Lithium ion battery

Abstract

The application relates to the technical field of batteries, in particular to a lithium ion battery. The lithium ion battery comprises a negative electrode sheet and an electrolyte; the negative electrode sheet comprises a negative electrode current collector and a negative electrode active coating layer; the negative electrode current collector comprises a copper foil and a protective layer located on at least one side of the copper foil, the protective layer comprises a first element, and the first element comprises chromium and / or nickel; the negative electrode active coating layer comprises a silicon-carbon material, the mass content c of element Si in the negative electrode active coating layer is 2%-50%; the pore volume v of the silicon-carbon material per unit mass is 0.5mm 3 / g-30.5mm 3 / g; the electrolyte comprises a first additive, and the mass content c1 of the first additive in the electrolyte is 0.1%-6%; c, v and c1 satisfy: 0.0005<=c1 / (vxc)<=5.5, wherein the unit of v is mm 3 / g. The lithium ion battery can effectively inhibit corrosion and copper precipitation of the negative electrode current collector, improve the K value, and improve the cycle performance and service life.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a lithium-ion battery. Background Technology

[0002] To improve the energy density of lithium-ion batteries, introducing silicon-carbon materials into the negative electrode has become an important technological development direction. However, compared with traditional graphite negative electrodes, silicon-carbon materials often have stronger hydrophilicity and are more likely to adsorb moisture from the environment. At the same time, silicon-carbon materials exhibit significant volume expansion during charge and discharge processes, and their particles also show greater resistance to crushing and deformation during electrode processing (such as rolling). In related technologies, to address these issues, conventional film-forming additives are typically added to the electrolyte to protect the electrode interface.

[0003] However, the aforementioned technical solutions cannot systematically solve the series of chain problems caused by the characteristics of silicon-carbon materials. They still lead to damage and corrosion of the copper foil in the negative electrode current collector, with dissolved copper ions migrating to the negative electrode and depositing electrochemical copper, causing self-discharge, severely damaging the battery's interface stability, and resulting in a rapid decline in battery cycle life.

[0004] Therefore, while pursuing high energy density by using silicon-carbon anodes, how to effectively improve copper deposition and poor K-value of anode sheets and improve the cycle life of batteries has become a key technical problem that urgently needs to be solved. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide a lithium-ion battery. This invention addresses the damage and corrosion of the negative electrode current collector caused by silicon-carbon materials during negative electrode cycling by constructing a synergistic protection system of the negative electrode and electrolyte. This effectively suppresses corrosion and copper deposition in the negative electrode current collector, improves poor K-value, and enhances the battery's cycle performance and lifespan.

[0006] The existing technologies have not been ideal in improving the damage and corrosion of the negative electrode current collector caused by cycling. This is because increasing the energy density of the battery requires increasing the silicon content and electrode compaction density. However, the inherent water absorption and high resistance to crushing and deformation of silicon-carbon materials inevitably damage the negative electrode current collector, and may even trigger a chain reaction where electrolyte decomposition products corrode the copper foil, leading to copper deposition. Specifically, trace amounts of moisture adsorbed by the silicon-carbon material react with lithium hexafluorophosphate to generate the corrosive substance hydrofluoric acid (HF). Simultaneously, the high resistance to crushing and deformation and expansion characteristics of silicon-carbon materials can cause mechanical damage to the copper foil during negative electrode rolling or cyclic expansion, further leading to copper foil corrosion and ultimately forming copper pitting on the negative electrode surface. This results in battery interface deterioration and accelerated cycle life decay.

[0007] Through in-depth analysis, the inventors discovered that the aforementioned problems arise from several factors: First, the silicon surface contains numerous dangling bonds, whose hydrogen bond energy with water molecules is far higher than that of graphite. Furthermore, silicon-carbon materials typically have a large specific surface area, resulting in significantly stronger water absorption compared to traditional graphite anodes. Second, the interaction between the silicon-carbon material and the anode current collector during compaction may damage the underlying copper foil. Additionally, the hydrolysis of lithium salts in the electrolyte is an autocatalytic process; once the generated HF comes into contact with exposed copper, the corrosion reaction continues. These factors collectively lead to copper foil corrosion, the formation of copper pitting, and the deterioration of the battery interface and cycle performance.

[0008] To overcome the aforementioned problems, this invention proposes a different technical approach: by constructing a synergistic protection system from negative electrode plate regulation to electrolyte interface repair, key aspects of the aforementioned problems are intervened in simultaneously. This effectively suppresses copper foil corrosion and avoids copper deposition without significantly sacrificing battery energy density, thereby improving the battery's long-term cycle life. Based on this, the inventors of this invention propose the following solution: This invention provides a lithium-ion battery, comprising a negative electrode and an electrolyte; the negative electrode includes a negative current collector and a negative active coating located on at least one side of the surface of the negative current collector; the negative current collector includes a copper foil and a protective layer located on at least one side of the copper foil, the protective layer containing a first element, the first element including chromium and / or nickel; the negative active coating includes a silicon-carbon material, wherein the mass content c of element Si in the negative active coating is 2%-50%; the silicon-carbon material has pores, and the pore volume v per unit mass of the silicon-carbon material is 0.5 mm. 3 / g-30.5mm 3 / g; the electrolyte includes a first additive, the first additive including , , , , , , , and At least one of the following; the mass content c1 of the first additive in the electrolyte is 0.1%-6%; c, v (unit: mm) 3 The condition for c1 to satisfy 0.0005 ≤ c1 / (v×c) ≤ 5.5.

[0009] Copper foil, due to its excellent conductivity, ductility, and cost advantages, is the most commonly used negative electrode current collector substrate in this field. The protective layer on the surface of the copper foil is the first physical barrier constructed in this invention. The introduction of the first element (chromium and / or nickel) makes the protective layer relatively dense and possesses good corrosion resistance, thereby effectively preventing the electrolyte and its corrosive components from directly contacting the copper foil. Synergistically optimizing the overall pore volume of the silicon-carbon material can reduce the specific surface area of ​​the silicon-carbon material in contact with moisture, reducing its ability to absorb moisture and minimizing side reactions between moisture and the electrolyte at the source. However, the pore volume of the silicon-carbon material cannot be too low (e.g., v less than 0.5 mm). 3 Otherwise, it cannot provide an effective buffer space for the expansion of the internal silicon material, which will still lead to the compression of the negative electrode current collector and damage to the copper foil. Although controlling the pore volume of the silicon-carbon material can reduce the damage to the negative electrode current collector, the presence of pores still cannot prevent water absorption and damage to the negative electrode current collector. By adding a first additive (polycyclic sulfur-containing additive) to the electrolyte, the protective layer on the outer surface of the copper foil can be continuously improved and repaired, and the attack of HF on the internal copper foil can be suppressed. Further control of the content of the first additive and the ratio of the product of the pore volume per unit mass of silicon-carbon material and the mass content of elemental Si in the negative electrode active coating within a certain range can control the absorption of moisture by the silicon-carbon material and the compression damage to the copper foil caused by expansion during cycling. On the other hand, it can continuously improve and repair the protective layer of the copper foil to improve the corrosion effect of the copper foil. This further suppresses copper foil corrosion, improves copper deposition, and increases the cycle life of the battery.

