent of the protective layer. The structural formula of the first protective agent is shown in formula (I), and the structural formula of the second protective agent is shown in formula (II):

[0098]

[0099] In formula (I), R1 and R2 are each independently selected from any one of alkylene, alkenylene, alkynylene, arylene or methylsilyl; X1 is selected from O or S;

[0100] In formula (II), R3 is selected from any one of sub-alkyl, sub-alkenyl, sub-alkynyl, sub-aryl or sub-methylsilyl; R4 and R5 are each independently selected from any one of alkylene, alkenylene, alkynylene or arylene; X2 and X3 are each independently selected from O or S.

[0101] In the process of pretreating the negative electrode sheet with the negative electrode sheet treatment liquid, the first protective agent and the second protective agent can react with the water in the negative electrode sheet. The first protective agent can react with water to generate a third protective agent shown in formula (III), and the second protective agent can react with water to generate a fourth protective agent shown in formula (IV). For the specific reaction process, reference can be made to the description of the negative electrode sheet treatment liquid part in the examples of the present application. In the present application, the first protective agent, the second protective agent, the third protective agent and the fourth protective agent can all react with the electrolyte to form an interfacial film similar to the SEI film, thereby protecting the negative electrode sheet. In some embodiments of the present application, the protective layer includes the first protective agent and the third protective agent. In some embodiments of the present application, the protective layer includes the second protective agent and the fourth protective agent. In some embodiments of the present application, the protective layer includes the first protective agent, the second protective agent, the third protective agent and the fourth protective agent at the same time.

[0102] In the embodiments of the present application, the negative electrode sheet body includes one or more of a carbon-based negative electrode and a silicon-based negative electrode. In some embodiments of the present application, the negative electrode sheet body includes a graphite negative electrode.

[0103] In the embodiments of the present application, the thickness of the protective layer is less than or equal to 50 nm. In some embodiments of the present application, the thickness of the protective layer is 10 nm - 50 nm. Specifically, the thickness of the protective layer may be, but is not limited to, 1 nm, 3 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, or 50 nm. Controlling the thickness of the protective layer within the above range can ensure that the battery has a high discharge capacity and a long cycle life, and will not cause a large interfacial impedance, thus ensuring the effective transmission of lithium ions.

[0104] The present application also provides a lithium secondary battery, including a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. Among them, the negative electrode plate includes the surface-modified negative electrode plate provided by the present application, and the surface-modified negative electrode plate includes a negative electrode plate body and a protective layer provided on the negative electrode plate body. Specifically, the negative electrode plate may directly act as the negative electrode with a protective layer, or may include a current collector and a negative electrode with a protective layer provided on the current collector. The current collector may be a conventional negative electrode current collector, such as copper foil, carbon-coated copper foil, etc. The lithium secondary battery provided by the present application has high cycle performance and high safety due to the adoption of the surface-modified negative electrode plate provided by the present application.

[0105] The technical solution of the present application will be further described below through multiple embodiments.

[0106] Example 1

[0107] A negative electrode plate treatment solution includes an additive with a molecular structural formula shown in formula (A), an organic solvent formed by mixing dimethoxymethane and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 1.0 mol / L.

[0108]

[0109] 1) Preparation of the surface-modified negative electrode plate

[0110] Mix graphite, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a weight ratio of 100:3:2 and add water to stir into a uniform slurry. Coating the slurry on a 10-μm copper foil current collector, controlling the surface density of the negative electrode so that the P:N ratio (the capacity ratio of the positive electrode material to the negative electrode material per unit area) of the positive and negative electrodes is 1.1:1, and vacuum drying at 100 °C, and then obtaining the negative electrode plate after slitting.

[0111] In a drying room with a dew point of -50 °C, immerse the negative electrode plate in the above negative electrode plate treatment solution, take it out after soaking for 12 hours and vacuum dry to obtain the surface-modified negative electrode plate.

[0112] 2) Preparation of the positive electrode plate

[0113] Mix LiNi 0.3 Co0.3 Mn 0.3 MnO₂, acetylene black, and polyvinylidene fluoride were mixed in a weight ratio of 95:3:2 and added to the positive electrode solvent N-methylpyrrolidone, and stirred into a uniform slurry. The slurry was coated on a 12-μm aluminum foil and dried at 80 °C for 24 h, and then roll-pressed and cut to obtain the positive electrode sheet.

