Lithium ion battery, preparation method thereof and power utilization device

Abstract

The invention relates to the technical field of batteries, in particular to a lithium ion battery, a preparation method thereof and an electric device. Comprising a positive pole piece, a negative pole piece, electrolyte and a diaphragm, the negative pole piece comprises a negative current collector and a negative active material layer positioned on at least one side surface of the negative current collector; the negative electrode active material layer contains a negative electrode active material and a negative electrode binder; the negative electrode binder comprises a cross-linked polymer, and the cross-linked polymer contains a polyacrylic acid structural unit and a carboxymethyl cellulose salt structural unit; the negative active material comprises a silicon-containing material; the roughness Ra of the negative electrode current collector is 0.2 mu m-1 mu m; the electrolyte contains a functional additive, and the functional additive comprises a carbonic ester additive and a sulfur-containing additive. The lithium ion battery provided by the invention realizes multiple balance of reversible capacity, interface stability and fast charging capacity of the silicon-containing material negative pole piece, and has a good engineering application prospect.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a lithium-ion battery and its preparation method and electrical device. Background Technology

[0002] With the large-scale application of lithium-ion batteries in electric vehicles and high-energy storage systems, improving their fast-charging capability, cycle stability, and safety has become a core technological challenge. Silicon-containing materials are widely used in anode systems due to their high specific capacity, but their significant volume expansion (up to 300%) leads to SEI film rupture, electrode structure pulverization, and binder failure, severely affecting cycle life. Summary of the Invention

[0003] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide a lithium-ion battery, its preparation method, and an electrical device thereof. This lithium-ion battery has advantages such as reversible capacity, interface stability, and fast charging capability.

[0004] Traditional CMC / SBR binders struggle to provide the necessary interfacial support for both high modulus and high flexibility, resulting in insufficient adhesion and increased interfacial resistance. Furthermore, the formation mechanism of the SEI film is highly dependent on the choice of electrolyte additives. Currently, there is a lack of a systematic fast-charging negative electrode solution that integrates the negative electrode and electrolyte in a synergistic and reversibly controllable manner. The inventors of this invention have developed a lithium-ion battery that incorporates a specific binder to enhance the interfacial strength between the binder network and the electrode. Adding additives matching the binder to the electrolyte enables controllable inorganic / organic phase ratios in the SEI film, stable film formation behavior, and the construction of an electrochemical buffer structure to accommodate volume changes during fast charging. Furthermore, the roughening of the negative electrode current collector enhances the interfacial anchoring force between the electrode and the current collector, comprehensively improving the structural stability and electrochemical performance of the negative electrode under high-rate and long-cycle conditions. Therefore, this solution addresses the problems of SEI film rupture, electrode structure pulverization, and binder failure caused by the volume expansion of silicon-containing materials, which severely impact cycle life.

[0005] To achieve the objectives of this invention, a first aspect of this invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative current collector and a negative active material layer located on at least one side of the surface of the negative current collector. The negative active material layer contains a negative active material and a negative binder. The negative binder comprises a cross-linked polymer containing polyacrylic acid structural units and carboxymethyl cellulose salt structural units. The negative active material includes a silicon-containing material. The roughness Ra of the negative current collector is 0.2 μm-1 μm. The electrolyte contains functional additives, including carbonate additives and sulfur-containing additives.

[0006] A second aspect of the present invention provides a method for preparing a lithium-ion battery, the method comprising:

[0007] Preparation of negative electrode sheet: A negative electrode slurry containing negative electrode active material and negative electrode binder is coated on at least one side surface of the negative electrode current collector, and then dried to obtain a negative electrode sheet.

[0008] Battery assembly: The positive electrode, separator, and negative electrode are stacked sequentially and then wound or pressed to obtain a bare cell. An electrolyte is then injected, and the cell is packaged to obtain a lithium-ion battery. The negative electrode binder comprises a cross-linked polymer containing polyacrylic acid structural units and carboxymethyl cellulose salt structural units. The negative electrode active material comprises silicon-containing materials. The surface roughness Ra of the negative electrode current collector is 0.2 μm-1 μm. The electrolyte contains functional additives, including carbonate additives and sulfur-containing additives.

[0009] A third aspect of the present invention provides an electrical device comprising the lithium-ion battery described in the first aspect, or a lithium-ion battery prepared by the method described in the second aspect.

[0010] Through the above technical solution, this invention provides a lithium-ion battery. By adding a specific cross-linked polymer as a negative electrode binder to the negative electrode sheet, and simultaneously combining this with a negative electrode current collector roughness Ra of 0.2μm-1μm, and functional additives in the electrolyte, a stable and functionalized solid electrolyte interphase (SEI) film can be synergistically constructed. This significantly improves the interfacial bonding force between the negative electrode binder and the negative electrode active material, optimizes the conductive network structure and electrode flexibility, thereby effectively reducing interfacial impedance, enhancing electrode structural stability and film uniformity, and suppressing electrode expansion and debonding during cycling. This multi-factor synergistic approach significantly improves the overall performance of the lithium-ion battery under high-rate charge / discharge and long-life cycling conditions, achieving a multiple balance between reversible capacity, interfacial stability, and fast-charging capability of silicon-containing negative electrode sheets, and possesses promising engineering application prospects. Attached Figure Description

[0011] Figure 1 The image shows the infrared spectrum of the cross-linked PAA-CMC polymer in Example 1. Detailed Implementation

[0012] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0013] The first aspect of this invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator; the negative electrode includes a negative current collector and a negative active material layer located on at least one side of the surface of the negative current collector; the negative active material layer contains a negative active material and a negative binder; the negative binder includes a cross-linked polymer, the cross-linked polymer containing polyacrylic acid structural units and carboxymethyl cellulose salt structural units; the negative active material includes a silicon-containing material; the roughness Ra of the negative current collector is 0.2 μm-1 μm; the electrolyte contains functional additives, the functional additives including carbonate additives and sulfur-containing additives.

[0014] In this invention, a specific cross-linked polymer is added as a negative electrode binder. Simultaneously, the roughness Ra of the negative electrode current collector is between 0.2 μm and 1 μm. Functional additives in the electrolyte achieve stable construction of the SEI film and comprehensive optimization of its interfacial mechanical properties. Consequently, the negative electrode sheet in the lithium-ion battery of this invention exhibits low interfacial resistance and excellent peel strength. The lithium-ion battery demonstrates excellent rate performance and cycle life, while effectively suppressing electrode expansion, exhibiting excellent fast-charging adaptability and structural stability. This makes the lithium-ion battery possess significant engineering application value.

[0015] [Negative electrode binder]

[0016] Polyacrylic structural units refer to structural units provided by polyacrylic polymers. In some embodiments, polyacrylic structural units include polyacrylic structural units and / or polymethacrylic structural units, preferably polyacrylic structural units.

[0017] The use of the above-mentioned polyacrylic acid structural units in this invention can further enhance the strength of the bonding network and the electrode interface.

[0018] According to the present invention, in some embodiments, the carboxymethyl cellulose salt structural unit includes at least one of the carboxymethyl cellulose lithium structural unit, carboxymethyl cellulose sodium structural unit, and carboxymethyl cellulose potassium structural unit, preferably including the carboxymethyl cellulose sodium structural unit.

[0019] The use of the above-mentioned carboxymethyl cellulose salt in this invention can further enhance the bonding network and electrode interface strength.

[0020] According to some embodiments of the present invention, polyacrylic acid structural units and carboxymethyl cellulose salt structural units are connected by ester bonds.

[0021] According to the present invention, in some embodiments, the weight-average molecular weight of the crosslinked polymer is 90,000 Da to 210,000 Da.

[0022] The weight-average molecular weight of the cross-linked polymer in this invention can be obtained by gel chromatography.

[0023] According to the present invention, in some embodiments, the mass ratio of polyacrylic acid structural units to carboxymethyl cellulose salt structural units is 1:(0.5-1.5), for example, 1:0.5, 1:1, 1:1.5, or any range of two of the above ratios.

