Electrochemical device and electronic device

Abstract

The application provides an electrochemical device and an electronic device, wherein the electrochemical device comprises a positive electrode sheet and a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector; the negative electrode active material layer comprises an active material layer and a lithium-containing layer arranged on the surface of the active material layer; and the active material layer comprises SiOC material and graphite. The negative electrode material provided by the application can improve the first cycle coulombic efficiency of the electrochemical device and improve the energy density.

Description

[0001] This application is a divisional application, with its parent application having application number 202180001361.6, an application date of March 30, 2021, and an invention titled "Electrochemical Device and Electronic Device". Technical Field

[0002] This application relates to the field of energy storage technology, and more specifically, to electrochemical devices and electronic devices. Background Technology

[0003] Currently, silicon-based anode materials possess high specific capacity and are considered the most promising next-generation lithium-ion anode materials. However, silicon's low conductivity (>10⁻⁶) 8 The silicon anode material exhibits a volume expansion of approximately 300% during charge and discharge, leading to the formation of an unstable solid electrolyte interphase (SEI) film. During charge and discharge, the silicon anode material pulverizes and falls off the current collector, causing a loss of electrical contact between the active material and the current collector. This results in deteriorated electrochemical performance, capacity decay, and decreased cycle stability, hindering its further application to some extent. Currently, methods to improve the electrochemical performance of silicon materials include combining silicon with carbon materials. Among these, SiOC materials have attracted market attention due to their minimal volume expansion. However, SiOC materials achieve lithium storage through the breaking of Si-O bonds, forming irreversible LiSiO4, resulting in low first-cycle coulombic efficiency and reduced energy density of the electrochemical device. Summary of the Invention

[0004] In view of this, this application proposes an electrochemical device and an electronic device that can improve the first-cycle coulombic efficiency of the electrochemical device and increase the energy density.

[0005] In a first aspect, this application provides an electrochemical device, including a positive electrode and a negative electrode. The negative electrode includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector. The negative active material layer includes an active material layer and a lithium-containing layer located on the surface of the active material layer. The active material layer includes SiOC material and graphite.

[0006] In some feasible implementations, the lithium-containing layer comprises stable lithium metal powder.

[0007] In some feasible embodiments, the electrochemical device satisfies at least one of the following features (1) to (4): (1) The Si2p spectrum obtained by X-ray diffraction analysis of the negative electrode active material layer includes at least one of the following: 101.4 eV ± 0.3 eV, 102.2 eV ± 0.3 eV, 103.1 eV ± 0.3 eV, and 104.40 eV ± 0.3 eV; (2) The binding energy peak of Li was found to be between 55.6 eV ± 0.3 eV by X-ray diffraction analysis of the negative electrode active material layer; (3) The negative electrode active material layer was analyzed by X-ray diffraction, and the negative electrode active material layer has Li 22 Si5 diffraction peaks, Li 22 Ge5 diffraction peak, Li 22 At least one of the following: Sn5 diffraction peak, Li2O diffraction peak, Li2SiO3 diffraction peak, or Li2Si2O5 diffraction peak; (4) The chemical shift values ​​of Si were obtained by analyzing the negative electrode active material layer using solid-state nuclear magnetic resonance (NMR) technology. The chemical shift values ​​of Si included -5ppm±1ppm, -35ppm±1ppm, -75ppm±1ppm, and -100ppm±1ppm. The full width at half maximum (FWHM) K of the chemical shift peak of Si at -5ppm±1ppm satisfies the following relationship: 7ppm <K<28ppm。

[0008] In some feasible embodiments, the electrochemical device satisfies at least one of the following features (5) to (9): (5) The median particle size of the SiOC material and graphite mixed powder is R1μm, and the value of R1 ranges from 0.01 to 50. (6) The median particle size of the stabilized lithium metal powder is R2μm, and the value of R2 ranges from 0.1 to 20; (7) The thickness of the active material layer is D1 μm, and the value of D1 ranges from 40 to 150; (8) The thickness of the lithium-containing layer is D2μm, and the value of D2 ranges from 2 to 20; (9) When the electrochemical device is fully charged, X-ray diffraction reveals that the negative electrode active material layer has Li 15 Diffraction peaks of Si4.