[0114] 3) Preparation of the electrolyte

[0115] Ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 1:1:1, and then vinylene carbonate (VC) was added thereto to obtain an organic solvent. The mass percentage of vinylene carbonate in the organic solvent was 2%. Then, lithium hexafluorophosphate (LiPF₆) was dissolved in the above organic solvent and stirred and mixed evenly to obtain the electrolyte.

[0116] 4) Preparation of the lithium secondary battery

[0117] The surface-modified negative electrode sheet, positive electrode sheet, electrolyte, and 12-μm PE separator prepared above were assembled into a soft-pack battery.

[0118] Example 2

[0119] A negative electrode sheet treatment liquid includes an additive shown by the molecular structural formula as formula (B), an organic solvent formed by mixing 1,4-dioxane and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 1.0 mol / L.

[0120]

[0121] 1) Preparation of the surface-modified negative electrode sheet

[0122] The preparation method of the negative electrode sheet was the same as that in Example 1.

[0123] In a drying room with a dew point of -50 °C, the negative electrode sheet was immersed in the above negative electrode sheet treatment liquid, taken out after soaking for 10 h and dried in vacuum to obtain the surface-modified negative electrode sheet.

[0124] 2) Preparation of the lithium secondary battery

[0125] The positive electrode sheet and the electrolyte were prepared in the same method as in Example 1. The surface-modified negative electrode sheet, positive electrode sheet, electrolyte, and 12-μm PE separator prepared were assembled into a soft-pack battery.

[0126] Example 3

[0127] A negative electrode sheet treatment liquid includes an additive shown by the molecular structural formula as formula (C), an organic solvent formed by mixing dimethoxymethane and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 1.0 mol / L.

[0128]

[0129] 1) Preparation of surface-modified negative electrode sheet

[0130] The preparation method of the negative electrode sheet is the same as that in Example 1.

[0131] In a drying room with a dew point of -50 °C, the negative electrode sheet is immersed in the above-mentioned negative electrode sheet treatment liquid, taken out after 12 h of immersion and dried in vacuum to obtain a surface-modified negative electrode sheet.

[0132] 2) Preparation of lithium secondary battery

[0133] The positive electrode sheet and the electrolyte are prepared in the same method as in Example 1, and the prepared surface-modified negative electrode sheet, positive electrode sheet, electrolyte and a 12-μm PE separator are assembled into a soft-pack battery.

[0134] Example 4

[0135] A negative electrode sheet treatment liquid includes an additive with a molecular structural formula shown in Formula (D), an organic solvent formed by mixing 1,4-dioxane and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 1.0 mol / L.

[0136]

[0137] 1) Preparation of surface-modified negative electrode sheet

[0138] The preparation method of the negative electrode sheet is the same as that in Example 1.

[0139] In a drying room with a dew point of -50 °C, the negative electrode sheet is immersed in the above-mentioned negative electrode sheet treatment liquid, taken out after 10 h of immersion and dried in vacuum to obtain a surface-modified negative electrode sheet.

[0140] 2) Preparation of lithium secondary battery

[0141] The positive electrode sheet and the electrolyte are prepared in the same method as in Example 1, and the prepared surface-modified negative electrode sheet, positive electrode sheet, electrolyte and a 12-μm PE separator are assembled into a soft-pack battery.

[0142] Example 5

[0143] A negative electrode sheet treatment liquid includes an additive with a molecular structural formula shown in Formula (E), an organic solvent formed by mixing dimethoxymethane and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 1.0 mol / L.

[0144]

[0145] 3) Preparation of surface-modified negative electrode sheet

[0146] The preparation method of the negative electrode sheet is the same as that in Example 1.

[0147] In a drying room with a dew point of -50°C, the negative electrode sheet was immersed in the above-mentioned negative electrode sheet treatment solution, taken out after 12 hours of immersion and dried in vacuum to obtain a surface-modified negative electrode sheet.

[0148] 4) Preparation of lithium secondary battery

[0149] The positive electrode sheet and the electrolyte were prepared in the same method as in Example 1, and the prepared surface-modified negative electrode sheet, positive electrode sheet, electrolyte and 12-μm PE separator were assembled into a soft-pack battery.

[0150] Example 6

[0151] A negative electrode sheet treatment solution includes an additive with a molecular structural formula shown in formula (F), an organic solvent formed by mixing 1,4-dioxane and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 1.0 mol / L.

