Negative plate preparation method and lithium battery

Abstract

The invention provides a negative plate preparation method and a lithium battery, and relates to the technical field of lithium batteries, and the method comprises the following steps: preparing an ultrathin lithium foil, and attaching the ultrathin lithium foil to a protective film; s2, placing the lithium foil prepared in the step S1 in a gas environment for heat preservation to obtain an artificial SEI film; s3, covering the surface of the negative plate with the artificial SEI film prepared in S2 to obtain a composite negative plate; and S4, selecting the composite negative plate prepared in S3, assembling the composite negative plate, a positive plate, a diaphragm and an electrolyte to form a battery, adjusting the composition and proportion of gas to obtain SEI films with different composition and proportions, transferring the artificial SEI film to the surface of the negative plate, and then assembling the battery, and in the formation stage of the battery, because a layer of SEI film is formed on the negative plate in advance, the SEI film is formed on the surface of the negative plate. Therefore, consumed lithium ions are greatly reduced, and the initial efficiency and capacity of the battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and more specifically, to a method for preparing a negative electrode sheet and a lithium battery. Background Art

[0002] During the formation stage of lithium-ion batteries, lithium ions react with electrolytes on the surface of the negative electrode to form a solid electrolyte interface membrane (SEI membrane). The SEI membrane is composed of a dense inner layer of inorganic lithium compounds and a loose and porous outer layer of organic lithium compounds. It can prevent the electrolyte from directly contacting the negative electrode, reduce the decomposition of the electrolyte, and also prevent Li+ from being co-embedded with solvent molecules. The SEI membrane is an ion conductor that allows lithium ions to be transported through it, enter the graphite surface, and perform lithium deintercalation. It is also an electronic insulator that can reduce internal short circuits. The composition, structure, and stability of the SEI membrane are crucial for lithium-ion batteries.

[0003] However, lithium-ion batteries consume some lithium ions during the formation of SEI films, which reduces the capacity of lithium-ion batteries. In addition, SEI films increase the lithium-ion interface transmission impedance and reduce the dynamics of the entire system. In response to the above problems, the present application provides a solution that can artificially prepare SEI films to reduce the consumption of lithium ions, and at the same time optimize the composition of artificial SEI films, improve the interface lithium ion conductivity, and improve the dynamic performance of lithium-ion batteries. Summary of the invention

[0004] The technical problem to be solved by the present invention is that traditional lithium-ion batteries consume part of the lithium ions in the process of forming SEI film in the formation stage, which reduces the capacity of the lithium-ion battery. In view of the problems existing in the prior art, a method for preparing a negative electrode sheet and a lithium battery are provided.

[0005] The purpose and effect of the present invention are achieved by the following specific technical means: A method for preparing a negative electrode sheet, comprising the following steps:

[0006] S1. Prepare ultra-thin lithium foil and attach it to the protective film;

[0007] S2, placing the lithium foil prepared in S1 in a gas environment for heat preservation to obtain an artificial SEI film;

[0008] S3, covering the surface of the negative electrode sheet with the artificial SEI film prepared in S2 to obtain a composite negative electrode sheet;

[0009] S4, select the composite negative electrode sheet made in S3, and assemble it with the positive electrode sheet, separator, and electrolyte into a battery.

[0010] A further preferred embodiment: in step S1, the method for preparing the ultra-thin lithium foil comprises one or more combinations of vacuum evaporation, vacuum magnetron sputtering, roll calendering, melt coating, plasma grinding, and chemical reagent thinning.

[0011] A further preferred embodiment: the ultra-thin lithium foil has a thickness of 0.1-100 um and a width of 1-200 cm.

[0012] A further preferred solution: in step S1, the protective film includes one or more combinations of PET film, PP film, and PI film.

[0013] A further preferred embodiment: in step S2, the gas environment includes one or more combinations of nitrogen, oxygen, carbon dioxide, argon, sulfur dioxide, fluorine, chlorine, ethylene carbonate vapor, propylene carbonate vapor, diethyl carbonate vapor, dimethyl carbonate vapor, and ethyl methyl carbonate vapor.

[0014] A further preferred embodiment: in step S2, the insulation temperature is 10-80°C and the insulation time is 0.5-100h.

[0015] A further preferred solution: in step S3, the artificial SEI film covering method includes one of roll lamination and thermal transfer or a combination of the two.

[0016] A further preferred solution: in step S3, the negative electrode sheet components include active material, binder, dispersant and conductive agent;

[0017] The active material includes one or more combinations of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbon, silicon oxygen, and lithium titanate.

