Electrochemical device and electronic equipment

Abstract

The present application discloses an electrochemical device and an electronic device. The electrochemical device includes an electrolyte and a negative electrode sheet; the electrolyte includes lithium bis(fluorosulfonyl)imide, an organic polymer monomer, a compound of Formula I, and an organic solvent; the negative electrode sheet includes a silicon-based material; based on the mass of the electrolyte, the mass percentage of the compound of Formula I is denoted as m%, the mass percentage of the organic solvent is denoted as n%, and the mass percentage of lithium bis(fluorosulfonyl)imide is denoted as p%, satisfying: 20 ≤ m ≤ 70, 15 ≤ n ≤ 50, 7 ≤ p ≤ 40, and 0.25 ≤ p / (n + p) ≤ 0.56. Through the above electrolyte system, the present application can improve the cycling performance and rate performance of the silicon-based electrochemical device.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly relates to an electrochemical device and an electronic device. Background Art

[0002] With the wide application of lithium-ion batteries in fields such as mobile phones, laptops, drones, and electric vehicles, the requirements for the energy density of lithium-ion batteries are getting higher and higher. However, the existing graphite anode materials and electrolyte systems are difficult to meet the requirements of high energy density. The theoretical specific capacity of silicon materials is about 4200 mAh / g, which is much higher than that of graphite materials (about 372 mAh / g). Silicon materials have become ideal anode materials for high-energy-density lithium-ion batteries. However, silicon materials have a large volume expansion during charge and discharge processes, especially during high-rate charging, their volume expands rapidly, which easily causes damage to the solid electrolyte interface film (SEI) on the anode, resulting in continuous consumption and decomposition of the electrolyte on its surface, thereby leading to serious attenuation of the cycle capacity and restricting the wide application of silicon materials in lithium-ion batteries. Summary of the Invention

[0003] In view of this, the present application provides an electrochemical device and an electronic device to improve the cycle performance and rate performance of silicon-based high-energy-density lithium-ion batteries.

[0004] In a first aspect, the present application provides an electrochemical device, including an electrolyte and a negative electrode sheet. The electrolyte includes lithium bis(fluorosulfonyl)imide, an organic polymer monomer, a compound of Formula I, and an organic solvent;

[0005]

[0006] Wherein, R1 to R6 are each independently selected from hydrogen, fluorine, a C1-C 12 , 12 , 12 alkyl group which may be fluorine-substituted or unsubstituted, a C1-C 12 alkoxy group which may be fluorine-substituted or unsubstituted, a C1-C 12 oxyalkyl group which may be fluorine-substituted or unsubstituted. Two adjacent groups among R1 to R6 may optionally be connected to form a ring, and at least one of R1 to R6 contains fluorine; the negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material. Based on the mass of the electrolyte, the mass percentage content of the compound of Formula I is denoted as m%, the mass percentage content of the organic solvent is denoted as n%, and the mass percentage content of lithium bis(fluorosulfonyl)imide is denoted as p%, satisfying: 20 ≤ m ≤ 70, 15 ≤ n ≤ 50, 7 ≤ p ≤ 40, and 0.25 ≤ p / (n + p) ≤ 0.56.

[0007] The present application meets the above limitations by regulating the electrolyte system in the silicon-based electrochemical device, so that the compound of Formula I in the electrolyte can cooperate with the lithium salt lithium bis(fluorosulfonyl)imide (LiFSI) and the organic solvent. On the one hand, the compound of Formula I can reduce the viscosity of the electrolyte, which is beneficial to reducing the ionic transport impedance between the negative electrode active material and the electrolyte, thereby improving the kinetic performance of the electrochemical device. At the same time, it can make the electrochemical device not prone to grow lithium dendrites during the charge-discharge cycle, avoiding the increase of polarization, and thus improving the cycle performance of the electrochemical device. On the other hand, when the contents of each component meet the above limitations, it can promote the in-situ formation of a uniform and dense negative electrode solid electrolyte interface film (SEI film) rich in LiF on the surface of the negative electrode by the anion in lithium bis(fluorosulfonyl)imide, enhancing the mechanical strength of the protective film, so that the SEI film can adapt to the large volume change of the silicon-based material; at the same time, the organic polymer monomer can in-situ polymerize on the surface of the negative electrode to form an organic polymer, which can enhance the flexibility of the SEI film and the stability of the interface between silicon-based material particles, reducing the risk of SEI film rupture and increasing impedance between silicon-based material particles during the cycle, thereby further improving the cycle performance of the electrochemical device.

