A lithium ion battery with a silicon-containing negative electrode, a polymer film loaded with intercalated lithium state graphite, and a preparation method and applications thereof

Abstract

The present application belongs to the technical field of lithium ion batteries, and particularly relates to a lithium intercalated graphite loaded polymer film, a preparation method and application thereof, and a lithium ion battery with a silicon negative electrode. The lithium intercalated graphite loaded polymer film comprises a polymer microporous film and a lithium intercalated graphite layer bonded to any side surface of the polymer microporous film. The lithium intercalated graphite layer is a porous rough coating. The lithium intercalated graphite layer comprises one or more of LiC6, LiC12, and LiC24, which can inhibit the volume expansion of the silicon negative electrode and improve the coulombic efficiency and cycle stability of the lithium ion battery with the silicon negative electrode. 12 18 24 and LiC​​

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a polymer film loaded with lithium-intercalated graphite, its preparation method and application, and a lithium-ion battery containing a silicon anode. Background Technology

[0002] With the rapid development of portable electronic devices and electric vehicles, the research and development of high-performance lithium-ion batteries is crucial. Silicon anodes possess extremely high theoretical specific capacity, more than ten times that of traditional graphite anodes. The high specific capacity and safety of silicon (Si) anodes have attracted widespread attention for their application in high-energy, high-power-density lithium-ion batteries (LIBs). However, silicon particles undergo significant volume expansion during cycling, leading to interfacial side reactions, which in turn reduces the coulombic efficiency (CE) and impairs the cycle stability of lithium-ion batteries. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a polymer film loaded with lithium-intercalated graphite, a method for preparing the same and its application, and a lithium-ion battery with a silicon anode. The polymer film loaded with lithium-intercalated graphite can suppress the volume expansion of the silicon anode and improve the coulombic efficiency and cycle stability of the lithium-ion battery with the silicon anode.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] The present invention provides a polymer film loaded with lithium-intercalated graphite, comprising a polymer microporous membrane and a lithium-intercalated graphite layer bonded to either side of the polymer microporous membrane; the lithium-intercalated graphite layer is a porous rough coating.

[0006] The lithium-intercalated graphite layer contains LiC6 and LiC. 12 LiC 18 and LiC 24 One or more of them.

[0007] Preferably, the polymer microporous membrane is a polypropylene / polyethylene composite microporous membrane.

[0008] Preferably, the pore size of the polymer microporous membrane is 5–200 nm; and the thickness of the polymer microporous membrane is 10–30 μm.

[0009] Preferably, the thickness of the lithium-intercalated graphite layer is 10–30 μm.

[0010] The present invention also provides a method for preparing a polymer film of lithium-intercalated graphite as described in the above technical solution, comprising the following steps:

[0011] After coating a slurry containing graphite and binder onto one side surface of a polymer microporous membrane, the membrane is dried to obtain a polymer membrane coated with graphite.

[0012] In an inert atmosphere, the graphite coating side of the polymer film coated with graphite is brought into contact with a lithium anode and then immersed in an electrolyte to form a galvanic cell. During short-circuit discharge, the graphite coating undergoes lithiation to form a lithium-intercalated graphite layer, thus obtaining the polymer film loaded with lithium-intercalated graphite.

[0013] Preferably, the adhesive comprises one or more of sodium alginate, polyacrylic acid, and polyvinylidene fluoride.

[0014] Preferably, the lithium anode is a lithium metal foil; the thickness of the lithium metal foil is 30–600 μm.

[0015] Preferably, the short-circuit discharge time is 4 to 10 hours.

[0016] The present invention also provides the application of the polymer film of lithium-ion graphite supported by the above-described technical solution or the polymer film of lithium-ion graphite supported by the preparation method described in the above-described technical solution in a lithium-ion battery containing a silicon anode.

[0017] The present invention also provides a lithium-ion battery with a silicon anode, wherein the separator of the lithium-ion battery with a silicon anode is a polymer film of lithium-intercalated graphite supported as described in the above technical solution or a polymer film of lithium-intercalated graphite supported as prepared by the preparation method described in the above technical solution.

[0018] This invention provides a polymer film supported on lithium-intercalated graphite, comprising a polymer microporous membrane and a lithium-intercalated graphite layer bonded to either side of the polymer microporous membrane; the lithium-intercalated graphite layer is a porous, rough coating; the lithium-intercalated graphite layer comprises LiC6 and LiC. 12 LiC 18 and LiC 24 One or more of the following. In the polymer film loaded with lithium-intercalated graphite provided by this invention, the lithium-intercalated graphite layer serves as a pre-lithiation agent for the silicon anode. The lithium-intercalated graphite layer is a porous, rough coating. When the silicon undergoes lithium intercalation and softens to form a lithium-silicon alloy, the lithium-silicon alloy at the interface embeds into the porous, rough coating, thereby suppressing silicon anode particle displacement and crack formation. Furthermore, the silicon anode expands after lithium intercalation, and the relatively hard lithium-intercalated graphite layer (graphite hardens after lithium intercalation) causes the expanded silicon anode and the lithium-intercalated graphite layer to press against each other, effectively limiting the expansion of the silicon anode. Moreover, during cycling, the lithium-intercalated graphite layer can provide additional lithium ions, thereby improving the coulombic efficiency and cycle stability of the lithium-ion battery containing the silicon anode.