[0152]

[0153] 3) Preparation of surface-modified negative electrode sheet

[0154] The preparation method of the negative electrode sheet is the same as that in Example 1.

[0155] In a drying room with a dew point of -50°C, the negative electrode sheet was immersed in the above-mentioned negative electrode sheet treatment solution, taken out after 10 hours of immersion and dried in vacuum to obtain a surface-modified negative electrode sheet.

[0156] 4) Preparation of lithium secondary battery

[0157] The positive electrode sheet and the electrolyte were prepared in the same method as in Example 1, and the prepared surface-modified negative electrode sheet, positive electrode sheet, electrolyte and 12-μm PE separator were assembled into a soft-pack battery.

[0158] Example 7

[0159] A negative electrode sheet treatment solution includes an additive with a molecular structural formula shown in formula (G), an organic solvent formed by mixing dimethoxymethane and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 1.0 mol / L.

[0160]

[0161] 1) Preparation of surface-modified negative electrode sheet

[0162] The preparation method of the negative electrode sheet is the same as that in Example 1.

[0163] In a drying room with a dew point of -50°C, the negative electrode plate is immersed in the above-mentioned negative electrode plate treatment solution. After soaking for 10 hours, it is taken out and vacuum dried to obtain a surface-modified negative electrode plate.

[0164] 2) Preparation of lithium secondary battery

[0165] The positive electrode plate and the electrolyte are prepared in the same method as in Example 1. The prepared surface-modified negative electrode plate, positive electrode plate, electrolyte, and a 12-μm PE separator are assembled into a soft-pack battery.

[0166] Example 8

[0167] A negative electrode plate treatment solution includes an additive with a molecular structural formula shown in Formula (H), an organic solvent formed by mixing 2,5-dimethyltetrahydrofuran and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 1.0 mol / L.

[0168]

[0169] 1) Preparation of surface-modified negative electrode plate

[0170] The preparation method of the negative electrode plate is the same as that in Example 1.

[0171] In a drying room with a dew point of -50°C, the negative electrode plate is immersed in the above-mentioned negative electrode plate treatment solution. After soaking for 10 hours, it is taken out and vacuum dried to obtain a surface-modified negative electrode plate.

[0172] 2) Preparation of lithium secondary battery

[0173] The positive electrode plate and the electrolyte are prepared in the same method as in Example 1. The prepared surface-modified negative electrode plate, positive electrode plate, electrolyte, and a 12-μm PE separator are assembled into a soft-pack battery.

[0174] Example 9

[0175] A negative electrode plate treatment solution includes an additive with a molecular structural formula shown in Formula (I), an organic solvent formed by mixing dimethoxymethane and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 1.0 mol / L.

[0176]

[0177] 1) Preparation of surface-modified negative electrode plate

[0178] The preparation method of the negative electrode plate is the same as that in Example 1.

[0179] In a drying room with a dew point of -50°C, the negative electrode plate is immersed in the above-mentioned negative electrode plate treatment solution. After soaking for 10 hours, it is taken out and vacuum dried to obtain a surface-modified negative electrode plate.

[0180] 2) Preparation of Lithium Secondary Battery

[0181] The positive electrode sheet and the electrolyte were prepared in the same manner as in Example 1, and the surface-modified negative electrode sheet, the positive electrode sheet, the electrolyte, and a 12-μm PE separator prepared were assembled into a soft-pack battery.

[0182] Example 10

[0183] A treatment solution for negative electrode sheet, comprising an additive with a molecular structural formula as shown in formula (J), an organic solvent formed by mixing 2,2,2-trifluoroethyl methyl ether and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 1.0 mol / L.

[0184]

[0185] 1) Preparation of Surface-Modified Negative Electrode Sheet

[0186] The preparation method of the negative electrode sheet is the same as that in Example 1.

[0187] In a drying room with a dew point of -50°C, the negative electrode sheet was immersed in the above-mentioned treatment solution for negative electrode sheet, taken out after soaking for 10 h and dried in vacuum to obtain a surface-modified negative electrode sheet.

[0188] 2) Preparation of Lithium Secondary Battery

[0189] The positive electrode sheet and the electrolyte were prepared in the same manner as in Example 1, and the surface-modified negative electrode sheet, the positive electrode sheet, the electrolyte, and a 12-μm PE separator prepared were assembled into a soft-pack battery.