[0008] Exemplarily, in some embodiments, each of R1 to R6 is independently selected from hydrogen, fluorine, C1-C3 alkyl substituted or unsubstituted with fluorine, C1-C3 alkoxy substituted or unsubstituted with fluorine, and C1-C3 oxyalkyl substituted or unsubstituted with fluorine. Exemplarily, in some embodiments, the mass percentage content m% of the compound of Formula I is 20%, 25%, 30%, 40%, 50%, 55%, 60%, 70% or a range composed of any two of the above values. In some embodiments, 25 ≤ m ≤ 50. Exemplarily, in some embodiments, the mass percentage content n% of the organic solvent is 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or a range composed of any two of the above values. In some embodiments, 25 ≤ n ≤ 40. Exemplarily, in some embodiments, the mass percentage content p% of the lithium bis(fluorosulfonyl)imide is 7%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or a range composed of any two of the above values. In some embodiments, 15 ≤ p ≤ 35. Exemplarily, in some embodiments, p / (n + p) is 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.56 or a range composed of any two of the above values. In some embodiments, 0.3 ≤ p / (n + p) ≤ 0.45.

[0009] In some embodiments, based on the mass of the electrolyte, the mass percentage content of the organic polymer monomer is denoted as q%, satisfying: 0.5 ≤ q ≤ 20. By further controlling the mass percentage content q% of the organic polymer monomer within the above range, on the one hand, the protection effect on the silicon-based material can be enhanced, preventing the rupture and decomposition of the SEI film during cycling. On the other hand, it can prevent the protective film formed by the polymerization of the organic polymer monomer from being too thick, resulting in insufficient liquid components in the electrolyte and too large impedance of the electrochemical device, so that the electrochemical device can take into account good fast charge and discharge capabilities and long cycle performance. Exemplarily, in some embodiments, the mass percentage content q% of the organic polymer monomer is 0.5%, 1%, 3%, 5%, 10%, 15%, 20% or the range composed of any two of the above values. In some embodiments, 1 ≤ q ≤ 15.

[0010] In some embodiments, 0.01 ≤ q / (q + n) ≤ 0.4. When q / (q + n) is within the above range, it is beneficial for the organic polymer monomer to form a uniform film on the surface of the negative electrode active material, thereby improving the cycle performance of the electrochemical device. Exemplarily, in some embodiments, q / (q + n) is 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, 0.2, 0.3, 0.4 or the range composed of any two of the above values. In some embodiments, 0.02 ≤ q / (q + n) ≤ 0.3.

[0011] In some embodiments, the organic polymer monomer includes at least one of acrylate polymer monomers, unsaturated carbonate polymer monomers, olefin polymer monomers, unsaturated ether polymer monomers or heterocyclic polymer monomers.

[0012] In some embodiments, the acrylate polymer monomer includes at least one of the compounds of formula II;

[0013]

[0014] Among them, R7 is selected from any one of hydrogen and C1-C5 alkyl, and R8 is selected from any one of C1-C5 alkyl. Optionally, R7 is selected from any one of hydrogen and C1-C3 alkyl, and R8 is selected from any one of C1-C3 alkyl.

[0015] In some embodiments, the unsaturated carbonate polymer monomer includes at least one of the compounds of formula III or vinylene carbonate;

[0016]

[0017] Among them, R9 is selected from any one of C2-C4 alkenyl.

[0018] In some embodiments, the olefinic polymerization monomer includes at least one of the compounds of Formula IV;

[0019]

[0020] wherein R 10 ~R 13 are each independently selected from hydrogen, fluorine, cyano, fluorine-substituted or unsubstituted C1-C3 alkyl, and any one of the groups represented by Formula a;

[0021]

[0022] In some embodiments, the unsaturated ether polymerization monomer includes at least one of the compounds of Formula V;

[0023]

[0024] wherein R 14 and R 15 are each independently selected from hydrogen, C1-C3 alkyl, or any one of the groups represented by Formula b, and at least one of R 14 and R 15 is selected from the groups represented by Formula b;

[0025]

[0026] R 16 is selected from C1-C3 alkylene, and n is an integer from 0 to 3.

[0027] In some embodiments, the heterocyclic polymerization monomer includes at least one of ethylene oxide, propylene oxide, or dioxolane.

[0028] In some embodiments, the organic solvent includes at least one of saturated carbonate solvents or saturated carboxylate solvents. In some embodiments, the saturated carbonate solvents include at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, or propylene carbonate. In some embodiments, the saturated carboxylate solvents include at least one of ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl butyrate, ethyl difluoroacetate, difluoroethyl acetate, ethyl trifluoroacetate, trifluoroethyl acetate, or methyl trifluoropropionate.

