Negative electrode composite material, negative electrode plate, battery, battery pack and electric equipment

Abstract

The invention provides a negative electrode composite material, a negative electrode plate, a battery, a battery pack and electric equipment. The negative electrode composite material comprises a negative electrode active material, a polyether gel polymer layer existing on the surface of the negative electrode active material, and a polyion liquid electrolyte layer located on the side, away from the negative electrode active material, of the polyether gel polymer layer. The negative electrode composite material is high in ion conduction efficiency, and the cycle life of the lithium ion battery can be effectively prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a negative electrode composite material, a negative electrode sheet, a battery, a battery pack and an electrical device. Background Art

[0002] Lithium-ion batteries are widely used in fields such as aerospace and electric vehicles due to their advantages of high energy density, long cycle life, and wide applicable temperature range. However, during the first charge and discharge process of lithium-ion batteries, a solid electrolyte interface (SEI) is formed on the surface of the negative electrode, consuming a part of the lithium ions, resulting in a decrease in the first Coulombic efficiency of the lithium-ion battery, which has an adverse effect on the energy density and cycle life of the lithium-ion battery. Existing technologies mainly improve the performance such as the energy density and cycle life of lithium-ion batteries by pre-lithiation, using metallic lithium or lithium-carbon composite materials as the negative electrode material. However, the above methods have problems such as low ion conduction efficiency, resulting in poor performance such as the cycle life of the battery. Summary of the Invention

[0003] The present invention provides a negative electrode composite material, a negative electrode sheet, a battery, a battery pack and an electrical device to at least solve the problems of low ion conduction efficiency of the negative electrode material and low cycle life of the battery existing in the prior art.

[0004] The present invention provides a negative electrode composite material, including a negative electrode active material, a polyether-based gel polymer layer existing on the surface of the negative electrode active material, and a polyionic liquid electrolyte layer located on the side of the polyether-based gel polymer layer facing away from the negative electrode active material.

[0005] According to an embodiment of the present invention, the thickness of the polyether-based gel polymer layer is 20-40 μm; and / or,

[0006] The thickness of the polyionic liquid electrolyte layer is 15-40 μm.

[0007] According to an embodiment of the present invention, the polyether-based gel polymer layer is polymerized from a heterocyclic oxygen compound;

[0008] The heterocyclic oxygen compound includes at least one of dioxolane, oxacyclohexane, dioxacyclohexane, and tetrahydrofuran.

[0009] According to an embodiment of the present invention, the polyionic liquid electrolyte layer is polymerized from an ionic liquid monomer;

[0010] The ionic liquid monomer includes an imidazole-based ionic liquid monomer and / or a pyrrole-based ionic liquid monomer.

[0011] According to an embodiment of the present invention, the negative electrode active material includes a carbon material and metallic lithium existing in the carbon material.

[0012] According to an embodiment of the present invention, the mass percentage content of metallic lithium in the negative electrode active material is greater than or equal to 50%.

[0013] According to an embodiment of the present invention, the carbon material includes at least one of carbon nanotubes, acetylene black, and conductive carbon black.

[0014] According to an embodiment of the present invention, the Dv50 of the negative electrode composite material is 50 μm - 100 μm.

[0015] On the other hand, the present invention provides a method for preparing the above-mentioned negative electrode composite material, comprising the following steps:

[0016] (1) Form a polyether-based gel polymer layer on the surface of the negative electrode active material to obtain an intermediate;

[0017] (2) Form a polyionic liquid electrolyte layer on the side of the polyether-based gel polymer layer of the intermediate facing away from the negative electrode active material to obtain the negative electrode composite material.

[0018] According to an embodiment of the present invention, the preparation process of the negative electrode active material includes: mixing metallic lithium and carbon material to obtain the negative electrode active material;

[0019] And / or, the process of forming a polyether-based gel polymer layer on the surface of the negative electrode active material includes: mixing a first lithium salt, a heterocyclic oxygen compound, and a first solvent to obtain a mixed solution, putting the negative electrode active material into the mixed solution, and performing a first polymerization reaction to form a polyether-based gel polymer layer on the surface of the negative electrode active material to obtain the intermediate;

[0020] And / or, the process of forming a polyionic liquid electrolyte layer on the side of the polyether-based gel polymer layer of the intermediate facing away from the negative electrode active material includes: mixing an ionic liquid monomer, a second lithium salt, and an initiator to obtain a precursor solution, putting the intermediate into the precursor solution, and performing a second polymerization reaction to form a polyionic liquid electrolyte layer on the side of the polyether-based gel polymer layer of the intermediate facing away from the negative electrode active material to obtain the negative electrode composite material.

[0021] On the other hand, the present invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, and the negative electrode active material layer includes the above-mentioned negative electrode composite material.

[0022] On the other hand, the present invention provides a battery, comprising the above-mentioned negative electrode sheet.

[0023] On the other hand, the present invention provides a battery pack, comprising the above-mentioned battery.

[0024] According to an embodiment of the present invention, the battery is a lithium-ion battery.

[0025] On the other hand, the present invention provides an electrical device including the above battery pack.

[0026] The negative electrode composite material, negative electrode sheet, battery, battery pack and electrical device provided by the present invention, the negative electrode composite material includes a negative electrode active material, a polyether-based gel polymer layer existing on the surface of the negative electrode active material, and a polyionic liquid electrolyte layer located on the side of the polyether-based gel polymer layer facing away from the negative electrode active material. The ion conduction efficiency of this negative electrode composite material is high, which can effectively improve the cycle life of the lithium-ion battery. Description of the Drawings

[0027] Figure 1 It is a schematic structural diagram of the negative electrode composite material of the present invention;

[0028] Figure 2 It is a graph of the capacity retention rate of the battery in some embodiments of the present invention.