[0024] In this invention, the mass of the polyacrylic acid structural unit and the carboxymethyl cellulose salt structural unit is measured by the mass of their respective polymer monomers.

[0025] In this invention, controlling the ratio of polyacrylic acid structural units to carboxymethyl cellulose salt structural units within the above-mentioned range can further enhance the bonding network and electrode interface strength.

[0026] According to the present invention, the negative electrode binder may be entirely composed of the above-mentioned cross-linked polymer, or may be partially composed of the above-mentioned cross-linked polymer, preferably partially composed of the above-mentioned cross-linked polymer. In some embodiments, the mass content of the cross-linked polymer in the negative electrode binder is 20%-70%, for example, 20%, 30%, 34%, 50%, 60%, 70%, or any combination of two of the above values.

[0027] According to the present invention, in some embodiments, the negative electrode binder further includes styrene-butadiene rubber, preferably the mass content of styrene-butadiene rubber in the negative electrode binder is 30%-80%, for example 30%, 34%, 50%, 60%, 70%, 80%, or any two of the above values.

[0028] In this invention, cross-linked polymers and styrene-butadiene rubber are used together as negative electrode binders, which can further enhance the bonding network and the interface strength of the electrode sheet.

[0029] According to the present invention, the amount of negative electrode binder can be selected within a wide range as long as the purpose of the present invention can be achieved. In some embodiments, the mass content of negative electrode binder in the negative electrode active material layer is 0.5%-7%, for example, 0.5%, 1%, 2%, 2.5%, 4%, 5%, 6% or 7%.

[0030] [Negative Electrode Active Material]

[0031] According to the present invention, in some embodiments, the silicon-containing material includes silicon-carbon material and / or crystalline silicon, preferably including silicon-carbon material.

[0032] In this invention, the silicon-containing material can exist in the form of silicon-carbon material or crystalline silicon, preferably in the form of silicon-carbon material. That is, in some embodiments, the silicon-carbon material includes deposited silicon-carbon. Deposited silicon-carbon refers to a negative electrode active material formed by combining silicon material and carbon-based material through deposition processes (such as chemical vapor deposition, physical vapor deposition, etc.), which has a higher specific capacity.

[0033] According to the present invention, in order to better control the dispersion of silicon-containing materials in the system, the silicon-containing materials are generally controlled at the micrometer level. In some embodiments, the D of the silicon-containing material... v The particle size of 50 particles ranges from 5.5 μm to 14.5 μm.

[0034] According to the present invention, in some embodiments, the negative electrode active material further includes carbon materials; that is, the negative electrode active material includes silicon-containing materials and carbon materials.

[0035] In this invention, carbon materials and silicon-containing materials are used together as negative electrode active materials, which enables the lithium-ion battery to form a better conductive network, alleviates the volume expansion stress during charging and discharging, thereby reducing the electrode interface resistance and increasing the stability of the lithium-ion battery.

[0036] According to the present invention, in some embodiments, the carbon material includes at least one of artificial graphite, natural graphite, soft carbon and hard carbon, preferably including artificial graphite and / or natural graphite, and more preferably artificial graphite.

[0037] The present invention uses graphite and silicon-containing materials as negative electrode active materials, which enables lithium-ion batteries to form a stable conductive network.

[0038] According to the present invention, in order to better control the dispersion of carbon materials in the system, in some embodiments, the D of the carbon materials... v The particle size of 50 particles ranges from 5.5 μm to 14.5 μm.

[0039] In some embodiments of the present invention, the mass ratio of silicon-containing material to carbon material is 1:(1.5-19), for example 1:1.5, 1:1.8, 1:2.3, 1:3, 1:5.7, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:15, 1:18, 1:19, or any range of two of the above ratios.

[0040] In this invention, by controlling the ratio of silicon-containing materials to carbon materials within the above-mentioned range, a more compact and elastic structural network can be constructed, which effectively alleviates the volume expansion stress during the charging and discharging process and avoids the "conductive phase dilution" effect.

[0041] [Negative electrode active material layer]

[0042] In the process of preparing the negative electrode active material layer, a thickener is usually added in order to coordinate the dispersibility and stability of the system. In some embodiments, the negative electrode active material layer also includes a thickener.

[0043] According to the present invention, the thickener may be a thickener well known to those skilled in the art. In some embodiments, the thickener includes carboxymethyl cellulose salt; examples of carboxymethyl cellulose salt include, but are not limited to, potassium carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, etc.

[0044] According to the present invention, the content of the thickener in the negative electrode active material layer can be selected within a wide range. In some embodiments, the mass content of the thickener in the negative electrode active material layer is 0.5%-1.8%, for example, 0.5%, 1%, 1.5% or 1.8%.

[0045] According to the present invention, in some embodiments, the negative electrode active material layer further includes a conductive agent; the specific type and amount of the conductive agent are well known to those skilled in the art. Among them, the conductive agents that can be listed include, but are not limited to, at least one of conductive carbon black (Super P), acetylene black, carbon nanofibers, graphene, and carbon nanotubes. As an example, the conductive agent is conductive carbon black (Super P) and carbon nanotubes in a mass ratio of 1:(1-3), preferably single-walled carbon nanotubes (SWCNTs), that is, the conductive agent is conductive carbon black (Super P) and single-walled carbon nanotubes (SWCNTs) in a mass ratio of 1:(1-3). As an example, the mass content of the conductive agent in the negative electrode active material layer is 0.5%-2%, for example, 0.5%, 1%, 1.5%, or 2%, etc.

[0046] [Negative electrode current collector]

[0047] According to some embodiments of the present invention, the surface of the negative electrode current collector contains polar oxygen-containing functional groups.

[0048] In this invention, the polar oxygen-containing functional groups in the negative electrode current collector can form chemical bonds with the functional groups on the surface of the negative electrode binder or active material, which greatly improves the interfacial adhesion, inhibits the shedding of the negative electrode active material and the repeated rupture of the SEI film, thereby increasing the mechanical stability and electrochemical performance of the lithium-ion battery.

[0049] According to the present invention, in some embodiments, the polar oxygen-containing functional group includes at least one selected from hydroxyl, carboxyl and carbonyl groups.

[0050] According to the present invention, the specific type of negative electrode current collector can be a specific type conventional in the art. In some embodiments, the material of the negative electrode current collector includes, but is not limited to, copper.

[0051] [Negative electrode plate]

[0052] In this invention, "the negative electrode sheet includes a negative current collector and a negative active material layer located on at least one side surface of the negative current collector" means that a negative active material layer is provided on one or both sides surface of the negative current collector, preferably both sides surface of the negative current collector are provided with a negative active material layer; wherein, the thickness of the negative current collector and the negative active material layer can be the conventional thickness in the art, and this invention does not have any special limitation on this, so it will not be described in detail.

[0053] According to the present invention, in some embodiments, the compaction density of the negative electrode sheet is 1.35 g / cm³. 3 -1.65g / cm 3 For example, 1.35 g / cm³ 3 1.55g / cm 3 1.55g / cm 3 1.65g / cm 3 or a range consisting of any two of the above values.

[0054] In this invention, controlling the compaction density of the negative electrode sheet within the aforementioned range allows the negative electrode active material layer to have a dense structure with low porosity and high particle contact. This simultaneously strengthens the conductive network and bonding interface, and shortens the electron and lithium-ion transport paths, resulting in reduced interface resistance and increased peel strength. When the compaction density of the negative electrode sheet is too high, the internal pore structure of the negative electrode active material layer closes, leading to restricted electrolyte penetration, hindered SEI formation, and decreased lithium-ion diffusion rate. Consequently, both the capacity retention and cycle stability of the lithium-ion battery decrease, demonstrating the defects of the synergistic mechanism of "diffusion restriction" and "interface deterioration" caused by excessive compaction.