[0190] Example 11

[0191] A treatment solution for negative electrode sheet, comprising an additive with a molecular structural formula as shown in formula (K), an organic solvent formed by mixing dimethoxymethane and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 1.0 mol / L.

[0192]

[0193] 1) Preparation of Surface-Modified Negative Electrode Sheet

[0194] The preparation method of the negative electrode sheet is the same as that in Example 1.

[0195] In a drying room with a dew point of -50°C, the negative electrode sheet was immersed in the above-mentioned treatment solution for negative electrode sheet, taken out after soaking for 10 h and dried in vacuum to obtain a surface-modified negative electrode sheet.

[0196] 2) Preparation of Lithium Secondary Battery

[0197] The positive electrode sheet and the electrolyte were prepared in the same manner as in Example 1, and the surface-modified negative electrode sheet, positive electrode sheet, electrolyte, and 12-μm PE separator prepared were assembled into a soft-pack battery.

[0198] Example 12

[0199] A treatment solution for a negative electrode sheet includes an additive with a molecular structural formula as shown in formula (L), an organic solvent formed by mixing bis-2,2,2-trifluoroethyl ether and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 1.0 mol / L.

[0200]

[0201] 1) Preparation of the surface-modified negative electrode sheet

[0202] The preparation method of the negative electrode sheet is the same as that in Example 1.

[0203] In a drying room with a dew point of -50°C, the negative electrode sheet was immersed in the above-mentioned treatment solution for the negative electrode sheet. After soaking for 10 h, it was taken out and vacuum-dried to obtain the surface-modified negative electrode sheet.

[0204] 2) Preparation of the lithium secondary battery

[0205] The positive electrode sheet and the electrolyte were prepared in the same manner as in Example 1, and the surface-modified negative electrode sheet, positive electrode sheet, electrolyte, and 12-μm PE separator prepared were assembled into a soft-pack battery.

[0206] Example 13

[0207] A treatment solution for a negative electrode sheet includes an additive with a molecular structural formula as shown in formula (M), an organic solvent formed by mixing dimethoxymethane and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 1.0 mol / L.

[0208]

[0209] 1) Preparation of the surface-modified negative electrode sheet

[0210] The preparation method of the negative electrode sheet is the same as that in Example 1.

[0211] In a drying room with a dew point of -50°C, the negative electrode sheet was immersed in the above-mentioned treatment solution for the negative electrode sheet. After soaking for 10 h, it was taken out and vacuum-dried to obtain the surface-modified negative electrode sheet.

[0212] 2) Preparation of the lithium secondary battery

[0213] The positive electrode sheet and the electrolyte were prepared in the same manner as in Example 1, and the surface-modified negative electrode sheet, positive electrode sheet, electrolyte, and 12-μm PE separator prepared were assembled into a soft-pack battery.

[0214] Example 14

[0215] A negative electrode sheet treatment liquid, including an additive with a molecular structural formula as shown in formula (N), an organic solvent formed by mixing 1,4-dioxane and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 1.0 mol / L.

[0216]

[0217] 3) Preparation of a surface-modified negative electrode sheet

[0218] The preparation method of the negative electrode sheet is the same as that in Example 1.

[0219] In a drying room with a dew point of -50°C, soak the negative electrode sheet in the above-mentioned negative electrode sheet treatment liquid, take it out after soaking for 10 h and perform vacuum drying to obtain a surface-modified negative electrode sheet.

[0220] 4) Preparation of a lithium secondary battery

[0221] Prepare a positive electrode sheet and an electrolyte in the same method as in Example 1, and assemble the prepared surface-modified negative electrode sheet, positive electrode sheet, electrolyte, and a 12-μm PE separator into a soft-pack battery.

[0222] Example 15

[0223] A negative electrode sheet treatment liquid, including an additive with a molecular structural formula as shown in formula (N), an organic solvent formed by mixing 1,4-dioxane and triethylamine in a volume ratio of 1:2, and the concentration of the additive is 1.0 mol / L.

[0224]

[0225] 1) Preparation of a surface-modified negative electrode sheet

[0226] The preparation method of the negative electrode sheet is the same as that in Example 1.

[0227] In a drying room with a dew point of -50°C, soak the negative electrode sheet in the above-mentioned negative electrode sheet treatment liquid, take it out after soaking for 10 h and perform vacuum drying to obtain a surface-modified negative electrode sheet.