[0029] Description of the Reference Numerals:

[0030] 1 - Negative electrode active material; 2 - Polyether-based gel polymer layer; 3 - Polyionic liquid electrolyte layer. Detailed Embodiments

[0031] To enable those skilled in the art to better understand the solution of the present invention, the present invention will be further described in detail below. The following specific embodiments listed are only used to describe the principles and features of the present invention, and the examples given are only used to explain the present invention, not to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0032] The existing technology mainly adopts the following methods to improve the energy density and cycle life of lithium-ion batteries: (1) pre-lithiation. By pre-lithiating the negative electrode during the first charge and discharge process, the lithium ions consumed due to the formation of the solid electrolyte interface (SEI) layer can be compensated, effectively improving the energy density and cycle life of the lithium-ion battery. However, the structure of the negative electrode material is unstable, which reduces the ion conduction efficiency of the negative electrode material. (2) Using metallic lithium as the negative electrode of the lithium-ion battery. Lithium metal has a high specific capacity (3860mAh / g) and a low redox potential (-3.04V), which can greatly improve the energy density of the lithium-ion battery. However, there are problems such as large volume change of the negative electrode and easy generation of lithium dendrites, which shortens the cycle life of the lithium-ion battery. (3) Using lithium-carbon hybrid materials as the negative electrode of the lithium-ion battery. Combining lithium with carbon materials (such as graphite, graphene or carbon nanotubes) can improve the energy density, power density and cycle life of the battery. However, the interface compatibility between the lithium-carbon hybrid material and the electrolyte is poor, and a stable and strong SEI cannot be formed, resulting in low ion conduction efficiency of the negative electrode material. Therefore, how to provide a negative electrode material with high ion conduction efficiency and effectively improve the cycle life of lithium-ion batteries is still a technical problem to be solved urgently in this field.

[0033] In view of this, an embodiment of the present invention provides a negative electrode composite material, Figure 1 Schematic diagram of the structure of the negative electrode composite material of the present invention, such as Figure 1 As shown, the negative electrode composite material includes a negative electrode active material 1, a polyether gel polymer layer 2 present on the surface of the negative electrode active material, and a polyionic liquid electrolyte layer 3 located on the side of the polyether gel polymer layer 2 away from the negative electrode active material 1.

[0034] According to the inventor's research, under the composition system of the above-mentioned negative electrode composite material, the polyether gel polymer layer has excellent mechanical properties and flexibility, and is easy to process and shape, which can effectively protect the structural stability and integrity of the negative electrode active material; at the same time, the elasticity of the polyether gel polymer layer enables it to adapt to the volume change of the negative electrode active material during the charging and discharging process, thereby improving the cycle life of the lithium-ion battery; the polyether gel polymer layer can also improve the transmission performance of ions and electrons at the solid-liquid interface and improve the ion conduction efficiency of the negative electrode composite material. The polyionic liquid electrolyte layer can well infiltrate the surface of the electrode material, improve the interface compatibility between the electrolyte and the negative electrode composite material, and reduce the interface impedance; and the polyionic liquid electrolyte layer further improves the ion conduction efficiency of the negative electrode composite material by promoting the rapid migration of lithium ions.

[0035] In some embodiments, the thickness of the polyether gel polymer layer is 20 - 40 μm, which enables the polyether gel polymer layer to provide sufficient mechanical support and protection, better protect the structural stability and integrity of the negative electrode active material, and further improve the transport performance of ions and electrons at the solid-liquid interface.

[0036] Exemplarily, the thickness of the polyether gel polymer layer can be 20 μm, 25 μm, 30 μm, 35 μm or 40 μm, etc.

[0037] In some embodiments, the polyether gel polymer layer is formed by polymerizing heterocyclic oxygen compounds, endowing the polyether gel polymer layer with more excellent mechanical properties, flexibility, and being easy to process and form.

[0038] Further, the heterocyclic oxygen compounds include at least one of dioxolane, oxacyclohexane, dioxacyclohexane, and tetrahydrofuran, further enhancing the mechanical properties and flexibility of the polyether gel polymer layer.

[0039] In some embodiments, the thickness of the poly(ionic liquid) electrolyte layer is 15 - 40 μm, which can reduce the ion migration path, further improve the ionic conductivity; meanwhile, it provides better mechanical stability and interfacial contact, reduces the interfacial impedance, and further improves the cycle life of the lithium-ion battery.

[0040] Exemplarily, the thickness of the poly(ionic liquid) electrolyte layer can be 15 μm, 20 μm, 30 μm, 35 μm or 40 μm.

[0041] In some embodiments, the poly(ionic liquid) electrolyte layer is formed by polymerizing ionic liquid monomers, further improving the ionic conductivity of the poly(ionic liquid) electrolyte layer and its interfacial compatibility with the electrolyte.

[0042] Further, the ionic liquid monomers include imidazole-based ionic liquid monomers and / or pyrrole-based ionic liquid monomers, that is, the ionic liquid monomers can only include imidazole-based ionic liquid monomers, or only include pyrrole-based ionic liquid monomers, or can also be a combination of imidazole-based ionic liquid monomers and pyrrole-based ionic liquid monomers, enabling the poly(ionic liquid) electrolyte layer to have higher ionic conductivity.

[0043] In some embodiments, the imidazole-based ionic liquid monomers include at least one of 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; the pyrrole-based ionic liquid monomers include at least one of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium hexafluorophosphate, 1-butyl-1-methylpyrrolidinium tetrafluoroborate, 1-propyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-propyl-1-methylpyrrolidinium hexafluorophosphate, and 1-propyl-1-methylpyrrolidinium tetrafluoroborate.

[0044] The ionic liquid monomers of the present invention can be obtained by conventional means, such as commercially available or prepared by conventional methods.

[0045] In some embodiments, the negative electrode active material includes a carbon material and metallic lithium present in the carbon material. The negative electrode active material combines the high energy density of lithium and the excellent electrical conductivity and structural stability of the carbon material, and can improve the interfacial stability and electrical conductivity of the negative electrode composite while alleviating the problems of volume change of the negative electrode composite and lithium dendrite growth.

[0046] In some embodiments, the negative electrode active material includes a carbon material and metallic lithium present in the carbon material. The metallic lithium is distributed in the pores and on the surface of the carbon material, and the porous structure of the carbon material can provide mechanical support to buffer the volume change of metallic lithium during charge and discharge.

[0047] Generally, for the negative electrode active material including a carbon material and metallic lithium present in the carbon material, it can specifically be a lithium-carbon composite sphere, and the metallic lithium can be distributed in the pores and on the surface of the carbon material.

[0048] In some embodiments, the carbon material includes at least one of carbon nanotubes, acetylene black, and conductive carbon black, so that the negative electrode active material has more excellent electrical conductivity and structural stability.

[0049] In some embodiments, the mass percentage content of metallic lithium in the negative electrode active material is greater than or equal to 50%, which can enable the negative electrode active material to have both high energy density, excellent electrical conductivity and structural stability. Further, the mass percentage content of metallic lithium in the negative electrode active material is 50% - 80%.

[0050] Exemplarily, the mass percentage content of metallic lithium in the negative electrode active material can be 50%, 55%, 60%, 65%, 70%, 75% or 80%, etc.