[0055] The negative electrode sheet in this invention has an excellent bonding interface. In some embodiments, the peel strength of the negative electrode sheet is 9.5 N / m-19 N / m, for example, 9.5 N / m, 10.5 N / m, 11.5 N / m, 12.8 N / m, 13.3 N / m, 14.5 N / m, 15.5 N / m, 16.5 N / m, 18 N / m, or 19 N / m, etc.

[0056] The negative electrode in this invention has a low interface resistance. In some embodiments, the interface resistance R of the negative electrode is... α 1×10 -3 Ω·cm 2 -2.2×10 -2 Ω·cm 2 For example, 1×10 -3 Ω·cm 2 5.8×10 -3 Ω·cm 2 6.3×10 -3 Ω·cm 27.2×10 -3 Ω·cm 2 7.8×10 -3 Ω·cm 2 1.1×10 -2 Ω·cm 2 2.2×10 -2 Ω·cm 2 wait.

[0057] Electrolyte

[0058] The present invention utilizes sulfur-containing additives that preferentially induce electron reduction on the negative electrode surface, generating a stable and dense inorganic-rich phase, thereby constructing a primary SEI film structure with uniform interface and good ion permeability. According to the present invention, in some embodiments, the sulfur-containing additives include at least one of vinyl sulfate (DTD), vinyl sulfite (ES), propylene sulfite (PS), and dimethyl sulfite (DMS), preferably including vinyl sulfate (DTD).

[0059] The aforementioned sulfur-containing additives possess moderate LUMO energy levels and extremely strong electron affinity, and can preferentially form a dense inorganic phase at low potentials.

[0060] According to the present invention, in some embodiments, the sulfur-containing additive has a mass content of 4%-25% in the functional additive, for example, 4%, 6%, 9%, 12%, 14%, 19%, 21%, 23%, 25%, or any combination of two of the above values.

[0061] In this invention, by controlling the amount of sulfur-containing additives within the above-mentioned range, a primary SEI membrane structure with uniform interface and good ion permeability can be constructed. At the same time, it avoids the gradual accumulation of reduction byproducts and chain intermediates on the SEI surface, which would cause the proportion of organic components in the membrane to be too high, making the structure rigid and brittle, thereby hindering the continuity of Li+ migration channels and resulting in "excessive instability".

[0062] The use of carbonate additives and sulfur-containing additives in this invention helps to construct inorganic / organic SEI films and suppress dendrite formation and interfacial side reactions. According to some embodiments of the invention, the carbonate additives include at least one selected from ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), ethylene carbonate (VC), and fluoroethylene carbonate (FEC).

[0063] According to the present invention, in some embodiments, the preferred carbonate additives include vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0064] In this invention, vinylene carbonate (VC) and fluoroethylene carbonate (FEC) are used in synergy with sulfur-containing additives to preferentially generate a dense LiF phase at low potentials, thereby better constructing an inorganic- and organic SEI film and suppressing dendrite formation and interfacial side reactions.

[0065] According to the present invention, the amounts of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) can be selected within a wide range as long as the purpose of the present invention can be achieved. In some embodiments, the mass ratio of vinylene carbonate (VC) to fluoroethylene carbonate (FEC) is (1-3):1, for example, 1:1, 2:1 or 3:1.

[0066] According to the present invention, in some embodiments, the carbonate additives in the functional additives have a mass content of 75%-96%, for example 75%, 80%, 85%, 90%, 93% or 96%, or a range of any two of the above values.

[0067] In this invention, by controlling the content of carbonate additives in functional additives, a primary SEI film structure with a more uniform interface and strong ion permeability can be constructed, thereby inhibiting dendrite formation and interfacial side reactions.

[0068] According to the present invention, in some embodiments, the functional additive has a mass content of 4.5%-12.5% ​​in the electrolyte, for example, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12.5%, or any range of two of the above ratios.

[0069] In this invention, by controlling the functional additives within the above-mentioned range, dendrite formation and interfacial side reactions can be better suppressed.

[0070] According to the present invention, in some embodiments, the electrolyte further contains lithium electrolyte and organic solvent.

[0071] In this invention, the type and amount of lithium electrolyte can be those well known in the art. For example, the lithium electrolyte includes LiPF6; in some embodiments, the mass content of lithium electrolyte in the electrolyte is 10%-20%.

[0072] The aforementioned organic solvents are mainly used as carriers for lithium electrolytes. Their types and amounts can be those well known in the art, and carbonate solvents are generally selected. For example, the organic solvents include ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) in a mass ratio of 1:1:1. In some embodiments, the mass content of the organic solvent in the electrolyte is 67.5%-85.5%.

[0073] [Positive electrode plate]

[0074] The positive electrode sheet is a type of positive electrode sheet well known to those skilled in the art. Specifically, it is a layer of positive active material coated on at least one surface of the positive current collector, consisting of a mixture of positive active material, conductive agent, and binder, preferably coated on both surfaces of the positive current collector. The positive active material includes, but is not limited to, lithium nickel cobalt manganese oxide (LiNiO2). x Co y Mn z M b O2) and / or lithium iron phosphate, wherein 0.70≤x≤0.95, 0.15≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1, and M includes at least one of zirconium (Zr), tungsten (W), titanium (Ti), aluminum (Al), strontium (Sr), boron (B), and neodymium (Nd). For example, lithium nickel cobalt manganese oxide can be NMC811. The conductive agent and binder are materials well known to those skilled in the art. For example, conductive agents include, but are not limited to, conductive carbon black and / or carbon nanotubes, and binders include, but are not limited to, polyvinylidene fluoride (PVDF). The positive electrode current collector is also a positive electrode current collector well known to those skilled in the art, including, but not limited to, aluminum foil. The thickness of the positive electrode current collector and the positive electrode active material layer can each be a thickness conventional in the art, and this invention does not have any special limitations on this, so it will not be described in detail.

[0075] As an example, the positive electrode active material layer includes NMC811, conductive carbon black, carbon nanotubes, and polyvinylidene fluoride (PVDF) in a mass ratio of 96:1:1:2.

[0076] [Septum]

[0077] The diaphragm is a well-known diaphragm to those skilled in the art. As an example, the diaphragm is generally selected from those with high porosity (typically 40% to 60%). The diaphragm includes a base membrane and ceramic coatings located on both sides of the base membrane. The base membrane includes, but is not limited to, polyethylene (PE) with a thickness of 9 μm, and the ceramic coating has a thickness of 1 μm.

[0078] [Preparation of Lithium-ion Batteries]

[0079] In this invention, the lithium-ion battery can be prepared according to the conventional steps of the invention with the required components, or it can be prepared according to the lithium-ion battery preparation method provided in the second aspect of the invention below.

[0080] According to some embodiments of the present invention, a second aspect of the present invention provides a method for preparing a lithium-ion battery, the method comprising:

[0081] Preparation of negative electrode sheet: A negative electrode slurry containing negative electrode active material and negative electrode binder is coated on at least one side surface of the negative electrode current collector, and then dried to obtain a negative electrode sheet.

[0082] Battery assembly: The positive electrode, separator and negative electrode are stacked in sequence and then wound or pressed to obtain a bare cell. Then, electrolyte is injected and packaged to obtain a lithium-ion battery.

[0083] The negative electrode binder includes a cross-linked polymer containing polyacrylic acid structural units and carboxymethyl cellulose salt structural units; the negative electrode active material includes silicon-containing materials; the roughness Ra of the negative electrode current collector is 0.2μm-1μm; the electrolyte contains functional additives, including carbonate additives and sulfur-containing additives.

[0084] It should be understood that all the features and advantages described above regarding "lithium-ion batteries" also apply to this "method for preparing lithium-ion batteries," and will not be repeated here.

[0085] The interaction between the negative electrode and the electrolyte in the lithium-ion battery prepared in this invention results in excellent structural stability and electrochemical performance of the lithium-ion battery under high-rate and long-cycle conditions, and it has great potential for engineering conversion.