[0010] Through the above technical solution, the present invention has at least the following advantages compared with the prior art: the lithium-ion battery of the present invention can effectively suppress the corrosion and copper deposition of the negative electrode current collector, improve the poor K value of the battery, and enhance cycle performance and service life.

[0011] The endpoints and any values ​​of the ranges 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 endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0012] Figure 1 The figure shown is a cross-sectional schematic diagram of the negative electrode current collector along the thickness direction in an embodiment of the present invention. Detailed Implementation

[0013] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0014] The present invention provides a lithium-ion battery, which includes a negative electrode and an electrolyte.

[0015] In this invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active coating located on at least one side of the surface of the negative electrode current collector. The negative electrode current collector includes a copper foil and a protective layer located on at least one side of the copper foil. The protective layer contains a first element, which includes chromium and / or nickel.

[0016] In one example, the negative electrode current collector includes the copper foil and the protective layer located on both sides of the copper foil. For example... Figure 1 The figure shows a cross-sectional schematic diagram of the negative electrode current collector along the thickness direction in an embodiment of the present invention. As can be seen from the figure, the negative electrode current collector 1 includes a copper foil 11 and a protective layer 12 located on both sides of the copper foil 11.

[0017] In this invention, chromium or nickel may exist in the protective layer in the form of an element, an alloy, or a compound (such as an oxide, a nitride, etc.).

[0018] In one example, the protective layer contains chromium. The chromium in the protective layer exists in at least one of the following forms: Cr2O3, Cr2O3·xH2O, Cr(OH)3, Cr(OH)3·3H2O, CrOOH, and CuCrO4.

[0019] In this invention, the protective layer can be achieved in a variety of ways, including but not limited to forming on the surface of copper foil through processes such as physical vapor deposition, chemical vapor deposition, electroplating (e.g., electroplating of chromium, electroplating of nickel), vacuum coating, or chemical passivation (e.g., chromate passivation).

[0020] In this invention, the negative electrode active coating comprises silicon-carbon material, and the mass content (c) of elemental Si in the negative electrode active coating is 2%-50%, for example, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 42%, 45%, or 50%. Silicon-carbon material, as a high-capacity active material, is key to improving energy density. Limiting the mass content of elemental Si in the negative electrode active coating to 2%-50% represents a balance between improving energy density and controlling side reactions caused by silicon. When c is below 2%, the contribution of silicon-carbon material to improving energy density is limited. However, when c is above 50%, the volume expansion effect of silicon and interfacial side reactions increase sharply, making it difficult to guarantee cycle stability.

[0021] In this invention, the "mass content c of element Si in the negative electrode active coating" refers to the percentage of the total mass of all silicon elements (regardless of their chemical form, such as elemental silicon, silicon oxide, silicon alloy, etc.) in the negative electrode active coating relative to the total mass of the entire negative electrode active coating (including all solid components such as negative electrode active material, conductive agent, and binder). This can be obtained through conventional methods in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled, soaked in dimethyl carbonate (DMC) solvent for 12 hours, then rinsed with DMC solvent to remove lithium salts adhering to the negative electrode sheet. After drying, the negative electrode sheet is subjected to high-temperature treatment at 400°C in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active coating can then be peeled off from the negative electrode current collector, and collected as a test sample. Using a thermogravimetric analyzer (e.g., a TGA550 thermogravimetric analyzer), the sample size is 5mg-15mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature (25℃) to 900℃ at a rate of 10℃ / min, and held at 900℃ for 40min. This allows the non-silicon components in the negative electrode active coating to volatilize while the silicon is fully oxidized to silicon dioxide. The remaining substance is the ash content of the negative electrode active coating. The mass content of elemental Si in the negative electrode active coating can be calculated based on the mass of the ash, using the following formula: Mass content of elemental Si in the negative electrode active coating = 7 × mass of ash / (15 × mass of test sample).

[0022] In this invention, the silicon-carbon material has pores, and the pore volume v per unit mass of the silicon-carbon material is 0.5 mm. 3 / g-30.5mm 3 / g, for example, 0.5mm 3 / g, 1mm 3 / g, 2mm 3 / g, 3mm 3 / g, 4mm 3 / g, 5mm 3 / g, 6mm 3 / g, 7mm 3 / g, 8mm 3 / g, 9mm 3 / g, 10mm 3 / g, 11mm 3 / g, 12mm 3 / g, 13mm 3 / g, 14mm 3 / g, 15mm 3 / g, 16mm 3 / g, 17mm 3 / g, 18mm 3 / g, 19mm 3 / g, 20mm3 / g, 25mm 3 / g, 30mm 3 / g or 30.5mm 3 / g. Porosity is an important structural feature of silicon-carbon materials, and the size of the pore volume per unit mass, v, directly affects the material's water absorption and buffering capacity. When v is controlled within the above range, on the one hand, a certain pore volume provides space to accommodate the huge volume expansion of silicon during charging and discharging, which can buffer expansion stress and reduce particle breakage and squeezing damage to the negative electrode current collector; on the other hand, the pore volume should not be too large, as an excessively large specific surface area will significantly increase the material's ability to adsorb moisture, introducing more moisture sources that lead to side reactions.

[0023] In one example, v is 0.8 mm 3 / g-25mm 3 / g.

[0024] In this invention, the pore volume v per unit mass of the silicon-carbon material can be obtained by conventional methods in the art. For example, 1.2g of silicon-carbon material powder is taken as a sample and degassed at 100°C for 12h. The amount of nitrogen adsorbed by the material under different pressures is tested using a physical adsorption analyzer, and nitrogen adsorption-desorption isotherms are plotted. Then, the pore size distribution curve is fitted using a DFT model, and the pore volume of the silicon-carbon material is calculated.