[0029] In this application, the in-situ polymerization of the polymerization monomer can be initiated during the formation charging process of the electrochemical device, or can be initiated by an initiator during the heating process in the formation process. In some embodiments, the electrolyte further includes an initiator. The introduction of the initiator can promote the polymerization and film formation of the organic polymerization monomer on the surface of the negative electrode active material, improve the uniformity and compactness of the film formation, and reduce the risks of SEI film rupture and increased impedance between silicon-based material particles during the cycling process.

[0030] In some embodiments, the initiator includes at least one of a peroxide initiator, an azo initiator, or a redox initiator. In some embodiments, the initiator includes at least one of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, benzoyl peroxide, or methyl ethyl ketone peroxide.

[0031] In some embodiments, based on the mass of the electrolyte, the mass percentage content of the initiator is 0.01% to 2%. Exemplarily, the mass percentage content of the initiator is 0.01%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range composed of any two of the above values. In some embodiments, the mass percentage content of the initiator is 0.1% to 1%.

[0032] In some embodiments, the compound of Formula I includes at least one of the following compounds:

[0033]

[0034] In some embodiments, the negative electrode active layer further includes an inorganic solid electrolyte. The inorganic solid electrolyte has good ionic conductivity and mechanical stability, can enhance the protection of the surface of the negative electrode active material. At the same time, the protective film formed by the in-situ polymerization of the organic polymerization monomer in the electrolyte on the negative electrode surface can effectively improve the interfacial stability between the inorganic solid electrolyte and the negative electrode active material, inhibit the impedance growth of the negative electrode plate during the cycling process, and thus further improve the kinetic performance and cycling stability of the electrochemical device.

[0035] In some embodiments, based on the mass of the negative electrode active layer, the mass percentage content of the inorganic solid electrolyte is denoted as s%, satisfying: 0.1 ≤ s ≤ 10. Exemplarily, in some embodiments, the mass percentage content s% of the inorganic solid electrolyte is 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 8%, 10%, or a range composed of any two of the above values. In some embodiments, 0.2 ≤ s ≤ 5.

[0036] In some embodiments, the inorganic solid electrolyte includes at least one of an oxide solid electrolyte or a sulfide solid electrolyte.

[0037] In some embodiments, the inorganic solid electrolyte includes at least one of lithium germanium aluminum phosphate, lithium titanium aluminum phosphate, or lithium lanthanum zirconium composite oxide.

[0038] In some embodiments, the oxide solid electrolyte includes at least one of Formulas VI to VII;

[0039] Li 1+x A x B 2-x (PO4)3, Formula VI

[0040] wherein A is selected from at least one of Al, Y, Ga, Cr, In, Fe, Se, or La, B is selected from at least one of Ti, Ge, Ta, Zr, Sn, Fe, V, or Hf, and 0 < x ≤ 0.7; for example, the substance represented by Formula VI can be Li 1.5 Al 0.5 Ge 1.5 (PO4)3 (LAGP), Li 1.5 Al 0.5 Ti 1.5 (PO4)3 (LATP), or at least one of them.

[0041] Li Z A'3B'2O 12 Formula VII

[0042] wherein A' is selected from at least one of La, Ca, Sr, Ba, or K, B' is selected from at least one of Zr, Ta, Nb, or Hf, and 6 ≤ Z ≤ 7; for example, the substance represented by Formula VII can be Li7La3Zr2O 12 (LLZO), Li 6.5 La3Zr 1.5 Ta 0.5 O 12 (LLZTO), or at least one of them.

[0043] In some embodiments, the sulfide solid electrolyte contains lithium. The sulfide solid electrolyte includes at least one of lithium germanium phosphorus sulfur (LGPS), lithium phosphorus sulfur (LPS), lithium phosphorus sulfur chlorine (LPSCl), lithium tin phosphorus sulfur (LSnPS), lithium silicon phosphorus sulfur (LSiPS), lithium germanium silicon phosphorus sulfur (LGSiPS), lithium aluminum phosphorus sulfur (LAPS), lithium germanium sulfur (LGS), or lithium silicon sulfur (LSiS).