[0086] [Preparation of cross-linked polymers]

[0087] The cross-linked polymer is prepared by polymerizing polyacrylic acid monomers that provide polyacrylic acid structural units and carboxymethyl cellulose salts that provide carboxymethyl cellulose salt structural units, preferably including polycondensation.

[0088] According to some embodiments of the present invention, the preparation method of the cross-linked polymer includes: under acidic conditions, carrying out a polymerization reaction of a raw material liquid containing polyacrylic acid polymer monomers, carboxymethyl cellulose salts and water, followed by filtration, washing and drying to obtain the cross-linked polymer.

[0089] According to the present invention, in some embodiments, the polyacrylic acid polymer monomers include polyacrylic acid and / or polymethacrylic acid. Polyacrylic acid is used as an example to illustrate the advantages of the present invention, but it does not represent a limitation of the present invention.

[0090] According to the present invention, in some embodiments, the carboxymethyl cellulose salt includes at least one selected from lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, and potassium carboxymethyl cellulose. Sodium carboxymethyl cellulose is used as an example to illustrate the advantages of the present invention, but this does not constitute a limitation thereof.

[0091] In some embodiments, the weight-average molecular weight of the polyacrylic acid monomers is 40,000 Da to 150,000 Da.

[0092] In some embodiments, the carboxymethyl cellulose salt has a weight-average molecular weight of 40,000 Da to 150,000 Da.

[0093] According to the present invention, in some embodiments, the mass ratio of polyacrylic acid polymeric monomer to carboxymethyl cellulose salt is 1:(0.5-1.5), for example, 1:0.5, 1:1, 1:1.5, or any range of two of the above ratios.

[0094] According to the present invention, in order to enable the polymerization reaction to occur better, in some embodiments, the total mass content of polyacrylic acid monomers and carboxymethyl cellulose salts in the feed liquid is 0.5%-10%.

[0095] According to the present invention, in order to facilitate better polymerization of polyacrylic acid monomers and carboxymethyl cellulose salts, in some embodiments, the pH value of the feed solution is 3-4. In this invention, dilute hydrochloric acid can be used to adjust the pH value of the feed solution to 3-4. Here, dilute hydrochloric acid is a conventional term, and its concentration is generally 0.1-10 mol / L. The present invention does not have any special limitations on it, as long as it can adjust the pH value of the feed solution to 3-4.

[0096] According to the present invention, in some embodiments, the polymerization reaction conditions include: a temperature of 140-160°C and a time of 5-12 hours.

[0097] In the preparation of cross-linked polymers in this invention, the system still contains water after the polymerization reaction. Water and other components can be removed by means of filtration, washing, and drying. Washing can be done with water. Filtration, washing, and drying are all conventional operations in the field and will not be described in detail.

[0098] According to the present invention, a method for obtaining a raw material solution comprising polyacrylic acid monomers, carboxymethyl cellulose salts and water may include: mixing polyacrylic acid monomers and carboxymethyl cellulose salts separately with water to obtain corresponding polyacrylic acid monomer solutions and carboxymethyl cellulose salt solutions, and then thoroughly stirring the polyacrylic acid monomer solutions and carboxymethyl cellulose salt solutions to adjust the pH value to 3-4 using dilute hydrochloric acid.

[0099] As an example, the preparation method of the cross-linked polymer includes: mixing polyacrylic acid monomers and carboxymethyl cellulose salts with water to obtain corresponding polyacrylic acid monomer solutions and carboxymethyl cellulose salt solutions; then mixing the polyacrylic acid monomer solutions and carboxymethyl cellulose salt solutions thoroughly under magnetic stirring for 4-7 hours; adjusting the pH value to 3-4 with dilute hydrochloric acid; then heat-treating at 140-160℃ for 5-12 hours to obtain the cross-linked product; then filtering the cross-linked product, washing it with deionized water, and drying it to obtain the cross-linked polymer.

[0100] [Preparation of negative electrode current collector]

[0101] In order to obtain the above-mentioned roughness of the negative electrode current collector, the negative electrode current collector precursor can be etched by means of etching, including but not limited to acid etching, laser etching, ozone etching, etc., with ozone etching being preferred.

[0102] The precursor of the negative electrode current collector is a conventional negative electrode current collector in the art that does not have the above-mentioned roughness. That is, in this invention, the existing negative electrode current collector is processed to obtain the processed negative electrode current collector as the negative electrode current collector in this invention.

[0103] According to some embodiments of the present invention, the method for preparing the negative electrode current collector includes: treating the negative electrode current collector precursor under ozone conditions to obtain the negative electrode current collector.

[0104] According to the present invention, in some embodiments, the conditions for ozone treatment include: an ozone concentration of 200-500 ppm, for example, 200 ppm, 300 ppm, 400 ppm, 500 ppm, or a range of any two of the above values.

[0105] According to the present invention, in some embodiments, the conditions for ozone treatment include a temperature of 35-45°C, for example, 35°C, 40°C, 45°C, or any combination of two of the above values.

[0106] According to the present invention, in some embodiments, the conditions for ozone treatment include a time of 3-8 minutes, for example, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, or any range of two of the above values.

[0107] There are no particular limitations on the way ozone is obtained in this invention. For example, high-energy UV can be used to induce O2 in the air to be converted into O3 and then decomposed to form active oxygen atoms.

[0108] According to the present invention, in some embodiments, the negative electrode current collector precursor comprises copper foil.

[0109] In this invention, to avoid the influence of impurities or oil on the negative electrode current collector precursor on ozone treatment, the negative electrode current collector precursor can be cleaned before ozone treatment, for example, by using ethanol for cleaning.

[0110] As an example, the preparation method of the negative electrode current collector includes: cleaning the surface of the copper foil with ethanol to remove oil and organic impurities, and then placing it in a UV / O3 treatment device for 3-8 minutes under the conditions of ozone concentration of 200-500ppm and temperature of 35-45℃. The high-energy UV induces the conversion of O2 in the air into O3, which then decomposes to form active oxygen atoms. These active oxygen atoms can react with the copper surface to generate polar oxygen-containing functional groups such as –OH, –COOH, and –C=O.

[0111] [Preparation of the negative electrode sheet]

[0112] In this invention, the negative electrode slurry is used to form a negative electrode active material layer. The negative electrode active material, negative electrode binder, thickener, conductive agent and solvent can be mixed evenly with a solvent to form a slurry and coated on at least one side surface of the negative electrode current collector. The solvent can be a solvent well known in the art, including but not limited to water. The solid content of the negative electrode slurry can generally be 40wt%-65wt%.

[0113] As an example, the preparation method of the negative electrode sheet includes: adding negative electrode active material, conductive agent, thickener and negative electrode binder to deionized water and stirring to form a negative electrode slurry, then coating it on both sides of the negative electrode current collector, and then drying and cold pressing to form a negative electrode sheet.

[0114] [Preparation of the positive electrode sheet]

[0115] The positive electrode sheet can be prepared according to conventional methods in the art. As an example, the preparation method of the positive electrode sheet includes: taking the positive active material, conductive agent and binder and stirring and mixing them evenly in an N-methylpyrrolidone solvent system to obtain a positive electrode slurry, then coating the positive electrode slurry onto the positive current collector, and then drying and cold pressing to obtain the positive electrode sheet.

[0116] [Preparation of Electrolyte]

[0117] According to the present invention, the electrolyte can be obtained by uniformly mixing the various components in the electrolyte. As an example, the preparation method of the electrolyte includes: firstly, in an argon glove box, a high-purity homogeneous solvent system is added, followed by a slow addition of lithium electrolyte to avoid local overheating and decomposition of lithium salt; after complete dissolution, carbonate additives and sulfur-containing additives are added sequentially and stirred to ensure molecular-level dispersion of the additives; finally, the electrolyte is obtained by pressure filtration through a 0.2 μm PTFE filter membrane to remove trace particulate impurities.