[0019] The results of the examples show that when the polymer film (PP / PE@LiC6) with lithium-intercalated graphite provided by the present invention is used as the separator, the initial coulombic efficiency (ICE) of the Si|PP / PE@LiC6|Li coin cell reaches 108.51%, and the electrochemical stability is enhanced. Furthermore, the LiFePO4|PP / PE@LiC6|Si coin cell exhibits an ICE of 93.02% and good electrochemical stability at 0.33C (1C = 160 A·g⁻¹). -1 After 100 cycles, the capacity retention rate is 100.94%, while maintaining an average coulombic efficiency (CE) of 99.83%. This invention provides a safe and easy-to-implement pre-lithiation method for the industrial application of high-energy-density silicon-based batteries. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the synthesis process of the polymer film (PP / PE@LiC6) loaded with lithium-intercalated graphite in Example 1;

[0021] Figure 2 High-resolution SEM image of the polymer film (PP / PE@Gr) coated with graphite in Comparative Example 1 (inset is an optical image);

[0022] Figure 3 High-resolution SEM image of PP / PE@LiC6 in Example 1 (inset is optical image);

[0023] Figure 4 XRD patterns of PP / PE@Gr in Comparative Example 1 and PP / PE@LiC6 in Example 1;

[0024] Figure 5 Raman spectra of PP / PE@Gr in Comparative Example 1 and PP / PE@LiC6 in Example 1;

[0025] Figure 6 To compare the Si|PP / PE|Li coin cell in Application Example 1 at 0.01 mV·s -1 CV curves between 0.01V and 2V (the inset shows a schematic diagram of the structure of a Si|PP / PE|Li coin cell);

[0026] Figure 7 The Si|PP / PE@LiC6|Li coin cell of Application Example 1 was tested at 0.01 mV·s. -1 CV curves between 0.01V and 2V (the inset is a schematic diagram of the structure of a Si|PP / PE@LiC6|Li coin cell);

[0027] Figure 8The first charge-discharge curves of the Si|PP / PE|Li button cell and the Si|PP / PE@LiC6|Li button cell in Application Example 1 are shown for comparison.

[0028] Figure 9 To compare the dQ / dV curves of the Si|PP / PE|Li button cell in Application Example 1 and the Si|PP / PE@LiC6|Li button cell in Application Example 1 during the first cycle;

[0029] Figure 10 To compare the Si|PP / PE|Li coin cell of Application Example 1 and the Si|PP / PE@LiC6|Li coin cell of Application Example 1 at 0.1 A·g -1 up to 2A·g -1 Rate performance diagram under varying current;

[0030] Figure 11 To compare the Si|PP / PE|Li coin cell of Application Example 1 and the Si|PP / PE@LiC6|Li coin cell of Application Example 1 at 0.5 A·g -1 Long-term cycling performance and corresponding coulomb efficiency plots;

[0031] Figure 12 To compare the electrochemical impedance spectroscopy (EIS) diagrams (a) and fitted equivalent circuit diagrams (b) of the Si|PP / PE|Li coin cell of Application Example 1 and the Si|PP / PE@LiC6|Li coin cell of Application Example 1 after 100 cycles;

[0032] Figure 13 Characterization diagrams of surface and thickness variations of the silicon anode in the Si|PP / PE|Li coin cell of Application Example 1 and the Si|PP / PE@LiC6|Li coin cell of Application Example 1;

[0033] Figure 14 To compare the first charge-discharge curves of the LiFePO4|PP / PE|Si coin cell and the LiFePO4|PP / PE@LiC6|Si coin cell in Application Example 2;

[0034] Figure 15 For 0.33C (1C = 160A·g) -1 The following is a comparison chart of the long-term cycle performance and corresponding coulombic efficiency of the LiFePO4|PP / PE|Si coin cell and the LiFePO4|PP / PE@LiC6|Si coin cell in Application Example 2.

[0035] Figure 16 This is a schematic diagram illustrating the evolution of the silicon anode when LiC6 is not coated on the PP / PE separator.

[0036] Figure 17 This is a schematic diagram illustrating the evolution of the silicon anode when LiC6 is coated on a PP / PE separator. Detailed Implementation

[0037] The present invention provides a polymer film loaded with lithium-intercalated graphite, comprising a polymer microporous membrane and a lithium-intercalated graphite layer bonded to either side of the polymer microporous membrane; the lithium-intercalated graphite layer is a porous rough coating.

[0038] The lithium-intercalated graphite layer includes LiC6 and LiC. 12 LiC 18 and LiC 24 One or more of them.

[0039] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0040] The polymer film of lithium-intercalated graphite provided by the present invention includes a polymer microporous membrane.

[0041] In one embodiment, the polymer microporous membrane comprises a polypropylene / polyethylene composite microporous membrane (PP / PE) or a polypropylene diaphragm coated with ceramic particles, specifically a polypropylene / polyethylene composite microporous membrane; the pore size of the polymer microporous membrane is 5–200 nm, specifically 20–100 nm; the thickness of the polymer microporous membrane is 10–30 μm, specifically 20 μm; the model of the polypropylene / polyethylene composite microporous membrane is Canrd 2320.