[0228] 2) Preparation of a lithium secondary battery

[0229] Prepare a positive electrode sheet and an electrolyte in the same method as in Example 1, and assemble the prepared surface-modified negative electrode sheet, positive electrode sheet, electrolyte, and a 12-μm PE separator into a soft-pack battery.

[0230] Example 16

[0231] A negative electrode sheet treatment liquid includes an additive with a molecular structural formula shown in formula (N), an organic solvent formed by mixing 1,4-dioxane and triethylamine in a volume ratio of 2:1, and the concentration of the additive is 1.0 mol / L.

[0232]

[0233] 3) Preparation of a surface-modified negative electrode sheet

[0234] The preparation method of the negative electrode sheet is the same as that in Example 1.

[0235] In a drying room with a dew point of -50°C, immerse the negative electrode sheet in the above-mentioned negative electrode sheet treatment liquid, take it out after soaking for 10 h and vacuum dry it to obtain a surface-modified negative electrode sheet.

[0236] 4) Preparation of a lithium secondary battery

[0237] Prepare a positive electrode sheet and an electrolyte in the same method as in Example 1, and assemble the prepared surface-modified negative electrode sheet, positive electrode sheet, electrolyte and a 12-μm PE separator into a soft-pack battery.

[0238] To highlight the beneficial effects of this application, the following comparative examples are set.

[0239] Comparative Example 1

[0240] Preparation of a lithium secondary battery

[0241] Prepare a negative electrode sheet, a positive electrode sheet and an electrolyte in the same method as in Example 1, and assemble the prepared negative electrode sheet, positive electrode sheet, electrolyte and a 12-μm PE separator into a soft-pack battery.

[0242] Comparative Example 2

[0243] A negative electrode sheet treatment liquid includes an additive with a molecular structural formula shown in formula (N), an organic solvent formed by mixing 1,4-dioxane and triethylamine in a volume ratio of 1:1, and the concentration of the additive is 4.0 mol / L.

[0244]

[0245] 1) Preparation of a surface-modified negative electrode sheet

[0246] The preparation method of the negative electrode sheet is the same as that in Example 1.

[0247] In a drying room with a dew point of -50°C, immerse the negative electrode sheet in the above-mentioned negative electrode sheet treatment liquid, take it out after soaking for 10 h and vacuum dry it to obtain a surface-modified negative electrode sheet.

[0248] 2) Preparation of a lithium secondary battery

[0249] The positive electrode sheet and the electrolyte were prepared in the same manner as in Example 1, and the prepared surface-modified negative electrode sheet, positive electrode sheet, electrolyte, and 12-μm PE separator were assembled into a soft-pack battery.

[0250] Effect Example

[0251] To strongly support the beneficial effects brought by the technical solutions of the embodiments of the present application, the following tests are provided:

[0252] 1) The morphologies of the surface-modified negative electrode sheet of Example 1 and the negative electrode sheet of Comparative Example 1 were characterized by scanning electron microscopy. Please refer to Figure 1 and Figure 2 , where Figure 1 is the scanning electron micrograph of the surface-modified negative electrode sheet prepared in Example 1 of the present application, Figure 2 is the scanning electron micrograph of the negative electrode sheet prepared in Comparative Example 1 of the present application. It can be seen from Figure 1 that there is a waxy deposition layer on the surface of the negative electrode sheet, and this deposition layer is the protective layer. It can be seen from Figure 2 that the surface of the untreated negative electrode sheet is relatively smooth.

[0253] 2) The cycle performance of the soft-pack batteries of Examples 1-14 and Comparative Example 1 was tested. The specific test conditions were as follows: The soft-pack battery was charged at a constant current of 20 mA to 4.35 V at a temperature of 25 °C, and then discharged at a constant current of 20 mA to 3.0 V. Then it was charged to 4.35 V at a current of 200 mA, and the voltage was held constant until the current was 20 mA, and then discharged to 3.0 V at a current of 200 mA. This was taken as one cycle; the first charge capacity and discharge capacity were recorded, and the first Coulomb efficiency (%) was calculated; after repeating the charge and discharge cycle 500 times, the discharge capacity of the 500th cycle was recorded, and the capacity retention rate after cycling (%) = discharge capacity after 200 cycles / first discharge capacity × 100%; the test results are shown in Table 2.