[0118] [Battery Assembly]

[0119] The battery structures in this invention include, but are not limited to, button cells, pouch cells, cylindrical cells, etc. A cylindrical cell is used as an example in this invention, and its assembly can be performed in accordance with conventional methods in the art; further details will not be elaborated upon here.

[0120] Furthermore, according to some embodiments of the present invention, a third aspect of the present invention provides an electrical device comprising the lithium-ion battery mentioned in the first aspect above, or a lithium-ion battery prepared by the method for preparing the lithium-ion battery mentioned in the second aspect above.

[0121] The electrical devices in this invention may include mobile devices, electric vehicles, ships and satellites, energy storage systems, etc.

[0122] In the context of this specification, including the following embodiments and comparative examples, tests were conducted as follows:

[0123] Preprocessing:

[0124] First, discharge the lithium-ion battery to a constant current of 2.5V to ensure it is in a safe state, reducing the risk of short circuits or thermal runaway during disassembly. Carefully disassemble the battery within a glove box (protected by argon or other inert atmosphere) and remove the negative electrode. Use tweezers or suitable tools to peel off the negative electrode, avoiding damage to the active material layer. Next, cut the removed negative electrode to an appropriate size and soak it in anhydrous dimethyl carbonate (DMC) solution for 30 minutes to dissolve and remove residual electrolyte and possible byproducts. After removing the negative electrode, gently wipe the surface with lint-free paper, then replace with fresh DMC solution, repeating the soaking-wiping process three times to ensure no residual contaminants remain on the negative electrode surface. Finally, rinse the negative electrode with anhydrous ethanol and wipe again to further remove solvent and impurities. After cleaning, place the negative electrode sheet in a glove box and let it stand for 48 hours to ensure that the negative electrode sheet is completely dry, so as to prevent subsequent tests from being interfered with by solvent residue. Then, perform subsequent compaction, interface resistance and peel strength tests.

[0125] Test method for compaction density of negative electrode sheet:

[0126] First, the negative electrode sheet, after being washed with dimethyl carbonate and vacuum dried, was cut into six standard-sized square samples (2.0cm × 2.0cm). Next, the negative electrode active material layer on both sides of three of these square samples was removed, rinsed with ethanol, dried, weighed, and the average mass M1 was calculated. Simultaneously, the average thickness L1 of the sample was measured using a micrometer. Then, the mass of the remaining three square samples was weighed, and the average mass M2 was calculated. The average thickness L2 of the sample was also measured. The thickness of the negative electrode current collector was calculated as L2 - L1 (in cm). The compaction density of the electrode sheet was also calculated. Unit g / cm 3 .

[0127] Method for testing the interface resistance of the negative electrode:

[0128] The film resistance of the negative electrode was determined using the 46-probe method (45 probes arranged in a square matrix, with one probe serving as a ground probe) of the RM2610 resistance testing system. The sample was placed on the testing apparatus, and the pressure applied to the probes was adjusted using a pressure gauge to ensure good contact between the probes and the sample, with a contact area of ​​0.01 cm². 2 During the test, a constant current was applied to the 20 peripheral probes, allowing the current to flow through the surface, interface, and current collector of the negative electrode. Simultaneously, the 25 central probes measured the voltage change in real time. Finally, the membrane resistance was calculated using Ohm's law and fitting analysis. Nine square grids were randomly selected from the front, middle, and rear sections of the electrode for membrane resistance measurement, and the obtained values ​​were recorded as R1, R2, R3, R4, R5, R6, R7, R8, and R9, respectively. Finally, the arithmetic mean of these values ​​was calculated to obtain the average membrane resistance R of the actual tested negative electrode (R = (R1 + R2 + R3 + R4 + R5 + R6 + R7 + R8 + R9) / 9).

[0129] Test method for peel strength of negative electrode sheet:

[0130] First, use double-sided tape to fix the strip sample onto a flat, thin steel plate, ensuring the tape is centered on the plate. Then, peel off the protective layer of the double-sided tape and attach the strip sample of the negative electrode to be tested onto the tape. Use a pressure roller to evenly press the strip sample to ensure good adhesion. Next, tear off the unattached end, bend the torn negative electrode sheet upwards, and clamp it in the upper fixture of a tensile testing machine for a 180° peel test. Record the tensile force curve. The segment where the tensile force changes by no more than 10% is selected as the stable peel segment. Finally, divide the average tensile force of this segment by the width of the strip sample electrode to calculate the peel strength of the negative electrode. Peel force tests are conducted on the front, middle, and rear segments of the electrode, and the obtained values ​​are recorded as N1, N2, and N3, respectively. Finally, the arithmetic mean of these values ​​is calculated to obtain the average peel force N of the actual tested negative electrode (N = (N1 + N2 + N3) / 3).

[0131] Ratio performance testing method:

[0132] The lithium-ion battery was discharged to 2.5V and placed in a 25°C constant temperature chamber for 6 hours, and then tested according to the following steps:

[0133] (1) Under 1C conditions, constant current and constant voltage charging to 4.2V, cutoff current is 0.1C, and stand for 30 minutes. The capacity of constant current charging to 4.2V is Q1 (capacity of constant current segment).

[0134] (2) Discharge under constant current at 1C until 2.5V cutoff, with a cutoff current of 0.1C, and let stand for 30 minutes;

[0135] (3) Under 6C conditions, constant current and constant voltage charging to 4.2V, the cutoff current is 0.1C, and it is left to stand for 30 minutes. The capacity of constant current charging to 4.2V is Q6.

[0136] (4) Discharge under constant current at 1C until 2.5V cutoff, with a cutoff current of 0.1C, and let stand for 30 minutes;

[0137] The capacity retention rate of a lithium-ion battery at 25℃ is calculated as: Q1 / Q6 × 100%.

[0138] Cyclic performance testing methods:

[0139] The lithium-ion battery was placed in a 25°C constant temperature chamber for 6 hours and tested according to the following steps:

[0140] (1) First round of constant current and constant voltage charging: Charge at a constant current of 0.1C to 4.2V, then switch to constant voltage charging until the current drops to 0.01C;

[0141] (2) Let it stand for 30 minutes after charging is complete;

[0142] (3) Perform constant current discharge, discharging to 2.5V at a rate of 0.1C;

[0143] (4) Cyclic charge and discharge process: Charge at a constant current rate of 1C to 4.2V, let stand for 30 minutes, and discharge at a constant current rate of 1C to 2.5V.

[0144] (5) Repeat the above charging and discharging process for a total of 800 cycles.

[0145] Statistical analysis of battery discharge capacities Q1 and Q after 1 cycle and 800 cycles. 800 Calculate the battery capacity decay rate: (Q1-Q 800 ) / Q1×100.

[0146] Method for determining the electrode expansion rate after 800 cycles:

[0147] Take the lithium-ion battery that has undergone 800 cycles and obtain a dry and clean negative electrode sheet by following the pretreatment steps described above. Measure the thickness of the electrode sheet at nine points using a micrometer and take the average value, i.e., T. 800 Formula for calculating electrode expansion rate: Where T0 is the initial thickness of the dried negative electrode sheet before cycling.

[0148] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0149] Example 1

[0150] 1. Method for manufacturing positive electrode plates:

[0151] Take positive electrode active material (LiNi) 0.8 Co 0.1 Mn 0.1 O2, NMC811), conductive carbon black, carbon nanotubes and polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96:1:1:2 to obtain a positive electrode slurry with a solid content of 65wt%. The positive electrode slurry was then coated onto a 12.0μm thick aluminum foil, dried and cold-pressed to obtain the positive electrode sheet.

[0152] 2. Method for manufacturing negative electrode plates:

[0153] Preparation of copper foil current collector: First, the surface of the copper foil is cleaned with ethanol to remove oil and organic impurities. Then, it is placed in a UV / O3 treatment device and treated for 5 minutes at an ozone concentration of 300 ppm and a temperature of 40°C. High-energy UV light induces the conversion of O2 in the air into O3, which then decomposes to form active oxygen atoms. These active oxygen atoms react with the copper surface to generate polar oxygen-containing functional groups such as –OH, –COOH, and –C=O. The roughness (Ra) of the negative electrode current collector copper foil is typically measured using a surface profilometer, according to standards ISO 4287 or GB / T 3505. The roughness R of this UV / O3 treated copper foil current collector... a It is 0.6μm.