[0044] In some embodiments, the negative electrode active layer further includes an organic polymer formed by polymerization of the organic polymer monomer, and the organic polymer connects the silicon-based material and the inorganic solid electrolyte. The organic polymer is generated by in-situ polymerization of the organic polymer monomer in the electrolyte, and connects the silicon-based material and the inorganic solid electrolyte together, which can effectively improve the reliability of the connection between the inorganic solid electrolyte and the silicon-based material, inhibit the impedance growth of the negative electrode plate during the cycle, and improve the interface stability of the negative electrode plate, thereby improving the cycle performance of the electrochemical device.

[0045] In some embodiments, the silicon-based material includes at least one of silicon, silicon-carbon material, and silicon-oxygen material. In some embodiments, the silicon-carbon material also contains oxygen. In some embodiments, the silicon-oxygen material includes SiO w ; Among them, 0.5≤w≤1.5.

[0046] In some embodiments, the electrolyte further includes fluoroethylene carbonate (FEC). By further introducing fluoroethylene carbonate, the anions in LiFSI can form a protective film on the negative electrode surface with an inner layer of an inorganic layer rich in LiF and an outer layer of an organic layer, thereby improving the interfacial compatibility between the inorganic layer rich in LiF and the organic polymer formed by in-situ polymerization of the organic polymer monomer, thereby enhancing the overall stability of the SEI film and further improving the cycle performance of the electrochemical device.

[0047] In some embodiments, based on the mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is 0.1% to 10%. Exemplarily, the mass percentage of the fluoroethylene carbonate is 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 8%, 10% or the range of any two of the above values. In some embodiments, the mass percentage of the fluoroethylene carbonate is 0.5% to 5%.

[0048] In some embodiments, the electrolyte further comprises a sulfur-oxygen double bond compound. The sulfur-oxygen double bond compound can participate in the formation of the SEI film. On the one hand, the protective film formed by the decomposition of the sulfur-oxygen double bond compound is rich in inorganic segments and organic segments, which can enhance the bonding between the inorganic layer rich in LiF and the organic polymer in the SEI film, thereby improving the overall stability of the SEI film and better adapting to the large volume change of silicon-based materials during the charging and discharging process. On the other hand, the sulfur-oxygen double bond compound has a low film-forming impedance, thereby further improving the kinetic performance and cycle stability of the electrochemical device.

[0049] In some embodiments, based on the mass of the electrolyte, the mass percentage content of the sulfur-oxygen double bond compound is from 0.1% to 5%. Exemplarily, the mass percentage content of the sulfur-oxygen double bond compound is 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range composed of any two of the above values. In some embodiments, the mass percentage content of the sulfur-oxygen double bond compound is from 0.5% to 3%.

[0050] In some embodiments, the sulfur-oxygen double bond compound includes at least one of 1,3-propane sultone, 1,4-butane sultone, ethylene sulfate, ethyl methyl sulfonate, butyl methyl sulfonate, 4-methyl ethylene sulfate, allyl-1,3-sultone, methylene methanedisulfonate, 2,4-butane sultone, 1,3-propane disulfonic anhydride, or pentaerythritol bis(cyclic sulfate).

[0051] In some embodiments, the negative electrode tab includes a negative electrode current collector and a negative electrode material layer disposed on the surface of the negative electrode current collector. The present application does not particularly limit the thickness of the negative electrode material layer, as long as the object of the present application can be achieved. For example, the thickness of the negative electrode material layer is 30 μm to 120 μm. In some embodiments, the negative electrode active material may further include a carbon material. In some embodiments, the carbon material includes, but is not limited to, at least one of natural graphite, artificial graphite, mesophase microbeads, hard carbon, or soft carbon. The present application does not particularly limit the negative electrode current collector, as long as the object of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (such as a composite current collector with a metal layer disposed on the surface of a polymer layer), etc. The present application does not particularly limit the thickness of the negative electrode current collector, as long as the object of the present application can be achieved. For example, the thickness of the negative electrode current collector is 5 μm to 12 μm. The negative electrode material layer may further include a binder and a thickener. The present application does not particularly limit the types of the binder and the thickener, as long as the object of the present application can be achieved. For example, the binder may include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinylidene fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, styrene-butadiene rubber, or acrylated styrene-butadiene rubber; the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. The negative electrode material layer may further include a conductive agent. The present application does not particularly limit the type of the conductive agent, as long as the object of the present application can be achieved. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, Ketjen black, graphene, metal materials, or conductive polymers. The present application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the object of the present application can be achieved. Optionally, the negative electrode tab may further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it may be a commonly used conductive layer in the art. For example, the conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and the binder in the conductive layer. For example, it may be at least one of the conductive agent and the binder in the above-mentioned negative electrode material layer.