[0009] In some feasible embodiments, the electrochemical device satisfies at least one of the following features (10) to (11): (10) The ratio range of the median particle size R2 of the stable lithium metal powder to the median particle size R1 of the mixed powder of SiOC material and graphite satisfies: 0.01≤R2 / R1≤1; (11) The ratio of the thickness D1 of the active material layer to the thickness D2 of the lithium-containing layer is: 2≤D1 / D2≤20.

[0010] In some feasible embodiments, the electrochemical device satisfies at least one of the following features (12) to (14): (12) The mass ratio of the SiOC material to the graphite is 5:95 to 45:55; (13) The total mass ratio of the SiOC material and the graphite to the mass ratio of the stable lithium metal powder is 1.99 to 9; (14) The graphite includes at least one of natural graphite, artificial graphite, and mesophase carbon microspheres.

[0011] In some feasible embodiments, the electrochemical device satisfies at least one of the following features (15) to (16): (15) The powder conductivity of the negative electrode active material layer is 2.0 S / cm to 30.0 S / cm; (16) The resistance of the negative electrode active material layer is in the range of 0.2Ω to 1.0Ω.

[0012] In some feasible embodiments, the negative electrode active material layer further includes a binder, which includes at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium carboxymethyl cellulose, and potassium carboxymethyl cellulose.

[0013] In some feasible embodiments, the electrochemical device further includes an electrolyte comprising an organic solvent and a lithium salt; The organic solvent includes at least one selected from ethylene carbonate, propylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, propylene carbonate, propyl propionate, or ethyl propionate; and / or, The lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalateborate)borate, or lithium difluorooxalateborate.

[0014] Secondly, this application also provides an electronic device, which includes the electrochemical device described in the first aspect above.

[0015] Compared with the prior art, this application has at least the following beneficial effects: The electrochemical device provided in this application allows the SiOC material in the active material layer and the stable lithium metal powder in the lithium-containing layer to be activated through contact with the electrolyte, providing more active lithium ions to the electrochemical device, replenishing the active lithium ions consumed after irreversible lithium storage in the SiOC material, improving the initial efficiency of the negative electrode material, and increasing the energy density of the battery. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the negative electrode sheet provided in the embodiments of this application; Figure 2 Solid-state NMR spectra of the negative electrode in the electrochemical device provided in the embodiments of this application; Figure 3 A comparison of the first-week coulombic efficiency of the negative electrode sheet provided in this application embodiment before and after adding a lithium-containing layer. Detailed Implementation

[0017] The following are preferred embodiments of the present application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of the embodiments of the present application, and these improvements and modifications are also considered to be within the protection scope of the embodiments of the present application.

[0018] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0019] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more.

[0020] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0021] In a first aspect, this application provides an electrochemical device, including a positive electrode and a negative electrode, wherein the positive electrode includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector; and the negative electrode includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector. The negative electrode active material layer includes an active material layer and a lithium-containing layer located on the surface of the active material layer; the active material includes SiOC material and graphite.

[0022] In this application, the SiOC material in the active material layer and the stable lithium metal powder in the lithium-containing layer can be activated by contact with the electrolyte, providing more active lithium ions for the electrochemical device, replenishing the active lithium ions consumed after irreversible lithium storage in the SiOC material, improving the first-time efficiency of the negative electrode material, and increasing the energy density of the battery.

[0023] As an optional technical solution in this application, SiOC material is uniformly mixed with graphite to form an active material.

