Lithium-ion battery

Abstract

Provided in the present disclosure is a lithium-ion battery. The lithium-ion battery comprises a negative electrode sheet and a positive electrode sheet. The positive electrode sheet comprises a nickel-based positive electrode active material, a negative electrode active layer of the negative electrode sheet comprises a negative electrode active material and nickel, and the negative electrode active material comprises a silicon-carbon material and graphite. The components of the negative electrode active layer satisfies 9500≤α*d / η≤24500, wherein α is the content of nickel in the negative electrode active layer, η is the content percentage by mass of silicon in the negative electrode active layer, and d is the median particle diameter of the negative electrode active material. The negative electrode sheet comprises a carbon-silicon negative electrode active material, such that good cycle performance and safety performance can be taken into account while improving the energy density of the lithium-ion battery.

Description

A lithium-ion battery Technical Field

[0001] The present disclosure relates to a pole piece, in particular to a negative pole piece and a lithium-ion battery, belonging to the field of new energy technology. Background Art

[0002] Lithium-ion batteries have the characteristics of high energy density, long cycle life and environmental friendliness. They have been widely used in electronic products such as mobile communication devices, laptops, digital cameras, and are gradually playing a role in electric vehicles and energy storage.

[0003] Anode materials are key components of lithium-ion batteries. Graphite is the most widely used commercial anode material for lithium-ion batteries, but its theoretical specific capacity is only 372 mAh / g, which currently cannot meet the requirements of high-energy-density lithium-ion batteries. Carbon-silicon anode materials, on the other hand, have a theoretical specific capacity exceeding 1500 mAh / g, making them a promising next-generation anode material.

[0004] However, carbon-silicon anode materials undergo significant volume expansion and contraction with each lithium insertion and removal, causing lithium-ion batteries to exhibit rapid thickness growth during the charge-discharge cycle. Therefore, while the volumetric energy density of batteries using carbon-silicon anode materials is initially high, it decreases significantly with increasing cycles, posing a certain degree of safety risk. Therefore, for lithium-ion batteries with silicon-carbon anode materials, significantly reducing the rate of thickness expansion during cyclic charge-discharge cycles is a key issue in promoting their commercial application. Summary of the Invention

[0005] To reduce the thickness expansion rate of carbon-silicon negative electrode materials during cyclic charge and discharge, thereby improving battery safety and cycling stability, the present disclosure provides a negative electrode sheet comprising carbon-silicon negative electrode active materials. This negative electrode sheet improves the energy density of lithium-ion batteries while also providing excellent cycling performance and safety. This lithium-ion battery exhibits excellent energy density, cycling performance, and safety.

[0006] The present disclosure provides a lithium-ion battery, comprising a negative electrode sheet and a positive electrode sheet, wherein the positive electrode sheet comprises a nickel-based positive electrode active material, and a negative electrode active layer of the negative electrode sheet comprises a negative electrode active material and nickel, wherein the negative electrode active material comprises a silicon-carbon material and graphite; and the composition of the negative electrode active layer satisfies 9500≤α*d / η≤24500;

[0007] Wherein, α is the content of nickel in the negative electrode active layer, in ppm; η is the mass percentage of silicon in the negative electrode active layer, in %; and d is the median particle size of the negative electrode active material, in μm.

[0008] The negative electrode sheet disclosed herein, whose negative electrode active materials include silicon-carbon material, graphite material, and nickel, effectively suppresses the expansion and deformation of the negative electrode sheet during lithium insertion and extraction by ensuring that the content of the silicon-carbon material, graphite material, and nickel element, as well as the size of the silicon-carbon material and graphite material, meet certain requirements, thereby facilitating the cycle performance and safety performance of the lithium-ion battery including the negative electrode sheet. Therefore, the silicon-containing negative electrode sheet and nickel-based positive electrode sheet disclosed herein not only improve the energy density of lithium-ion batteries, but also take into account the cycle performance and safety performance of lithium-ion batteries, overcome the shortcomings of silicon-based materials, and broaden the application range of silicon-based materials.

[0009] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. DETAILED DESCRIPTION

[0010] To make the objectives, technical solutions, and advantages of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present disclosure.

[0011] The present disclosure provides a lithium-ion battery, comprising a negative electrode sheet and a positive electrode sheet, wherein the positive electrode sheet comprises a nickel-based positive electrode active material, and a negative electrode active layer of the negative electrode sheet comprises the negative electrode active material and nickel, and the negative electrode active material comprises a silicon-carbon material and graphite; the composition of the negative electrode active layer satisfies 9500≤α*d / η≤24500 (for example, 9500, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 21000, 22000, 23000, 24000, or 24500);

[0012] Wherein, α is the nickel content in the negative electrode active layer, expressed in ppm; η is the mass percentage of silicon in the negative electrode active layer, expressed in %. d is the median particle size D50 of the negative electrode active material, expressed in μm. The median particle size referred to herein is the particle size at which the cumulative volume accounts for 50% of the total volume of all negative electrode active materials.

[0013] It should be noted that the negative electrode sheet with the above relationship in the present disclosure refers to the negative electrode sheet in the lithium-ion battery after the sorting process, or the negative electrode sheet in the lithium-ion battery that has undergone formation treatment and discharge treatment (the discharge treatment refers to the discharge treatment after a maximum of 10 cycles).

[0014] The negative electrode sheet disclosed herein comprises a silicon-carbon material, and the positive electrode sheet comprises a nickel-based positive active material. Thus, the lithium-ion battery can exhibit excellent energy density. Furthermore, when the negative electrode active layer satisfies the aforementioned relationship, the nickel content is more compatible with the silicon content and the morphology of the negative electrode active material. Based on the requirements for silicon content and the median particle size D50 of the negative electrode active material, an appropriate amount of nickel that matches these requirements helps the electrolyte form a stable and appropriately thick functional layer on the surface of the negative electrode active material. On the one hand, the functional layer structure is more stable and will not rupture due to the expansion and contraction of the silicon-carbon material. This prevents excessive consumption of electrolyte and lithium ions caused by SEI film reconstruction and continued surface side reactions, and prevents excessive accumulation of byproducts and interfacial corrosion or degradation of the silicon-carbon material. On the other hand, based on the specific specific surface area of ​​the negative electrode active material at a specific median particle size, the functional layer thickness is more suitable, ensuring smooth lithium ion intercalation and deintercalation, providing favorable conditions for improving cycling performance and safety performance. Therefore, the lithium-ion battery will not experience excessive expansion and deformation during long-term cycling, which not only ensures the smooth insertion and extraction of lithium ions, but also prevents the lithium-ion battery from rupturing and exploding under external forces due to expansion and deformation, significantly improving the cycle life.

[0015] In one embodiment, 20ppm≤α≤75ppm (e.g., 20ppm, 25ppm, 30ppm, 35ppm, 40ppm, 45ppm, 50ppm, 55ppm, 60ppm, 65ppm, 70ppm, or 75ppm); and / or, 1.5%≤η≤7.5% (e.g., 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, or 7.5%); and / or, 9μm≤d≤16μm (e.g., 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or 16μm). When at least one of the nickel content α, the mass percentage of silicon η, and the median particle size d meets the above ranges, the cycle performance and safety performance of the battery are further improved.

[0016] Furthermore, when the negative electrode active layer also includes cobalt, the content of cobalt in the negative electrode active layer is no more than 50 ppm. Studies have found that excessive cobalt may exacerbate side reactions on the surface of the silicon-carbon material, resulting in an excessively thick side reaction layer, thereby increasing the transport resistance of lithium ions. Therefore, when the negative electrode active layer includes no more than 50 ppm of cobalt, the rate performance of the lithium-ion battery is better.

[0017] It can be understood that, during the preparation process, the composition of the negative electrode active layer that satisfies the above relationship can be obtained by controlling the selection of raw materials in the negative electrode active layer slurry.

[0018] Of course, when the negative electrode sheet is in a lithium-ion battery, the relevant parameters can also be detected by disassembling the lithium-ion battery.

[0019] Among them, the disassembled negative electrode sheet was soaked in DMC for 2 hours, dried, and then soaked in deionized water to separate the negative electrode coating from the copper foil. It was then directly dried and the negative electrode current collector was removed to obtain the powder of the negative electrode active layer. The powder was tested according to the following method to obtain the nickel element content α, the cobalt element content, the mass percentage content η of the silicon element, and the median particle size d of the negative electrode active material.

[0020] The powder obtained above was subjected to an ICP test to obtain the mass percentage content α of the Ni element and the mass percentage content of the Co element therein.

[0021] The powder obtained above was placed in an argon atmosphere, heated to 230°C at 10°C / min, and the weight of the powder at this time was taken as the initial weight W1. Then, it was switched to an air atmosphere, heated to 800°C at 10°C / min and maintained for 8 hours to obtain the final weight W2 of the powder. W2 / W1 / 2.14 was used as the content η of the Si element in the negative electrode coating, where 2.14 was obtained by dividing the molar mass of silicon dioxide 60 by the molar mass of silicon element 28.