[0052] In some embodiments, the electrochemical device of the present application further includes a positive electrode tab and a separator, and the separator is disposed between the positive electrode tab and the negative electrode tab.

[0053] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on the surface of the positive electrode current collector, and the positive electrode material layer includes a positive electrode active material. There is no particular limitation on the positive electrode current collector in this application, as long as the purpose of this application can be achieved. For example, it can include aluminum foil, aluminum alloy foil, or a composite current collector (such as a composite current collector with a metal layer provided on the surface of a polymer layer), etc. There is no particular limitation on the thickness of the positive electrode current collector in this application, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 12 μm. There is no particular limitation on the positive electrode active material in this application, as long as the purpose of this application can be achieved. For example, the positive electrode active material can include, but is not limited to, lithium nickel cobalt manganate (such as common NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate, lithium manganate, or lithium manganese iron phosphate. There is no particular limitation on the thickness of the positive electrode material layer in this application, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode material layer is 30 μm to 120 μm. The positive electrode material layer may further include a conductive agent and a binder. There is no particular limitation on the types of the conductive agent and the binder in this application, as long as the purpose of this application can be achieved. For example, the conductive agent can include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, Ketjen black, graphene, metal materials, or conductive polymers. The above metal materials can include, but are not limited to, metal powders and / or metal fibers. Specifically, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above conductive polymers can include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. The binder can include, but is not limited to, at least one of polyacrylic acid, polyacrylates, acrylate polymers, polyvinyl alcohol, polyvinylidene fluoride, polytetrafluoroethylene, or vinylidene fluoride-hexafluoropropylene copolymer. There is no particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer in this application, and those skilled in the art can select according to actual needs as long as the purpose of this application can be achieved.

[0054] In some embodiments, the separator membrane may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be an adhesive layer or a heat-resistant layer. For example, the adhesive layer contains an adhesive, and the material of the adhesive includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, or polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer. The heat-resistant layer includes inorganic particles and an adhesive, and there is no particular limitation on the inorganic particles. For example, it may include at least one of alumina, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. There is no particular limitation on the adhesive, and for example, it may be at least one of the adhesives in the above-mentioned adhesive layer.

[0055] In some embodiments, the electrochemical device of the present application may include a primary battery or a secondary battery. In particular, the electrochemical device is a lithium-ion secondary battery.

[0056] In a second aspect, the present application provides an electronic device, and the electronic device includes the electrochemical device described in any one of the above. The electronic devices of the present application include, but are not limited to, laptop computers, pen input computers, mobile computers, e-book players, mobile phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal TVs, portable cleaners, portable CD players, mini-discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc. Detailed Embodiments

[0057] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below with reference to embodiments.

[0058] (1) Preparation of Lithium-Ion Battery

[0059] The lithium-ion batteries in the examples and comparative examples were all prepared according to the following method:

[0060] (1) Preparation of the positive electrode plate

[0061] Mix the positive active material Li[Ni 0.88 Co 0.02 Mn0.1 Mix O2, N-methylpyrrolidone (NMP), and polyvinylidene fluoride (PVDF) evenly, then add conductive carbon black SP and mix evenly to prepare the positive electrode paste. The mass ratio of the positive electrode active material:PVDF:SP is 98:1:1. Coat the positive electrode paste evenly on one surface of the positive electrode current collector aluminum foil and dry it at 85°C to obtain a positive electrode plate with a positive electrode material layer coated on one side. Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode plate with positive electrode material coated on both sides. Then, after cold pressing and slitting, dry it under vacuum conditions at 85°C for 4 hours to obtain the positive electrode plate.

[0062] (2) Preparation of the negative electrode plate

[0063] In Comparative Examples 1-1 to 1-2 and Examples 1-1 to 1-27, mix silicon-oxygen negative electrode active material SiO, conductive carbon black SP, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a weight ratio of 86:2:2:10, add deionized water, and stir evenly under the action of a vacuum mixer to obtain the negative electrode paste, where the solid content of the negative electrode paste is 54 wt%. Coat the negative electrode paste evenly on one surface of the negative electrode current collector copper foil and dry it at 85°C to obtain a negative electrode plate with a negative electrode material layer coated on one side. Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode plate with negative electrode material layers coated on both sides. Then, after cold pressing and slitting, dry it under vacuum conditions at 120°C for 12 hours to obtain the negative electrode plate.