[0025] In this invention, the electrolyte includes a first additive, the first additive comprising: (I-1) (I-2) (I-3) (I-4) (I-5) (I-6) (I-7) (I-8) and At least one of (I-9). The mass content c1 of the first additive in the electrolyte is 0.1%-6%, for example, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5% or 6%.

[0026] In one instance, c1 is 0.5%-5%.

[0027] The first additive, namely the polycyclic sulfur-containing additive, is a key component in the electrolyte of this invention. Controlling its content (c1) within the range of 0.1% to 6% is crucial. Too low a content (e.g., less than 0.1%) will prevent the formation of an effective and sustainable repair interface film; while too high a content (e.g., greater than 6%) may excessively increase the electrolyte viscosity and exacerbate side reactions. A specific content of the first additive can undergo a reduction reaction at the negative electrode (including the surface of the silicon-carbon material and the copper foil / protective layer) during battery formation or early cycling, forming a solid electrolyte interface film rich in sulfides or sulfates. This interface film not only helps stabilize the silicon-carbon material interface but also repairs the protective layer on the copper foil surface damaged by processing, or directly forms a protective adsorption layer on the exposed copper surface, inhibiting further corrosion by HF.

[0028] In this invention, the mass content c1 of the first additive in the electrolyte can be obtained by methods conventional in the art, such as gas chromatography (GC).

[0029] In this invention, c and v (unit: mm) 3 The following conditions must be met for c1 to satisfy: 0.0005 ≤ c1 / (v×c) ≤ 5.5, for example, 0.0005, 0.008, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or 5.5.

[0030] This invention does not simply list the three parameters c, v, and c1 and combine them arbitrarily, but rather dynamically links the water absorption and swelling characteristics of silicon-carbon materials with the interface repair requirements through a mathematical relationship. v×c can approximate the overall water absorption tendency and swelling stress of the silicon-carbon material. A larger v or c means the system needs to cope with more moisture and greater mechanical stress, resulting in a higher risk of damage to the protective layer. c1 represents the chemical repair capacity that the system can provide. When the ratio is less than 0.0005, it means the repair capacity is severely insufficient relative to the potential damage risk; the first additive is insufficient to repair the interface damage caused by water absorption and swelling, and corrosion will still occur. When the ratio is greater than 5.5, it means the repair agent is relatively excessive, which may cause an unnecessary excessively thick interface film, increasing interface impedance. Controlling the ratio between 0.0005 and 5.5 achieves a balance between the water absorption buffering capacity of the silicon-carbon material and the electrolyte repair capacity, effectively improving copper foil corrosion and copper deposition on the negative electrode, thus better improving the battery's cycle life.

[0031] In one instance, 0.001 ≤ c1 / (v×c) ≤ 0.65.

[0032] In one instance, 0.005 ≤ c1 / (v×c) ≤ 0.13 <Negative Electrode Current Collector> In one example, the thickness of the copper foil is 2μm-16μm, for example, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or 16μm. A thickness of not less than 2μm ensures that the negative electrode current collector has sufficient mechanical strength, making it less prone to breakage or deformation during electrode processing and battery assembly; a thickness of not more than 16μm helps to reduce the weight of inactive materials in the battery and improve energy density. It is understood that for special high-power or ultra-thin battery designs, the copper foil thickness may slightly exceed this range, but the basic concept of the present invention still applies.

[0033] In one example, the thickness 'a' of the protective layer is 0.02 μm to 0.1 μm, for example, 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, or 0.1 μm. The thickness 'a' of the protective layer refers to the thickness of the protective layer located on one side of the copper foil.

[0034] In one instance, a is 0.04μm-0.1μm.

[0035] The thickness 'a' of the protective layer is crucial to the effectiveness of the physical barrier. If the thickness is less than 0.02 μm, the protective layer may be discontinuous or too thin, making it easily damaged and resulting in insufficient protection. If the thickness is greater than 0.1 μm, it may slightly increase the overall resistance of the negative electrode current collector and hinder the penetration and repair of the first additive molecules. Controlling 'a' within the range of 0.02–0.1 μm, especially 0.04–0.1 μm, achieves a good balance between ensuring effective protection and minimizing negative impacts.

[0036] In one example, the thickness a (in μm) of the protective layer and the mass content c1 of the first additive in the electrolyte satisfy the following condition: 0.3 ≤ a / c1 ≤ 50, for example, 0.3, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45 or 50.

[0037] In one instance, 1 ≤ a / c1 ≤ 13.

[0038] In one instance, 2.5 ≤ a / c1 ≤ 5.5.

[0039] Maintaining the a / c1 ratio between 0.3 and 50 ensures a reasonable balance between physical protection and chemical repair, further suppressing corrosion and copper deposition in the negative electrode current collector, improving the battery's K-value, and enhancing cycle performance and lifespan. A ratio less than 0.3 may indicate an excessively thin protective layer and excessively high additive concentration, potentially leading to increased electrolyte viscosity and other side reactions. Conversely, a ratio greater than 50 may indicate an excessively thick protective layer and excessively low additive concentration, potentially increasing the overall resistance of the negative electrode current collector. By establishing the a / c1 ratio, the physical protection of the negative electrode current collector and the chemical protection of the electrolyte are no longer isolated but rather a mutually complementary whole.

[0040] In one example, the protective layer comprises chromium oxide. Chromium oxides (such as Cr2O3) have a dense structure and stable chemical properties, exhibiting excellent corrosion resistance in electrolyte environments and effectively blocking the penetration of corrosive media such as hydrofluoric acid. Using chromium oxide as a key component of the protective layer can further enhance the protective effect and durability of the physical barrier.

[0041] In this invention, the thickness of the copper foil and the thickness 'a' of the protective layer can be obtained by conventional methods in the art. For example, the thickness of the protective layer can be obtained by ellipsometer testing, and the thickness of the negative electrode current collector can be obtained by micrometer testing. The thickness of the copper foil is equal to the thickness of the negative electrode current collector minus the thickness of the protective layer.

[0042] In one example, the mass content of the first element in the negative electrode current collector is 40ppm-650ppm, for example, 40ppm, 50ppm, 60ppm, 70ppm, 80ppm, 90ppm, 100ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, or 650ppm. When the mass content of the first element in the negative electrode current collector is greater than 40ppm, sufficient chromium and / or nickel are ensured to form a continuous and effective protective layer.