[0042] The polymer film supported on lithium-intercalated graphite provided by the present invention includes a lithium-intercalated graphite layer bonded to either side of the surface of the polymer microporous membrane.

[0043] In one embodiment, the lithium-intercalated graphite layer is a porous, rough coating.

[0044] In one embodiment, the lithium-intercalated graphite layer comprises LiC6 and LiC2. 12 LiC 18 and LiC 24 One or more of them, specifically LiC6 in this embodiment.

[0045] In one embodiment, the thickness of the lithium-intercalated graphite layer is 10–30 μm, and in a specific embodiment it is 20 μm.

[0046] The lithium-intercalated graphite layer in the polymer film supported on lithium-intercalated graphite provided by this invention serves as a pre-lithiation agent for the silicon anode. This lithium-intercalated graphite layer is a porous, rough coating. When lithium intercalation of silicon results in the formation of a lithium-silicon alloy and subsequent softening, the lithium-silicon alloy at the interface embeds into the porous, rough coating, thereby suppressing particle displacement and crack formation in the silicon anode. Furthermore, the silicon anode expands after lithium intercalation, and the relatively hard lithium-intercalated graphite layer (graphite hardens after lithium intercalation) compresses against the expanded silicon anode, effectively limiting its expansion. Moreover, during cycling, the lithium-intercalated graphite layer can provide additional lithium ions, thereby improving the coulombic efficiency and cycle stability of the lithium-ion battery containing the silicon anode.

[0047] The present invention also provides a method for preparing a polymer film of lithium-intercalated graphite as described in the above technical solution, comprising the following steps:

[0048] After coating a slurry containing graphite and binder onto one side surface of a polymer microporous membrane, the membrane is dried to obtain a polymer membrane coated with graphite.

[0049] In an inert atmosphere, the graphite coating side of the polymer film coated with graphite is brought into contact with a lithium anode and then immersed in an electrolyte to form a galvanic cell. During short-circuit discharge, the graphite coating undergoes lithiation to form a lithium-intercalated graphite layer, thus obtaining the polymer film loaded with lithium-intercalated graphite.

[0050] In this invention, a slurry containing graphite and binder is coated onto one side of a polymer microporous membrane and then dried to obtain a polymer membrane coated with graphite.

[0051] In one embodiment, the graphite is micron-sized graphite powder; the diameter of the micron-sized graphite powder is 10–18 μm, and in a specific embodiment, the diameter (D) of the micron-sized graphite powder is... 50 =12μm; the graphite was provided by Shenzhen Intrinsic Equation Graphene Technology Co., Ltd.

[0052] In one embodiment, the binder includes one or more of sodium alginate, polyacrylic acid, and polyvinylidene fluoride, with sodium alginate being used in a specific embodiment; the mass ratio of graphite to binder is 80-97:3-20, with 90-95:5-10 being used in a specific embodiment; the solvent used in the slurry containing graphite and binder includes one or more of water, N-methylpyrrolidone (NMP), and ethanol, with ethanol being used in a specific embodiment; the mass ratio of solvent to graphite in the slurry containing graphite and binder is 0.5-3:1, with 2:1 being used in a specific embodiment.

[0053] In one embodiment, the coating thickness is 10–30 μm, with 20 μm in a specific example. The present invention does not impose any particular limitation on the coating process, as long as the coating is uniform.

[0054] The coating thickness in this invention is within the above-mentioned range, which can avoid the problem of insufficient lithium source due to an excessively thin coating layer, and also avoid the problem of an excessively thick coating layer, which not only has no effect on improving the first efficiency, but also reduces the overall energy density of the battery.

[0055] In one embodiment, the drying temperature is 40–120°C, and in a specific embodiment it is 60–80°C; the drying time is 5–24 hours, and in a specific embodiment it is 10–20 hours.

[0056] After drying, the process further includes cutting. The present invention does not specifically limit the cutting process; it can be performed according to actual needs. In this embodiment of the invention, the cutting is to obtain a circular piece with a diameter of 17 mm.

[0057] After obtaining the polymer film coated with graphite, the present invention, in an inert atmosphere, contacts the graphite coating side of the polymer film with the lithium anode and then immerses it in the electrolyte to form a galvanic cell and performs short-circuit discharge. The graphite coating undergoes lithiation to form a lithium-intercalated graphite layer, thus obtaining the polymer film loaded with lithium-intercalated graphite.

[0058] In one embodiment, the inert atmosphere is an argon atmosphere; the lithium anode is a lithium metal foil; the thickness of the lithium metal foil is 30–600 μm, specifically 100–500 μm in this embodiment. The concentration of the lithium salt affects the short-circuit discharge rate; if the concentration is too low, the pre-lithiation time needs to be longer.

[0059] In one embodiment, the electrolyte includes a lithium salt, an organic solvent, and an additive; the concentration of the lithium salt in the electrolyte is 0.5–1.5 mol / L, and in a specific embodiment it is 0.6–1 mol / L; the volume of the additive is 3–7% of the volume of the organic solvent, and in a specific embodiment it is 5%.

[0060] In one embodiment, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium tetrafluoroborate (LiBF4), lithium dioxoborate (LiBOB), and lithium difluorooxalate borate (LiODFB), with lithium hexafluorophosphate being a specific example.