[0254] Table 2 Performance parameter table of soft-pack batteries of Examples 1-14 and Comparative Example 1

[0255]

[0256] It can be seen from the test results in Table 2 that compared with the untreated negative electrode sheet of Comparative Example 1, the surface-modified negative electrode sheets of Examples 1-14 of the present application can significantly improve the performance of the battery through surface treatment. Using the surface-modified negative electrode sheet of the present application can improve the energy density of the battery and enhance the first Coulomb efficiency and cycle performance of the battery.

[0257] The above is the preferred embodiment of the present application, but it should not be construed as limiting the scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present application, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present application.

Claims

1. A negative electrode sheet treatment liquid, characterized in that, It includes an organic solvent and an additive, and the additive includes a first additive shown by the structural formula of formula (I) or a second additive shown by formula (Ⅱ): Formula (I); Formula (II); In formula (I), R1 and R2 are each independently selected from any one of alkylene, alkenylene, alkynylene, arylene or methylsilylene; X1 is selected from O or S; In formula (Ⅱ), R3 is selected from any one of hypoalkylene, hypoalkenylene, hypoalkynylene, hypoarylene or hypomethylsilylene; R4 and R5 are each independently selected from any one of alkylene, alkenylene, alkynylene or arylene; X2 and X3 are each independently selected from O or S.

2. The negative electrode sheet treatment liquid according to claim 1, characterized in that, The carbon atom numbers of R1, R2, R3, R4 and R5 are 1-20.

3. The negative electrode sheet treatment liquid according to claim 1 or 2, characterized in that, The organic solvent includes an ether solvent and an amine solvent.

4. The negative electrode sheet treatment liquid according to claim 3, characterized in that, The volume ratio of the ether solvent to the amine solvent is 1∶(0.3-3).

5. The negative electrode sheet treatment liquid according to claim 3 or 4, characterized in that, The ether solvent includes one or more of non-fluorinated ethers and fluorinated ethers; the amine solvent includes one or more of non-fluorinated tertiary amines and fluorinated tertiary amines.

6. The negative electrode sheet treatment liquid according to claim 5, characterized in that, The carbon atom numbers of the non-fluorinated ether, the fluorinated ether, the non-fluorinated tertiary amine and the fluorinated tertiary amine are 1-8.

7. The negative electrode sheet treatment liquid according to claim 5 or 6, characterized in that, The non-fluorinated ether includes one or more of diethyl ether, dimethoxymethane, 1,2-dimethoxyethane, 1,4-dioxane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, diethylene glycol dimethyl ether and triethylene glycol dimethyl ether; the fluorinated ether includes one or more of 2,2,2-trifluoroethyl methyl ether, bis-2,2,2-trifluoroethyl ether and nonafluoro-n-butyl methyl ether.

8. The negative electrode sheet treatment liquid according to any one of claims 1-7, characterized in that, The molar concentration of the additive in the negative electrode sheet treatment liquid is less than or equal to 3 mol / L.

9. A surface-modified negative electrode sheet, characterized in that, The surface-modified negative electrode sheet is obtained by treating with the negative electrode sheet treatment liquid according to any one of claims 1-8. The surface-modified negative electrode sheet includes a negative electrode sheet body and a protective layer provided on the negative electrode sheet body. The protective layer includes one or more of a third protective agent shown by the structural formula of formula (Ⅲ) and a fourth protective agent shown by formula (Ⅳ); Formula (III); Formula (IV); In formula (Ⅲ), R6 is selected from any one of alkyl, alkenyl, alkynyl, aryl or methylsilyl; R7 is selected from any one of alkylene, alkenylene, alkynylene, arylene or methylsilylene; X4 is selected from O or S; In formula (IV), the R8, R9, and R 10 are each independently selected from any one of an alkylene group, an alkenylene group, an alkynylene group, or an arylene group; the X5 and X6 are each independently selected from O or S.

10. The surface-modified negative electrode sheet according to claim 9, characterized in that, The negative electrode sheet body includes one or more of a carbon-based negative electrode and a silicon-based negative electrode.

11. The surface-modified negative electrode sheet according to claim 9 or 10, characterized in that, The thickness of the protective layer is less than or equal to 50 nm.

12. A lithium secondary battery, characterized in that, It includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The negative electrode sheet includes the surface-modified negative electrode sheet according to any one of claims 9-11.

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