[0018] A lithium battery, wherein a negative electrode sheet and a positive electrode sheet, a separator and an electrolyte are assembled to form a lithium battery, and the positive electrode sheet components include active materials, a binder, a dispersant and a conductive agent. The positive electrode active materials include but are not limited to a combination of one or more of lithium cobalt oxide, lithium iron phosphate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium vanadate, lithium manganate, lithium nickel oxide, lithium nickel cobalt manganate, lithium-rich manganese-based materials, etc.;

[0019] The diaphragm is one of PVDF coated diaphragm, ceramic diaphragm, PE base film, and PP base film;

[0020] The electrolyte is one of PVDF coated diaphragm, ceramic diaphragm, PE base film and PP base film.

[0021] Beneficial effects of the present invention:

[0022] The present application provides a method for preparing an artificial SEI film and a negative electrode sheet. When a metal lithium foil is placed in different gas environments, SEI films of different compositions can be obtained. For example, when placed in nitrogen, a Li3N film layer can be obtained. When placed in oxygen, a Li2O film layer can be obtained. When placed in a mixed gas of nitrogen and oxygen, a composite SEI film of Li3N and Li2O can be obtained. SEI films of different compositions and proportions can be obtained by adjusting the composition and proportion of the gas. The artificial SEI film is then transferred to the surface of the negative electrode sheet, and then the battery is assembled. In the formation stage of the battery, since the negative electrode has a layer of SEI film in advance, the consumption of lithium ions is greatly reduced, which can improve the initial efficiency and capacity of the battery. In addition, the artificial SEI film is composed of lithium compounds such as Li3N, Li2O, and Li2CO3, which can reduce the interface impedance, enhance the kinetic performance, and improve the electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below in conjunction with the accompanying drawings.

[0024] Figure 1 It is a schematic diagram of the process flow of the present invention;

[0025] Figure 2 This is the XRD pattern of the negative electrode sheet 2 obtained in Example 4 of the present invention;

[0026] Figure 3 Graph showing cycle data of cells 1-5 prepared in Example 6 of the present invention;

[0027] Figure 4 This is a cycle data diagram of battery cell 6-7 prepared in Example 6 of the present invention;

[0028] Figure 5 This is a rate performance diagram of battery cells 1-5 prepared in Example 6 of the present invention;

[0029] Figure 6 This is a rate performance diagram of battery cells 1-5 prepared in Example 6 of the present invention;

[0030] Figure 7 This is a table showing the XRD test results of various SEI films in Examples 2 and 3 of the present invention;

[0031] Figure 8 This is the XRD test table of the negative electrode surface samples in Examples 4 and 5 of the present invention;

[0032] Fig. 9 This is a performance test table of battery cells 1-7 in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, Figure 1-Figure 9The present invention is further described in detail with specific embodiments. The following embodiments are only examples for implementing the present invention. It must be pointed out that the disclosed embodiments do not limit the scope of the present invention. On the contrary, changes and modifications made without departing from the scope of the present invention are all within the scope of patent protection of the present invention.

[0034] See also Figure 1-Figure 9 , a method for preparing a negative electrode sheet, comprising the following steps:

[0035] S1. Prepare ultra-thin lithium foil and attach it to the protective film;

[0036] Furthermore, the method for preparing the ultra-thin lithium foil includes one or more combinations of vacuum evaporation, vacuum magnetron sputtering, roll calendering, melt coating, plasma grinding, and chemical reagent thinning, and the thickness of the ultra-thin lithium foil is 0.1-100um and the width is 1-200cm;

[0037] Furthermore, the protective film includes one or more combinations of PET film, PP film, and PI film;

[0038] S2, placing the lithium foil prepared in S1 in a gas environment for heat preservation at a temperature of 10-80° C. for a time of 0.5-100 h to obtain an artificial SEI film;

[0039] Further, the gas environment includes one or more combinations of nitrogen, oxygen, carbon dioxide, argon, sulfur dioxide, fluorine, chlorine, ethylene carbonate vapor, propylene carbonate vapor, diethyl carbonate vapor, dimethyl carbonate vapor, and ethyl methyl carbonate vapor;

[0040] Furthermore, the artificial SEI film covering method includes one or a combination of roll lamination and thermal transfer;

[0041] S3, covering the surface of the negative electrode sheet with the artificial SEI film prepared in S2 to obtain a composite negative electrode sheet;

[0042] Furthermore, the negative electrode sheet components include active materials, binders, dispersants and conductive agents, wherein the active materials include one or more combinations of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbon, silicon oxygen, and lithium titanate.

[0043] S4, select the composite negative electrode sheet made in S3, and assemble it with the positive electrode sheet, separator, and electrolyte into a battery.