[0061] In one embodiment, the organic solvent includes one or more of ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), with ethylene carbonate (EC) and diethyl carbonate (DEC) being used in a specific embodiment; the volume ratio of ethylene carbonate (EC) to diethyl carbonate (DEC) is 0.5-1.5:0.5-1.5, with 1:1 being used in a specific embodiment.

[0062] In one embodiment, the additive includes fluoroethylene carbonate (FEC) and / or vinylene carbonate (VC), with fluoroethylene carbonate being a specific example. The additive can form an interface film (SEI) between the negative electrode and the electrolyte.

[0063] In one implementation, the short-circuit discharge time is 4 to 10 hours, and in a specific embodiment it is 5 to 6 hours.

[0064] If the short-circuit discharge time is too short, the pre-lithiation is insufficient, and the amount of additional lithium ions provided is reduced.

[0065] In this embodiment of the invention, after the graphite-coated polymer film is brought into contact with the lithium anode, it is immersed in the electrolyte to form a primary cell: the graphite-coated polymer film is placed in the positive electrode shell of the lithium-ion battery, ensuring that the lithium anode is in contact with the graphite-coated side of the graphite-coated polymer film; then, electrolyte is added to fully immerse the graphite-coated polymer film and the lithium anode; the lithium-ion battery is a 2032 battery.

[0066] In a polymer film coated with graphite, the graphite layer is the positive electrode and the lithium metal foil is the negative electrode. The two are immersed in an electrolyte to form a galvanic cell and undergo short-circuit discharge. The lithium metal at the negative electrode dissolves, and the graphite layer at the positive electrode is lithiated to form a lithium-intercalated graphite layer, thus obtaining a polymer film loaded with lithium-intercalated graphite.

[0067] The present invention also provides the application of the polymer film of lithium-ion graphite supported by the above-described technical solution or the polymer film of lithium-ion graphite supported by the preparation method described in the above-described technical solution in a lithium-ion battery containing a silicon anode.

[0068] The present invention also provides a lithium-ion battery with a silicon anode, wherein the separator of the lithium-ion battery with a silicon anode is a polymer film of lithium-intercalated graphite supported as described in the above technical solution or a polymer film of lithium-intercalated graphite supported as prepared by the preparation method described in the above technical solution.

[0069] As one embodiment, the preparation method of the silicon anode in the lithium-ion battery containing the silicon anode includes the following steps: dispersing nano-Si, carbon black, and a binder in water, coating the resulting slurry onto a current collector, drying it, and then cutting it to obtain the silicon anode; the particle size of the nano-Si is 50-100 nm, specifically 80 nm in this embodiment; the binder is polyacrylic acid (PAA); the mass ratio of nano-Si, carbon black, and binder is 70-94:20-3:10-3, specifically 8:1:1 in this embodiment; the water is deionized water; the current collector is a copper current collector; the drying temperature is 60-120°C, specifically 80°C in this embodiment; the drying time is 6-24 h, specifically 10 h in this embodiment; the diameter of the silicon (Si) anode is 14 mm; and the coating density in the silicon anode is 1.0 mg·cm³. -2 The present invention does not impose any special limitations on the cutting process; it can be carried out according to actual needs.

[0070] In one embodiment, the positive electrode of the silicon-containing lithium-ion battery is a lithium sheet or a LiFePO4 electrode. The preparation method of the LiFePO4 electrode includes the following steps: dispersing LiFePO4, carbon black, and a binder in an organic solvent; coating the resulting slurry onto a current collector; drying and then cutting to obtain the LiFePO4 electrode; the binder is polyvinylidene fluoride (PVDF); the organic solvent is N-methylpyrrolidone (NMP); the mass ratio of LiFePO4, carbon black, and binder is 70–95:20–2:10–3, specifically 95:2:3 in this embodiment; the current collector is an aluminum current collector; the drying temperature is 90–130°C, specifically 110°C in this embodiment; the drying time is 6–24 hours, specifically 10 hours in this embodiment; the diameter of the LiFePO4 electrode is 12 mm. This invention does not specifically limit the cutting process; it can be carried out according to actual needs.

[0071] In one embodiment, the electrolyte of the lithium-ion battery containing a silicon negative electrode includes a solute, an additive, and a solvent; the solute is LiPF6; the concentration of LiPF6 in the electrolyte is 0.8–1.2 mol / L, and in a specific embodiment it is 1 mol / L; the additive is fluoroethylene carbonate (FEC); the volume of the additive is 5% of the volume of the solvent; the solvent is ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1.

[0072] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0073] Example 1

[0074] (1) Synthesis of a polymer film coated with graphite: A polymer film containing graphite (micrometer-sized graphite powder provided by Shenzhen Intrinsic Equation Graphene Technology Co., Ltd., with a mass ratio of 9:1, was prepared.) 50 A slurry of sodium alginate (SA) binder (using deionized water as the solvent, with a solvent-to-graphite mass ratio of 2:1) was uniformly coated on one side of a polypropylene / polyethylene composite microporous membrane (PP / PE, model Canrd 2320, 20 μm thick, 20 nm pore size). Subsequently, the membrane was dried at 60 °C for 10 h to remove the solvent. Then, circular pieces with a diameter of 17 mm were cut out to obtain a polymer membrane (PP / PE@Gr, graphite coating thickness of 20 μm) coated with graphite.