[0022] The powder obtained above was placed in an argon atmosphere, heated to 400°C at a rate of 10°C / min and maintained for 2 hours. After cooling, the median particle size d of the powder was measured using a laser particle size analyzer.

[0023] The negative electrode sheet disclosed herein includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector includes at least one of copper foil, nickel foam, and copper foam. The negative electrode active layer includes a negative electrode active material and a negative electrode binder. The negative electrode active material includes silicon-carbon materials and graphite that provide a site for lithium ion intercalation and deintercalation. The negative electrode binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, and styrene-butadiene rubber.

[0024] The present disclosure does not limit the specific form of silicon-carbon material. It can be a composite material of silicon material (silicon element or silicon oxide, etc.) and carbon material (graphite, graphene, or pyrolytic carbon, etc.), for example, a mixture of silicon material and carbon material, or silicon material filled in the pores of carbon material.

[0025] The present disclosure does not limit the specific form of graphite, and the graphite may be natural graphite, artificial graphite, or a coating of natural graphite and / or artificial graphite. For example, the graphite may be a product in which amorphous carbon is coated on the surface of artificial graphite, and the coating mass of the amorphous carbon may account for 0.1% to 3% (e.g., 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%) of the product.

[0026] Furthermore, the negative electrode active layer further includes a negative electrode conductive agent, which can be selected from at least one of carbon black, acetylene black, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, Ketjen black, and carbon fiber.

[0027] In a specific embodiment, the negative electrode sheet of the present disclosure also has a special crystal phase structure. Specifically, in the X-ray diffraction pattern, the negative electrode sheet active layer has a first diffraction peak with a 2θ range of 53.7° to 55.7° and a second diffraction peak with a 2θ range of 76.4° to 78.4°, and the intensity ratio of the first diffraction peak to the second diffraction peak is 1. 8 to 16. When the negative electrode has this strength ratio When the negative electrode is heated, the expansion deformation of the negative electrode during the cycle is further reduced.

[0028] Specifically, the above parameters can be obtained by performing X-ray diffraction detection on the negative electrode sheet.

[0029] For example, the graphite particles can be selected to make the negative electrode sheet have a thickness of 1.73 g / cm 3 Graphite particles with an OI value of 9 to 17 at compacted density to achieve this strength ratio The OI value can be obtained by performing X-ray diffraction on the negative electrode active layer of the negative electrode sheet, and detecting the height of the diffraction peak of the 004 crystal plane with 2θ of 53.7°~55.7° as I1, and the height of the diffraction peak of the 110 crystal plane with 2θ of 76.4°~78.4° as I2. I1 / I2 is the OI value.

[0030] In addition, the composition of the negative electrode active layer can be further adjusted on the basis of satisfying the above conditions so that the negative electrode sheet meets (For example, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55 or 0.6), thereby further balancing the energy density and cycle performance of the silicon-containing negative electrode. Specifically, by taking both the crystalline structure of the negative electrode active layer and the content of silicon element into consideration, the two are matched with each other, and the negative electrode active layer is expanded to an appropriate extent without significantly affecting the energy density of the lithium-ion battery and the structure of the negative electrode material, thereby improving the liquid retention rate of the negative electrode active layer, laying the foundation for the long-term effective cycle of the lithium-ion battery, so that the lithium-ion battery has excellent energy density and more outstanding cycle performance.

[0031] In a specific embodiment, when the negative electrode sheet has the following thermogravimetric analysis parameters, the energy density of the lithium-ion battery is more significantly improved without affecting the cycle performance of the lithium-ion battery.

[0032] Specifically, in differential scanning calorimetry analysis, the negative electrode active layer satisfies the following formulas 1 and 2:

[0033] 0.75%≤m*d≤4% (e.g., 0.75%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, or 4%) (Equation 1), 30%≤(1.27n-6.32m) / η≤95% (e.g., 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%) (Equation 2)

[0034] Among them, when the negative electrode active layer is heated from 25°C to 1000°C at 10°C / min in an argon atmosphere, the weight loss percentage in the range of 230-360°C is m, and the weight loss percentage in the range of 230-950°C is n.

[0035] Specifically, as the temperature of the negative electrode active layer increases at the above rate, its mass decreases. When the temperature increases from 230°C to 360°C, the percentage of the negative electrode active layer's mass loss relative to its mass at 230°C is m. When the temperature increases from 230°C to 950°C, the percentage of the negative electrode active layer's mass loss relative to its mass at 230°C is n.

[0036] The aforementioned weight loss primarily stems from the binder in the negative electrode active layer. Different binder compositions decompose and lose weight as the temperature gradually increases. Binder molecules that decompose between 230-360°C typically contain a rich array of hydroxyl, carboxyl, and ether bonds. These oxygen-containing groups interact well with elements like carbon and silicon in the negative electrode active material, effectively coating the surface of the negative electrode active material and providing excellent dispersion. Binder molecules that begin to decompose between 360-950°C are primarily composed of carbon and hydrogen. These carbon-based molecular chains possess excellent elasticity, allowing them to adhere to the negative electrode active material and the current collector or negative electrode material, effectively suppressing the continued expansion of the negative electrode coating. Therefore, when the binder content, the median particle size of the negative electrode active material, and the silicon content satisfy Equations 1 and 2, respectively, the binder effectively disperses and bonds the negative electrode active material, forming a binder network that is more compatible with the physical morphology and chemical composition of the current negative electrode active material. On the one hand, this binder network can inhibit the cyclic expansion of silicon materials, allowing the high specific capacity characteristics of silicon materials to be effectively demonstrated in the long term. On the other hand, it also effectively bonds the current negative electrode active material to ensure that it will not fall off from the current collector and will not affect the smooth transmission of lithium ions and electrons.

[0037] Furthermore, when 0.05%≤m≤0.35% (for example, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3% or 0.35%), 1.5%≤n≤3.5% (for example, 1.5%, 2%, 2.5%, 3% or 3.5%), the cycle life of the lithium-ion battery is even better.

[0038] In addition, further screening of negative electrode active materials can also have a certain degree of positive effect on the energy density, cycle performance, and safety performance of lithium-ion batteries.

[0039] In one embodiment, the median particle size Dv50 of the silicon-carbon material is 6 μm to 12 μm (e.g., 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, or 12 μm). Silicon-carbon materials with this median particle size are more easily controlled in terms of expansion and deformation, and exhibit more favorable lithium insertion kinetics, thereby preventing dendrite precipitation caused by obstructed lithium ion transport and reducing the probability of side reactions between the silicon-carbon material and the electrolyte.

[0040] In another specific embodiment, the mass percentage of silicon element in the silicon-carbon material is 40% to 60% (for example, 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58% or 60%), which is beneficial to improving the energy density of the battery.

[0041] In another specific embodiment, the median particle size Dv50 of the graphite is 8 μm to 20 μm (e.g., 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, or 20 μm). Graphite with this median particle size has more suitable lithium insertion kinetics, does not cause dendrite precipitation due to obstruction of lithium ion transport, and also reduces the probability of side reactions between the silicon-carbon material and the electrolyte.

[0042] Furthermore, the surface density of the negative electrode sheet is 8 mg / cm 2 ~15mg / cm 2 (e.g., 8 mg / cm 2 , 9mg / cm 2 、10mg / cm 2 、11mg / cm 2 , 12mg / cm 2 、13mg / cm 2 , 14mg / cm 2 or 15 mg / cm 2 ); and / or, the compaction density of the negative electrode is 1.2g / cm 3 ~1.8g / cm 3 (For example, 1.2 g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 or 1.8g / cm 3 It should be noted that the surface density and compacted density of the negative electrode sheet are for a lithium-ion battery that has only undergone a formation treatment and has not undergone a discharge treatment (not reaching 0% SOC), or for a lithium-ion battery that has undergone a formation treatment and a discharge treatment (the discharge treatment refers to a discharge treatment after a maximum of 10 cycles). A negative electrode sheet with such a surface density and / or compacted density is beneficial for balancing the battery's energy density and electron transport resistance, thereby exhibiting excellent electrical performance.

[0043] In a specific embodiment, the median particle size Dv50 of the silicon-carbon material is 6 μm to 12 μm; and / or,

[0044] The mass percentage of silicon element in the silicon-carbon material is 40% to 60%; and / or,

[0045] The median particle size Dv50 of the graphite is 10 μm to 20 μm; and / or,

[0046] The surface density of the negative electrode sheet is 8 mg / cm 2 ~15mg / cm 2and / or,

[0047] The compaction density of the negative electrode sheet is 1.2 g / cm 3 ~1.8g / cm 3 .

[0048] It should be noted that the negative electrode sheets that meet all the aforementioned arbitrary limited parameters refer to the negative electrode sheets in lithium-ion batteries after the sorting process, or the negative electrode sheets in lithium-ion batteries that have undergone formation treatment and discharge treatment (the discharge treatment refers to the discharge treatment after a maximum of 10 cycles).