[0024] The SiOC material mainly consists of a Si-OC framework and free carbon, which are connected by C-Si bonds. The Si-OC framework can be viewed as the O atoms in a SiO4 tetrahedron being replaced by C atoms. Therefore, the SiOC material can exist in four forms: SiO2C2, SiO3C, SiOC3, and SiO4. SiO2C2 and SiO3C are fully reversible lithium storage forms, SiOC3 is an irreversible lithium storage form (forming SiC4 after lithium storage), and SiO4 is a partially reversible lithium storage form (forming reversible Li2SiO5 and irreversible LiSiO4 after lithium storage). Irreversible LiSiO4 consumes some of the active lithium ions in the electrochemical device. However, the SiOC material exhibits excellent resistance to external forces, and during pyrolysis, it generates abundant nanoporous structures, which improves the material's toughness.

[0025] As an optional technical solution in this application, SiOC materials include, but are not limited to, crystalline, amorphous carbon or mixtures thereof. The morphology of crystalline SiOC materials can be amorphous, lamellar, flake-shaped, spherical, cubic, nanoparticle-shaped, or fibrous, etc.

[0026] As an optional technical solution in this application, the mass ratio of the SiOC material to the graphite is 5:95 to 45:55; specifically, it can be 5:95, 10:90, 15:85, 45:55, etc., or other values ​​within the above range, which are not limited here. In this application, the graphite can include at least one of natural graphite, artificial graphite, and mesophase carbon microspheres, as long as the graphite and SiOC material are uniformly mixed.

[0027] As an optional technical solution of this application, the mass ratio of the active material to the stable lithium metal powder is 1.99 to 9; specifically, it can be 1.99, 2.5, 3.0, 4.5, 5.0, 5.8, 6.7, 8.0 or 9, etc., and of course, it can also be other values ​​within the above range, which are not limited here.

[0028] like Figure 1As shown, the active material layer 11 is located on the surface of the negative electrode current collector 10, and the lithium-containing layer 12 is located on the surface of the active material layer 11. The lithium-containing layer 12 contains stable lithium metal powder.

[0029] As an optional technical solution in this application, the negative electrode current collector includes, but is not limited to: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal. Preferably, the negative electrode current collector is copper foil.

[0030] The thickness of the active material layer 11 is D1μm, and the value of D1 ranges from 40 to 150. Specifically, the thickness of the active material layer 11 can be 40μm, 50μm, 60μm, 80μm, 100μm, 120μm or 150μm, etc., or other values ​​within the above range, which are not limited here.

[0031] The thickness of the lithium-containing layer 12 is D2μm, where D2 ranges from 2 to 20. Specifically, the thickness of the lithium-containing layer 12 can be 2μm, 4μm, 5μm, 6μm, 8μm, 10μm, 12μm, 15μm, 18μm, or 20μm, etc., or other values ​​within the above range, which are not limited here.

[0032] The ratio of the thickness D1 of the active material layer 11 to the thickness D2 of the lithium-containing layer satisfies the following range: 2 ≤ D1 / D2 ≤ 20. The specific ratio of D1 / D2 can be 2, 4, 5, 8, 10, 12, 15, 18 or 20, etc., and of course, it can also be other values ​​within the above range, which are not limited here.

[0033] As an optional technical solution of this application, the stable lithium metal powder may be stable lithium metal powder and / or stable lithium metal compounds. Specifically, the stable lithium metal powder includes elements such as Li, Ge, and Sn.

[0034] As an optional technical solution in this application, the negative electrode active material layer is analyzed by X-ray diffraction, and the negative electrode active material layer has Li 22 Si diffraction peaks, Li 22 Ge diffraction peaks, Li 22 At least one of the following: Sn diffraction peak, Li2O diffraction peak, Li2SiO3 diffraction peak, or Li2Si2O5 diffraction peak.

[0035] As an optional technical solution of this application, the median particle size of the active material is R1μm, and the value of R1 ranges from 0.01 to 50. Specifically, the median particle size of the active material can be 0.01μm, 0.05μm, 0.1μm, 0.5μm, 1μm, 5μm, 10μm, 20μm, 30μm, 40μm or 50μm, etc., or other values ​​within the above range, which are not limited here.