[0154] Preparation of cross-linked PAA-CMC polymer: First, PAA (LA132, Indira) and CMC (MAC500, Nippon Paper) were dissolved separately in deionized water at a concentration of 5 wt%, then mixed at a mass ratio of 1:1 and reacted thoroughly for 6 hours under magnetic stirring. Next, the pH of the mixed solution was adjusted to 3.0 (dilute HCl can be used for acid adjustment). Then, the mixed solution was heat-treated at 150°C for 8 hours to form a stable cross-linked structure and obtain the cross-linked product. Finally, the cross-linked product was filtered, washed with deionized water, and dried to obtain powdered cross-linked PAA-CMC polymer.

[0155] The infrared spectrum of the cross-linked PAA-CMC polymer is as follows: Figure 1 As shown, from Figure 1 It can be seen that the cross-linked PAA-CMC polymer at 1710 cm⁻¹ -1 -1720cm -1 and 1800cm -1 ~1810cm -1 The presence of characteristic infrared absorption peaks for ester bonds (-COO) indicates successful crosslinking of PAA and CMC. Specifically, the carboxyl group (-COOH) in PAA exhibits a peak at 1700 cm⁻¹. -1 -1710cm -1 Infrared characteristic absorption peaks appear. After successful cross-linking, -COOH is transformed into -COO, and its infrared characteristic peaks shift towards longer wavelengths.

[0156] Preparation of the negative electrode sheet: The negative electrode slurry, by mass percentage, comprises 23.75% deposited silicon carbide, 71.25% artificial graphite (SiC:Graphite mass ratio 1:3), 0.75% SWCNT, 0.75% Super P, 1.0% thickener sodium carboxymethyl cellulose (CMC), 1.25% styrene-butadiene rubber (SBR), and 1.25% cross-linked PAA-CMC polymer. These substances are added to deionized water and stirred to form a negative electrode slurry with a solid content of 65 wt%. The negative electrode slurry is then coated onto both sides of the copper foil current collector. After drying and cold pressing, the negative electrode sheet is formed with a compaction density of 1.55 g / cm³. 3 .

[0157] 3. Preparation of electrolyte:

[0158] In an argon-filled glove box, high-purity ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were first mixed in a mass ratio of 25.0 wt%:25.0 wt%:25.0 wt%, and stirred at 300 rpm for 30 minutes to form a homogeneous solvent system. Then, 14.5 wt% of LiPF6 was slowly added to avoid local overheating and decomposition of the lithium salt. After complete dissolution, 6.0 wt% of vinylene carbonate (VC), 3.0 wt% of fluoroethylene carbonate (FEC), and 1.5 wt% of DTD bifunctional additive were added sequentially, and the stirring rate was increased to 600 rpm for 2 hours to ensure molecular-level dispersion of the additives. Finally, the electrolyte was obtained by pressure filtration through a 0.2 μm PTFE membrane to remove trace particulate impurities.

[0159] 4. Diaphragm:

[0160] A high-porosity membrane is selected, in which the thickness of the polyethylene (PE) base membrane is 9.0 μm, the thickness of the ceramic coating on both sides of the base membrane is 1.0 μm, and the thickness of the polyvinylidene fluoride (PVDF) coating is 1.0 μm.

[0161] 5. Assembly of lithium-ion batteries:

[0162] After the positive and negative electrode sheets are rolled and slit, they are wound together with the separator according to a set process to form a 21700 cylindrical battery core. The battery core is then fixed to pre-made connecting pieces by welding and installed into a metal battery casing. After completing key processes such as electrolyte injection, sealing, and formation, a lithium-ion battery is obtained. This lithium-ion battery uses a cylindrical casing with external dimensions of 21.0 mm in diameter and 70.0 mm in length, conforming to the 21700 standard specifications.

[0163] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0164] Example 2

[0165] The method according to Example 1 differs in that:

[0166] The content of styrene-butadiene rubber (SBR) is 2% by mass, and the content of cross-linked PAA-CMC polymer is 0.5% by mass.

[0167] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0168] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0169] Example 3

[0170] The method according to Example 1 differs in that:

[0171] The mass content of styrene-butadiene rubber (SBR) is 1.63%, and the mass content of cross-linked PAA-CMC polymer is 0.87%.

[0172] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0173] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0174] Example 4

[0175] The method according to Example 1 differs in that:

[0176] The content of styrene-butadiene rubber (SBR) is 1% by mass, and the content of cross-linked PAA-CMC polymer is 1.5% by mass.

[0177] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0178] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0179] Example 5

[0180] The method according to Example 1 differs in that:

[0181] The mass content of styrene-butadiene rubber (SBR) is 0.75%, and the mass content of cross-linked PAA-CMC polymer is 1.75%.

[0182] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0183] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0184] Example 6

[0185] The method according to Example 1 differs in that:

[0186] Add 6.7 wt% vinylene carbonate (VC), 3.3 wt% fluoroethylene carbonate (FEC) and 0.5 wt% DTD bifunctional additive;

[0187] The electrolyte and the corresponding lithium-ion battery were finally prepared.

[0188] The results of the 6C charging capacity retention rate, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C for lithium-ion batteries are shown in Table 1.

[0189] Example 7

[0190] The method according to Example 1 differs in that:

[0191] Add 6.3 wt% vinylene carbonate (VC), 3.2 wt% fluoroethylene carbonate (FEC) and 1 wt% DTD bifunctional additive;

[0192] The electrolyte and the corresponding lithium-ion battery were finally prepared.

[0193] The results of the 6C charging capacity retention rate, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C for lithium-ion batteries are shown in Table 1.

[0194] Example 8

[0195] The method according to Example 1 differs in that:

[0196] Add 5.7 wt% vinylene carbonate (VC), 2.8 wt% fluoroethylene carbonate (FEC) and 2 wt% DTD bifunctional additive;

[0197] The electrolyte and the corresponding lithium-ion battery were finally prepared.

[0198] The results of the 6C charging capacity retention rate, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C for lithium-ion batteries are shown in Table 1.

[0199] Example 9

[0200] The method according to Example 1 differs in that:

[0201] Add 5.3 wt% vinylene carbonate (VC), 2.7 wt% fluoroethylene carbonate (FEC) and 2.5 wt% DTD bifunctional additive;

[0202] The electrolyte and the corresponding lithium-ion battery were finally prepared.

[0203] The results of the 6C charging capacity retention rate, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C for lithium-ion batteries are shown in Table 1.

[0204] Example 10

[0205] The method according to Example 1 differs in that:

[0206] The mass content of deposited silicon-carbon is 4.75%, and the mass content of artificial graphite is 90.25%.

[0207] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0208] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0209] Example 11

[0210] The method according to Example 1 differs in that:

[0211] The deposited silicon-carbon mass content is 14.25%, and the artificial graphite mass content is 80.75%.

[0212] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0213] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0214] Example 12

[0215] The method according to Example 1 differs in that:

[0216] The mass content of deposited silicon-carbon is 28.5%, and the mass content of artificial graphite is 66.5%.

[0217] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0218] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0219] Example 13

[0220] The method according to Example 1 differs in that:

[0221] The mass content of deposited silicon-carbon is 33.25%, and the mass content of artificial graphite is 61.75%.