[0044] The composite negative electrode sheet made of the above S3 is assembled with a common positive electrode sheet, a separator, and an electrolyte to form a lithium battery. The components of the positive electrode sheet include active materials, binders, dispersants, and conductive agents. The positive electrode active materials include but are not limited to one or more combinations of lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium vanadate, lithium manganate, lithium nickel oxide, lithium nickel cobalt manganate, lithium-rich manganese-based materials, etc.;

[0045] The diaphragm is one of PVDF coated diaphragm, ceramic diaphragm, PE base film, and PP base film;

[0046] The electrolyte is one of PVDF coated diaphragm, ceramic diaphragm, PE base film and PP base film.

[0047] Example 1

[0048] First, the rollers of the roller calendering equipment are coated with PET to prevent the metal lithium from directly contacting the rollers. Then, a double-roll calendering equipment is used to calender the 120um metal lithium tape to 2um metal lithium foil and attach it to the PET film.

[0049] Example 2

[0050] The metal lithium foil in Example 1 was placed in a mixed gas comprising nitrogen, oxygen and carbon dioxide in a ratio of 6:2:2 at a temperature of 45°C for 24 hours to obtain artificial SEI film 1, SEI film 2, SEI film 3 and SEI film 4, respectively.

[0051] Example 3

[0052] The metal lithium foil in Example 1 was placed in a nitrogen environment, and the insulation temperatures were set to 20°C, 30°C, 40°C, 50°C, 60°C, and 70°C for 24 hours, respectively, to obtain artificial SEI film 5, SEI film 6, SEI film 7, SEI film 8, SEI film 9, and SEI film 10, respectively.

[0053] Example 4

[0054] Artificial graphite, a binder, a dispersant and a conductive agent are mixed, stirred, coated and roll-pressed in a ratio of 95:2:1:2, and a graphite negative electrode sheet 1 is prepared according to a conventional negative electrode sheet preparation process. Then, the artificial SEI film 1, SEI film 2, SEI film 3 and SEI film 4 in Example 2 are transferred to the surface of the graphite negative electrode sheet by a roller lamination process to obtain a composite negative electrode sheet 2, a composite negative electrode sheet 3, a composite negative electrode sheet 4 and a composite negative electrode sheet 5.

[0055] Example 5

[0056] Artificial graphite, silicon carbon, binder, dispersant and conductive agent are mixed, stirred, coated and rolled in a ratio of 75:20:2:1:2, and a graphite and silicon carbon negative electrode sheet 6 is prepared according to a conventional negative electrode sheet preparation process. Then, the artificial SEI film 1 in Example 2 is transferred to the surface of the graphite & silicon carbon negative electrode sheet using a double-roll lamination process to obtain a composite negative electrode sheet 7.

[0057] Example 6

[0058] Positive electrode sheets were prepared using lithium iron phosphate as the positive electrode material, and were matched with negative electrode sheet 1, negative electrode sheet 2, negative electrode sheet 3, negative electrode sheet 4, and negative electrode sheet 5 in Example 4, respectively. Then, wound 3.5Ah soft-pack batteries were prepared according to conventional procedures in the industry, and were recorded as battery cell 1, battery cell 2, battery cell 3, battery cell 4, and battery cell 5. Positive electrode sheets were prepared using nickel cobalt manganese oxide ternary positive electrode material, and were matched with negative electrode sheet 6 and negative electrode sheet 7 in Example 5, respectively. Then, wound 3.5Ah soft-pack batteries were prepared according to conventional procedures in the industry, and were recorded as battery cell 6 and battery cell 7.

[0059] Test example:

[0060] The SEI films in the above-mentioned Examples 2 and 3 were subjected to XRD tests, and the test data are shown in Figure 7 Through test data, it was found that metallic lithium foil would generate different lithium compounds in different gases, Li3N in nitrogen, Li2O in oxygen, Li2CO3 in carbon dioxide, and three lithium compounds, Li3N, Li2O, and Li2CO3, in a mixture of nitrogen, oxygen, and carbon dioxide. As the temperature increases, the SEI film is generated more rapidly. At 40°C, 2um metallic lithium can be completely reacted into Li3N in a nitrogen environment within 24 hours.

[0061] The surface samples of the negative electrode sheets of the above-mentioned Examples 4 and 5 were sampled and XRD test and analysis was performed. The test data are shown in Figure 8 Through the test data, it is found that SEI can be successfully laminated with the electrode to form a dense artificial SEI film on the surface. The XRD data of the negative electrode 2 is as follows Figure 2 As shown, the characteristic peaks of C and Li3N can be clearly detected (In addition: During the test, the sample was prevented from contacting with air and sealed with tape, so Figure 2 In addition, SEI films of different compositions can be selected to be laminated with the negative electrode sheet to obtain composite electrodes of different compositions.