[0075] (2) Synthesis of polymer film loaded with lithium-intercalated graphite: 1 mol / L lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (v / v = 1:1), and then 5% by volume of fluoroethylene carbonate (FEC) was added as an additive to obtain an electrolyte; in an inert atmosphere glove box, the above-mentioned graphite-coated polymer film was placed in the positive electrode shell of a 2032 battery (lithium-ion battery), ensuring that the lithium metal foil (500 μm thick) was in contact with the graphite coating of the above-mentioned graphite-coated polymer film. Subsequently, the electrolyte was added to fully immerse the lithium metal foil and the graphite-coated polymer film to form a galvanic cell. After short-circuit discharge for 6 hours, the graphite coating was lithiated to form a lithium-intercalated graphite layer, and a polymer film loaded with lithium-intercalated graphite (PP / PE@LiC6, wherein the thickness of the lithium-intercalated graphite layer is 20 μm) was obtained.

[0076] Example 2

[0077] The difference from Example 1 is that the mass ratio of graphite to sodium alginate is 95:5.

[0078] Example 3

[0079] The difference from Example 1 is that the mass ratio of graphite to sodium alginate is 85:15.

[0080] Comparative Example 1

[0081] The graphite-coated polymer film (PP / PE@Gr) prepared in Example 1 was used as a comparative example.

[0082] Comparative Example 2

[0083] The difference from Example 1 is that the polypropylene / polyethylene composite microporous membrane is replaced with a polypropylene microporous membrane.

[0084] Comparative Example 3

[0085] The difference from Example 1 is that the thickness of the graphite coating is 5 μm.

[0086] Comparative Example 4

[0087] The difference from Example 1 is that the thickness of the graphite coating is 50 μm.

[0088] Application Example 1

[0089] Nano-sized Si (80 nm), carbon black, and polyacrylic acid (PAA) were dispersed in deionized water at a mass ratio of 8:1:1. The resulting slurry was coated onto a copper current collector (copper foil current collector) and dried at 80 °C for 10 h. After cutting, a coating with a diameter of 14 mm and a coating density of 1.0 mg·cm³ was obtained. -2 Silicon anode;

[0090] The electrolyte is composed of a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (v / v = 1:1), in which 1 mol / L of LiPF6 is dissolved, and 5% by volume of FEC is added as an additive.

[0091] Using the polymer film (PP / PE@LiC6) of lithium-intercalated graphite prepared in Example 1 as the separator, silicon anode as the negative electrode, lithium sheet as the positive electrode, and the above electrolyte as the assembly, a Si|PP / PE@LiC6|Li coin cell was formed, and the N / P ratio was maintained at 1.15.

[0092] The N / P ratio (Negative / Positive) refers to the ratio of the specific capacity of the negative electrode active material × the surface density of the negative electrode × the content of the negative electrode active material ÷ (specific capacity of the positive electrode active material × surface density of the positive electrode × the content of the positive electrode active material).

[0093] In the half-cell structure, the silicon anode serves as the working electrode, and the lithium metal foil serves as the reference electrode.

[0094] Application Example 2

[0095] The difference from Application Example 1 is that a LiFePO4 electrode is used as the positive electrode to obtain a LiFePO4|PP / PE@LiC6|Si coin cell; the preparation process of the LiFePO4 electrode is as follows:

[0096] LiFePO4, carbon black, and PVDF were dispersed in NMP at a mass ratio of 95:2:3. The resulting slurry was coated onto an aluminum current collector and dried at 110°C for 10 hours. After cutting, a LiFePO4 electrode with a diameter of 12 mm was obtained.

[0097] Comparative Application Example 1

[0098] The difference from Application Example 1 is that the separator was replaced by the polymer film (PP / PE@LiC6) with lithium-intercalated graphite prepared in Example 1 with the polymer film (PP / PE@Gr) with graphite coating in Comparative Example 1, resulting in a Si|PP / PE|Li coin cell.

[0099] Comparative Application Example 2

[0100] The difference from Application Example 2 is that the separator was replaced by the polymer membrane (PP / PE@LiC6) with lithium-intercalated graphite prepared in Example 1 with the polymer membrane (PP / PE@Gr) with graphite coating in Comparative Example 1, resulting in a LiFePO4|PP / PE|Si coin cell.

[0101] Performance testing

[0102] (1) Figure 1 This is a schematic diagram of the synthesis process of the polymer film (PP / PE@LiC6) loaded with lithium-intercalated graphite in Example 1; Figure 2 High-resolution SEM image of the polymer film (PP / PE@Gr) coated with graphite in Comparative Example 1 (inset is an optical image); Figure 3 High-resolution SEM image of PP / PE@LiC6 in Example 1 (inset is optical image); Figure 4 XRD patterns of PP / PE@Gr in Comparative Example 1 and PP / PE@LiC6 in Example 1; Figure 5 The images show the Raman spectra of PP / PE@Gr in Comparative Example 1 and PP / PE@LiC6 in Example 1.

[0103] Depend on Figure 1 It is known that, in an inert atmosphere glove box, lithium metal foil is brought into contact with the graphite-coated side of the PP / PE@Gr separator and completely immersed in the electrolyte. After short-circuit discharge, the PP / PE@LiC6 separator was successfully obtained.