[0049] The lithium-ion battery disclosed in the present invention not only takes advantage of the silicon-containing negative electrode and thus has excellent energy density, but also effectively overcomes the disadvantage of silicon-based materials that are easy to expand and deform, while taking into account suitable cycle performance and safety performance.

[0050] The positive electrode sheet specifically includes a positive electrode current collector and a positive electrode active layer including a positive electrode active material and disposed on one side or both sides of the positive electrode current collector.

[0051] When preparing the positive electrode sheet, for example, the positive electrode active material, the positive electrode conductive agent and the positive electrode binder can be dispersed in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and fully stirred and mixed to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector, and the positive electrode sheet is obtained after drying, rolling and slitting.

[0052] In a specific embodiment, the positive electrode active layer includes 70wt%-99wt% (for example, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt% or 99wt%) of the positive electrode active material, 0.5wt%-15wt% (for example, 0.5wt%, 1wt%, 3wt%, 5wt%, 8wt%, 10wt%, 13wt% or 15wt%) of the positive electrode conductor, and 0.5wt%-15wt% (for example, 0.5wt%, 1wt%, 3wt%, 5wt%, 8wt%, 10wt%, 13wt% or 15wt%) of the positive electrode binder, and further includes 80wt%-98wt% of the positive electrode active material, 1wt%-10wt% of the positive electrode conductor, and 1wt%-10wt% of the positive electrode binder. Among them, the material of the positive electrode current collector can be at least one of aluminum foil and nickel foil; the positive electrode conductive agent can be selected from at least one of carbon black, acetylene black, graphene, single-walled carbon nanotubes, multi-walled carbon nanotubes, Ketjen black, and carbon fiber; the positive electrode binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polymers containing ethylene oxide, polyvinyl pyrrolidone, and polyurethane.

[0053] The present disclosure does not limit the choice of positive electrode active material. For example, it can be at least one composite oxide of lithium and cobalt, manganese, nickel, other elements, and combinations thereof. Specifically, it can be at least one of lithium cobalt oxide, nickel-based positive electrode active materials, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium-rich manganese-based materials, and the like.

[0054] In a specific embodiment, the positive electrode active material includes a nickel-based positive electrode active material.

[0055] In a specific embodiment, based on the demand for energy density, the positive electrode active material in the positive electrode sheet is a nickel-based positive electrode active material. For example, the nickel-based positive electrode active material can be lithium nickelate, lithium nickel manganese oxide, Li x Ni y1 Co y2 M1 y3 M2 y4 O2 ternary material (0.99≤x≤1.05, 0.99<y1+y2+y3≤1.05, 1 / 3≤y1≤0.8, 0≤y4≤0.1, M1 is selected from Mn or Al, M2 is at least one of Mg, Ti, Mn, Al, Te, W, Ni, Nb, Zr, La, F, Ce, Sr, Y, K, B and P elements, and at least one of the doping elements different from M1).

[0056] It should be noted that, in addition to controlling the selection of raw materials in the negative electrode active layer slurry, when the positive electrode active material is a nickel-based positive electrode active material, the negative electrode sheet of the present disclosure can also be prepared in situ in a lithium-ion battery.

[0057] Specifically, after assembling a negative electrode sheet (negative electrode sheet precursor) that does not include nickel and / or cobalt elements with a positive electrode sheet to obtain a bare battery cell, the nickel and / or cobalt elements in the nickel-based positive electrode active material in the positive electrode sheet are dissolved and enter the negative electrode active layer of the negative electrode sheet precursor by controlling the formation and pre-circulation after formation, thereby realizing the preparation of the negative electrode sheet of the aforementioned first aspect.

[0058] For the positive electrode sheet, when the surface density of the positive electrode sheet is 16.7 mg / cm 2 ~26.2mg / cm 2 (For example, 16.7 g / cm 3 、17g / cm 3 、、18g / cm 3 、、19g / cm 3 、、20g / cm 3 , 21g / cm 3 , 22g / cm 3 , 23g / cm 3 , 24g / cm3 , 25g / cm 3 or 26.2g / cm 3 ); and / or, the compaction density of the positive electrode is 3.1g / cm 3 ~4.2g / cm 3 (For example, 3.1 g / cm 3 , 3.3g / cm 3 , 3.5g / cm 3 、3.8g / cm 3 , 4g / cm 3 or 4.2g / cm 3 ), the cycle performance of the lithium-ion battery will be more significantly improved. Similarly, the positive electrode sheet is a positive electrode sheet in a lithium-ion battery that has only undergone a formation treatment and has not undergone a discharge treatment (not reaching 0% SOC), or a positive electrode sheet in a lithium-ion battery that has undergone a formation treatment and a discharge treatment (the discharge treatment refers to a discharge treatment after a maximum of 10 cycles).

[0059] Furthermore, based on the requirements for safety and cycle performance of lithium-ion batteries, the present disclosure defines the relationship between the gram capacity of the positive and negative electrodes in lithium-ion batteries, wherein the ratio of the gram capacity per unit area of ​​the negative electrode sheet to the positive electrode sheet is 0.97 to 1.1 (for example, 0.97, 0.98, 0.99, 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09 or 1.1), and further 0.99 to 1.05.

[0060] The method for testing the gram capacity of the negative electrode sheet comprises: assembling the negative electrode sheet into a 2403 type button battery (battery diameter 24mm, thickness 3mm, wherein the negative electrode sheet diameter is 16mm, the separator diameter is 22mm, and the counter electrode is a lithium foil with a diameter of 20mm), inserting lithium into the negative electrode sheet at a current of 0.05C, and when the potential reaches 5mV (relative Li / Li + ), let it stand for 10 minutes, insert lithium into the negative electrode again with a current of 0.02C, and when the potential reaches 5mV, let it stand for 10 minutes, and remove lithium from the negative electrode with a current of 0.05C until the potential reaches 0.9V (relative Li / Li + After three cycles according to the above procedure, the third lithium removal capacity divided by the surface area of ​​the negative electrode sheet is the gram capacity per unit area of ​​the negative electrode sheet (mAh / cm 2 ).

[0061] The method for testing the gram capacity of the positive electrode sheet comprises: assembling the positive electrode sheet into a 2403 type button battery (battery diameter 24mm, thickness 3mm, wherein the positive electrode sheet diameter is 16mm, the diaphragm diameter is 22mm, and the counter electrode is a lithium foil with a diameter of 20mm), delithiating the positive electrode sheet at a current of 0.05C, and when the potential is 50mV higher than the rated maximum voltage of the lithium-ion battery (relative Li / Li + ), let it stand for 10 minutes, and then remove lithium from the positive electrode again with a current of 0.02C. When the potential is 50mV higher than the rated maximum voltage of the lithium-ion battery, let it stand for 10 minutes, and insert lithium into the positive electrode with a current of 0.05C until the potential reaches 3.3V (relative Li / Li + After three cycles according to the above procedure, the third lithium insertion capacity is divided by the surface area of ​​the positive electrode to obtain the gram capacity per unit area of ​​the positive electrode (mAh / cm 2 ).

[0062] In the button-type batteries tested for the gram capacity of the positive and negative electrodes, the electrolyte composition is: organic solvent, lithium salt, and additives. The organic solvent includes EC, PC, and EMC in a mass ratio of 1:1:1, the lithium salt is LiPF6 at a concentration of 1 mol / L, and the additives include FEC and PS at a mass percentage of 7% and 3%, respectively. The surface density of the negative electrode is 9.1 mg / cm 2 , compacted density is 1.73g / cm 3 The surface density of the positive electrode is 19 mg / cm 2 , compacted density is 3.4g / cm 3 .

[0063] The present invention controls A / B within the range of 0.97 to 1.1, and further controls it within the range of 0.99 to 1.05. Studies have found that satisfying the above-mentioned ratio of gram capacity per unit area, on the one hand, ensures the effective embedding of lithium ions in the negative electrode during charging, avoids the precipitation of lithium dendrites caused by uneven lithium deintercalation sites at the positive and negative electrodes, eliminates the risk of short circuit caused by dendrites piercing the diaphragm, and maintains the amount of lithium that can be deintercalated inside the battery; on the other hand, it avoids the dissolution of transition metal ions in the positive electrode active material caused by the lack of lithium ions in the positive electrode sheet, maintains the structural stability of the positive electrode active material, and facilitates the increase of charging voltage, thereby significantly improving the safety performance, cycle performance and energy density of lithium-ion batteries.

[0064] For example, in one embodiment, the gram capacity per unit area of ​​the negative electrode sheet is 3.5 mAh / cm 2 ~5.73mAh / cm 2 (e.g., 3.5 mAh / cm 2 , 4mAh / cm 2, 4.5mAh / cm 2 , 5mAh / cm 2 、5.5mAh / cm 2 or 5.73 mAh / cm 2 ), the gram capacity per unit area of ​​the positive electrode is 3.43 mAh / cm 2 ~5.61mAh / cm 2 (e.g., 3.43 mAh / cm 2 、3.5mAh / cm 2 , 4mAh / cm 2 , 4.5mAh / cm 2 , 5mAh / cm 2 、5.5mAh / cm 2 or 5.61 mAh / cm 2 ).