[0051] In some embodiments, the Dv50 of the negative electrode composite material is 50 μm - 100 μm, which can provide a sufficient surface area to facilitate the transport of lithium ions, and at the same time helps to achieve a higher packing density, thereby improving the energy density of the lithium-ion battery.

[0052] Exemplarily, the Dv50 of the negative electrode composite material can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, etc.

[0053] On the other hand, the present invention provides a method for preparing the above-mentioned negative electrode composite material, comprising the following steps:

[0054] (1) Forming a polyether-based gel polymer layer on the surface of the negative electrode active material to obtain an intermediate;

[0055] (2) Forming a polyionic liquid electrolyte layer on the side of the polyether-based gel polymer layer of the intermediate facing away from the negative electrode active material to obtain the negative electrode composite material.

[0056] In some embodiments, the preparation process of the negative electrode active material includes: mixing metallic lithium and a carbon material, and the metallic lithium exists in the pores and on the surface of the carbon material to obtain the negative electrode active material.

[0057] In some embodiments, the preparation process of the negative electrode active material includes: dispersing the carbon material in a second solvent, obtaining carbon spheres through spray drying treatment, and then melting and mixing the metallic lithium and the carbon spheres to obtain the negative electrode active material with metallic lithium filled in the pores and on the surface of the carbon spheres, i.e., lithium-carbon composite spheres.

[0058] In some embodiments, the process of dispersing the carbon material in the second solvent includes: dispersing the carbon material in the second solvent by means of ultrasonic dispersion, which is beneficial to the uniform dispersion of the carbon material in the second solvent.

[0059] Furthermore, the ultrasonic dispersion time is 5 h - 7 h to make the carbon material more uniformly dispersed in the second solvent.

[0060] Furthermore, the second solvent includes at least one of n-hexane, toluene, xylene, hexane, cyclohexane, heptane, octane, decane, ethylene carbonate, dimethyl ether, diethyl ether, phenyl ether, toluene, xylene, tetrahydrofuran, tetrahydropyran, dimethyl sulfoxide, dimethylformamide, N-methylpyrrolidone.

[0061] In the embodiments of the present invention, a conventional spray dryer in the art can be used for spray drying treatment, and the inlet air temperature and atomization pressure of the spray dryer can be adjusted by conventional means according to needs, and no special limitation is made thereto.

[0062] Further, in the spray drying process, the inlet air temperature of the spray dryer is 220 - 240 °C, and the atomization pressure of the spray dryer is 0.4 MPa - 0.6 MPa, which can quickly evaporate the second solvent in the droplets and form carbon spheres with uniform particle sizes.

[0063] In some embodiments, the process of melting and mixing lithium metal and carbon spheres includes: placing lithium metal in a high-temperature furnace, melting it under an inert atmosphere, and then adding carbon materials and stirring to melt, to obtain the negative electrode active material. Further, the inert atmosphere includes argon or nitrogen.

[0064] In some embodiments, the melting temperature of lithium metal is 240 - 260 °C, and the melting time of lithium metal is 5 - 7 h to ensure that lithium metal is completely melted. The stirring and melting temperature of lithium metal and carbon materials is 240 - 260 °C, and the stirring and melting time of lithium metal and carbon materials is 10 - 13 h to fully mix the carbon materials and lithium metal to obtain the negative electrode active material.

[0065] Exemplarily, the stirring and melting temperature of lithium metal and carbon materials can be 240 °C, 244 °C, 248 °C, 252 °C, 256 °C or 260 °C, etc.

[0066] Exemplarily, the stirring and melting time of lithium metal and carbon materials can be 10 h, 11 h, 12 h or 13 h, etc.

[0067] In some embodiments, the process of forming a polyether-based gel polymer layer on the surface of the negative electrode active material includes: mixing a first lithium salt, a heterocyclic oxygen compound and a first solvent to obtain a mixed solution, putting the negative electrode active material into the mixed solution, and performing a first polymerization reaction to form a polyether-based gel polymer layer on the surface of the negative electrode active material to obtain an intermediate.

[0068] In some embodiments, the mass ratio of the first lithium salt to the heterocyclic oxygen compound is 1:(5 - 6), which can improve the completeness of the first polymerization reaction.

[0069] Exemplarily, the mass ratio of the first lithium salt to the heterocyclic oxygen compound can be 1:5, 1:5.2, 1:5.4, 1:5.6, 1:5.8 or 1:6, etc.

[0070] In some embodiments, the temperature of the first polymerization reaction is 15 - 30 °C, and the time of the first polymerization reaction is 60 min - 120 min, which can effectively improve the efficiency of the first polymerization reaction.

[0071] Exemplarily, the temperature of the first polymerization reaction can be 15 °C, 18 °C, 21 °C, 24 °C, 27 °C or 30 °C, etc., and the time of the first polymerization reaction can be 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min, etc.

[0072] In specific implementation, the process of forming a polyether-based gel polymer layer on the surface of the negative electrode active material includes: in a glove box under an argon atmosphere, mixing a first lithium salt, a heterocyclic oxygen compound, and a first solvent and stirring for 10 - 13 h until the solution is clear and transparent without solid residue to obtain a mixed solution. Putting the negative electrode active material into the mixed solution, stirring, and carrying out a first polymerization reaction at 15 - 30 °C for 60 min - 120 min, then filtering to remove the first solvent, and subsequently drying in vacuum for 12 - 14 h to completely remove the first solvent. After the first solvent has completely volatilized, the heterocyclic oxygen compound spontaneously undergoes ring-opening polymerization on the surface of the negative electrode active material to form a polyether-based gel polymer layer.

[0073] In some embodiments, the first solvent includes acetonitrile, which has good solubility and can provide an environment for the synthesis reaction.

[0074] In some embodiments, the first lithium salt includes lithium hexafluorophosphate, which can promote the ring-opening of the heterocyclic oxygen compound to carry out the first polymerization reaction, form a polyether-based gel polymer layer on the surface of the negative electrode active material, and obtain an intermediate.

[0075] In some embodiments, the process of forming a polyionic liquid electrolyte layer on the side of the polyether-based gel polymer layer of the intermediate facing away from the negative electrode active material includes: mixing an ionic liquid monomer, a second lithium salt, and an initiator to obtain a precursor solution, putting the intermediate into the precursor solution, and carrying out a second polymerization reaction to form a polyionic liquid electrolyte layer on the side of the polyether-based gel polymer layer of the intermediate facing away from the negative electrode active material, thereby obtaining a negative electrode composite material.