[0104] Depend on Figure 2 and Figure 3 It can be seen that the surface morphology of the prepared PP / PE@Gr and PP / PE@LiC6 separators changed significantly after short-circuit discharge, with the graphite surface transitioning from smooth to rough. Furthermore, from... Figure 2 and Figure 3 Optical images of the PP / PE@Gr and PP / PE@LiC6 separators show that the black graphite coating transforms into brownish-yellow LiC6 during short-circuit discharge.

[0105] pass Figure 4X-ray diffraction (XRD) analysis confirmed the interaction between the graphite coating and the lithium metal foil during short-circuit discharge. The diffraction peaks of the PP / PE@LiC6 separator corresponded well with the LiC6 material (JCPDS No. 34-1320), indicating that LiC6 was successfully formed.

[0106] Raman spectra of PP / PE@Gr and PP / PE@LiC6 separators are as follows: Figure 5 As shown, where I D :I G The ratio decreased from 1.06 to 0.2, indicating a significant increase in graphite defects. This observation further confirms the intercalation of lithium ions within the graphite layer, forming LiC6.

[0107] (2) Electrochemical performance testing: Electrochemical performance was evaluated at 25℃. Constant current charge-discharge performance was measured using a LAND CT2001A system. A CHI 760E electrochemical workstation was used to measure the constant current charge-discharge performance at 0.01 mV·s. -1 The voltage range is 0.01-2V (vs. Li + Cyclic voltammetry curves were obtained at (Li). Electrochemical impedance spectroscopy (EIS) measurements were performed in the frequency range of 0.01 to 105 Hz.

[0108] 1) The electrochemical performance of the Si|PP / PE|Li coin cell of Comparative Application Example 1 and the Si|PP / PE@LiC6|Li coin cell of Application Example 1 were evaluated in the voltage range of 0.01-2V. The results are as follows: Figures 6-11 As shown, where Figure 6 To compare the Si|PP / PE|Li coin cell in Application Example 1 at 0.01 mV·s -1 The CV curves between 0.01V and 2V (the inset shows a schematic diagram of the structure of a Si|PP / PE|Li coin cell). Figure 7 The Si|PP / PE@LiC6|Li coin cell of Application Example 1 was tested at 0.01 mV·s. -1 The CV curves between 0.01V and 2V (the inset shows a schematic diagram of the structure of a Si|PP / PE@LiC6|Li coin cell). Figure 8 To compare the first charge-discharge curves of the Si|PP / PE|Li coin cell and the Si|PP / PE@LiC6|Li coin cell of Application Example 1, Figure 9 To compare the dQ / dV curves of the Si|PP / PE|Li coin cell and the Si|PP / PE@LiC6|Li coin cell of Application Example 1 during the first cycle, Figure 10To compare the Si|PP / PE|Li coin cell of Application Example 1 and the Si|PP / PE@LiC6|Li coin cell of Application Example 1 at 0.1 A·g -1 up to 2A·g -1 Rate performance diagram under varying current. Figure 11 To compare the Si|PP / PE|Li coin cell of Application Example 1 and the Si|PP / PE@LiC6|Li coin cell of Application Example 1 at 0.5 A·g -1 The long-term cycling performance and corresponding coulomb efficiency plots are shown below.

[0109] exist Figure 6 In the figure, the oxidation peaks observed at potentials of 0.205 V and 0.548 V correspond to the dealloying process of LixSi, while the reduction peaks observed at potentials of 0.125 V and 0.665 V correspond to the formation of the lithiation reaction of LixSi alloy and the decomposition of electrolyte into a solid electrolyte interphase (SEI) film, respectively.

[0110] Figure 7 The CV peaks at 0.417 V and 0.654 V indicate that the polarization of the Si|PP / PE@LiC6|Li coin cell is significantly reduced compared to the Si|PP / PE|Li coin cell. Furthermore, the absence of any observable electrolyte decomposition peaks suggests the formation of an SEI on the anode of the Si|PP / PE@LiC6|Li coin cell.

[0111] Figure 8 The two samples were compared at 0.1 A·g -1 The initial charge-discharge curves revealed that the initial coulombic efficiency (CE) of the Si|PP / PE@LiC6|Li coin cell was significantly higher than that of the Si|PP / PE|Li coin cell (90.40%), reaching 108.51%. Furthermore, the discharge capacity of the Si|PP / PE@LiC6|Li coin cell (3019 mAh·g) was also significantly higher. -1 The discharge capacity exceeds that of Si|PP / PE|Li coin cells (2344 mAh·g). -1 ).

[0112] The differential capacity diagram (dQ / dV) of Si|PP / PE|Li coin cells and Si|PP / PE@LiC6|Li coin cells is shown below. Figure 9 As shown, compared with Si|PP / PE|Li coin cells, the peak separation potential of Si|PP / PE@LiC6|Li coin cells is reduced by 26.5 mV. This indicates that the PP / PE@LiC6 separator effectively alleviates electrochemical polarization, consistent with the improved rate performance of Si|PP / PE@LiC6|Li coin cells. Figure 10 ).