[0065] In addition to the negative electrode and the positive electrode, the lithium-ion battery of the present disclosure also includes an electrolyte. Generally, the electrolyte includes an organic solvent, a lithium salt, and an additive.

[0066] Among them, when the additive includes fluoroethylene carbonate, fluoroethylene carbonate can help form a stable interface film on the surface of the silicon-carbon material and inhibit the continued occurrence of side reactions. However, fluoroethylene carbonate has poor high-temperature performance in the battery and can easily induce gas production problems, causing safety hazards.

[0067] Therefore, in order to better utilize fluoroethylene carbonate to help improve the cycle performance and safety performance of lithium-ion batteries, the present disclosure controls 0.3≤γ / η≤3.6 (for example, 0.3, 0.5, 0.8, 1, 1.3, 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3, 3.3, 3.5 or 3.6), where γ is the mass percentage of fluoroethylene carbonate in the electrolyte, and the electrolyte in the battery can be extracted and detected by gas chromatography.

[0068] It should be noted that the above parameters of lithium-ion batteries are all for lithium-ion batteries that have only undergone formation treatment and not discharge treatment (not reaching 0% SOC), or for lithium-ion batteries that have undergone formation treatment and discharge treatment (the discharge treatment refers to the discharge treatment after a maximum of 10 cycles).

[0069] When preparing a lithium-ion battery, the positive electrode sheet, the separator and the negative electrode sheet are wound or stacked to obtain a bare cell, and the bare cell is packaged in a pre-stamped aluminum-plastic film bag. After the packaged battery is dried at 85°C to remove moisture, the electrolyte is injected into the dry battery. After the battery is processed including shelving, formation, secondary sealing and sorting, the preparation of the lithium-ion battery is completed. The present disclosure does not strictly limit the material selection of the separator, and it can be a separator material commonly used in lithium-ion batteries, such as a polypropylene separator (PP), a polyethylene separator (PE), a polypropylene / polyethylene double-layer composite film (PP / PE), a polyimide electrospun separator (PI), a polypropylene / polyethylene / polypropylene three-layer composite film (PP / PE / PP), a cellulose non-woven separator, or a separator with a ceramic coating.

[0070] Hereinafter, the negative electrode sheet and lithium-ion battery of the present disclosure will be described in detail through specific embodiments.

[0071] Example 1

[0072] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0073] 1. Preparation of negative electrode precursor

[0074] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed with deionized water at mass percentages of 6.76%, 89.84%, 0.5%, 0.05%, 1.2% and 1.65%, respectively, to obtain a slurry.

[0075] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 9.1 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0076] The median particle size D50 of artificial graphite is 13.3 μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73 g / cm 3 The OI value at compaction density is 12.9. Specifically, the negative electrode sheet includes a negative electrode active layer and a negative electrode current collector. The negative electrode active layer includes selected silicon carbon particles and graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose, and styrene-butadiene rubber in proportions of 96.6%, 0.5%, 0.05%, 1.2%, and 1.65%, respectively. The negative electrode current collector is a 6μm copper foil with an area density of 8 to 15 mg / cm 2 (The surface density in the specific embodiment is 8 to 10 mg / cm 2 ), compacted density is 1.73g / cm 3 .

[0077] The slurry was coated on both sides of the copper foil current collector with a thickness of 6 μm (the two sides with the largest area), and after drying, rolling and slitting, the surface density was 9.1 mg / cm 2 , compacted density is 1.73g / cm 3 negative electrode precursor.

[0078] 2. Preparation of positive electrode

[0079] NCM811 material (LiNi 0.8 Co 0.1 Mn 0.1 O2), carbon black, and polyvinylidene fluoride are mixed with NMP according to the mass percentage of 96.5%, 1.5%, and 2%, respectively, to obtain a slurry.

[0080] The slurry was coated on both sides of the aluminum foil current collector with a thickness of 10 μm (the two sides with the largest area), and after drying, rolling and slitting, the surface density of the slurry was 19 mg / cm 2 , compacted density is 3.4g / cm 3 The positive electrode.

[0081] 3. Assembly

[0082] The positive electrode sheet, separator, and negative electrode sheet are wound together to form a bare cell, which is then encapsulated in a pre-stamped aluminum-plastic film bag. The encapsulated battery is dried at 85°C, and then the electrolyte is injected into the dried battery. After storage, formation, pre-cycling, secondary sealing, and sorting, the resulting lithium-ion battery has a voltage of 3.69V, an initial thickness D0 of 3.79mm, and a capacity of 3959mAh.

[0083] The electrolyte is composed of an organic solvent, a lithium salt and an additive; the organic solvent includes EC, PC, and EMC in a mass ratio of 1:1:1, the lithium salt is LiPF6 and has a concentration of 1 mol / L, and the additives include FEC and PS (their mass percentage is 3%).

[0084] The separator consists of a polyethylene layer, a boehmite layer coated on one side of the polyethylene layer, and a polyvinylidene fluoride layer coated on the outside of each of the polyethylene and boehmite layers. The polyethylene layer is 5 μm thick and is located on the negative electrode side; the boehmite layer is 2 μm thick and is located on the positive electrode side; and the polyvinylidene fluoride layer is 1 μm thick.

[0085] The formation system is as follows: charge to 3.7V at 0.05C, let stand for 10 minutes, charge to 3.9V at 0.1C, let stand for 10 minutes, charge to 4.2V at 0.33C, and then charge at constant voltage until the current is less than 0.05C.

[0086] The pre-cycle system is as follows: charge to 4.3V at 0.3C, charge at constant voltage until the current is less than 0.2C, let it stand for 10 minutes, discharge to 2.65V at 0.2C, let it stand for 10 minutes, and then charge to 4V at 0.5C.

[0087] The sorting system is: discharge to 2.65V at 0.2C, stand for 10 minutes, charge to 4.25V at 0.5C, charge at constant voltage until the current is less than 0.05C, stand for 10 minutes, discharge to 2.65V at 0.2C, stand for 10 minutes, charge to 3.69V at 0.5C, and charge at constant voltage until the current is less than 20mA.

[0088] 4. Related tests

[0089] The lithium-ion battery was disassembled and the surface density SD1 (g / cm 3 ), compacted density CD1(g / cm 3 ) and gram capacity B1 (mAh / cm 2 ) was tested; the surface density SD2 (g / cm 3 ), compacted density CD2(g / cm 3 ), gram capacity B2 (mAh / cm 2 ), the intensity ratio of the first diffraction peak to the second diffraction peak After testing the weight loss percentage m in the range of 230-360°C and the weight loss percentage n in the range of 230-950°C, the negative electrode sheet was immersed in DMC for 2 hours, dried, and then immersed in deionized water to separate the negative electrode coating from the copper foil. It was then dried and the negative electrode current collector was removed to obtain the powder of the negative electrode active layer.

[0090] The nickel element content α (ppm), cobalt element content β, silicon element content η and median particle size d (μm) of the negative electrode active layer powder were tested.

[0091] Among them, the detection method of surface density SD1 and SD2 is as follows: after disassembling the battery, obtain the electrode with coating on both sides, after drying, cut according to a fixed area, weigh and calculate the electrode weight per unit area, and at the same time take the electrode to remove the coating, cut according to a fixed area, weigh and calculate the current collector weight per unit area, subtract the electrode weight per unit area from the current collector weight per unit area and divide by 2 to obtain the surface density of the coating; or disassemble the battery to obtain the electrode with coating on one side, after drying, cut according to a fixed area, weigh and calculate the electrode weight per unit area, subtract the current collector weight per unit area from the electrode weight per unit area to obtain the surface density of the coating.

[0092] The compaction density CD1 and CD2 are measured as follows: After disassembling the battery, obtain the electrode with coating on both sides and measure its thickness with a micrometer. Remove the coating to obtain the current collector and measure its thickness with a micrometer. Subtract the current collector thickness from the electrode thickness and divide by 2 to obtain the coating thickness. Alternatively, disassemble the battery to obtain the electrode with coating on one side and measure its thickness with a micrometer. Subtract the current collector thickness to obtain the coating thickness. Divide the coating's areal density by its thickness to obtain its compaction density.

[0093] The gram capacity A and B are tested as follows: disassemble the battery, obtain the electrode including the active layer, soak it in DMC for 2 hours, remove it and dry it, wipe off the active layer on one side with a cloth dampened with deionized water, and prepare a button cell for capacity testing according to the above method. The gram capacity B per unit area of ​​the positive electrode of this lithium-ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0094] Strength ratio Detected by X-ray diffractometer.

[0095] m and n were measured using a thermogravimetric analyzer. Under an argon atmosphere, the temperature was raised from room temperature to 1000°C at a rate of 10°C / min. The powder masses at 230°C, 360°C, and 950°C were recorded and calculated.