[0222] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0223] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0224] Example 14

[0225] The method according to Example 1 differs in that:

[0226] The roughness R of the copper foil current collector treated with UV / O3 was determined after 3 minutes of treatment at an ozone concentration of 100 ppm and a temperature of 30°C. a It is 0.2μm;

[0227] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0228] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0229] Example 15

[0230] The method according to Example 1 differs in that:

[0231] The roughness R of the copper foil current collector treated with UV / O3 was determined after 5 minutes of treatment at an ozone concentration of 200 ppm and a temperature of 35°C. a It is 0.4μm;

[0232] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0233] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0234] Example 16

[0235] The method according to Example 1 differs in that:

[0236] The roughness R of the copper foil current collector treated with UV / O3 was determined after 8 minutes of treatment at an ozone concentration of 400 ppm and a temperature of 40°C. a It is 0.8μm;

[0237] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0238] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0239] Example 17

[0240] The method according to Example 1 differs in that:

[0241] The roughness R of the copper foil current collector treated with UV / O3 was determined after 8 minutes of treatment at an ozone concentration of 500 ppm and a temperature of 45°C. a It is 1μm;

[0242] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0243] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0244] Example 18

[0245] The method according to Example 1 differs in that:

[0246] The negative electrode sheet has a compacted density of 1.35 g / cm³. 3 ;

[0247] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0248] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0249] Example 19

[0250] The method according to Example 1 differs in that:

[0251] The negative electrode sheet has a compacted density of 1.65 g / cm³. 3 ;

[0252] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0253] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0254] Comparative Example 1

[0255] The method according to Example 1 differs in that:

[0256] The styrene-butadiene rubber (SBR) has a mass content of 2.5% and does not contain cross-linked PAA-CMC polymer;

[0257] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0258] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0259] Comparative Example 2

[0260] The method according to Example 1 differs in that:

[0261] It contains 7% vinylene carbonate (VC) and 3.5% fluoroethylene carbonate (FEC), but no DTD bifunctional additives.

[0262] The electrolyte and the corresponding lithium-ion battery were finally prepared.

[0263] The results of the 6C charging capacity retention rate, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C for lithium-ion batteries are shown in Table 1.

[0264] Comparative Example 3

[0265] The method according to Example 1 differs in that:

[0266] The copper foil is not treated with UV / O3.

[0267] The negative electrode and the corresponding lithium-ion battery were finally prepared.

[0268] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0269] Comparative Example 4

[0270] The method according to Example 1 differs in that:

[0271] The negative electrode slurry, calculated by mass percentage, comprises 23.75% deposited silicon carbide, 71.25% graphite (mass ratio SiC:Graphite = 1:3), 0.75% SWCNT, 0.75% Super P, 1% thickener sodium carboxymethyl cellulose (CMC), 1.25% styrene-butadiene rubber (SBR), and 1.25% PAA (LA132, Indira).

[0272] The results of the interface resistance and peel strength of the negative electrode, as well as the capacity retention rate of the lithium-ion battery at 6C charging, the capacity decay rate after 800 cycles at 1C, and the electrode expansion rate after 800 cycles at 1C are shown in Table 1.

[0273] Table 1. Performance results of negative electrode sheets and lithium-ion batteries in the examples and comparative examples.

[0274]

[0275]

[0276] The test results from Examples 1-19 and Comparative Examples 1-4 show that the synergistic effect of the negative electrode and electrolyte in this invention enables the lithium-ion battery to maintain structural stability and improve electrochemical performance under high-rate and long-cycle conditions. This is because the negative electrode and electrolyte work together to construct a stable and functional solid electrolyte interphase (SEI) film, significantly enhancing the interfacial bonding between the negative electrode binder and the active material, optimizing the conductive network structure and electrode flexibility, thereby effectively reducing interfacial impedance, enhancing electrode structural stability and film uniformity, and suppressing electrode expansion and debonding during cycling. This synergistic optimization scheme significantly improves the overall performance of the battery under high-rate charge-discharge and long-life cycle conditions, achieving a multiple balance between reversible capacity, interfacial stability, and fast-charging capability of the silicon-containing negative electrode, and possesses promising engineering application prospects.

[0277] Specifically:

[0278] As can be seen from Example 1 and Comparative Examples 1-4, the preparation without cross-linked PAA-CMC polymer: first, PAA (LA132, Indira) and CMC (MAC500, Nippon Paper) are separated. If no sulfur-containing additive is added to the electrolyte or the negative electrode current collector does not have the required roughness, the electrode interface resistance increases significantly, the peel strength decreases significantly, the 6C capacity retention rate and 800-cycle stability decrease significantly, and the electrode expansion rate also increases significantly, showing poor interface stability and mechanical integrity.

[0279] Examples 1-5 show that as the amount of cross-linked PAA-CMC polymer added increases from 0.5% to 1.25%, the interfacial resistance increases from 1.1 × 10⁻⁶. -2 Significantly decreased to 5.5×10 -3 Ω·cm 2 The peel strength was improved to 16.5 N / m, and the 6C capacity retention rate reached a maximum of 94.2%. After 800 cycles, the capacity decay rate and electrode expansion rate dropped to the lowest values ​​of 5.3% and 5.2%, respectively. When the amount of cross-linked PAA-CMC polymer was further increased to 1.75%, the interfacial resistance and expansion rate increased again, while the capacity retention rate and bond strength decreased. This phenomenon is attributed to the following: when the mass percentage of cross-linked PAA-CMC polymer is 1.25%, sufficient hydrogen and ester bonds are provided to enhance interfacial toughness without hindering ion channels, thus achieving optimal lithium-ion battery performance. When it exceeds 1.25%, excess polymer segments occupy the surface and pores of the active material, hindering electrolyte contact and ion migration. At the same time, excessive cohesion and lack of buffer space lead to stress concentration and performance degradation, resulting in a decline in various performance characteristics of the lithium-ion battery.

[0280] Examples 1 and 6-9 show that as the DTD addition increases from 0.5 wt% to 1.5 wt%, the 6C rate performance, 800-cycle capacity retention, and electrode expansion rate improve simultaneously. This is attributed to the fact that with the increase of DTD, it preferentially undergoes electron reduction on the negative electrode surface, generating a stable and dense LiF-rich inorganic phase, which can construct a primary SEI film structure with uniform interface and good ion permeability. However, when the DTD ratio is too high, for example, exceeding 1.5 wt%, the expansion rate and capacity decay rate increase significantly after 800 cycles, showing typical "excess instability" behavior. This result is attributed to the gradual accumulation of reduction byproducts and chain intermediates on the SEI surface, resulting in an excessively high proportion of organic components in the film layer, making the structure rigid and brittle, and thus hindering the continuity of Li+ migration channels.

[0281] Examples 1 and 10-13 show that as the ratio of deposited silicon-carbon and graphite in the composite anode increases from 1 / 19 to 1 / 3, the electrode interface resistance increases from 6.3 × 10⁻⁶. -3 Ω·cm 2 Decreased to 5.5×10 -3 Ω·cm 2 The peel strength increased to 16.5 N / m, and the 6C rate capacity and 800-cycle stability reached their peak values. This result is attributed to the fact that within this ratio range, SiC and graphite construct a more compact and elastic structural network, which can effectively alleviate the volume expansion stress during the charging and discharging process. However, when the ratio of deposited silicon-carbon and graphite continues to increase to 7 / 13, the interfacial resistance rises again, the electrode expansion intensifies, and the electrochemical performance declines, showing a significant "conductive phase dilution" effect. This result is attributed to the corresponding reduction in graphite content, which impairs the connectivity of the conductive network.

[0282] Examples 1 and 14-17 show that as the roughness Ra of the copper foil gradually increases from 0.2 μm to 0.6 μm, the 6C rate performance and long-cycle expansion control effect are significantly enhanced. This result is attributed to the formation of a more pronounced micro-convex structure on the current collector surface, which establishes a stronger mechanical interlock and anchoring effect with the binder network in the electrode, effectively improving interfacial adhesion and ion diffusion uniformity. However, when Ra increases further, the interfacial resistance rebounds and the electrochemical performance decreases. This result is attributed to the excessive undulation structure leading to stress concentration and enhanced electric field edges, resulting in discontinuous SEI film formation and unbalanced electrolyte distribution.