[0113] At 0.5A·g -1 The cycle performance of Si|PP / PE|Li coin cells and Si|PP / PE@LiC6|Li coin cells was compared at different current densities. Figure 11 As shown in the results, the Si|PP / PE|Li coin cell exhibits rapid capacity decay after 30 cycles, lower than the Si|PP / PE@LiC6|Li coin cell (capacity retention of 61.21% after 100 cycles). In contrast, the Si|PP / PE@LiC6|Li coin cell demonstrates excellent cycle stability, with a capacity retention of 77.93% after 100 cycles. Furthermore, the reversible capacity of the Si|PP / PE@LiC6|Li coin cell begins to increase after 20 cycles and then remains stable with increasing cycle number. This behavior can be attributed to the volume expansion of Si particles, leading to enhanced connectivity between the silicon anode and the PP / PE@LiC6 separator, resulting in higher capacity release. Moreover, the average CE of the Si|PP / PE|Li coin cell and the Si|PP / PE@LiC6|Li coin cell are 96.82% and 99.08%, respectively, indicating that the PP / PE@LiC6 separator can continuously provide an additional lithium source during cycling.

[0114] 2) Figure 12 To compare the Si|PP / PE|Li coin cell of Application Example 1 and the Si|PP / PE@LiC6|Li coin cell of Application Example 1 after 100 cycles, the electrochemical impedance spectroscopy (EIS) diagram (a) and the fitted equivalent circuit diagram (b) are shown.

[0115] Depend on Figure 12 As shown in (a), the resistances Rs, RSEI, and Rct of the Si|PP / PE|Li coin cell are 9.0Ω, 136.4Ω, and 209.5Ω, respectively. In stark contrast, the resistances Rs, RSEI, and Rct of the Si|PP / PE@LiC6|Li coin cell are 8.6Ω, 55.9Ω, and 8.2Ω, respectively. Notably, after 100 cycles, the Rct of the Si|PP / PE@LiC6|Li coin cell decreased by two orders of magnitude compared to the Si|PP / PE|Li coin cell; this finding further confirms the enhanced connectivity between the silicon anode and the LiC6 layer using the PP / PE@LiC6 separator after cycling.

[0116] 3) The surface and thickness variations of the silicon anode in the Si|PP / PE|Li coin cell of Application Example 1 and the Si|PP / PE@LiC6|Li coin cell of Application Example 1 were characterized, and the results are as follows: Figure 13As shown, the SEM images are top view of the silicon anode of Si|PP / PE|Li coin cells (a) and Si|PP / PE@LiC6|Li coin cells (b) after 100 cycles; the SEM cross-sectional images are of the silicon anode of Si|PP / PE|Li coin cells (c) and Si|PP / PE@LiC6|Li coin cells (d) after 100 cycles; the cross-sectional CT images are of the silicon anode of Si|PP / PE|Li coin cells (e) and Si|PP / PE@LiC6|Li coin cells (f) after 100 cycles; and the pore network models of the silicon anode of Si|PP / PE|Li coin cells (g) and Si|PP / PE@LiC6|Li coin cells (h) after 100 cycles are shown.

[0117] Figure 13 The top-view SEM image in (a) shows obvious cracking in the cycled silicon anode of the Si|PP / PE|Li coin cell. In contrast, Figure 13 (b) shows that the silicon anode of the Si|PP / PE@LiC6|Li coin cell maintains a relatively intact electrode structure after 100 cycles, without the formation of any cracks.

[0118] Figure 13 The SEM cross-sectional image in (c) confirms that after 100 cycles, the silicon anode of the Si|PP / PE|Li coin cell exhibits Si particle displacement and electrode cracking. However, due to the presence of a LiC6 coating on the PP / PE separator, [further details are needed]. Figure 13 In the case of dense expansion shown in (d), no electrode cracking was observed after 100 cycles. Figure 13 (e) and Figure 13 Compared with the cross-sectional computed tomography (CT) images in the middle (f) section, it is also shown that the PP / PE@LiC6 separator effectively protects the integrity of the silicon anode.

[0119] also, Figure 13 (g) and Figure 13 The figures (h) show the pore network models of the silicon anode after 100 cycles for Si|PP / PE|Li coin cells and Si|PP / PE@LiC6|Li coin cells, respectively. Furthermore, the quantitative evaluation results of the pore throat structure (Table 1) confirm that, compared with the Si|PP / PE|Li coin cell, the pore size and pore volume of the silicon anode in the Si|PP / PE@LiC6|Li coin cell decrease after 100 cycles. This indicates that the LiC6 layer on the PP / PE separator effectively suppresses the volume expansion of the silicon anode during cycling. Table 1: Quantitative Evaluation Results of the Pore Throat Structure of the Silicon Anode in Si|PP / PE|Li Coin Cells and Si|PP / PE@LiC6|Li Coin Cells.