[0096] The nickel element content α and the cobalt element content β were measured using an ICP detector.

[0097] The mass percentage of Si (η) was determined using a thermogravimetric analyzer. The powder was placed in an argon atmosphere and heated to 230°C at a rate of 10°C / min. The initial weight of the powder at this temperature was defined as W1. The powder was then switched to air and heated to 800°C at a rate of 10°C / min and held for 8 hours. The final weight of the powder was W2, and the Si content (η) was calculated as W2 / W1 / 2.14.

[0098] The median particle size d was measured using a laser particle size analyzer. The powder was placed in an argon atmosphere, heated at 10°C / min to 400°C and maintained for 2 hours, and then tested after cooling.

[0099] The electrolyte was extracted from the disassembled battery and analyzed by gas chromatography, and the mass percentage of fluoroethylene carbonate in the electrolyte was γ.

[0100] Among them, α*d / η=45*13.01 / 3.38%=17321, m*d=0.18%*13.01=2.34%, (1.27n-6.32m) / eta=(1.27*2.2-6.32*0.18) / 3.38%=49.0%.

[0101] The results are shown in Table 1.

[0102] Example 2

[0103] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0104] 1. Preparation of negative electrode precursor

[0105] Same as Example 1.

[0106] 2. Preparation of positive electrode

[0107] Same as Example 1.

[0108] 3. Assembly

[0109] The positive electrode sheet, separator, and negative electrode sheet are wound together to form a bare cell, which is then encapsulated in a pre-stamped aluminum-plastic film bag. The encapsulated battery is dried at 85°C, and then the electrolyte is injected into the dried battery. After storage, formation, pre-cycling, secondary sealing, and sorting, the resulting lithium-ion battery has a voltage of 3.69V, an initial thickness D0 of 3.80mm, and a capacity of 3957mAh.

[0110] The gram capacity per unit area of ​​the positive electrode of the lithium-ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode is 3.98 mAh / cm 2 .

[0111] The formation system is as follows: charge to 3.7V at 0.05C, let stand for 10 minutes, charge to 3.9V at 0.1C, let stand for 10 minutes, charge to 4.2V at 0.33C, and then charge at constant voltage until the current is less than 0.05C.

[0112] The pre-cycle system is as follows: charge to 4.35V at 0.3C, charge at constant voltage until the current is less than 0.2C, let it stand for 10 minutes, discharge to 2.65V at 0.2C, let it stand for 10 minutes, and then charge to 4V at 0.5C.

[0113] The sorting system is: discharge to 2.65V at 0.2C, stand for 10 minutes, charge to 4.25V at 0.5C, charge at constant voltage until the current is less than 0.05C, stand for 10 minutes, discharge to 2.65V at 0.2C, stand for 10 minutes, charge to 3.69V at 0.5C, and charge at constant voltage until the current is less than 20mA.

[0114] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0115] Example 3

[0116] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0117] 1. Preparation of negative electrode precursor

[0118] Same as Example 1.

[0119] 2. Preparation of positive electrode

[0120] Same as Example 1.

[0121] 3. Assembly

[0122] The positive electrode sheet, separator, and negative electrode sheet are wound together to form a bare cell, which is then encapsulated in a pre-stamped aluminum-plastic film bag. The encapsulated battery is dried at 85°C, and then the electrolyte is injected into the dried battery. After storage, formation, pre-cycling, secondary sealing, and sorting, the resulting lithium-ion battery has a voltage of 3.69V, an initial thickness D0 of 3.80mm, and a capacity of 3958mAh.

[0123] The formation system is as follows: charge to 3.7V at 0.05C, let stand for 10 minutes, charge to 3.9V at 0.1C, let stand for 10 minutes, charge to 4.2V at 0.33C, and then charge at constant voltage until the current is less than 0.05C.

[0124] The pre-cycle system is as follows: charge to 4.25V at 0.3C, charge at constant voltage until the current is less than 0.2C, let it stand for 10 minutes, discharge to 2.65V at 0.2C, let it stand for 10 minutes, and then charge to 4V at 0.5C.

[0125] The sorting system is: discharge to 2.65V at 0.2C, stand for 10 minutes, charge to 4.25V at 0.5C, charge at constant voltage until the current is less than 0.05C, stand for 10 minutes, discharge to 2.65V at 0.2C, stand for 10 minutes, charge to 3.69V at 0.5C, and charge at constant voltage until the current is less than 20mA.

[0126] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0127] Example 4

[0128] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0129] 1. Preparation of negative electrode sheet

[0130] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose, styrene-butadiene rubber and nickel chloride are mixed according to the mass percentage of 6.76%, 89.83%, 0.5%, 0.05%, 1.2%, 1.65% and 0.01% respectively to obtain a slurry.

[0131] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 9.1 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0132] The median particle size Dv50 of artificial graphite is 13.3 μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73 g / cm 3 The OI value at compacted density is 12.9.

[0133] The slurry was coated on the surface of a 6 μm thick copper foil current collector, and after drying, rolling and slitting, a surface density of 9.1 mg / cm was obtained. 2 , compacted density is 1.73g / cm 3 The negative electrode.

[0134] 2. Preparation of positive electrode

[0135] Lithium cobaltate, carbon black, and polyvinylidene fluoride were mixed with NMP at mass percentages of 96.5%, 1.5%, and 2%, respectively, to obtain a slurry.

[0136] The slurry was coated on the surface of the aluminum foil current collector with a thickness of 10 μm, and after drying, rolling and slitting, the surface density of the aluminum foil was 21.8 mg / cm 2 , compacted density is 4.15g / cm 3 The positive electrode.

[0137] 3. Assembly

[0138] The positive electrode sheet, separator, and negative electrode sheet are wound together to form a bare cell, which is then encapsulated in a pre-stamped aluminum-plastic film bag. The encapsulated battery is dried at 85°C, and then the electrolyte is injected into the dried battery. After storage, formation, pre-cycling, secondary sealing, and sorting, the resulting lithium-ion battery has a voltage of 3.83V, an initial thickness D0 of 3.75mm, and a capacity of 3807mAh.

[0139] The formation system is as follows: charge to 3.7V at 0.05C, let stand for 10 minutes, charge to 3.9V at 0.1C, let stand for 10 minutes, charge to 4.3V at 0.33C, and then charge at constant voltage until the current is less than 0.05C.

[0140] The pre-cycle system is as follows: charge to 4.45V at 0.3C, charge at constant voltage until the current is less than 0.2C, let it stand for 10 minutes, discharge to 3V at 0.2C, let it stand for 10 minutes, and then charge to 4.2V at 0.5C.

[0141] The sorting system is: discharge to 3V at 0.2C, stand for 10 minutes, charge to 4.45V at 0.5C, charge at constant voltage until the current is less than 0.05C, stand for 10 minutes, discharge to 3V at 0.2C, stand for 10 minutes, charge to 3.83V at 0.5C, and charge at constant voltage until the current is less than 20mA.

[0142] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0143] Example 5

[0144] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0145] 1. Preparation of negative electrode precursor

[0146] Same as Example 1.

[0147] 2. Preparation of positive electrode

[0148] The same as Example 1, except that the NCM811 material is replaced with Ni90 material (LiNi 0.9 Co 0.05 Mn 0.05 O2), and the surface density of the positive electrode coating is 18.6 mg / cm 2 .

[0149] 3. Assembly

[0150] The positive electrode sheet, separator, and negative electrode sheet are wound together to form a bare cell, which is then encapsulated in a pre-stamped aluminum-plastic film bag. The encapsulated battery is dried at 85°C, and then the electrolyte is injected into the dried battery. After storage, formation, pre-cycling, secondary sealing, and sorting, the resulting lithium-ion battery has a voltage of 3.67V, an initial thickness D0 of 3.75mm, and a capacity of 3932mAh.

[0151] The gram capacity per unit area of ​​the positive electrode of the lithium-ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode is 3.98 mAh / cm 2 .

[0152] The formation system is as follows: charge to 3.7V at 0.05C, let stand for 10 minutes, charge to 3.9V at 0.1C, let stand for 10 minutes, charge to 4.15V at 0.33C, and then charge at constant voltage until the current is less than 0.05C.

[0153] The pre-cycle system is as follows: charge to 4.2V at 0.3C, charge at constant voltage until the current is less than 0.2C, let it stand for 10 minutes, discharge to 2.6V at 0.2C, let it stand for 10 minutes, and then charge to 4V at 0.5C.

[0154] The sorting system is: discharge to 2.6V at 0.2C, stand for 10 minutes, charge to 4.2V at 0.5C, charge at constant voltage until the current is less than 0.05C, stand for 10 minutes, discharge to 2.6V at 0.2C, stand for 10 minutes, charge to 3.67V at 0.5C, and charge at constant voltage until the current is less than 20mA.