[0043] In this invention, the mass content of the first element in the negative electrode current collector refers to the mass percentage of the first element in the entire negative electrode current collector, including the copper foil and the protective layer. This can be measured using methods conventional in the art, such as inductively coupled plasma (ICP).

[0044] In one instance, the protective layer further comprises a second element. The second element includes zinc and / or tin.

[0045] Silicon-carbon materials In one example, the silicon-carbon material has a coating layer on its surface, the coating layer comprising at least one of amorphous carbon, graphite, carbon nanotubes, graphene, alumina, and silicon oxide.

[0046] In one example, after the silicon-carbon material reacts with deionized water in a sealed container, the volume percentage of hydrogen in the sealed container is 30%-90%, for example, 30%, 40%, 50%, 60%, 70%, 80%, or 90%. Within this range, the surface silicon-carbon material has a sufficiently complete and dense coating layer, which can effectively prevent the direct adsorption of moisture by the internal silicon. The mass ratio of the silicon-carbon material to the deionized water is 1:5, and the volume of the sealed container is twice the volume of the deionized water; the reaction condition is to store the material in a 60°C oven for 12 hours.

[0047] Building upon the suppression of copper foil corrosion, this invention further reduces moisture contact and side reactions at the source of silicon-carbon materials by regulating the integrity of the coating layer on the surface of the silicon-carbon material. The aforementioned testing method provides a means to quantitatively evaluate the coating integrity of silicon-carbon materials. In well-coated silicon-carbon materials, the internal active silicon is effectively isolated by a dense coating layer, resulting in a slow reaction with deionized water and a relatively low proportion of hydrogen in the generated gas. Conversely, in poorly coated or insufficiently dense silicon-carbon materials, a large amount of active silicon is exposed, reacting violently with water to generate a large amount of hydrogen (Si + 2H₂O → SiO₂ + 2H₂), leading to an increased hydrogen content. When the hydrogen content exceeds 90%, it indicates severe inadequacy of the coating, with significant water absorption and gas generation. Controlling the hydrogen content within the range of 30%-90% indicates that the silicon-carbon material has a good coating state, significantly suppressing the direct and rapid reaction between internal active silicon and moisture, thereby fundamentally reducing moisture consumption and HF generation in the battery system.

[0048] In this invention, the volume percentage of hydrogen can be obtained by the following method: take a 10ml vial, add 1g of silicon carbide powder, and inject 5ml of deionized water. Then, store it in a 60℃ oven for 12h. Finally, use GC to test the H2 content in the gas composition.

[0049] In one example, the sphericity of the silicon-carbon material is 0.8-0.99, for example, 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, or 0.99. To reduce the localized mechanical damage to the negative electrode current collector caused by silicon-carbon material particles during the rolling process of the negative electrode sheet, this invention further limits the sphericity of the silicon-carbon material. Sphericity is a parameter that measures how close a particle is to a perfect sphere; the closer the value is to 1, the more regular the particle shape and the fewer sharp edges. By controlling the sphericity of the silicon-carbon material to 0.8 or higher, it means that the particles have a relatively rounded shape. During the negative electrode rolling process, the contact between the highly spherical particles and the negative electrode current collector is smoother, and the pressure distribution per unit area is more uniform. This avoids stress concentration caused by sharp edges and corners, thereby effectively reducing the damage to the negative electrode current collector caused by the rolling process and protecting the integrity of the protective layer.

[0050] In this invention, the sphericity of the silicon-carbon material can be tested using conventional methods in the art. For example, the negative electrode sheet can be sliced ​​using an ion polisher, the cross-section of the negative electrode sheet can be observed in the backscatter mode of SEM, 100 silicon-carbon material particles can be randomly selected, and the perimeter and cross-sectional area of ​​the silicon-carbon material particles can be measured using ImageJ image analysis software. The perimeter equivalent diameter D1 and the area equivalent diameter D2 can be calculated respectively, and the sphericity = D2 / D1.

[0051] In one example, the mass content of element Si in the silicon-carbon material is 20%-80%, for example, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%.

[0052] In one example, the mass content of element Si in the silicon-carbon material is 35%-60%.

[0053] In this invention, the mass content of element Si in the silicon-carbon material can be tested using conventional methods in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled, soaked in DMC solvent for 12 hours, and then rinsed with DMC solvent to remove the lithium salt attached to the negative electrode sheet. The negative electrode sheet is then cut with an argon ion milling machine using a CP laser and observed using SEM (Back-scattered Electrons BSE mode). In this mode, the contrast of the silicon-carbon material is brighter (which can be used to distinguish the graphite material and conductive agent in the negative electrode active coating). Combined with an energy dispersive spectroscopy (EDS) instrument, at least 10 silicon-carbon materials are randomly selected, and the mass content of silicon element in each particle is obtained by spot scanning and taking the average value.

[0054] In one example, the silicon-carbon material comprises a porous carbon matrix and silicon particles located within the porous carbon matrix. The porous carbon matrix not only provides a continuous conductive network, but its abundant pores also provide space for the expansion of the silicon particles and constrain their expansion, preventing them from detaching from the composite material and failing during cycling. The silicon particles, located within the porous carbon, are also physically isolated by the carbon layer, which helps mitigate direct side reactions with the electrolyte.

[0055] In one example, the silicon-carbon material further includes a carbon coating layer located on the outer surface of the silicon-carbon material.

[0056] Negative electrode film In one example, the compaction density of the negative electrode is 1.2 g / cm³. 3 -1.95g / cm 3 For example, 1.2 g / cm³ 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 Or 1.95g / cm 3 Compacted density is the mass per unit volume of an electrode after it has been rolled, and it directly affects the electrode's porosity, conductivity, and volumetric energy density. For silicon-containing anodes, especially when the silicon content is high, silicon-carbon materials have high hardness, and if the compacted density is too high (e.g., exceeding 1.95 g / cm³), it can cause problems. 3 During the rolling process, silicon-carbon material particles exert extremely high local pressure on the negative electrode current collector, which can easily cause the protective layer to crack. If the compaction density is too low (e.g., below 1.2 g / cm³), the protective layer will be damaged. 3 If the compaction density is too loose, the electron conductivity network will deteriorate, and the volumetric energy density will be too low. Controlling the compaction density within a certain range is the key to maximizing the integrity of the protective layer on the copper foil surface while ensuring that the negative electrode has reasonable electrical performance.