[0062] The electrochemical performance test was carried out on the battery cell of Example 6 above:

[0063] Cycle performance test: soft pack batteries 1-5 are placed in a blue electric test cabinet for charge and discharge test, with a charge and discharge rate of 1.0C and a voltage range of 2.5-3.65V; soft pack batteries 6-7 are placed in a blue electric test cabinet for charge and discharge test, with a charge and discharge rate of 0.5C and a voltage range of 2.5-4.3V;

[0064] Rate performance test: soft-pack batteries 1-5 were placed in a blue-electric test cabinet for charge and discharge tests, with charge rates of 0.33, 0.5, 1.0, 2.0, and 3.0C, discharge rates of 0.5C, and voltage ranges of 2.5-3.65V. soft-pack batteries 6-7 were placed in a blue-electric test cabinet for charge and discharge tests, with charge rates of 0.33, 0.5, 1.0, 2.0, and 3.0C, discharge rates of 0.5C, and voltage ranges of 2.5-4.3V.

[0065] Among them, the cycle data of soft pack batteries 1-5 are as follows Figure 3 As shown, the cycle data of battery 6-7 is as follows Figure 4 As shown in the figure, it can be seen that in the lithium iron phosphate / graphite or ternary / graphite & silicon carbon battery system, the artificial SEI film can improve the battery cycle performance.

[0066] The rate of soft pack battery 1-5 is as follows Figure 5 As shown, the rate of battery 6-7 is as follows Figure 6 As shown in the figure, it can be seen that in the lithium iron phosphate / graphite or ternary / graphite & silicon carbon battery cell system, the artificial SEI film can improve the battery cell rate performance.

[0067] See Figure 3-Figure 6 and Fig. 9 The data shows that the artificial SEI film can reduce the loss of lithium ions in the formation stage and improve the initial coulombic efficiency and capacity of the battery cell. At the same time, the artificial SEI film layer can improve the conductivity of the negative electrode interface, reduce the interface impedance, improve the kinetic performance, and improve the cycle and rate performance.

Claims

1. A method for preparing a negative electrode sheet, characterized in that: The following steps are involved: S1. Prepare ultra-thin lithium foil and attach it to the protective film; S2, placing the lithium foil prepared in S1 in a gas environment for heat preservation to obtain an artificial SEI film; S3, covering the surface of the negative electrode sheet with the artificial SEI film prepared in S2 to obtain a composite negative electrode sheet; S4, select the composite negative electrode sheet made in S3, and assemble it with the positive electrode sheet, separator, and electrolyte into a battery.

2. A method for preparing a negative electrode sheet according to claim 1, characterized in that: In step S1, the method for preparing the ultra-thin lithium foil includes one or more combinations of vacuum evaporation, vacuum magnetron sputtering, roll calendering, melt coating, plasma grinding, and chemical reagent thinning.

3. A method for preparing a negative electrode sheet according to claim 2, characterized in that: The ultra-thin lithium foil has a thickness of 0.1-100 um and a width of 1-200 cm.

4. The method for preparing a negative electrode sheet according to claim 1, characterized in that: In the step S1, the protective film includes one or more combinations of PET film, PP film, and PI film.

5. The method for preparing a negative electrode sheet according to claim 1, characterized in that: In step S2, the gas environment includes one or more combinations of nitrogen, oxygen, carbon dioxide, argon, sulfur dioxide, fluorine, chlorine, ethylene carbonate vapor, propylene carbonate vapor, diethyl carbonate vapor, dimethyl carbonate vapor, and ethyl methyl carbonate vapor.

6. A method for preparing a negative electrode sheet according to claim 1, characterized in that: In step S2, the insulation temperature is 10-80° C. and the insulation time is 0.5-100 h.

7. The method for preparing a negative electrode sheet according to claim 1, characterized in that: In step S3, the artificial SEI film covering method includes one of roll lamination and thermal transfer or a combination of the two.

8. The method for preparing a negative electrode sheet according to claim 1, characterized in that: In step S3, the negative electrode sheet components include active material, binder, dispersant and conductive agent; The active material includes one or more combinations of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbon, silicon oxygen, and lithium titanate.

9. A lithium battery, using a negative electrode sheet made by the method of any one of claims 1 to 8, wherein the negative electrode sheet is assembled with a positive electrode sheet, a separator, and an electrolyte to form a lithium battery, characterized in that: The positive electrode sheet components include active materials, binders, dispersants and conductive agents. The positive electrode active materials include but are not limited to one or more combinations of lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium vanadate, lithium manganate, lithium nickel oxide, lithium nickel cobalt manganate, lithium-rich manganese-based materials, etc. The diaphragm is one of PVDF coated diaphragm, ceramic diaphragm, PE base film, and PP base film; The electrolyte is one of PVDF coated diaphragm, ceramic diaphragm, PE base film and PP base film.

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