[0036] As an optional technical solution of this application, the median particle size of the stable lithium metal powder is R2μm, and the value of R2 ranges from 0.1 to 20. Specifically, the median particle size of the active material can be 0.1μm, 0.5μm, 1μm, 3μm, 5μm, 8μm, 10μm, 15μm, 18μm or 20μm, etc., and of course it can also be other values ​​within the above range, which are not limited here.

[0037] As an optional technical solution of this application, the ratio range of the median particle size R2 of the stable lithium metal powder to the median particle size R1 of the active material satisfies: 0.01≤R2 / R1≤1; the ratio of R2 / R1 can specifically be 0.01, 0.02, 0.03, 0.05, 0.1, 0.3, 0.5, 0.7, 0.8 or 1, etc., and of course, it can also be other values ​​within the above range, which are not limited here.

[0038] As an optional technical solution in this application, the Si2p spectrum obtained by analyzing the negative electrode active material layer by X-ray diffraction includes at least one of the following binding energy peak positions: 101.4 eV ± 0.3 eV, 102.2 eV ± 0.3 eV, 103.1 eV ± 0.3 eV, and 104.40 eV ± 0.3 eV. That is, each binding energy peak position corresponds to a different form of Si.

[0039] As an optional technical solution in this application, the binding energy peak of Li was found to be between 55.6 eV ± 0.3 eV by analyzing the negative electrode active material layer using X-ray diffraction.

[0040] As an optional technical solution in this application, such as Figure 2 As shown, the chemical shift values ​​of Si were obtained by analyzing the negative electrode active material layer using solid-state nuclear magnetic resonance (NMR) technology. The chemical shift values ​​of Si included -5ppm±1ppm, -35ppm±1ppm, -75ppm±1ppm, and -100ppm±1ppm. Furthermore, the full width at half maximum (FWHM) K of the chemical shift peak at -5ppm±1ppm satisfies the following relationship: 7ppm <K<28ppm。

[0041] As an optional technical solution in this application, when the electrochemical device is in a fully charged state, X-ray diffraction reveals that the negative electrode active material layer has Li... 15 Diffraction peaks of Si4.

[0042] As an optional technical solution in this application, Li can also be observed through high-resolution images obtained by transmission electron microscopy (TEM). 15 Si4 grains, Li2SiO3 grains and Li2Si2O5 grains, Li 15 The interplanar spacing of Si4 grains is approximately 0.2 nm; the interplanar spacing of Li2SiO3 grains is approximately 0.27 nm; and the interplanar spacing of Li2Si2O5 grains is approximately 0.196 nm.

[0043] As an optional technical solution in this application, the negative electrode active material layer includes a binder, which can improve the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the negative electrode current collector. The binder includes at least one of the following: polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium carboxymethyl cellulose, and potassium carboxymethyl cellulose; no specific limitation is imposed herein.

[0044] As an optional technical solution in this application, the negative electrode active material layer also includes conductive materials, including natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, metal fiber, copper, nickel, aluminum, silver or polyphenylene derivatives, etc., which are not limited here.

[0045] As an optional technical solution of this application, the resistance of the negative electrode active material layer is in the range of 0.2Ω to 1.0Ω, specifically 0.2Ω, 0.3Ω, 0.5Ω, 0.6Ω, 0.8Ω, 0.9Ω or 1Ω, etc., or other values ​​within the above range.

[0046] As an optional technical solution of this application, the powder conductivity of the negative electrode active material layer is 2.0S / cm to 30.0S / cm; specifically, it can be 2.0S / cm, 5.0S / cm, 8.0S / cm, 10S / cm, 12S / cm, 15S / cm, 18S / cm, 20S / cm, 25S / cm or 30S / cm, etc., or other values ​​within the above range.

[0047] As an optional technical solution of this application, the electrochemical device also includes a positive electrode plate, which includes a positive current collector and a layer of positive active material located on the positive current collector.

[0048] As an optional technical solution in this application, the positive electrode active material includes at least one of lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary material, lithium iron phosphate, lithium manganese iron phosphate, and lithium manganese oxide.