[0076] In some embodiments, the mass ratio of the second lithium salt to the ionic liquid monomer is 1:(4 - 5), which can improve the completeness of the second polymerization reaction.

[0077] In some embodiments, the second lithium salt includes at least one of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perfluoroethanesulfonylimide, and lithium perfluoromethanesulfonylmethyl.

[0078] The present invention does not limit the specific type of the initiator. In some embodiments, it can be an azo-based initiator, such as azobisisobutyronitrile, azodicarbonamide, etc.

[0079] In some embodiments, the time of the second polymerization reaction is 10 - 15 h. The second polymerization reaction can be carried out by thermal initiation or photoinitiation. Further, the condition for photoinitiation is ultraviolet light irradiation, and the temperature for thermal initiation is 75 - 85 °C.

[0080] Exemplarily, the time of the second polymerization reaction can be 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, etc.

[0081] Exemplarily, the temperature for thermal initiation can be 75 °C, 77 °C, 79 °C, 81 °C, 83 °C, 85 °C, etc.

[0082] In specific implementation, the process of forming the polyionic liquid electrolyte layer on the side of the polyether-based gel polymer layer facing away from the negative electrode active material includes: in a glove box under an argon atmosphere with both the moisture content and the oxygen content less than 0.1 ppm, stirring the second lithium salt, the ionic liquid monomer, and the initiator for 3 - 5 h until they are uniformly mixed to obtain a precursor solution. Drop the precursor solution onto the intermediate so that the intermediate is completely immersed in the precursor solution, and then carry out a second polymerization reaction at 75 - 85 °C or under ultraviolet light irradiation for 10 - 15 h to obtain the negative electrode composite material.

[0083] On the other hand, the present invention provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes the above-mentioned negative electrode composite material.

[0084] In some embodiments, the negative electrode active material layer may further include a first binder and a first conductive agent. The first binder can enhance the adhesion between the negative electrode active material layer and the negative electrode current collector, and the first conductive agent can improve the conductivity of the negative electrode active material layer to ensure that electrons can be effectively transmitted to the negative electrode active material layer.

[0085] In some embodiments, the mass ratio of the negative electrode composite material to the first binder is (85 - 95):(5 - 10), and the mass ratio of the first conductive agent to the first binder is (0 - 5):(5 - 10).

[0086] Exemplarily, the mass ratio of the negative electrode composite material to the first binder can be 85:5, 85:6, 85:7, 85:8, 85:9, 85:10, 87:5, 87:6, 87:7, 87:8, 87:9, 87:10, 90:5, 90:6, 90:7, 90:8, 90:9, 90:10, 95:5, 95:6, 95:7, 95:8, 95:9, or 95:10, etc.

[0087] Exemplarily, the mass ratio of the first conductive agent to the first binder can be 0:5, 0:6, 0:7, 0:8, 0:9, 0:10, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 3:5, 3:6, 3:7, 3:8, 3:9, 3:10, 4:5, 4:6, 4:7, 4:8, 4:9, 4:10, 5:5, 5:6, 4:7, 5:8, 5:9, or 5:10, etc.

[0088] In some embodiments, the first conductive agent may be a conventional conductive material in the art. For example, the first conductive agent may include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNT), carbon fiber, graphene, acetylene black, and Ketjen black.

[0089] In some embodiments, the first binder may be any binder suitable for the negative electrode known in the art. For example, it may include at least one of polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), tetrafluoroethylene and its copolymers, polyvinylidene fluoride and its copolymers, carboxymethyl cellulose, styrene-butadiene latex, nitrile rubber, and polyacrylic acid (PAA).

[0090] Embodiments of the present invention may use a conventional negative electrode current collector in the art. For example, the negative electrode current collector includes copper foil.

[0091] On the other hand, the present invention provides a method for preparing a negative electrode sheet, including the following steps: dispersing the negative electrode composite material in a third solvent to obtain a slurry, and then coating the slurry on at least one surface of the negative electrode current collector, and drying to obtain the negative electrode sheet. In some embodiments, the third solvent includes at least one of n-hexane, toluene, xylene, hexane, cyclohexane, heptane, octane, decane, ethylene carbonate, dimethyl ether, diethyl ether, phenyl ether, toluene, xylene, tetrahydrofuran, tetrahydropyran, dimethyl sulfoxide, dimethylformamide, and N-methylpyrrolidone.

[0092] In some embodiments, the method for preparing a negative electrode sheet includes the following steps: dispersing the negative electrode composite material, the first conductive agent, and the first binder in a third solvent to obtain a slurry, and then coating the slurry on at least one surface of the negative electrode current collector, and after drying, vacuum drying, and rolling, a negative electrode active material layer is formed on at least one surface of the negative electrode current collector to obtain the negative electrode sheet.

[0093] Specifically, the method for preparing a negative electrode sheet includes the following steps: adding the negative electrode composite material, the first conductive agent, and the first binder to a third solvent, stirring at 50-60 °C for 7-9 h to obtain a uniform slurry. Using a doctor blade with a thickness of 150 microns to coat the slurry on at least one surface of the negative electrode current collector, drying at 50-60 °C for 10-12 h, then vacuum drying at 60-80 °C for 10-12 h, and then rolling to form a negative electrode active material layer on at least one surface of the negative electrode current collector to obtain the negative electrode sheet.

[0094] In embodiments of the present invention, unless otherwise specified, processes such as coating, drying, vacuum drying, and rolling are all conventional operations in the art, and the equipment used can be conventional equipment in the art, and no special limitation is made thereto.

[0095] Another aspect of the present invention provides a battery, comprising the above-mentioned negative electrode sheet or the negative electrode sheet prepared according to the above-mentioned method for preparing the negative electrode sheet. The battery has the advantages corresponding to the above-mentioned negative electrode sheet, which will not be described in detail.

[0096] In some embodiments, the battery may be a lithium-ion battery.

[0097] Generally, a battery includes an electrolyte, a battery cell, and a shell that encapsulates the battery cell. The electrolyte is injected into the battery cell in the shell. The battery cell includes a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet. The battery cell can be a laminated battery cell, that is, the battery cell is formed by staggered stacking of positive electrode sheets, separators, and negative electrode sheets; or the battery cell can also be a wound battery cell, that is, the battery cell is formed by stacking positive electrode sheets, separators, and negative electrode sheets and then winding them.