[0057] The compaction density here refers to the actual compaction density measured after the battery is disassembled and the negative electrode sheet is removed, which differs from the compaction density obtained by rolling the negative electrode sheet during battery manufacturing. This is because after the negative electrode sheet is assembled into a battery, there will be physical and chemical rebound, resulting in compaction rebound. Consequently, the actual compaction density of the negative electrode sheet measured after battery manufacturing is lower than the compaction density obtained after rolling. The compaction density of the negative electrode sheet can be tested using conventional methods in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled, soaked in DMC solvent for 12 hours, rinsed with DMC solvent to remove lithium salts adhering to the negative electrode sheet, and then washed with deionized water to remove any residue on the surface of the negative electrode sheet. After drying, at least 20 sites are selected on the negative electrode sheet, and the thickness of the negative electrode sheet at each site is measured using a micrometer. The average value h (in cm) is taken. The negative electrode sheet is then punched into a disc with a diameter of 44.3 mm using a die-cutting tool. Ten discs are taken, and the mass of each disc is weighed. The average value m (in mg) is taken. The areal density M1 is calculated as M1 = (m - m1) × 100 / 1540.25, where m1 is the mass of the negative electrode current collector in the disc (in mg), and the areal density is in mg / cm³. 2 The compaction density is calculated using the areal density M1 and the average thickness h, as follows: Compaction density = M1 / ​​(h - thickness of the negative electrode current collector), where the thickness of the negative electrode current collector is in cm, and the resulting compaction density is in mg / cm². 3 The unit for converting compacted density is g / cm³. 3 .

[0058] In this invention, the negative electrode active coating includes a negative electrode active material, and the negative electrode active material includes the silicon-carbon material.

[0059] In one example, the negative electrode active material further includes a carbon-based material. The carbon-based material includes at least one of artificial graphite, natural graphite, hard carbon, and soft carbon.

[0060] In this invention, the negative electrode active coating further includes a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, carbon dots, carbon nanotubes (including single-walled carbon nanotubes and / or multi-walled carbon nanotubes), graphene, and carbon nanofibers; the negative electrode binder includes at least one of polyvinylidene fluoride, carboxymethyl cellulose, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, and polytetrafluoroethylene.

[0061] In one example, based on the total weight of the negative electrode active coating, the mass content of the negative electrode material is 80%-99.8%, the mass content of the negative electrode conductive agent is 0.1%-10%, and the mass content of the negative electrode binder is 0.1%-10%.

[0062] Electrolyte In one example, the electrolyte includes a second additive, which includes at least one of butadionitrile, adiponitrile, trans-butadionitrile, malononitrile, o-phthalonitrile, iso-phthalonitrile, ethylene glycol bis(propionitrile) ether, glutaronitrile, and terephthalonitrile.

[0063] In one example, the mass content c2 of the second additive in the electrolyte is 0.1%-3.9%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5% or 3.9%. The mass content c2 of the second additive in the electrolyte can be determined by conventional testing methods in the art, such as GC.

[0064] In one instance, c2 is 1%-3.5%.

[0065] Building upon the repair of the protective layer using the first additive, this invention introduces a second additive into the electrolyte to further suppress the generation of HF from lithium salt hydrolysis and thus mitigate corrosion. The second additive contains two cyano groups in its molecular structure. These cyano groups possess lone pairs of electrons, enabling them to strongly complex the intermediate PF5 generated during the hydrolysis of lithium hexafluorophosphate. - Thus suppressing PF5 - The catalytic reaction continues the chain reaction between water and lithium salt, reducing HF generation at the source. Simultaneously, particularly symmetrically structured dianitronics (such as adiponitrile), whose cyano groups at both ends can chemically adsorb onto the copper surface, forming an ordered, dense barrier layer that physically blocks corrosive media. Furthermore, when C2 is within a specific range, it can effectively exert the complexing function of the second additive without affecting the basic physicochemical properties of the electrolyte or causing other side effects due to excessive amounts.

[0066] In one example, the electrolyte further includes lithium hexafluorophosphate, the mass content (c3) of which is 7%-22%, for example 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, or 22%. The mass content (c3) of lithium hexafluorophosphate in the electrolyte can be determined by methods conventional in the art, such as ion chromatography (IC).

[0067] In one instance, c3 is 8%-16%.

[0068] In one instance, c2 and c3 satisfy: 0.005 ≤ c2 / c3 ≤ 0.5, for example, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, or 0.5.

[0069] In one instance, 0.05 ≤ c2 / c3 ≤ 0.4.

[0070] In one instance, 0.1 ≤ c2 / c3 ≤ 0.3.

[0071] If the C2 / C3 ratio is too low (e.g., less than 0.005), it means that the amount of the second additive is negligible relative to the abundant presence of lithium hexafluorophosphate, insufficient to effectively complex all hydrolysis intermediates PF5. - The inhibitory effect is limited. If the C2 / C3 ratio is too high (e.g., above 0.5), it means that the second additive is in excess, and the excess second additive may participate in other side reactions or affect lithium-ion migration. Controlling the C2 / C3 ratio within 0.005-0.5, especially within the range of 0.05-0.4, ensures that there is an appropriate proportion of second additive to neutralize the PF5 generated by the hydrolysis of lithium hexafluorophosphate. - This enables efficient HF suppression.

[0072] In this invention, the electrolyte may further include at least one of other additives and organic solvents. The other additives include, for example, fluoroethylene carbonate (FEC) and / or 1,3-propanesulfonate lactone (PS). The organic solvents include, for example, at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), and ethyl butyrate (EB).

[0073] <Positive Electrode Tablets> In this invention, the lithium-ion battery further includes a positive electrode sheet, which comprises a positive current collector and a positive active layer located on at least one side of the surface of the positive current collector. The positive active layer comprises a positive electrode material, which includes at least one of lithium cobalt oxide, ternary positive electrode materials, and lithium iron phosphate. The ternary positive electrode material includes, for example, nickel-cobalt-manganese ternary materials and / or nickel-cobalt-aluminum ternary materials.

[0074] In one example, the cathode material includes lithium cobalt oxide.

[0075] In one example, the lithium cobalt oxide comprises elemental aluminum, and the mass content of elemental aluminum, based on the total weight of the lithium cobalt oxide, is 5000ppm-15000ppm, for example, 5000ppm, 6000ppm, 7000ppm, 8000ppm, 9000ppm, 10000ppm, 11000ppm, 12000ppm, 13000ppm, 14000ppm, or 15000ppm. The mass content of elemental aluminum in the lithium cobalt oxide can be determined by methods conventional in the art, such as inductively coupled plasma (ICP).