[0049] As an optional technical solution in this application, the positive electrode active material layer also includes a binder and a conductive material. Understandably, the binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector.

[0050] Specifically, the adhesive includes at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon.

[0051] Specifically, conductive materials include carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0052] As an optional technical solution in this application, the positive current collector includes, but is not limited to, aluminum foil.

[0053] As an optional technical solution of this application, the electrochemical device further includes an electrolyte, which includes an organic solvent, a lithium salt, and additives.

[0054] The organic solvent of the electrolyte according to this application can be any organic solvent known in the prior art that can be used as an electrolyte solvent. There are no limitations on the electrolyte used in the electrolyte according to this application; it can be any electrolyte known in the prior art. The additives of the electrolyte according to this application can be any additives known in the prior art that can be used as electrolyte additives.

[0055] In specific embodiments, the organic solvent includes, but is not limited to, at least one of: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, propyl propionate, or ethyl propionate.

[0056] In a specific embodiment, the lithium salt includes at least one of organic lithium salt or inorganic lithium salt.

[0057] In specific embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalateborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalateborate LiBF2(C2O4) (LiDFOB).

[0058] In a specific embodiment, the concentration of lithium salt in the electrolyte can be from 0.5 mol / L to 3 mol / L.

[0059] As an optional technical solution of this application, the electrochemical device of this application includes, but is not limited to: all types of primary batteries, secondary batteries, fuel cells, solar cells or capacitors.

[0060] In a specific embodiment, the electrochemical device is a lithium secondary battery, wherein the lithium secondary battery includes, but is not limited to: lithium metal secondary battery, lithium-ion battery, lithium polymer secondary battery or lithium-ion polymer secondary battery.

[0061] Secondly, embodiments of this application also provide an electronic device, which includes the electrochemical device described in the fourth aspect above.

[0062] As an optional technical solution in this application, the electronic device includes, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries or lithium-ion capacitors, etc.

[0063] The following uses a lithium-ion battery as an example and combines specific embodiments to illustrate the preparation of a lithium-ion battery. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0064] (1) Preparation of negative electrode sheet SiOC material and graphite were mixed and stirred in a ratio (mass ratio between 5:95 and 45:55). The mixed powder, conductive agent acetylene black, and lithium polyacrylate were stirred in a deionized water solvent system in a ratio of 95:1.2:3.8 for 4 to 36 hours to obtain a uniformly mixed slurry. The slurry was coated onto copper foil and dried at 130°C under vacuum to obtain the initial electrode sheet. Stabilized lithium metal powder is dissolved in toluene and dispersed evenly, wherein the mass ratio of stabilized lithium metal powder to active material (SiOC + graphite) is between 1.99 and 9. Under argon protection, the evenly mixed stabilized lithium metal powder toluene solution is sprayed onto the surface of the initial electrode using an air spray gun and left to stand for 4-36 hours. Then, the electrode is subjected to cold pressing treatment.

[0065] By repeatedly spraying a stable lithium metal powder toluene solution and cold pressing it 1 to 7 times, SiOC / stable lithium metal powder negative electrode sheets were obtained.

[0066] Examples 1 to 16 and Comparative Examples 1 to 6 were prepared according to the above method, and the parameters are shown in Table 1.

[0067] (2) Preparation of positive electrode sheet The positive electrode active material, conductive carbon black, and binder polyvinylidene fluoride are mixed in a weight ratio of 95:2.5:2.5, and N-methylpyrrolidone (NMP) is added. The mixture is stirred evenly under vacuum to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode current collector aluminum foil. After drying, cold pressing, cutting, slitting, and welding of tabs, the positive electrode sheet is obtained.

[0068] (3) Electrolyte In a dry argon atmosphere glove box, LiPF6 was added to a solvent composed of propylene carbonate (PC) and ethylene carbonate (EC) in a weight ratio of 1:1 and mixed thoroughly to obtain an electrolyte, wherein the content of LiPF6 was 1 mol / L.