[0155] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0156] Example 6

[0157] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0158] 1. Preparation of negative electrode precursor

[0159] The invention is basically the same as Example 1, except that the slurry contains silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose, styrene-butadiene rubber, and cobalt chloride hexahydrate, and the mass contents are 6.76%, 89.83%, 0.5%, 0.05%, 1.2%, 1.65%, and 0.01%, respectively.

[0160] 2. Preparation of positive electrode

[0161] Same as Example 1

[0162] 3. Assembly

[0163] The method is basically the same as Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.81 mm, and the capacity is 3960 mAh.

[0164] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0165] Example 7

[0166] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0167] 1. Preparation of negative electrode precursor

[0168] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed according to the mass percentages of 6.76%, 89.84%, 0.5%, 0.05%, 1.2% and 1.65%, respectively, to obtain a slurry.

[0169] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 9.1 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0170] The median particle size Dv50 of artificial graphite is 13.3 μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73 g / cm 3 The OI value at compacted density is 8.4.

[0171] The slurry was coated on the surface of a 6 μm thick copper foil current collector, and after drying, rolling and slitting, a surface density of 9.1 mg / cm was obtained. 2 , compacted density is 1.73g / cm 3 negative electrode precursor.

[0172] 2. Preparation of positive electrode

[0173] Same as Example 1.

[0174] 3. Assembly

[0175] The method is basically the same as Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.78 mm, and the capacity is 3941 mAh.

[0176] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0177] Example 8

[0178] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0179] 1. Preparation of negative electrode precursor

[0180] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed according to the mass percentages of 6.76%, 89.84%, 0.5%, 0.05%, 1.2% and 1.65%, respectively, to obtain a slurry.

[0181] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 9.1 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0182] The median particle size Dv50 of artificial graphite is 13.3 μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73 g / cm 3 The OI value at compacted density is 18.1.

[0183] The slurry was coated on the surface of a 6 μm thick copper foil current collector, and after drying, rolling and slitting, a surface density of 9.1 mg / cm was obtained. 2 , compacted density is 1.73g / cm 3 negative electrode precursor.

[0184] 2. Preparation of positive electrode

[0185] Same as Example 1.

[0186] 3. Assembly

[0187] The method is basically the same as Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.81 mm, and the capacity is 3957 mAh.

[0188] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0189] Example 9

[0190] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0191] 1. Preparation of negative electrode precursor

[0192] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed according to the mass percentages of 6.76%, 89.84%, 0.5%, 0.05%, 1.2% and 1.65%, respectively, to obtain a slurry.

[0193] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 9.1 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0194] The median particle size Dv50 of artificial graphite is 13.3 μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73 g / cm 3 The OI value at compacted density is 6.8.

[0195] The slurry was coated on the surface of a 6 μm thick copper foil current collector, and after drying, rolling and slitting, a surface density of 9.1 mg / cm was obtained. 2 , compacted density is 1.73g / cm 3 negative electrode precursor.

[0196] 2. Preparation of positive electrode

[0197] Same as Example 1.

[0198] 3. Assembly

[0199] The method is basically the same as Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.76 mm, and the capacity is 3920 mAh.

[0200] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0201] Example 10

[0202] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0203] 1. Preparation of negative electrode precursor

[0204] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed according to the mass percentages of 6.76%, 89.84%, 0.5%, 0.05%, 1.2% and 1.65%, respectively, to obtain a slurry.

[0205] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 9.1 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0206] The median particle size Dv50 of artificial graphite is 13.3 μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73 g / cm 3 The OI value at compacted density is 20.5.

[0207] The slurry was coated on the surface of a 6 μm thick copper foil current collector, and after drying, rolling and slitting, a surface density of 9.1 mg / cm was obtained. 2 , compacted density is 1.73g / cm 3 negative electrode precursor.

[0208] 2. Preparation of positive electrode

[0209] Same as Example 1.

[0210] 3. Assembly

[0211] The method is basically the same as Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.82 mm, and the capacity is 3958 mAh.

[0212] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm2 .

[0213] Example 11

[0214] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0215] 1. Preparation of negative electrode precursor

[0216] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed according to the mass percentages of 6.7%, 89.0%, 0.5%, 0.05%, 2.1% and 1.65%, respectively, to obtain a slurry.

[0217] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 9.1 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0218] The median particle size Dv50 of artificial graphite is 13.3 μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73 g / cm 3 The OI value at compacted density is 12.9.

[0219] The slurry was coated on the surface of a 6 μm thick copper foil current collector, and after drying, rolling and slitting, a surface density of 9.18 mg / cm was obtained. 2 , compacted density is 1.73g / cm 3 negative electrode precursor.

[0220] 2. Preparation of positive electrode

[0221] Same as Example 1.

[0222] 3. Assembly

[0223] The method is basically the same as Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.80 mm, and the capacity is 3939 mAh.

[0224] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0225] Example 12

[0226] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0227] 1. Preparation of negative electrode precursor

[0228] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed according to the mass percentages of 6.8%, 90.65%, 0.5%, 0.05%, 0.35% and 1.65%, respectively, to obtain a slurry.

[0229] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 9.1 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0230] The median particle size Dv50 of artificial graphite is 13.3 μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73 g / cm 3 The OI value at compacted density is 12.9.

[0231] The slurry was coated on the surface of a 6 μm thick copper foil current collector, and after drying, rolling and slitting, a surface density of 9.02 mg / cm was obtained. 2 , compacted density is 1.73g / cm 3 negative electrode precursor.

[0232] 2. Preparation of positive electrode

[0233] Same as Example 1.

[0234] 3. Assembly

[0235] The method is basically the same as Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.80 mm, and the capacity is 3955 mAh.

[0236] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0237] Example 13

[0238] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0239] 1. Preparation of negative electrode precursor

[0240] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed according to the mass percentages of 6.65%, 88.4%, 0.5%, 0.05%, 1.2% and 3.2%, respectively, to obtain a slurry.

[0241] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 9.1 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0242] The median particle size Dv50 of artificial graphite is 13.3 μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73 g / cm 3 The OI value at compacted density is 12.9.

[0243] The slurry was coated on the surface of a 6 μm thick copper foil current collector, and after drying, rolling and slitting, a surface density of 9.25 mg / cm was obtained. 2 , compacted density is 1.73g / cm 3 negative electrode precursor.

[0244] 2. Preparation of positive electrode

[0245] Same as Example 1.

[0246] 3. Assembly

[0247] The method is basically the same as Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.81 mm, and the capacity is 3962 mAh.

[0248] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0249] Example 14

[0250] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0251] 1. Preparation of negative electrode precursor

[0252] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed according to the mass percentages of 6.81%, 90.44%, 0.5%, 0.05%, 1.2% and 1%, respectively, to obtain a slurry.

[0253] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 9.1 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0254] The median particle size Dv50 of artificial graphite is 13.3 μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73 g / cm 3 The OI value at compacted density is 12.9.

[0255] The slurry was coated on the surface of a 6 μm thick copper foil current collector, and after drying, rolling and slitting, a surface density of 9.04 mg / cm was obtained. 2 , compacted density is 1.73g / cm 3 negative electrode precursor.

[0256] 2. Preparation of positive electrode

[0257] Same as Example 1.

[0258] 3. Assembly

[0259] The method is basically the same as Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.82 mm, and the capacity is 3957 mAh.

[0260] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0261] Example 15

[0262] Compared with Example 1, this embodiment differs in that the electrolyte comprises an organic solvent, a lithium salt, and an additive; wherein the organic solvent comprises EC, PC, and EMC in a mass ratio of 1:1:1, the lithium salt is LiPF6 with a concentration of 1 mol / L, and the additives include FEC and PS (with a mass percentage of 3%); after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.79 mm, and the capacity is 3943 mAh.

[0263] The gram capacity per unit area B of the positive electrode of the lithium-ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0264] Example 16

[0265] The only difference between this embodiment and Example 1 is that the electrolyte composition is: organic solvent, lithium salt and additive; wherein the organic solvent includes EC, PC, EMC in a mass ratio of 1:1:1, the lithium salt is LiPF6 with a concentration of 1 mol / L, and the additives include FEC and PS (whose mass percentage is 3%); after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.79 mm, and the capacity is 3952 mAh.

[0266] The gram capacity per unit area B of the positive electrode of the lithium-ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0267] Example 17

[0268] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0269] 1. Preparation of negative electrode precursor

[0270] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed according to the mass percentages of 6.71%, 89.14%, 0.5%, 0.05%, 1.9% and 1.7%, respectively, to obtain a slurry.

[0271] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 6.4 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0272] The median particle size Dv50 of artificial graphite is 8.2μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73g / cm 3 The OI value at compacted density is 13.1.

[0273] The slurry was coated on the surface of a 6 μm thick copper foil current collector, and after drying, rolling and slitting, a surface density of 9.18 mg / cm was obtained. 2 , compacted density is 1.73g / cm 3 negative electrode precursor.

[0274] 2. Preparation of positive electrode

[0275] Same as Example 1.