[0076] In this invention, the compaction density of the positive electrode sheet is 3.4 g / cm³. 3 -4.5g / cm 3 For example, 3.4 g / cm³ 3 3.5g / cm 3 3.6g / cm 3 3.7g / cm 3 3.9g / cm 3 4g / cm 3 4.1g / cm 3 4.15g / cm 3 4.2g / cm 3 4.25g / cm 3 4.3g / cm 3 4.4g / cm 3 Or 4.5g / cm 3 The compaction density of the positive electrode sheet is determined with reference to that of the negative electrode sheet, and will not be repeated here.

[0077] In this invention, the positive electrode active layer further includes a positive electrode conductive agent and a positive electrode binder. The positive electrode conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, carbon nanotubes (including single-walled carbon nanotubes and / or multi-walled carbon nanotubes), and carbon fibers. The positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, polyethylene oxide, polyacrylic acid, and derivatives of the above substances.

[0078] In one example, based on the total weight of the positive electrode active layer, the mass content of the positive electrode material is 80%-99.8%, the mass content of the positive electrode conductive agent is 0.1%-10%, and the mass content of the positive electrode binder is 0.1%-10%.

[0079] In this invention, the charging cutoff voltage of the lithium-ion battery is ≥4.5V, for example, 4.5V, 4.51V, 4.52V, 4.53V, 4.54V, 4.55V, 4.56V, 4.57V, 4.58V, 4.59V or 4.6V.

[0080] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0081] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0082] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0083] The following examples illustrate the lithium-ion battery of the present invention.

[0084] Example 1 Lithium-ion batteries are prepared according to the following method: (1) Preparation of electrolyte In an argon glove box with a water content of <0.1ppm and an oxygen content of <0.1ppm, EC, PC, DEC, PP, and EP are mixed evenly in a mass ratio of 1:1:1:1:2. The first additive shown in I-1, PS, FEC, and lithium hexafluorophosphate are added and mixed to form a homogeneous solution. After passing the physical property test, the electrolyte is obtained. Among them, c1 is 2.6% and c3 is 13.6%; the mass contents of PS and FEC in the electrolyte are 1.5% and 13.5%, respectively.

[0085] (2) Preparation of negative electrode sheet Artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive carbon black, and carbon nanotubes were mixed evenly in a mass ratio of 81.5:13:2.5:1.5:1:0.5. Deionized water was added, and the mixture was stirred under vacuum until a uniform and fluid negative electrode active slurry was formed. The negative electrode active slurry was uniformly coated onto the surface of the negative electrode current collector. The coated negative electrode current collector was air-dried at room temperature, then transferred to an 80°C oven for 10 hours. After cold pressing and slitting, the negative electrode sheet was obtained. The silicon-carbon material comprises a porous carbon matrix, silicon particles located within the pores of the porous carbon matrix, and a coating layer on the surface of the porous carbon matrix; its sphericity is 0.99, the mass content of elemental Si in the silicon-carbon material is 59.2%, and its v is 19.6 mm.3 / g; Take a 10ml vial, add 1g of silicon carbide material, and simultaneously inject 5ml of deionized water. Then, store it in a 60℃ oven for 12 hours. GC testing shows that the volume percentage of H2 in the gas composition is 62%. c is 7.9%; the compaction density of the negative electrode is 1.52 g / cm³. 3 ; The negative electrode current collector includes a copper foil and protective layers on both sides of the copper foil. The thickness 'a' of the protective layers on both sides is 0.068 μm, and the protective layers contain chromium oxide. The mass content of elemental chromium in the negative electrode current collector is 297 ppm. The thickness of the copper foil is 6 μm.

[0086] (3) Preparation of positive electrode sheet Lithium cobalt oxide (Al content 10655ppm), polyvinylidene fluoride, conductive carbon black and carbon nanotubes were mixed evenly in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was added and stirred under vacuum until the mixture became a uniform and fluid positive electrode active slurry. The positive electrode active slurry was uniformly coated onto the surface of aluminum foil. The coated aluminum foil was dried and then rolled and slit to obtain the positive electrode sheet.

[0087] (4) Preparation of lithium-ion batteries The positive electrode sheet, separator (polyethylene film with a thickness of 5 μm) prepared in step (3) and the negative electrode sheet prepared in step (2) are stacked in order to ensure that the separator is between the positive and negative electrode sheets to play a role in isolation; then, the unfilled core is obtained by winding; the core is placed in the outer packaging foil, and the electrolyte prepared in step (1) is injected into the dried core. After vacuum sealing, standing, formation, shaping and sorting, a lithium-ion battery is obtained. Among them, c1 / (v×c) is 0.0168 and a / c1 is 2.62.

[0088] Example 2 group This set of examples is used to verify the impact of changing the "mass content c of element Si in the negative electrode active coating".

[0089] This set of embodiments follows the same procedure as Embodiment 1, except that c is controlled by changing the mass content of element Si in the silicon-carbon material and / or the mass ratio of silicon-carbon material in the negative electrode active slurry, as detailed below: In Example 2a, c is 2.3%, c1 / (v×c) is 0.0577, and the compaction density of the negative electrode is 1.26 g / cm³. 3 ; In Example 2b, c is 15.7%, c1 / (v×c) is 0.0084, and the compaction density of the negative electrode is 1.63 g / cm³. 3 ; Example 2c, where c is 32.6%, c1 / (v×c) is 0.0041, and the compaction density of the negative electrode is 1.78 g / cm³. 3 ; In Example 2d, c was 48.9%, c1 / (v×c) was 0.0027, and the compaction density of the negative electrode was 1.89 g / cm³. 3 .

[0090] Example 3 Used to verify the effects of changes to the "first element".

[0091] The procedure was carried out in accordance with Example 1, except that the protective layer contained elemental nickel.

[0092] Example 4 group This set of examples is used to verify the effect of changing the "pore volume v in a unit mass of silicon-carbon material".