[0069] (4) Separating membrane Polyethylene porous polymer film is used as the separator.

[0070] (5) Preparation of lithium-ion batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. After welding the tabs, the bare cell is placed in an outer packaging foil aluminum-plastic film. The prepared electrolyte is injected into the dried bare cell. After vacuum sealing, settling, formation, shaping, and capacity testing, a lithium-ion battery is obtained.

[0071] II. Performance Testing of Lithium-ion Batteries: (1) XPS test: The XPS testing equipment used was a Thermo Fisher ESCLAB 250Xi, with Al as the target excitation source, a power of 250 W, and a vacuum level >10⁻⁹ Pa. The binding energy peaks of Si 2p and Li were determined using XPS testing.

[0072] (2) TEM test: Characterization was performed using a JEOL JEM-2010 transmission electron microscope at an operating voltage of 200 kV.

[0073] (3) Solid-state NMR testing: 29 Si SNMR spectra were obtained on an AVANCE III 400 WB wide-cavity solid-state NMR spectrometer, with rotation speeds of 8 kHz corresponding to [missing information]. 29 Si.

[0074] (4) Particle size test: Add approximately 0.02g of powder sample to a 50ml clean beaker, add approximately 20ml of deionized water, and then add a few drops of 1% surfactant to completely disperse the powder in the water. Sonicate the mixture in a 120W ultrasonic cleaner for 5 minutes and test the particle size distribution using a MasterSizer2000.

[0075] (5) Resistance test of the negative electrode active material layer: The resistance of the negative electrode active material layer was tested using the four-probe method. The instrument used for the four-probe method was a precision DC voltage and current source (SB118 type), consisting of four probes, each 1.5 cm long. 1cm wide Two-mm thick copper plates are fixed at equal intervals along a line, with a spacing of L (1-2cm) between the two middle plates. The substrate for fixing the copper plates is an insulating material. During testing, the lower surfaces of the four copper plates are pressed onto the negative electrode being tested (pressure 3000 kg) for 60 seconds. A DC current I is applied to the two end plates, and the voltage V is measured at the two middle plates. The values ​​of I and V are read three times, and the average values ​​Ia and Va are recorded. The value of Va / Ia is the resistance of the active material layer of the negative electrode at the test point. Twelve points are tested on each negative electrode, and the average value is taken.

[0076] (6) Powder conductivity test: A resistivity meter (Suzhou Jinglü Electronics ST-2255A) was used. A 5g powder sample was taken and subjected to constant pressure of 5000kg ± 2kg using an electronic press, maintained for 15-25s. The sample was then placed between the electrodes of the meter. The sample height was h (cm), the voltage across the sample was U, the current was I, and the resistance was R (kΩ). The area of ​​the pressed powder sheet was S = 3.14 cm². 2 According to the formula δ=h / (S) The electronic conductivity of the powder is calculated by R) / 1000, and the unit is S / m.

[0077] (7) First-cycle coulomb efficiency and cyclic expansion rate test: The initial thickness of the lithium-ion battery was measured using a micrometer and designated as H0. The battery was charged at 25°C at a rate of 0.5C to the charging cutoff voltage, then charged at a constant voltage to 0.025C, and finally discharged at a rate of 0.5C to the discharging cutoff voltage. This yielded the first-cycle charging capacity and the first-cycle discharging capacity. The first-cycle coulombic efficiency = first-cycle discharging capacity / first-cycle charging capacity.

[0078] Repeat the above charge-discharge cycle for 400 cycles, and measure the thickness of the lithium-ion battery at this point using a micrometer; this thickness is H1. The expansion rate after 400 cycles is calculated as (H1 - H0) / H0 × 100%.

[0079] Cycle capacity retention rate refers to the discharge capacity at 400 cycles divided by the discharge capacity at the first cycle.