[0098] Specifically, the positive electrode sheet includes a positive electrode collector and a positive electrode active layer located on at least one side surface of the positive electrode collector. Specifically, the positive electrode active layer can be arranged on one side surface of the positive electrode collector in the thickness direction, or the positive electrode active layer can be arranged on the surfaces of the opposite sides in the thickness direction of the positive electrode collector.

[0099] Specifically, the positive electrode active layer may include a positive electrode active material, a second conductive agent, and a second binder. The mass ratio of the positive electrode active material, the second conductive agent, and the second binder may be (80-94):(2-10):(3-10).

[0100] In an embodiment of the present invention, the second conductive agent in the positive electrode active layer may be a conventional conductive material in the art. For example, the second conductive agent in the positive electrode active layer may include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNTs), carbon fibers, graphene, acetylene black, and Ketjen black.

[0101] In an embodiment of the present invention, the second binder in the positive electrode active layer may be a conventional binder material in the art. For example, the second binder in the positive electrode active layer may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, and the like.

[0102] The embodiment of the present invention may adopt a conventional positive electrode current collector in the art, for example, the positive electrode current collector includes aluminum foil.

[0103] In the embodiments of the present invention, the positive electrode sheet can be prepared by conventional methods in the art, for example, by the coating method. Specifically, components for forming the positive electrode active layer such as positive electrode active material, second conductive agent, and second binder can be dispersed in a fourth solvent. The fourth solvent includes, for example, N-methylpyrrolidone (NMP) to prepare a positive electrode slurry, and then it is coated on the surface of the positive electrode current collector. After processes such as drying and rolling, the positive electrode sheet is obtained. Among them, processes such as coating, drying, and rolling involved are conventional operations for preparing the positive electrode sheet by the coating method, and no special limitations are imposed thereon.

[0104] The electrolyte in the embodiments of the present invention can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which specifically can include a fifth solvent and an electrolyte salt. The fifth solvent includes, for example, one or more of ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC), and the electrolyte salt can include a lithium salt. The lithium salt includes, for example, lithium hexafluorophosphate (LiPF 6 ) etc., but is not limited thereto.

[0105] In some embodiments, the preparation method of the electrolyte includes the following steps: in an argon atmosphere glove box with a water content <1 ppm and an oxygen content <1 ppm, the fifth solvent and the electrolyte salt are uniformly mixed in a mass ratio of (10 - 15):1 to prepare the electrolyte.

[0106] In the embodiments of the present invention, the separator is used to separate the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from contacting and short-circuiting. Conventional separators in the art can be used in the embodiments of the present invention, and no special limitations are imposed thereon.

[0107] In the embodiments of the present invention, the battery cell can be encapsulated with conventional housing materials in the art. The housing includes, for example, soft packaging materials such as aluminum-plastic films, but is not limited thereto.

[0108] In the embodiments of the present invention, components such as the positive electrode sheet, the separator, and the negative electrode sheet can be assembled into a battery by conventional methods in the art. For example, the positive electrode sheet, the separator, and the negative electrode sheet can be stacked alternately to obtain a laminated battery cell (or wound into a wound battery cell); then the battery cell is placed in a housing (outer package), and after conventional processes such as liquid injection (i.e., injecting the electrolyte) and encapsulation, the battery is obtained.

[0109] The embodiments of the present invention also provide a battery pack, including the above battery. This battery pack has the corresponding advantages as the above negative electrode sheet, which will not be elaborated herein.

[0110] Generally, the battery pack includes a plurality of the above batteries. These batteries serve as single battery cells and are connected to form a battery pack. Among them, these batteries can be electrically connected by conventional methods in the art, such as series connection, parallel connection, or a hybrid connection including these connection methods simultaneously, and no special limitations are imposed thereon.

[0111] An embodiment of the present invention further provides an electrical device, including the above battery or the above battery pack. The electrical device has the advantages corresponding to the above negative electrode sheet, which will not be elaborated here.

[0112] The electrical device in the embodiment of the present invention can be a conventional electrical device in the art, such as a power device (such as an electric vehicle, an electric car), an electronic device (such as a mobile phone, a tablet computer, a laptop computer, a digital camera, etc.), a wearable device (such as a watch, a bracelet, a VR glasses, etc.), an energy storage power station, etc., and no special limitation is made thereto.

[0113] In the embodiment of the present invention, the volume average particle size Dv50 of the negative composite material is the volume average particle size Dv50 of the negative composite material, which refers to the particle size corresponding to 50% of the total volume starting from the small particle size side on the particle size distribution curve of the negative composite material. When testing the particle size Dv50 of the negative composite material in the negative active material layer, the negative active material layer can be scraped off from the negative electrode sheet, and then the solid particle product therein can be separated by washing with a solvent (such as water), etc., and then the volume average particle size Dv50 of the negative composite material can be measured by using a conventional particle size testing instrument in the art such as a laser particle size analyzer.

[0114] In the embodiment of the present invention, the thickness of the polyether-based gel polymer layer and the thickness of the polyionic liquid electrolyte layer are usually measured by a scanning electron microscope (SEM).

[0115] The present invention will be further introduced below through specific embodiments.

[0116] Example 1

[0117] 1. Preparation of the positive electrode sheet

[0118] Lithium iron phosphate (LiFePO 4 ), carbon nanotubes (CNT), and polyvinylidene fluoride are mixed in a mass ratio of 90:5:5, and N-methylpyrrolidone (NMP) is added and stirred under the action of a vacuum mixer to prepare a positive electrode slurry;

[0119] The positive electrode slurry is uniformly coated on the front and back sides of the aluminum foil, dried at 85 °C for 4 h, and roll-pressed to obtain a positive electrode sheet.

[0120] 2. Preparation of the negative electrode sheet

[0121] (1) Weigh 5 g of carbon tubes and ultrasonically disperse them in 10 g of n-hexane for 6 h, and prepare carbon materials through spray drying treatment. The inlet air temperature of the spray dryer is 230 °C, and the atomization pressure of the spray dryer is 0.5 MPa;

[0122] (2) Put 6 g of metallic lithium into a high-temperature furnace and melt it at 250 °C for 6 h. Subsequently, add 5 g of the carbon material prepared in step (1), and stir at 250 °C for 12 h to fully mix the metallic lithium and the carbon material, obtaining the negative electrode active material (lithium-carbon composite spheres).