[0064] In Comparative Example 2-1 and Examples 2-1 to 2-6 and Examples 3-1 to 3-17, the difference is that in the preparation of the negative electrode paste, inorganic solid electrolyte powder is added according to the types and mass percentages listed in the examples to replace part of the silicon-oxygen negative electrode active material SiO. Among them, Examples 3-1 to 3-17 are the same as Example 2-4.

[0065] (3) Preparation of the electrolyte

[0066] In a dry argon atmosphere glove box, mix the compound of Formula I, organic solvent, and LiFSI according to the contents shown in Tables 1 to 3, add organic polymerization monomers (the mass ratio of the two organic polymerization monomers mixed is 1:1) / initiator / other additives, and mix evenly. The weight percentages are shown in Tables 1 to 3 to obtain the electrolyte. In each table, the content of each component in the electrolyte is the mass percentage calculated based on the total mass of the electrolyte.

[0067] Among them, the composition of Examples 2-1 to 2-6 in Table 2 is the same as that of Example 1-24. Comparative Example 2-1 only does not add organic polymerization monomers on the basis of Example 1-24 and adjusts the content of the organic solvent.

[0068] Examples 3-1 to 3-17 in Table 3 were optimized based on Example 2-4 in Table 2, and the contents of the initiator and other additives were additionally added based on the electrolyte already mixed in Example 2-4.

[0069] (4) Preparation of the separator

[0070] A polyethylene (PE) porous membrane with a thickness of 9 μm was selected as the separator.

[0071] (5) Preparation of the lithium-ion battery

[0072] The positive electrode sheet, the separator, and the negative electrode sheet were stacked in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to play a role in isolation, and then wound to obtain an electrode assembly; after welding the electrode tabs, the electrode assembly was placed in an outer packaging aluminum-plastic film, and the prepared electrolyte was injected into the dried aluminum-plastic film. Through processes such as vacuum packaging, standing at 60 °C for 12 hours, forming, shaping, and capacity testing, a lithium-ion battery was obtained.

[0073] (2) Testing of Lithium-Ion Battery

[0074] (1) Cycle life test at different charging rates:

[0075] Three lithium-ion batteries were placed in a normal temperature environment of 25 °C and left to stand for 30 minutes. They were charged to a voltage of 4.25 V at 0.2C, 0.5C, and 1C respectively, charged at a constant voltage until 0.05C, and then discharged at a constant current of 0.5C to 2.5V. Charge and discharge cycles were carried out according to the above process. The first discharge capacity, the discharge capacity after each cycle, and the cumulative number of cycles were recorded as C1 and C1', ε respectively, and the cycle capacity retention rate was calculated using the following formula: θ = (C1' / C1) × 100%. When θ = 70%, the current cumulative number of cycles ε was taken as the cycle life.

[0076] Table 1 shows the influence of the electrolyte composition on the cycle life of the lithium-ion battery at different charging rates.

[0077] Table 1

[0078]

[0079] Among them, " / " means that the substance was not added.

[0080] Compared with Comparative Example 1-1, it can be seen from Example 1-1 that the addition of the organic polymerization monomer prolongs the cycle life of the lithium-ion battery in the wide rate range of 0.2C to 1C. Especially, the improvement effect is more obvious under the condition of high-rate charging. The possible reason is that under the condition of high-rate charging, the volume of the silicon-based material expands rapidly, and the inorganic SEI film rich in LiF is difficult to adapt to such rapid volume changes. However, the organic polymerization monomer can in-situ polymerize on the surface of the negative electrode to form an organic polymer, which can enhance the flexibility of the SEI film and the stability of the contact interface between the silicon-based material particles, maintain a good conductive network, and reduce the risk of SEI film rupture and increased impedance between the silicon-based material particles during cycling, thereby significantly improving the cycle performance of the lithium-ion battery under the condition of high-rate charging.

[0081] Examples 1-1 to 1-6 show that different compounds of Formula I have the advantage of improving the cycle performance and rate performance of lithium-ion batteries. From the comparison between Examples 1-7 to 1-11 and Comparative Example 1-2, it can be seen that the compound of Formula I, the solvent, and the lithium salt need to meet a certain content relationship to optimize the cycle performance and rate performance of the lithium-ion battery. When the mass percentage content p / (n + p) of LiFSI in the solvent is too high, the interaction force between the anions and Li+ increases, the viscosity of the electrolyte increases, which is not conducive to the formation of a uniform and dense LiF-rich protective film on the positive and negative electrodes, and thus affects the cycle performance and rate performance of lithium ions.

[0082] The comparison of the cycle life of the lithium-ion batteries in Examples 1-12 to 1-27 shows that the types and contents of the organic solvents and organic polymerization monomers in the electrolyte will affect the cycle life. By optimizing the component types and proportional relationships, the cycle life of the lithium-ion battery can be significantly improved.