[0120] project <![CDATA[PP / PE100 th ]]> <![CDATA[PP / PE@LiC6100 th ]]> Maximum pore radius 9.21μm 7.83μm Average pore radius 1.74μm 1.60μm Maximum throat radius 5.77μm 5.38μm Average laryngeal radius 0.92μm 0.78μm Maximum larynx length 18.37μm 33.12μm Average larynx length 4.2μm 3.53μm Maximum pore-throat ratio 17.5 14.01 Average pore-throat ratio 2.11 2.18 Maximum pore volume <![CDATA[47309μm 3 ]]> <![CDATA[44816μm 3 ]]> Average pore volume <![CDATA[726.75μm 3 ]]> <![CDATA[552.32μm 3 ]]> Maximum laryngeal volume <![CDATA[3981μm 3 ]]> <![CDATA[2758μm 3 ]]> Average laryngeal volume <![CDATA[49.73μm 3 ]]> <![CDATA[18.36μm 3 ]]> Maximum coordination number 32 64 Mean coordination number 5 8

[0121] 4) The electrochemical performance of the LiFePO4|PP / PE|Si coin cells prepared in Example 2 and the LiFePO4|PP / PE@LiC6|Si coin cells prepared in Example 2 were evaluated in the voltage range of 2.2-4.0V (N / P=1.15). Figure 14 To compare the first charge-discharge curves of the LiFePO4|PP / PE|Si coin cell and the LiFePO4|PP / PE@LiC6|Si coin cell in Application Example 2, Figure 15 For 0.33C (1C = 160A·g) -1 The following graph compares the long-term cycle performance and corresponding coulombic efficiency of the LiFePO4|PP / PE|Si coin cell and the LiFePO4|PP / PE@LiC6|Si coin cell from Application Example 2. Figure 16 This is a schematic diagram illustrating the evolution of the silicon anode without LiC6 coating on the PP / PE separator. Figure 17 This is a schematic diagram illustrating the evolution of the silicon anode when LiC6 is coated on a PP / PE separator.

[0122] Figure 14 The two samples were compared at 0.1C (1C = 160 A·g). -1 The initial charge-discharge curves under different conditions revealed that the initial charge-discharge (CE) of the LiFePO4|PP / PE@LiC6|Si coin cell (93.02%) was significantly higher than that of the LiFePO4|PP / PE|Si coin cell (80.97%). Furthermore, the charging capacity of the LiFePO4 cathode in the LiFePO4|PP / PE@LiC6|Si coin cell (155 mAh·g) was significantly higher. -1 The capacity is significantly greater than that of LiFePO4|PP / PE|Si coin cells (126mAh·g). -1 The cycling performance of LiFePO4|PP / PE|Si coin cells and LiFePO4|PP / PE@LiC6|Si coin cells at a current density of 0.33C was compared. Figure 15As shown in the results, after 100 cycles, the LiFePO4|PP / PE|Si coin cell exhibits rapid capacity decay, with a capacity retention of only 28.22%. In contrast, the LiFePO4|PP / PE@LiC6|Si coin cell demonstrates excellent cycle stability, maintaining a capacity retention of 100.94% after 100 cycles. Furthermore, the average CE values ​​of the LiFePO4|PP / PE@LiC6|Si coin cell and the LiFePO4|PP / PE|Si coin cell are 99.83% and 98.38%, respectively, indicating that the presence of LiC6 on the PP / PE@LiC6 separator ensures a continuous supply of additional lithium during cycling.

[0123] Figure 16 and Figure 17 The evolution of silicon anodes with and without a LiC6 layer on a PP / PE separator is described separately. Clearly, without a LiC6 layer, the silicon anode undergoes uncontrolled expansion during cycling, leading to significant changes in Si particle position, promoting electrode cracking, and causing debonding of the copper foil current collector from the Si particles, forming dead Si. Furthermore, excessive SEI growth hinders electron transfer between Si particles, resulting in capacity decay. Conversely, coating the PP / PE separator with a LiC6 layer allows for dense expansion of the silicon anode, effectively solving the problems of particle displacement and electrode cracking, while also providing additional lithium ions during cycling.

[0124] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A lithium-ion battery containing a silicon anode, characterized in that, The separator of the lithium-ion battery containing silicon negative electrode is a polymer membrane loaded with lithium-intercalated graphite. The polymer membrane loaded with lithium-intercalated graphite includes a polymer microporous membrane and a lithium-intercalated graphite layer bonded to either side of the polymer microporous membrane. The lithium-intercalated graphite layer is a porous rough coating. The lithium-intercalated graphite layer has the composition of LiC6; The polymer microporous membrane is a polypropylene / polyethylene composite microporous membrane; The polymer microporous membrane has a pore size of 5–200 nm and a thickness of 10–30 μm. The thickness of the lithium-intercalated graphite layer is 10–30 μm.

2. The lithium-ion battery with a silicon-containing negative electrode according to claim 1, characterized in that, The method for preparing the polymer film of lithium-intercalated graphite includes the following steps: After coating a slurry containing graphite and binder onto one side surface of a polymer microporous membrane, the membrane is dried to obtain a polymer membrane coated with graphite. In an inert atmosphere, the graphite coating side of the polymer film coated with graphite is brought into contact with a lithium anode and then immersed in an electrolyte to form a galvanic cell. During short-circuit discharge, the graphite coating undergoes lithiation to form a lithium-intercalated graphite layer, thus obtaining the polymer film loaded with lithium-intercalated graphite.

3. The lithium-ion battery with a silicon-containing negative electrode according to claim 2, characterized in that, The adhesive includes one or more of sodium alginate, polyacrylic acid, and polyvinylidene fluoride.

4. The lithium-ion battery with a silicon-containing negative electrode according to claim 2, characterized in that, The lithium anode is a lithium metal foil; the thickness of the lithium metal foil is 30–600 μm.

5. The lithium-ion battery with a silicon-containing negative electrode according to claim 2, characterized in that, The short-circuit discharge time is 4 to 10 hours.

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