[0123] (3) Prepare a mixed solution in a glove box under an argon atmosphere: Weigh 1.5191 g of lithium hexafluorophosphate into 8.8920 g of tetrahydrofuran, and stir for 12 h until the lithium salt is completely dissolved, obtaining a mixed solution. The concentration of lithium hexafluorophosphate in the mixed solution is 1 mol / L. Add the negative electrode active material obtained in step (2) to the above mixed solution, stir, and carry out the first polymerization reaction at 25 °C for 1 h. Subsequently, filter and vacuum dry at 90 °C for 12 h to obtain an intermediate (including the negative electrode active material and a polyether-based gel polymer layer coated on the surface of the negative electrode active material).

[0124] (4) Weigh 0.1712 g of lithium bis(trifluoromethanesulfonyl)imide, 0.8288 g of 1-propyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, and 0.625 g of azobisisobutyronitrile (AIBN), and stir for 3 h until evenly mixed to obtain a precursor solution. Immerse 1.8 g of the intermediate in the precursor solution, and then carry out the second polymerization reaction at 85 °C for 15 h to form a poly(ionic liquid) electrolyte layer on the surface of the polyether-based gel polymer layer of the intermediate. After filtering and vacuum drying at 70 °C for 8 h, a negative electrode composite material is obtained.

[0125] (5) Weigh 1.8 g of the negative electrode composite material, 0.1 g of acetylene black, and 0.1 g of styrene-butadiene rubber, add them to 4 g of n-hexane, stir at 50 °C for 8 h to obtain a homogeneous slurry. Use a doctor blade with a thickness of 150 µm to coat the slurry on the surface of a copper foil, dry at 50 °C for 12 h, then vacuum dry at 80 °C for 12 h, and then roll press to obtain a negative electrode sheet.

[0126] 3. Preparation of the electrolyte:

[0127] In a glove box under an argon atmosphere with a water content <1 ppm and an oxygen content <1 ppm, uniformly mix dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a mass ratio of 2:4:4, and then add LiPF 6 , and prepare a LiPF 6 electrolyte with a concentration of 1 mol / L.

[0128] 4. Assembly of the battery:

[0129] In a CR2032 coin-type battery case, cut the above positive electrode sheet, separator (polypropylene separator), and negative electrode sheet, stack them in sequence, use a pipette to inject 60 µL of the above electrolyte into the battery case, and use a tablet press to encapsulate the battery to obtain a lithium-ion coin cell.

[0130] Example 2

[0131] The difference between this example and Example 1 lies in that in the preparation step (2) of the negative electrode sheet, the content of metallic lithium in the negative electrode active material is increased from 54.5% to 61.5%: 8 g of metallic lithium is placed in a high-temperature furnace and melted at 250 °C for 6 h. Subsequently, 5 g of the carbon material prepared in step (1) is added, and stirring is carried out at 250 °C for 12 h to fully mix the metallic lithium and the carbon material, obtaining the negative electrode active material (lithium-carbon composite spheres).

[0132] Example 3

[0133] The difference between this example and Example 1 lies in that in the preparation step (3) of the negative electrode sheet, tetrahydrofuran is replaced by 1,3-dioxolane: 1.5191 g of lithium hexafluorophosphate is weighed into 8.67 g of 1,3-dioxolane, and stirring is carried out for 12 h until the lithium salt is completely dissolved, obtaining a mixed solution. The concentration of lithium hexafluorophosphate in the mixed solution is 1 mol / L.

[0134] Example 4

[0135] The difference between this example and Example 1 lies in that in the preparation step (4) of the negative electrode sheet, lithium bis(trifluoromethanesulfonyl)imide is replaced by lithium difluoro(oxalato)borate, and 1-propyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide is replaced by 1-propyl-3-methylimidazolium bis(fluorosulfonyl)imide: 0.1533 g of lithium difluoro(oxalato)borate, 0.8844 g of 1-propyl-3-methylimidazolium bis(fluorosulfonyl)imide, and 0.625 g of azobisisobutyronitrile (AIBN) are weighed and stirred for 3 h until evenly mixed, obtaining a precursor solution. The intermediate is immersed in the precursor solution, and then a second polymerization reaction is carried out at 85 °C for 15 h to form a poly(ionic liquid) electrolyte layer on the surface of the polyether-based gel polymer layer of the intermediate. After filtration and vacuum drying at 70 °C for 8 h, a negative electrode composite material is obtained.

[0136] Example 5

[0137] The difference between this example and Example 4 lies in that in the preparation step (4) of the negative electrode sheet, the polymerization method of the second polymerization reaction is changed from 15 h at 85 °C to 15 h under ultraviolet light: 0.1533 g of lithium difluoro(oxalato)borate, 0.8844 g of 1-propyl-3-methylimidazolium bis(fluorosulfonyl)imide, and 0.625 g of azobisisobutyronitrile (AIBN) are weighed and stirred for 3 h until evenly mixed, obtaining a precursor solution. The intermediate is immersed in the precursor solution, and then a second polymerization reaction is carried out under ultraviolet light for 15 h to form a poly(ionic liquid) electrolyte layer on the surface of the polyether-based gel polymer layer of the intermediate. After filtration and vacuum drying at 70 °C for 8 h, a negative electrode composite material is obtained.

[0138] Example 6

[0139] The difference between this example and Example 1 lies in that in the preparation step (2) of the negative electrode sheet, the content of metallic lithium in the negative electrode active material is reduced from 54.5% to 44.4%: 4 g of metallic lithium is placed in a high-temperature furnace and melted at 250 °C for 6 h. Subsequently, 5 g of the carbon material obtained in step (1) is added and stirred at 250 °C for 12 h to fully mix the metallic lithium and the carbon material, obtaining the negative electrode active material (lithium-carbon composite spheres).

[0140] Example 7

[0141] The difference between this example and Example 1 lies in that in the preparation step (3) of the negative electrode sheet, a mixed solution is prepared in a glove box under an argon atmosphere: 3.0384 g of lithium hexafluorophosphate is weighed into 8.8920 g of tetrahydrofuran and stirred for 12 h until the lithium salt is completely dissolved, obtaining a 2 mol / L mixed solution. The negative electrode active material obtained in step (2) is added to the above mixed solution, stirred, and subjected to a first polymerization reaction at 25 °C for 1 h. Subsequently, it is filtered and vacuum dried at 85 °C for 12 h to obtain an intermediate (including the negative electrode active material and a polyether-based gel polymer layer coated on the surface of the negative electrode active material).