[0276] 3. Assembly

[0277] The results are basically the same as those in Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.81 mm, and the capacity is 3943 mAh; the pre-cycle system is as follows: charging to 4.4 V at 0.3 C, then charging at a constant voltage until the current is less than 0.2 C, standing for 10 minutes, discharging to 2.65 V at 0.2 C, standing for 10 minutes, and then charging to 4 V at 0.5 C.

[0278] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0279] Example 18

[0280] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0281] 1. Preparation of negative electrode precursor

[0282] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed according to the mass percentages of 2.93%, 94.58%, 0.5%, 0.05%, 1.15% and 0.85%, respectively, to obtain a slurry.

[0283] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 9.1 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0284] The median particle size Dv50 of artificial graphite is 13.7μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73g / cm 3 The OI value at compacted density is 21.8.

[0285] The slurry was coated on the surface of a 6 μm thick copper foil current collector, and after drying, rolling and slitting, a surface density of 10.32 mg / cm was obtained. 2 , compacted density is 1.73g / cm 3 negative electrode precursor.

[0286] 2. Preparation of positive electrode

[0287] Same as Example 1.

[0288] 3. Assembly

[0289] The results are basically the same as those in Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.94 mm, and the capacity is 4013 mAh; the pre-cycle system is as follows: charging to 4.2 V at 0.3 C, then charging at a constant voltage until the current is less than 0.2 C, standing for 10 minutes, discharging to 2.65 V at 0.2 C, standing for 10 minutes, and then charging to 4 V at 0.5 C.

[0290] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0291] Example 19

[0292] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0293] 1. Preparation of negative electrode precursor

[0294] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed according to the mass percentages of 15.25%, 79.5%, 0.5%, 0.05%, 0.75% and 3.95%, respectively, to obtain a slurry.

[0295] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 12.7 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0296] The median particle size Dv50 of artificial graphite is 21.5μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73g / cm 3 The OI value at compacted density is 7.1.

[0297] The slurry was coated on the surface of a 6 μm thick copper foil current collector, and after drying, rolling and slitting, a surface density of 7.22 mg / cm was obtained. 2 , compacted density is 1.73g / cm 3 negative electrode precursor.

[0298] 2. Preparation of positive electrode

[0299] Same as Example 1.

[0300] 3. Assembly

[0301] The method is basically the same as Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.58 mm, and the capacity is 3823 mAh.

[0302] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0303] Example 20

[0304] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0305] 1. Preparation of negative electrode precursor

[0306] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed according to the mass percentages of 6.76%, 89.84%, 0.5%, 0.05%, 1.2% and 1.65%, respectively, to obtain a slurry.

[0307] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 9.1 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0308] The median particle size Dv50 of artificial graphite is 13.3 μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73 g / cm 3 The OI value at compacted density is 12.9.

[0309] The slurry was coated on the surface of a copper foil current collector with a thickness of 6 μm, and after drying, rolling and slitting, a surface density of 11.5 mg / cm was obtained. 2 , compacted density is 1.65g / cm 3 negative electrode precursor.

[0310] 2. Preparation of positive electrode

[0311] The same as Example 1, except that the surface density of the positive electrode coating is 24 mg / cm 2 .

[0312] 3. Assembly

[0313] The method is basically the same as Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 4.68 mm, and the capacity is 4995 mAh.

[0314] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 4.93 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 5.03 mAh / cm 2 .

[0315] Example 21

[0316] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0317] 1. Preparation of negative electrode precursor

[0318] Silicon carbon particles, artificial graphite, carbon black, single-walled carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed according to the mass percentages of 6.76%, 89.84%, 0.5%, 0.05%, 1.2% and 1.65%, respectively, to obtain a slurry.

[0319] The silicon-carbon particles are particles formed by silicon filling the pores of porous amorphous carbon, the median particle size D50 of the silicon-carbon particles is 9.1 μm, and the mass content of silicon element in the silicon-carbon particles is 50%.

[0320] The median particle size Dv50 of artificial graphite is 13.3 μm, with a secondary particle structure and a surface coating of 1% amorphous carbon. The negative electrode sheet with the artificial graphite as the active material has a density of 1.73 g / cm 3 The OI value at compacted density is 12.9.

[0321] The slurry was coated on the surface of a copper foil current collector with a thickness of 6 μm, and after drying, rolling and slitting, a surface density of 8.2 mg / cm was obtained. 2 , compacted density is 1.78g / cm 3 negative electrode precursor.

[0322] 2. Preparation of positive electrode

[0323] The same as Example 1, except that the surface density of the positive electrode coating is 17.1 mg / cm 2 .

[0324] 3. Assembly

[0325] The method is basically the same as Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.44 mm, and the capacity is 3564 mAh.

[0326] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.51 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.58 mAh / cm 2 .

[0327] Comparative Example 1

[0328] The preparation of the lithium ion battery of this comparative example comprises the following steps:

[0329] 1. Preparation of negative electrode precursor

[0330] The method is basically the same as Example 1, except that the median particle size D50 of the artificial graphite used is 19.3 μm.

[0331] 2. Preparation of positive electrode

[0332] Same as Example 1.

[0333] 3. Assembly

[0334] The method is basically the same as Example 1, except that after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.79 mm, and the capacity is 3951 mAh.

[0335] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0336] Comparative Example 2

[0337] The preparation of the lithium ion battery of this comparative example comprises the following steps:

[0338] 1. Preparation of negative electrode precursor

[0339] Same as Example 1.

[0340] 2. Preparation of positive electrode

[0341] Same as Example 1.

[0342] 3. Assembly

[0343] The battery is basically the same as Example 1, except that the pre-cycling system is as follows: charging to 4.38 V at 0.3C, then charging at constant voltage until the current is less than 0.2C, letting it stand for 10 minutes, discharging to 2.65 V at 0.2C, letting it stand for 10 minutes, and then charging to 4 V at 0.5C; after sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.80 mm, and the capacity is 3939 mAh.

[0344] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0345] Comparative Example 3

[0346] The preparation of the lithium ion battery of this comparative example comprises the following steps:

[0347] 1. Preparation of negative electrode precursor

[0348] Same as Example 1.

[0349] 2. Preparation of positive electrode

[0350] Same as Example 1.

[0351] 3. Assembly

[0352] The battery is basically the same as Example 1, except that the pre-cycling system is as follows: after charging to 4.21 V at 0.3C, constant voltage charging is performed until the current is less than 0.2C, and the battery is allowed to stand for 10 minutes. The battery is then discharged to 2.65 V at 0.2C, allowed to stand for 10 minutes, and then charged to 4 V at 0.5C. After sorting, the voltage of the lithium-ion battery is 3.67 V, the initial thickness D0 is 3.80 mm, and the capacity is 3947 mAh.

[0353] 4. The battery was disassembled and relevant parameters were tested according to the method of Example 1. The results are shown in Table 1. The gram capacity per unit area B of the positive electrode of the lithium ion battery is 3.91 mAh / cm 2 The gram capacity per unit area of ​​the negative electrode A is 3.98 mAh / cm 2 .

[0354] Table 1

[0355] Test example

[0356] 1. Cycle performance

[0357] For Examples 1 to 3, Examples 6 to 21, and Comparative Examples 1 to 3, the positive electrode active material is NCM811 material, and the following test steps are adopted: at 45°C, charge to 4.1V at a constant current of 1.2C, charge to 4.25V at 0.7C, then charge to 0.05C at a constant voltage, let stand for 10 minutes, discharge to 2.65V at 0.5C, let stand for 10 minutes, and perform a cycle test 800 times with this charge and discharge step, and measure the discharge capacity Q1 at the first cycle and the discharge capacity Q at the 800th cycle. 800 And the full-charge thickness at every 100 cycles, with the full-charge thickness at the 800th cycle as D 800 .

[0358] For Example 4, the positive electrode active material is lithium cobalt oxide, and the following test steps are adopted: at 45°C, charge to 4.3V at a constant current of 1.2C, charge to 4.45V at 0.7C, charge to 0.05C at a constant voltage, let stand for 10 minutes, discharge to 3V at 0.5C, let stand for 10 minutes, and perform a cycle test 800 times with this charge and discharge step. The discharge capacity Q1 at the first cycle and the discharge capacity Q at the 800th cycle are measured. 800 And the full-charge thickness at every 100 cycles, with the full-charge thickness at the 800th cycle as D 800 .

[0359] For Example 5, the positive electrode active material is Ni90 material, and the following test steps are adopted: at 45°C, charge to 4.05V at a constant current of 1.2C, charge to 4.2V at 0.7C, charge to 0.05C at a constant voltage, let stand for 10 minutes, discharge to 2.6V at 0.5C, let stand for 10 minutes, and perform a cycle test 800 times with this charge and discharge step. The discharge capacity Q1 at the first cycle and the discharge capacity Q at the 800th cycle are measured. 800 And the full-charge thickness at every 100 cycles, with the full-charge thickness at the 800th cycle as D 800 .

[0360] The capacity retention rate and thickness change rate H after 800 cycles were calculated according to the following formula. The results are shown in Table 2.