[0080] The preparation process parameters of the negative electrode sheets of Examples 1 to 16 and Comparative Examples 1 to 6 prepared according to the above method are shown in Table 1, the performance parameters of the prepared negative electrode sheets are shown in Table 2, and the performance test results of the lithium batteries prepared from them are shown in Table 3.

[0081] Table 1. Process parameters for preparing negative electrode sheets

[0082] Table 2. Performance parameters of negative electrode sheet

[0083] Table 3. Lithium-ion battery performance parameters

[0084] like Figure 3 As shown, the first-week coulombic efficiency of the negative electrode sheets in Examples 1 to 8 was significantly improved before and after covering with a lithium-containing layer. Covering the surface of the active material layer with a lithium-containing layer can improve the first-week coulombic efficiency of the battery.

[0085] The test data from Examples 1 to 4 illustrate the impact of different SiOC material to graphite ratios on material and cell performance. Under the same preparation process, stable lithium metal powder content, and electrode thickness, the specific capacity of the negative electrode increases with the increase of SiOC material in the active material. However, the increase of SiOC material consumes more active lithium ions, thus reducing the first-cycle coulombic efficiency of the negative electrode.

[0086] The test data from Examples 3, 5 to 7 illustrate the impact of different stirring times on the material and cell performance during the preparation of the negative electrode sheet. With other influencing factors remaining constant, controlling the stirring time within the range of 4 to 36 hours ensures uniform mixing of the materials in the negative electrode slurry. Therefore, different stirring times have little impact on the performance of the negative electrode sheet and the cell.

[0087] The comparison of test data from Examples 3, 8 to 10 illustrates the impact of different settling times on the material and cell performance during the preparation of the negative electrode sheet. With other influencing factors remaining constant, controlling the settling time within the range of 4 to 36 hours ensures stable lithium metal powder coverage on the active material layer. Therefore, different settling times have little impact on the performance of the negative electrode sheet and the cell.

[0088] The comparison of test data from Examples 3, 11 to 13 illustrates the impact of the number of spraying times of the stabilized lithium metal powder toluene solution on the material and cell performance during the preparation of the negative electrode. With other influencing factors remaining constant, the number of spraying times of the stabilized lithium metal powder toluene solution was controlled within the range of 1 to 7 times. As the number of spraying times increased, the content of stabilized lithium metal powder on the surface of the active material layer also increased, and the electrode thickness also increased. This allows the stabilized lithium metal powder to generate more active lithium ions during contact with the electrolyte, thus improving the first-cycle coulombic efficiency of the electrode, and consequently improving both the first-cycle coulombic efficiency and cycle retention rate of the battery.

[0089] The comparison of test data from Examples 3, 14, and 16 illustrates the impact of the ratio between the median particle size of the stabilized lithium metal powder and the median particle size of the active material on the performance of the material and the battery cell during the preparation of the negative electrode sheet. With other influencing factors remaining constant, a larger ratio between the median particle size of the stabilized lithium metal powder and the median particle size of the active material indicates a smaller median particle size of the active material, resulting in a lower expansion rate during cycling; conversely, a smaller ratio indicates a larger median particle size of the active material, resulting in an increased expansion rate during cycling. Therefore, it is necessary to control the ratio between the median particle size of the stabilized lithium metal powder and the median particle size of the active material to improve the battery's cycle stability.

[0090] Although this application discloses preferred embodiments as described above, it is not intended to limit the claims. Any person skilled in the art can make several possible changes and modifications without departing from the concept of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.

Claims

1. An electrochemical device, comprising a positive electrode and a negative electrode, wherein the negative electrode comprises a negative current collector and a negative active material layer disposed on the surface of the negative current collector; characterized in that, The negative electrode active material layer includes an active material layer and a lithium-containing layer located on the surface of the active material layer; the active material layer includes SiOC material and graphite; The electrochemical device further includes an electrolyte, which comprises propylene carbonate and ethylene carbonate.

2. The electrochemical device according to claim 1, characterized in that, The lithium-containing layer comprises stable lithium metal powder.