[0093] This set of embodiments is based on Embodiment 1, except that v is changed, as follows: Example 4a, v is 0.5 mm 3 / g; c1 / (v×c) is 0.6582, and after the silicon-carbon material reacts with deionized water, the volume percentage of hydrogen in the sealed container is 32%; Example 4b, v is 1.3 mm 3 / g; c1 / (v×c) is 0.2532, and after the silicon-carbon material reacts with deionized water, the volume percentage of hydrogen in the sealed container is 39%; Example 4c, v is 10.8 mm 3 / g; c1 / (v×c) is 0.0305, and after the silicon-carbon material reacts with deionized water, the volume percentage of hydrogen in the sealed container is 57%; Example 4d, v is 24.7 mm 3 / g; c1 / (v×c) is 0.0133, and after the silicon-carbon material reacts with deionized water, the volume percentage of hydrogen in the sealed container is 78%; Example 4e, v is 30.2 mm 3 / g; c1 / (v×c) is 0.0109, and after the silicon-carbon material reacts with deionized water, the volume ratio of hydrogen in the sealed container is 89%.

[0094] Example 5 group This set of examples is used to verify the effect of changing the "mass content c1 of the first additive in the electrolyte".

[0095] This set of embodiments is based on Embodiment 1, except that c1 is changed, as follows: Example 5a, c1 is 0.2%; c1 / (v×c) is 0.0013; Example 5b, c1 is 0.5%; c1 / (v×c) is 0.0032; Example 5c, c1 is 4.5%; c1 / (v×c) is 0.0291; In Example 5d, c1 was 5.8%; c1 / (v×c) was 0.0375.

[0096] Example 6 group This set of examples is used to verify the impact of changing the thickness 'a' of the protective layer.

[0097] This set of embodiments is based on Embodiment 1, except that 'a' is changed, as follows: Example 6a, where a is 0.021 μm; a / c1 is 0.81; and the mass content of elemental chromium in the negative electrode current collector is 58 ppm. Example 6b, where a is 0.04 μm; a / c1 is 1.54; and the mass content of elemental chromium in the negative electrode current collector is 195 ppm. Example 6c, a is 0.1 μm; a / c1 is 3.85, and the mass content of elemental chromium in the negative electrode current collector is 632 ppm.

[0098] Example 7 This was used to verify the effects of adding a second additive to the electrolyte.

[0099] The procedure was carried out in accordance with Example 1, except that a second additive, succinic anionyl nitrile, was added and the c2 was 2.6%.

[0100] Example 8 group This set of examples is used to verify the impact of changing the "mass content c2 of the second additive in the electrolyte".

[0101] This set of embodiments is based on embodiment 7, except that c2 is as follows: Example 8a, c2 is 0.5%; c2 / c3 is 0.037; Example 8b, c2 is 1.2%; c2 / c3 is 0.088; Example 8c, c2 is 3%; c2 / c3 is 0.221; In Example 8d, c2 was 3.8%; c2 / c3 was 0.279.

[0102] Example 9 group The procedure is the same as in Example 1, except that steps (1) and (2) are as follows: Example 9a: (1) Preparation of electrolyte In an argon glove box with a water content of <0.1ppm and an oxygen content of <0.1ppm, EC, PC, DEC, PP, and EP are mixed evenly in a mass ratio of 1:1:1:1:2. The first additive, the second additive (butadiene nitrile), PS, FEC, and lithium hexafluorophosphate shown in I-1 are added and mixed to form a homogeneous solution. After passing the physical property test, the electrolyte is obtained. Among them, c1 is 2.5%, c2 is 2.5%, and c3 is 11.6%; the mass contents of PS and FEC in the electrolyte are 1.5% and 13.5% respectively; and the c2 / c3 ratio is 0.216.

[0103] (2) Preparation of negative electrode sheet Artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive carbon black, and carbon nanotubes were mixed evenly in a mass ratio of 68:26.5:2.5:1.5:1:0.5. Deionized water was added, and the mixture was stirred under vacuum until a homogeneous and fluid negative electrode active slurry was formed. The negative electrode active slurry was uniformly coated onto the surface of the negative electrode current collector. The coated negative electrode current collector was air-dried at room temperature, then transferred to an 80°C oven for 10 hours. After cold pressing and slitting, the negative electrode sheet was obtained. The silicon-carbon material comprises a porous carbon matrix, silicon particles located within the pores of the porous carbon matrix, and a coating layer on the surface of the porous carbon matrix; its sphericity is 0.99, the mass content of elemental Si in the silicon-carbon material is 59.2%, and its v is 11.2 mm. 3 / g; Take a 10ml vial, add 1g of silicon carbide material, and simultaneously inject 5ml of deionized water. Then, store it in a 60℃ oven for 12h. GC testing shows that the volume percentage of H2 in the gas composition is 61%. c is 15.7%; the compaction density of the negative electrode is 1.63 g / cm³. 3 ; The negative electrode current collector includes a copper foil and protective layers on both sides of the copper foil. The thickness 'a' of the protective layers on both sides is 0.065 μm, and the protective layers contain chromium oxide. The mass content of elemental chromium in the negative electrode current collector is 305 ppm. The thickness of the copper foil is 8 μm. c1 / (v×c) is 0.0142, and a / c1 is 2.6.

[0104] Example 9b: (1) Preparation of electrolyte In an argon glove box with a water content of <0.1ppm and an oxygen content of <0.1ppm, EC, PC, DEC, PP, and EP are mixed evenly in a mass ratio of 1:1:1:1:2. The first additive, the second additive (adiponitrile), PS, FEC, and lithium hexafluorophosphate shown in I-2 are added and mixed to form a homogeneous solution. After passing the physical property test, the electrolyte is obtained. Among them, c1 is 0.8%, c2 is 1.2%, and c3 is 10.3%; the mass contents of PS and FEC in the electrolyte are 1.5% and 13.5%, respectively; and the c2 / c3 ratio is 0.117.

[0105] (2) Preparation of negative electrode sheet Artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive carbon black, and carbon nanotubes were mixed evenly in a mass ratio of 72.5:22:2.5:1.5:1:0.5. Deionized water was added, and the mixture was stirred under vacuum until a uniform and fluid negative electrode active slurry was formed. The negative electrode active slurry was uniformly coated onto the surface of the negative electrode current collector. The coated negative electrode current collector was air-dried at room temperature, then transferred to an 80°C oven for 10 hours. After cold pressing and slitting, the negative electrode sheet was obtained. The silicon-carbon material comprises a porous carbon matrix, silicon particles located within the pores of the porous carbon matrix, and a coating layer on the surface of the porous carbon matrix; its sphericity is 0.95, the mass content of elemental Si in the silicon-carbon material is 35.6%, and its v is 0.8 mm. 3 / g; Take a 10ml vial, add 1g of silicon carbide material, and simultaneously inject 5ml of deionized water. Then, store it in a 60℃ oven for 12 hours. GC testing shows that the volume percentage of H2 in the gas composition is 62%. c is 7.9%; the compaction density of the negative electrode is 1.52 g / cm³. 3 ; The negative electrode current collector includes a copper foil and protective layers on both sides of the copper foil. The thickness 'a' of both protective layers is 0.043 μm, and the protective layers contain chromium oxide. The mass content of elemental chromium in the negative electrode current collector is 62 ppm. The thickness of the copper foil is 6 μm. c1 / (v×c) is 0.1266, and a / c1 is 5.38.