[0083] Table 2 shows the influence of the content of the inorganic solid electrolyte in the negative electrode active layer on the cycle life of the lithium-ion battery at different charging rates.

[0084] Table 2

[0085]

[0086] Among them, " / " means that this substance is not added.

[0087] From the comparison between Examples 2-1 to 2-6 and Comparative Example 2-1 and Example 1-24, it can be seen that the introduction of the inorganic solid electrolyte can significantly improve the cycling performance of lithium-ion batteries under different charging rates. The possible reason is that although the inorganic solid electrolyte has good ionic conductivity and mechanical stability, which can enhance the protection of the surface of the silicon-based material to a certain extent, the stability of the connection interface between it and the silicon-based material particles is still insufficient. However, the protective film formed by the in-situ polymerization of the organic polymer monomer in the electrolyte of this application on the negative electrode surface can effectively improve the stability of the connection interface between the inorganic solid electrolyte and the silicon-based material, inhibit the impedance growth of the negative electrode sheet during cycling, and thus greatly improve the cycling stability of lithium-ion batteries under different charging rates.

[0088] Table 3 shows the effects of the initiator and other additives in the electrolyte.

[0089] Table 3

[0090]

[0091]

[0092] Among them, " / " means that this substance is not added.

[0093] Comparing Examples 3-1 to 3-4 with Example 2-4, it can be seen that the introduction of the initiator can promote the film formation by polymerization of the organic polymer monomer on the surface of the negative electrode active material, improve the uniformity and denseness of the film formation, and reduce the risk of SEI film rupture and increased impedance between silicon-based material particles during cycling.

[0094] Comparing Examples 3-5 to 3-10 with Example 3-2, it can be seen that adding FEC is beneficial to further improve the cycling performance of lithium-ion batteries under different charging rates. The possible reason is that by further introducing fluoroethylene carbonate, it can cooperate with the anion in LiFSI to form a protective film with an inner inorganic layer rich in LiF and an outer organic layer on the negative electrode surface, improve the interfacial compatibility between the inorganic layer rich in LiF and the organic polymer formed by the in-situ polymerization of the organic polymer monomer, and further enhance the overall stability of the SEI film, thereby further improving the cycling performance of lithium-ion batteries.

[0095] Comparing Examples 3-11 to 3-16 with Example 3-2, it can be seen that adding a sulfur-oxygen double bond compound is also beneficial to further improving the cycling performance of the lithium-ion battery at different charging rates. The sulfur-oxygen double bond compound can participate in the formation of the SEI film. On the one hand, the protective film formed by the decomposition of the sulfur-oxygen double bond compound is rich in inorganic segments and organic segments, which can enhance the binding between the inorganic layer rich in LiF and the organic polymer in the SEI film, thereby improving the overall stability of the SEI film and better adapting to the large volume change of the silicon-based material during charge and discharge. On the other hand, the sulfur-oxygen double bond compound has a low film-forming impedance, thus further improving the kinetic performance and cycling stability of the lithium-ion battery.

[0096] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. An electrochemical device, characterized in that, It includes an electrolyte and a negative electrode plate; The electrolyte includes lithium bis(fluorosulfonyl)imide, an organic polymer monomer, a compound of Formula I, and an organic solvent; Among them, R1 to R6 are each independently selected from hydrogen, fluorine, a C1-C 12 alkyl group which is fluorine-substituted or unsubstituted, a C1-C 12 alkoxy group which is fluorine-substituted or unsubstituted, a C1-C 12 oxyalkyl group which is fluorine-substituted or unsubstituted. Two adjacent groups among R1 to R6 may optionally be connected to form a ring, and at least one of R1 to R6 contains fluorine; The negative electrode plate includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material; Based on the mass of the electrolyte, the mass percentage content of the compound of Formula I is denoted as m%, the mass percentage content of the organic solvent is denoted as n%, and the mass percentage content of lithium bis(fluorosulfonyl)imide is denoted as p%, satisfying: 20 ≤ m ≤ 70, 15 ≤ n ≤ 50, 7 ≤ p ≤ 40, and 0.25 ≤ p / (n + p) ≤ 0.

56.

2. The electrochemical device according to claim 1, wherein Based on the mass of the electrolyte, the mass percentage content of the organic polymer monomer is denoted as q%, satisfying at least one of the following conditions: (1)0.5≤q≤20； (2) 0.01 ≤ q / (q + n) ≤ 0.