[0142] Example 8

[0143] The difference between this example and Example 1 lies in that in the preparation step (4) of the negative electrode sheet, 0.0856 g of lithium bis(trifluoromethanesulfonyl)imide, 0.4144 g of 1-propyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, and 0.625 g of azobisisobutyronitrile (AIBN) are weighed and stirred for 3 h until evenly mixed, obtaining a precursor solution. The intermediate is soaked in the precursor solution, and then a second polymerization reaction is carried out at 85 °C for 15 h to form a polyionic liquid electrolyte layer on the surface of the polyether-based gel polymer layer of the intermediate. After filtration and vacuum drying at 70 °C for 8 h, a negative electrode composite material is obtained.

[0144] Comparative Example 1

[0145] The difference between this comparative example and Example 1 lies in that in the preparation of the negative electrode sheet, a polyionic liquid electrolyte layer is not formed on the surface of the intermediate. The specific steps are as follows:

[0146] (1) Weigh 5 g of carbon nanotubes and ultrasonically disperse them in 10 g of n-hexane for 6 h, and prepare carbon materials through spray drying treatment. The inlet air temperature of the spray dryer is 230 °C, and the atomization pressure of the spray dryer is 0.5 MPa;

[0147] (2) Place 6 g of metallic lithium in a high-temperature furnace and melt it at 250 °C for 6 h. Subsequently, add 5 g of the carbon material obtained in step (1) and stir at 250 °C for 12 h to fully mix the metallic lithium and the carbon material, obtaining the negative electrode active material (lithium-carbon composite spheres);

[0148] (3) Prepare a mixed solution in a glove box under an argon atmosphere: Weigh 1.5191 g of lithium hexafluorophosphate and dissolve it in 8.8920 g of tetrahydrofuran, and stir for 12 h until the lithium hexafluorophosphate is completely dissolved to obtain a mixed solution. The concentration of lithium hexafluorophosphate in the mixed solution is 1 mol / L. Add the negative electrode active material obtained in step (2) to the above mixed solution, stir, and carry out the first polymerization reaction at 25 °C for 1 h, then filter and vacuum dry at 90 °C for 12 h to obtain an intermediate (including the negative electrode active material and a polyether-based gel polymer layer coated on the surface of the negative electrode active material);

[0149] (4) Weigh 1.8 g of the intermediate, 0.1 g of acetylene black, and 0.1 g of styrene-butadiene rubber, add them to 4 g of n-hexane, stir at 50 °C for 8 h to obtain a uniform slurry, use a scraper with a thickness of 150 microns to coat the slurry on the surface of the copper foil, then dry at 50 °C for 12 h, and then vacuum dry at 80 °C for 12 h to obtain a negative electrode sheet.

[0150] Comparative Example 2

[0151] The difference between this comparative example and Example 1 is that in the preparation of the negative electrode sheet, a polyether-based gel polymer layer was not formed on the surface of the negative electrode active material. The specific steps are as follows:

[0152] (1) Weigh 5 g of carbon nanotubes, ultrasonically disperse them in 10 g of n-hexane for 6 h, and obtain carbon materials through spray drying. The inlet air temperature of the spray dryer is 230 °C, and the atomization pressure of the spray dryer is 0.5 MPa;

[0153] (2) Put 6 g of metallic lithium into a high-temperature furnace, melt it at 250 °C for 6 h, then add 5 g of the carbon materials prepared in step (1), and stir at 250 °C for 12 h to fully mix the metallic lithium and the carbon materials to obtain a negative electrode active material (lithium-carbon composite spheres);

[0154] (3) Weigh 0.1712 g of lithium bis(trifluoromethanesulfonyl)imide, 0.8288 g of 1-propyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, and 0.625 g of azobisisobutyronitrile (AIBN), stir for 3 h until evenly mixed to obtain a precursor solution. Immerse the negative electrode active material obtained in step (2) in the precursor solution, then carry out the second polymerization reaction at 85 °C for 15 h to form a polyionic liquid electrolyte layer on the surface of the negative electrode active material, filter and vacuum dry at 70 °C for 8 h to obtain a negative electrode composite material;

[0155] (4) Weigh 1.8 g of the negative electrode composite material, 0.1 g of acetylene black, and 0.1 g of styrene-butadiene rubber, add them to 4 g of n-hexane, stir at 50 °C for 8 h to obtain a uniform slurry, use a scraper with a thickness of 150 microns to coat the slurry on the surface of the copper foil, then dry at 50 °C for 12 h, and then vacuum dry at 80 °C for 12 h to obtain a negative electrode sheet.

[0156] Comparative Example 3

[0157] The difference between this comparative example and Example 1 is that the negative electrode composite material is a lithium-carbon composite sphere prepared by steps (1) to (2) in the process of preparing the negative electrode sheet. The preparation of the negative electrode sheet includes the following steps:

[0158] (1) Weigh 5 g of carbon nanotubes and disperse them in 10 g of n-hexane. After ultrasonic dispersion for 6 h, carbon materials are obtained by spray drying. The inlet air temperature of the spray dryer is 230 °C, and the atomization pressure of the spray dryer is 0.5 MPa;

[0159] (2) Put 6 g of metallic lithium into a high-temperature furnace and melt it at 250 °C for 6 h. Then add 5 g of the carbon materials prepared in step (1) and stir at 250 °C for 12 h to fully mix the metallic lithium and the carbon materials to obtain the negative electrode active material;

[0160] (3) Add the negative electrode active material obtained in step (2), 0.1 g of acetylene black and 0.1 g of styrene-butadiene rubber to 4 g of n-hexane, and stir at 50 °C for 8 h to obtain a uniform slurry. Use a scraper with a thickness of 150 microns to coat the slurry on the surface of the copper foil, then dry it at 50 °C for 12 h, and then vacuum dry it at 80 °C for 12 h to obtain the negative electrode sheet.

[0161] Comparative Example 4

[0162] The difference between this comparative example and Comparative Example 1 is that in the preparation of the negative electrode sheet, the content of metallic lithium in the negative electrode active material is reduced from 54.5% to 44.4%, and a polyether-based gel polymer layer is not formed on the surface of the negative electrode active material. The specific steps are as follows:

[0163] (1) Weigh 5 g of carbon nanotubes and ultrasonically disperse them in 10 g of n-hexane for 6 h, and obtain carbon materials through spray drying treatment. The inlet air temperature of the spray dryer is 230 °C, and the atomization pressure of the spray dryer is 0.5 MPa;

[0164] (2) Put 4 g of metallic lithium into a high-temperature furnace and melt it at 250 °C for 6 h. Then add 5 g of the carbon materials prepared in step (1) and stir at 250 °C for 12 h to fully mix the metallic lithium and the carbon materials to obtain the negative electrode active material (lithium-carbon composite sphere);

[0165] (3) Add the negative electrode active material obtained in step (2), 0.1 g of acetylene black and 0.1 g of styrene-butadiene rubber to 4 g of n-hexane, and stir at 50 °C for 8 h to obtain a uniform slurry. Use a scraper with a thickness of 150 microns to coat the slurry on the surface of the copper foil, then dry it at 50 °C for 12 h, and then vacuum dry it at 80 °C for 12 h to obtain the negative electrode sheet.