[0361] Capacity retention rate Q = Q 800 / Q1*100%

[0362] Thickness change rate H (%) = (D 800 -D0) / D0*100%

[0363] 2. Rate performance

[0364] For Examples 1 to 3, Examples 6 to 21, and Comparative Examples 1 to 3, the batteries were subjected to charge and discharge tests at 25°C using a battery charge and discharge tester. The charge and discharge regime was as follows: 0.2C constant current charging to 4.25V, then switching to 4.25V constant voltage charging until the current decreased to 0.02C, standing for 5 minutes, and then 0.2C constant current discharging to 2.65V. The discharge capacity Q was recorded. 0.2c After standing for 5 minutes, charge at 0.2C constant current to 4.25V, switch to 4.25V constant voltage charging until the current decreases to 0.02C, stand for 5 minutes, discharge at 2C constant current to 2.65V, and record the discharge capacity Q 2c .

[0365] For Example 4, the battery was charged and discharged at 25°C using a battery charge and discharge tester. The charge and discharge regime was as follows: 0.2C constant current charging to 4.45V, then switching to 4.45V constant voltage charging until the current decreased to 0.02C, standing for 5 minutes, and then 0.2C constant current discharging to 3V. The discharge capacity Q was recorded. 0.2c After standing for 5 minutes, charge at a constant current of 0.2C to 4.45V, then switch to a constant voltage of 4.45V until the current decreases to 0.02C. After standing for 5 minutes, discharge at a constant current of 2C to 3V, and record the discharge capacity Q. 2c .

[0366] For Example 5, the battery was charged and discharged at 25°C using a battery charge and discharge tester. The charge and discharge regime was as follows: 0.2C constant current charging to 4.2V, then switching to 4.2V constant voltage charging until the current decreased to 0.02C, standing for 5 minutes, and then 0.2C constant current discharging to 2.6V. The discharge capacity Q was recorded. 0.2c After standing for 5 minutes, charge at 0.2C constant current to 4.2V, switch to 4.2V constant voltage charging until the current decreases to 0.02C, and after standing for 5 minutes, discharge at 2C constant current to 2.6V, and record the discharge capacity Q 2c .

[0367] The 2C discharge rate capacity retention rate R can be calculated as follows:

[0368] 2C discharge rate capacity retention rate R=Q 2c / Q 0.2c ×100%

[0369] The results are shown in Table 2.

[0370] 3. Energy density

[0371] Use a battery charge and discharge tester to charge the lithium-ion battery at 25°C at a constant current of 0.5C to 4.25V, then charge it at a constant voltage until the current drops to 0.02C. After standing for 5 minutes, discharge the battery at a constant current of 0.5C to 2.8V, and record the battery's first discharge capacity Q. 放 and the first discharge energy E 放 , measure the thickness, width and length of the battery and calculate the product of the three to get the volume X of the battery, and calculate the volume energy density of the battery ED = E 放 / X, unit is Wh / L.

[0372] The results are shown in Table 2.

[0373] Table 2

[0374] According to Table 2, the silicon-containing negative electrode sheet disclosed herein has excellent performance in terms of safety performance, cycle performance and rate performance.

[0375] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, 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 disclosure.

Claims

1. A lithium-ion battery, characterized in that: The lithium-ion battery comprises a negative electrode sheet and a positive electrode sheet, the positive electrode sheet comprises a nickel-based positive electrode active material, the negative electrode active layer of the negative electrode sheet comprises a negative electrode active material and nickel, and the negative electrode active material comprises a silicon-carbon material and graphite; the composition of the negative electrode active layer satisfies 9500≤α*d / η≤24500; Wherein, α is the content of nickel in the negative electrode active layer, in ppm; η is the mass percentage of silicon in the negative electrode active layer, in %; and d is the median particle size of the negative electrode active material, in μm.

2. The lithium-ion battery according to claim 1, wherein 20ppm≤α≤75ppm; and / or, 1.5%≤η≤7.5%; and / or, 9μm≤d≤16μm.

3. The lithium-ion battery according to claim 1 or 2, characterized in that The negative electrode active layer further includes cobalt element, and the content of the cobalt element in the negative electrode active layer is not higher than 50 ppm.

4. The lithium-ion battery according to any one of claims 1 to 3, wherein: In the X-ray diffraction pattern, the negative electrode active layer has a first diffraction peak with a 2θ of 53.7° to 55.7° and a second diffraction peak with a 2θ of 76.4° to 78.4°, and the intensity ratio of the first diffraction peak to the second diffraction peak is 8 to 16.

5. The lithium-ion battery according to claim 4, characterized in that The negative electrode sheet satisfies:

6. The lithium-ion battery according to any one of claims 1 to 5, characterized in that: In thermogravimetric analysis, the negative electrode active layer satisfies the following formulas 1 and 2: 0.75%≤m*d≤4% Formula 1, 30%≤(1.27n-6.32m) / η≤95% Formula 2 Wherein, when the negative electrode active layer is heated from 25°C to 1000°C at 10°C / min in an argon atmosphere, the weight loss percentage in the range of 230-360°C is m, and the weight loss percentage in the range of 230-950°C is n; Preferably, 0.05%≤m≤0.35%, and 1.5%≤n≤3.5%.

7. The lithium-ion battery according to any one of claims 1 to 6, characterized in that: The median particle size Dv50 of the silicon-carbon material is 6 μm to 12 μm; and / or, The mass percentage of silicon element in the silicon-carbon material is 40% to 60%; and / or, The median particle size Dv50 of the graphite is 8 μm to 20 μm; and / or, The surface density of the negative electrode sheet is 8 mg / cm 2 ~15mg / cm 2 and / or, The compaction density of the negative electrode sheet is 1.2 g / cm 3 ~1.8g / cm 3 .

8. The lithium-ion battery according to any one of claims 1 to 7, characterized in that: The nickel-based positive electrode active materials include lithium nickelate, lithium nickel manganese oxide, Li x Ni y1 Co y2 M1 y3 M2 y4 O2, 0.99≤x≤1.05, 0.99<y1+y2+y3≤1.05, 1 / 3≤y1≤0.8, 0≤y4≤0.1, M1 is selected from Mn or Al, M2 is at least one of Mg, Ti, Mn, Al, Te, W, Ni, Nb, Zr, La, F, Ce, Sr, Y, K, B and P elements and is different from M1.

9. The lithium-ion battery according to any one of claims 1 to 8, characterized in that: The surface density of the positive electrode sheet is 16.7 mg / cm 2 ~26.2mg / cm 2 and / or, The compaction density of the positive electrode sheet is 3.1 g / cm 3 ~4.2g / cm 3 .

10. The lithium-ion battery according to any one of claims 1 to 9, characterized in that: The ratio of the gram capacity per unit area of the negative electrode sheet to the positive electrode sheet is 0.97 to 1.1; Preferably, the ratio of the gram capacity per unit area of the negative electrode sheet to that of the positive electrode sheet is 0.99 to 1.05; Preferably, the gram capacity per unit area of the negative electrode sheet is 3.5 mAh / cm 2 ~5.73mAh / cm 2 The gram capacity per unit area of the positive electrode sheet is 3.43 mAh / cm 2 ~5.61mAh / cm 2 .

11. The lithium-ion battery according to any one of claims 1 to 10, characterized in that: The electrolyte of the lithium ion battery includes fluoroethylene carbonate with a mass percentage of γ, and 0.3≤γ / η≤3.

6.

12. The lithium-ion battery according to any one of claims 1 to 11, characterized in that: The graphite is selected from natural graphite, artificial graphite or a coating of natural graphite and / or artificial graphite; And / or, the negative electrode active layer further includes a negative electrode conductor and a negative electrode binder, the negative electrode conductor is selected from at least one of carbon black, acetylene black, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, Ketjen black, and carbon fibers, and the negative electrode binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, and styrene-butadiene rubber.

13. The lithium-ion battery according to claim 12, characterized in that The graphite is selected from the product of artificial graphite surface coated with amorphous carbon, and the coating mass of the amorphous carbon accounts for 0.1% to 3% of the product.

14. The lithium-ion battery according to any one of claims 1 to 13, characterized in that: The positive electrode sheet includes a positive electrode collector and a positive electrode active layer including a positive electrode active material arranged on one side or both sides of the positive electrode collector. The positive electrode active material includes a nickel-based positive electrode active material, a positive electrode conductor and a positive electrode binder. The positive electrode active layer includes 70wt%-99wt% of the positive electrode active material, 0.5wt%-15wt% of the positive electrode conductor, and 0.5wt%-15wt% of the positive electrode binder in terms of mass percentage.

15. The lithium-ion battery according to claim 14, characterized in that The positive electrode conductive agent is selected from at least one of carbon black, acetylene black, graphene, single-walled carbon nanotubes, multi-walled carbon nanotubes, Ketjen black, and carbon fiber; And / or, the positive electrode binder is selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polymers containing ethylene oxide, polyvinyl pyrrolidone, and polyurethane.

Images