4.

3. The electrochemical device according to claim 2, wherein Satisfying at least one of the following conditions: (1)25≤m≤50； (2)25≤n≤40； (3)15≤p≤35； (4)1≤q≤15； (5) 0.3 ≤ p / (n + p) ≤ 0.45; (6) 0.02 ≤ q / (q + n) ≤ 0.

3.

4. The electrochemical device according to claim 1, characterized in that, Satisfying at least one of the following conditions: (1) The organic polymer monomer includes at least one of acrylate polymer monomers, unsaturated carbonate polymer monomers, olefin polymer monomers, unsaturated ether polymer monomers, or heterocyclic polymer monomers; (2) The organic solvent includes at least one of saturated carbonate solvents or saturated carboxylate solvents; (3) The electrolyte further includes an initiator.

5. The electrochemical device according to claim 4, characterized in that, Satisfying at least one of the following conditions: (1) The acrylate polymer monomer includes at least one of the compounds of Formula II; wherein, R7 is selected from any one of hydrogen and C1-C5 alkyls, and R8 is selected from any one of C1-C5 alkyls; (2) The unsaturated carbonate polymer monomer includes at least one of the compound of Formula III or vinylene carbonate; wherein, R9 is selected from any one of C2-C4 alkenyls; (3) The olefin polymer monomer includes at least one of the compounds of Formula IV; Among them, R 10 ~R 13 are each independently selected from any one of hydrogen, fluorine, cyano group, C1-C3 alkyl group which is substituted or unsubstituted by fluorine, and the group represented by formula a; (4) The unsaturated ether polymer monomer includes at least one of the compounds of Formula V; Among them, R 14 , R 15 are each independently selected from any one of hydrogen, C1-C3 alkyl or the group represented by formula b, and at least one of R 14 and R 15 is selected from the group represented by formula b; Wherein, R 16 is selected from C1-C3 alkylene groups, and n is an integer from 0 to 3; (5) The heterocyclic polymer monomer includes at least one of ethylene oxide, propylene oxide, or dioxolane; (6) The saturated carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, or propylene carbonate; (7) The saturated carboxylate solvent includes at least one of ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl butyrate, ethyl difluoroacetate, difluoroethyl acetate, ethyl trifluoroacetate, trifluoroethyl acetate, or methyl trifluoropropionate; (8) The initiator includes at least one of peroxide initiators, azo initiators, or redox initiators; (9) The initiator includes at least one of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, benzoyl peroxide, or methyl ethyl ketone peroxide; (10) Based on the mass of the electrolyte, the mass percentage content of the initiator is 0.01% - 2%.

6. The electrochemical device according to claim 1, wherein The compound of formula I includes at least one of the following compounds:

7. The electrochemical device according to claim 1, characterized in that The negative electrode active layer further includes an inorganic solid electrolyte.

8. The electrochemical device according to claim 7, characterized in that, At least one of the following conditions is satisfied: (1) Based on the mass of the negative electrode active layer, the mass percentage content of the inorganic solid electrolyte is denoted as s%, and 0.1 ≤ s ≤ 10; (2) The inorganic solid electrolyte includes at least one of an oxide solid electrolyte or a sulfide solid electrolyte; (3) The negative electrode active layer further includes an organic polymer formed by polymerization of the organic polymer monomer, and the organic polymer connects the silicon-based material and the inorganic solid electrolyte; (4) The inorganic solid electrolyte includes at least one of lithium aluminum germanium phosphate, lithium aluminum titanium phosphate, or lithium lanthanum zirconium composite oxide.

9. The electrochemical device according to claim 1, wherein The electrolyte further includes at least one of fluoroethylene carbonate or a sulfur-oxygen double bond compound, and the electrolyte satisfies at least one of the following conditions: (1) Based on the mass of the electrolyte, the mass percentage content of the fluoroethylene carbonate is 0.1% to 10%; (2) Based on the mass of the electrolyte, the mass percentage content of the sulfur-oxygen double bond compound is 0.1% to 5%; (3) The sulfur-oxygen double bond compound includes at least one of 1,3-propane sultone, 1,4-butane sultone, ethylene sulfate, ethyl methyl sulfonate, butyl methyl sulfonate, 4-methyl ethylene sulfate, allyl-1,3-sultone, methylene methanedisulfonate, 2,4-butane sultone, 1,3-propane disulfonic anhydride, or pentaerythritol bis(cyclic sulfate).

10. An electronic device, comprising the electrochemical device according to any one of claims 1 to 9.

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