[0166] Performance Test:

[0167] 300-cycle capacity retention rate: The lithium-ion button cells obtained from the examples and comparative examples were charged and discharged on a Neware battery tester with a current density of 1 mA / cm 2 , and the voltage range was 3.0 V - 4.2 V. First, it was charged at a constant current of 1 C to 4.20 V, then charged at a constant voltage of 0.05 C to 4.20 V, and then discharged at a discharge rate of 1 C to 3.0 V. Such charge-discharge cycles were repeated 300 times, and the discharge capacity Q 1 at the first cycle and the discharge capacity Q 300 at the 300th cycle were measured;

[0168] 300-cycle capacity retention rate = Q 300 / Q 1 × 100%, and the results are shown in Table 1.

[0169] Ionic conduction efficiency: Inside a glove box filled with an argon atmosphere, the positive and negative electrodes in the examples and comparative examples were replaced with stainless steel sheets with a diameter of 15.6 mm, assembled into a CR2032 battery, and the EIS curve of the CR2032 battery was tested at a frequency of 100000 - 1 Hz at room temperature (25°C) to obtain the R s of the CR2032 battery, and the ionic conduction efficiency (E) of the negative composite material was calculated according to the following formula:

[0170] E = d / (R s A)

[0171] where d is the electrolyte thickness (cm), R s is the electrolyte resistance ( ), and A is the electrode area (cm 2 ); the results of the ionic conduction efficiency are shown in Table 1.

[0172] Table 1

[0173]

[0174] It can be seen from Figure 2 that the 300-cycle discharge specific capacity of the battery in Example 1 is higher than that of the battery in Comparative Example 3, indicating that the polyionic liquid electrolyte layer can well infiltrate the surface of the electrode material and improve the interfacial compatibility between the electrolyte and the negative composite material; the polyether-based gel polymer layer has excellent mechanical properties and flexibility, and can effectively protect the structural stability and integrity of the negative composite material, so that the battery containing the negative composite material has a higher discharge specific capacity.

[0175] The following conclusions can be drawn from Table 1: By comparing Examples 1-8 with Comparative Examples 1-4, it can be seen that the negative electrode composite materials in Examples 1-8 have higher ion conduction efficiency and 300-cycle capacity retention rate, indicating that the negative electrode composite materials of the present invention can effectively improve the ion conduction efficiency and capacity retention rate of the negative electrode composite materials by forming a polyether-based gel polymer layer and a polyionic liquid electrolyte layer on the surface of the negative electrode active material.

[0176] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode composite material, characterized in that: The invention comprises a negative electrode active material, a polyether gel polymer layer existing on the surface of the negative electrode active material, and a polyionic liquid electrolyte layer located on a side of the polyether gel polymer layer away from the negative electrode active material.

2. The negative electrode composite material according to claim 1, characterized in that: The thickness of the polyether gel polymer layer is 20-40 μm; and / or, The thickness of the polyionic liquid electrolyte layer is 15-40 μm.

3. The negative electrode composite material according to claim 1 or 2, characterized in that: The polyether gel polymer layer is formed by polymerization of heterocyclic oxygen compounds; The heterocyclic oxygen compound includes at least one of dioxolane, oxane, dioxane and tetrahydrofuran.

4. The negative electrode composite material according to any one of claims 1 to 3, characterized in that: The polyionic liquid electrolyte layer is formed by polymerization of ionic liquid monomers; The ionic liquid monomers include imidazole ionic liquid monomers and / or pyrrole ionic liquid monomers.

5. The negative electrode composite material according to any one of claims 1 to 4, characterized in that: The negative electrode active material includes a carbon material and metallic lithium present in the carbon material.

6. The negative electrode composite material according to claim 5, characterized in that: The mass percentage of metallic lithium in the negative electrode active material is greater than or equal to 50%.

7. The negative electrode composite material according to claim 5 or 6, characterized in that: The carbon material includes at least one of carbon nanotubes, acetylene black and conductive carbon black.

8. The negative electrode composite material according to any one of claims 1 to 7, characterized in that: The Dv50 of the negative electrode composite material is 50 μm-100 μm.

9. A method for preparing the negative electrode composite material according to any one of claims 1 to 8, characterized in that: The following steps are involved: (1) forming a polyether gel polymer layer on the surface of the negative electrode active material to obtain an intermediate; (2) forming a polyionic liquid electrolyte layer on the side of the polyether gel polymer layer of the intermediate away from the negative electrode active material to obtain a negative electrode composite material.

10. The preparation method according to claim 9, characterized in that: The preparation process of the negative electrode active material comprises: mixing metallic lithium and carbon material to obtain the negative electrode active material; And / or, the process of forming a polyether gel polymer layer on the surface of the negative electrode active material comprises: mixing a first lithium salt, a heterocyclic compound and a first solvent to obtain a mixed solution, placing the negative electrode active material in the mixed solution, and performing a first polymerization reaction to form a polyether gel polymer layer on the surface of the negative electrode active material to obtain the intermediate; And / or, the process of forming a polyionic liquid electrolyte layer on the side of the polyether gel polymer layer of the intermediate away from the negative electrode active material includes: mixing an ionic liquid monomer, a second lithium salt and an initiator to obtain a precursor solution, placing the intermediate into the precursor solution, and performing a second polymerization reaction to form a polyionic liquid electrolyte layer on the side of the polyether gel polymer layer of the intermediate away from the negative electrode active material to obtain the negative electrode composite material.

11. A negative electrode sheet, characterized in that: The invention comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode composite material according to any one of claims 1 to 8.

12. A battery, characterized in that: Includes the negative electrode sheet as claimed in claim 11.

13. The battery according to claim 12, characterized in that The battery is a lithium-ion battery.

14. A battery pack, characterized in that: A battery comprising the battery of claim 12 or 13.

15. An electrical equipment, characterized in that: Comprising the battery according to claim 12 or 13 or the battery pack according to claim 14.

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