[0283] Through Examples 1 and 18-19, it can be seen that as the compaction density increases from 1.35 g / cm³, the following results are obtained: 3 Increased to 1.5g / cm 3The interfacial resistance decreased, the peel strength increased, the 6C capacity retention reached a peak of 94.2%, the cycle decay rate was as low as 5.3%, and the electrode expansion rate decreased to 5.2%; however, further compaction was carried out to 1.65 g / cm³. 3 At this point, both capacity retention and cycling stability decreased, demonstrating the synergistic mechanism of "diffusion restriction" and "interface deterioration" caused by over-compaction. The reason for this result can be attributed to the fact that, within a certain range, as compaction density increases, the electrode structure gradually transitions to a dense state with low porosity and high particle contact. The conductive network and bonding interface are simultaneously strengthened, and the electron and lithium-ion transport paths are shortened. However, when the compaction density is too high, the internal channels gradually close, electrolyte penetration is restricted, SEI formation is hindered, and lithium-ion diffusion rate decreases.

[0284] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector; The negative electrode active material layer contains negative electrode active material and negative electrode binder; The negative electrode binder includes a cross-linked polymer, which contains polyacrylic acid structural units and carboxymethyl cellulose salt structural units; The negative electrode active material includes silicon-containing materials; The surface roughness Ra of the negative electrode current collector is 0.2 μm-1 μm; The electrolyte contains functional additives, including carbonate additives and sulfur-containing additives.

2. The lithium-ion battery according to claim 1, wherein, The lithium-ion battery includes at least one of the following features (1)-(8): (1) The polyacrylic acid structural unit includes a polyacrylic acid structural unit and / or a polymethacrylic acid structural unit; (2) The carboxymethyl cellulose salt structural unit includes at least one of the carboxymethyl cellulose lithium structural unit, carboxymethyl cellulose sodium structural unit and carboxymethyl cellulose potassium structural unit; (3) The polyacrylic acid structural unit and the carboxymethyl cellulose salt structural unit are connected by ester bonds; (4) The weight-average molecular weight of the cross-linked polymer is 90,000 Da-210,000 Da; (5) The mass ratio of the polyacrylic acid structural unit to the carboxymethyl cellulose salt structural unit is 1:(0.5-1.5); (6) The cross-linked polymer in the negative electrode binder has a mass content of 20%-70%; (7) The negative electrode binder also includes styrene-butadiene rubber, and the mass content of styrene-butadiene rubber in the negative electrode binder is 30%-80%; (8) The negative electrode binder has a mass content of 0.5%-7% in the negative electrode active material layer.

3. The lithium-ion battery according to claim 1, wherein, The lithium-ion battery includes at least one of the following features (1)-(10): (1) The silicon-containing material includes silicon-carbon materials and / or crystalline silicon; (2) The silicon-containing material D v The particle size of 50 particles ranges from 5.5 μm to 14.5 μm. (3) The negative electrode active material also includes carbon materials; (4) The surface of the negative electrode current collector contains polar oxygen-containing functional groups; (5) The material of the negative electrode current collector includes copper; (6) The compaction density of the negative electrode sheet is 1.35 g / cm³. 3 -1.65g / cm 3 ; (7) The peel strength of the negative electrode sheet is 9.5 N / m-19 N / m; (8) The interface resistance R of the negative electrode sheet α 1×10 -3 Ω·cm 2 -2.2×10 -2 Ω·cm 2 ; (9) The negative electrode active material layer also includes a thickener; (10) The negative electrode active material layer also includes a conductive agent.

4. The lithium-ion battery according to claim 3, wherein, The lithium-ion battery includes at least one of the following features (1)-(9): (1) The silicon-containing material includes silicon-carbon material; (2) The silicon-carbon material includes deposited silicon-carbon; (3) The carbon material includes at least one of artificial graphite, natural graphite, soft carbon and hard carbon; (4) The carbon material D v The particle size of 50 particles ranges from 5.5 μm to 14.5 μm. (5) The mass ratio of the silicon-containing material to the carbon material is 1:(1.5-19); (6) The polar oxygen-containing functional group includes at least one of hydroxyl, carboxyl and carbonyl groups; (7) The thickener includes carboxymethyl cellulose salt; (8) The thickener has a mass content of 0.5%-1.8% in the negative electrode active material layer; (9) The conductive agent has a mass content of 0.5%-2% in the negative electrode active material layer.

5. The lithium-ion battery according to any one of claims 1-4, wherein, The lithium-ion battery includes at least one of the following features (1)-(6): (1) The sulfur-containing additives include at least one of vinyl sulfate, vinyl sulfite, propylene sulfite and dimethyl sulfite; (2) The sulfur-containing additive has a mass content of 4%-25% in the functional additive; (3) The carbonate additives include at least one of ethylene carbonate, propylene carbonate, butyl carbonate, and fluoroethylene carbonate; (4) The carbonate additives in the functional additives have a mass content of 75%-96%; (5) The functional additive in the electrolyte has a mass content of 4.5%-12.5%; (6) The electrolyte also contains lithium electrolyte and organic solvent.

6. The lithium-ion battery according to claim 5, wherein, The lithium-ion battery includes at least one of the following features (1)-(6): (1) The sulfur-containing additives include vinyl sulfate; (2) The carbonate additives include vinylene carbonate and fluoroethylene carbonate, wherein the mass ratio of vinylene carbonate to fluoroethylene carbonate is (1-3):

1. (3) The lithium electrolyte has a mass content of 10%-20% in the electrolyte; (4) The organic solvent in the electrolyte has a mass content of 67.5%-85.5%.

7. A method for preparing a lithium-ion battery, characterized in that, The preparation method includes: Preparation of negative electrode sheet: A negative electrode slurry containing negative electrode active material and negative electrode binder is coated on at least one side surface of the negative electrode current collector, and then dried to obtain a negative electrode sheet. Battery assembly: The positive electrode, separator and negative electrode are stacked in sequence and then wound or pressed to obtain a bare cell. Then, electrolyte is injected and packaged to obtain a lithium-ion battery. The negative electrode binder includes a cross-linked polymer, which contains polyacrylic acid structural units and carboxymethyl cellulose salt structural units. The negative electrode active material includes silicon-containing materials; The surface roughness Ra of the negative electrode current collector is 0.2 μm-1 μm; The electrolyte contains functional additives, including carbonate additives and sulfur-containing additives.

8. The method for preparing a lithium-ion battery according to claim 7, wherein, The method for preparing the lithium-ion battery further includes at least one of the following conditions (1)-(2): (1) The preparation method of the cross-linked polymer includes: under acidic conditions, a raw material liquid containing polyacrylic acid polymer monomers, carboxymethyl cellulose salt and water is subjected to a polymerization reaction, followed by filtration, washing and drying to obtain the cross-linked polymer; (2) The preparation method of the negative electrode current collector includes: treating the negative electrode current collector precursor with ozone under ozone conditions to obtain the negative electrode current collector.

9. The method for preparing a lithium-ion battery according to claim 8, wherein, The method for preparing the lithium-ion battery further includes at least one of the following conditions (1)-(7): (1) The weight average molecular weight of the polyacrylic acid polymer monomer is 40,000 Da-150,000 Da; (2) The weight-average molecular weight of the carboxymethyl cellulose salt is 40,000 Da-150,000 Da; (3) The total mass content of the polyacrylic acid monomer and the carboxymethyl cellulose salt in the raw material liquid is 0.5%-10%; (4) The pH value of the raw material solution is 3-4; (5) The conditions for the polymerization reaction include: a temperature of 140-160℃ and a time of 5-12 hours; (6) The negative electrode current collector precursor includes copper foil; (7) The conditions for ozone treatment include: ozone concentration of 200-500ppm, temperature of 35-45℃, and time of 3-8 minutes.

10. An electrical device, characterized in that, The lithium-ion battery includes any one of the lithium-ion batteries described in claims 1-6, or lithium-ion batteries prepared by the method described in any one of claims 7-9.

Images