3. The electrochemical device according to claim 1, characterized in that, It satisfies at least one of the following characteristics (1) to (4): (1) The Si2p spectrum obtained by X-ray diffraction analysis of the negative electrode active material layer includes at least one of the following: 101.4 eV ± 0.3 eV, 102.2 eV ± 0.3 eV, 103.1 eV ± 0.3 eV, and 104.40 eV ± 0.3 eV; (2) The binding energy peak of Li was found to be between 55.6 eV ± 0.3 eV by X-ray diffraction analysis of the negative electrode active material layer; (3) The negative electrode active material layer was analyzed by X-ray diffraction, and the negative electrode active material layer has Li 22 Si diffraction peaks, Li 22 Ge diffraction peaks, Li 22 At least one of the following: Sn diffraction peak, Li2O diffraction peak, Li2SiO3 diffraction peak or Li2Si2O5 diffraction peak; (4) The chemical shift values ​​of Si were obtained by analyzing the negative electrode active material layer using solid-state nuclear magnetic resonance (NMR) technology. The chemical shift values ​​of Si included -5ppm±1ppm, -35ppm±1ppm, -75ppm±1ppm, and -100ppm±1ppm. The full width at half maximum (FWHM) K of the chemical shift peak of Si at -5ppm±1ppm satisfies the following relationship: 50ppm <K<450ppm。 4. The electrochemical device according to claim 1 or 2, characterized in that, It satisfies at least one of the following characteristics (5) to (9): (5) The median particle size of the SiOC material and graphite mixed powder is R1μm, and the value of R1 ranges from 0.01 to 50. (6) The median particle size of the stable lithium metal powder is R2μm, and the value of R2 ranges from 0.1 to 20; (7) The thickness of the active material layer is D1 μm, and the value of D1 ranges from 40 to 150; (8) The thickness of the lithium-containing layer is D2μm, and the value of D2 ranges from 2 to 20; (9) When the electrochemical device is fully charged, X-ray diffraction reveals that the negative electrode active material layer has Li 15 Diffraction peaks of Si4.

5. The electrochemical device according to claim 1 or 2, characterized in that, It satisfies at least one of the following characteristics (10) to (11): (10) The ratio range of the median particle size R2 of the stable lithium metal powder to the median particle size R1 of the mixed powder of SiOC material and graphite satisfies: 0.01≤R2 / R1≤1, preferably, 0.2≤R2 / R1≤1, and even more preferably, 0.2≤R2 / R1≤0.5; (11) The ratio of the thickness D1 of the active material layer to the thickness D2 of the lithium-containing layer is: 2≤D1 / D2≤20.

6. The electrochemical device according to claim 1 or 2, characterized in that, It satisfies at least one of the following characteristics (12) to (14): (12) The mass ratio of the SiOC material to the graphite is 5:95 to 45:55; (13) The total mass ratio of the SiOC material and the graphite to the mass ratio of the stable lithium metal powder is 1.99 to 9; (14) The graphite includes at least one of natural graphite, artificial graphite, and mesophase carbon microspheres.

7. The electrochemical device according to claim 1, characterized in that, It satisfies at least one of the following characteristics (15) to (16): (15) The powder conductivity of the negative electrode active material layer is 2.0 S / cm to 30.0 S / cm; (16) The resistance of the negative electrode active material layer ranges from 0.2Ω to 1.0Ω; (17) The total mass ratio of the SiOC material and the graphite to the mass ratio of the stable lithium metal powder is 2.5 to 4.

5.

8. The electrochemical device according to claim 1, characterized in that, The negative electrode active material layer also includes a binder, which includes at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose, and potassium hydroxymethyl cellulose.

9. The electrochemical device according to claim 1, characterized in that, The electrolyte further includes at least one of diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, propylene carbonate, propyl propionate, or ethyl propionate; and / or, The electrolyte further includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalateborate)borate, or lithium difluorooxalateborate.

10. An electronic device, characterized in that, The electronic device includes the electrochemical device according to any one of claims 1 to 9.

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