[0106] Example 9c: (1) Preparation of electrolyte In an argon glove box with a water content of <0.1ppm and an oxygen content of <0.1ppm, EC, PC, DEC, PP, and EP are mixed evenly in a mass ratio of 1:1:1:1:2. The first additive, the second additive (malononitrile), PS, FEC, and lithium hexafluorophosphate shown in I-6 are added and mixed to form a homogeneous solution. After passing the physical property test, the electrolyte is obtained. Among them, c1 is 4%, c2 is 3.5%, and c3 is 14.2%; the mass contents of PS and FEC in the electrolyte are 1.5% and 13.5% respectively; and the c2 / c3 ratio is 0.246.

[0107] (2) Preparation of negative electrode sheet Artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive carbon black, and carbon nanotubes were mixed evenly in a mass ratio of 50.5:44:2.5:1.5:1:0.5. Deionized water was added, and the mixture was stirred under vacuum until a uniform and fluid negative electrode active slurry was formed. The negative electrode active slurry was uniformly coated onto the surface of the negative electrode current collector. The coated negative electrode current collector was air-dried at room temperature, then transferred to an 80°C oven for 10 hours. After cold pressing and slitting, the negative electrode sheet was obtained. The silicon-carbon material comprises a porous carbon matrix, silicon particles located within the pores of the porous carbon matrix, and a coating layer on the surface of the porous carbon matrix; its sphericity is 0.89, the mass content of elemental Si in the silicon-carbon material is 47.3%, and its v is 24.5 mm. 3 / g; Take a 10ml vial, add 1g of silicon carbide material, and simultaneously inject 5ml of deionized water. Then, store it in a 60℃ oven for 12h. GC testing shows that the volume percentage of H2 in the gas composition is 61%. c is 20.6%; the compaction density of the negative electrode is 1.75 g / cm³. 3 ; The negative electrode current collector includes a copper foil and protective layers on both sides of the copper foil. The thickness 'a' of the protective layers on both sides is 0.1 μm, and the protective layers contain chromium oxide. The mass content of elemental chromium in the negative electrode current collector is 558 ppm. The thickness of the copper foil is 10 μm. c1 / (v×c) is 0.0079, and a / c1 is 2.5.

[0108] Example 10 group This set of examples is used to verify the impact of the change in "c1 / (v×c)".

[0109] This set of embodiments refers to embodiments 9a, 9b and 9c respectively. The difference is that c1 / (v×c) is adjusted by changing c1 and / or v and / or c, as follows: Example 10a was carried out with reference to Example 9c, except that the electrolyte of Example 9b was used and c1 / (v×c) was 0.0016; Example 10b was carried out with reference to Example 9b, except that the electrolyte of Example 9c was used and c1 / (v×c) was 0.6329; Example 10c was performed in accordance with Example 9a, except that c1 was 5.8%, c was 2.3%, and v was 0.5 mm. 3 / g, c1 / (v×c) is 5.0435; Example 10d was performed in accordance with Example 9a, except that c1 was 0.6%, c was 32.3%, and v was 23.6 mm. 3 / g, c1 / (v×c) is 0.0008.

[0110] Example 11 group This set of examples is used to verify the impact of the change in "a / c1".

[0111] This set of embodiments refers to embodiments 9a, 9b and 9c, the difference being that a / c1 is adjusted by changing a and / or c1, as follows: Example 11a was carried out with reference to Example 9b, except that a was 0.1 μm and a / c1 was 12.5; Example 11b was carried out with reference to Example 9c, except that a was 0.43 μm and a / c1 was 1.08; Example 11c was carried out with reference to Example 9a, except that a was 0.1 μm, c1 was 0.2%, and a / c1 was 50; Example 11d was carried out with reference to Example 9a, except that a was 0.02 μm, c1 was 5.8%, and a / c1 was 0.34.

[0112] Example 12 group This set of examples is used to verify the impact of the change in "c2 / c3".

[0113] This set of embodiments refers to embodiments 9a, 9b and 9c, the difference being that c2 / c3 is adjusted by changing c2 and / or c3, as detailed below: Example 12a was carried out with reference to Example 9b, except that c3 was 14.2% and c2 / c3 was 0.085; Example 12b was carried out with reference to Example 9c, except that c3 was 10.3% and c2 / c3 was 0.34; Example 12c was carried out with reference to Example 9a, except that c2 was 0.2%, c3 was 20%, and c2 / c3 was 0.01; Example 12d was carried out with reference to Example 9a, except that c2 was 3.9%, c3 was 8.1%, and c2 / c3 was 0.481.

[0114] Comparative Example 1 The procedure was carried out in accordance with Example 1, except that the outer surface of the copper foil did not have a protective layer.

[0115] Comparative Example 2 The procedure was carried out in accordance with Example 1, except that no first additive was added to the electrolyte.

[0116] Comparative Example 3 The experiment was conducted in accordance with Example 1, except that c was 49.2% and v was 30.5 mm. 3 / g, c1 is 0.1%, c1 / (v×c) is 0.0001.

[0117] Comparative Example 4 The procedure was carried out in accordance with Example 1, except that v was 40.8 mm. 3 / g.

[0118] Test case (1) Test for copper deposition on negative electrode The lithium-ion batteries prepared in the examples and comparative examples were discharged at 25°C with a current of 0.5C to 3.0V, then charged at a constant current of 1C to 4.55V, and then charged at a constant voltage of 4.55V to a current of 0.05C. After standing for 5 minutes, they were fully charged and dissected to observe whether copper deposits appeared on the surface of the negative electrode. Copper deposits are black spots on the surface of the golden negative electrode. If no black spots appeared on the surface of the negative electrode, it was recorded as "no copper deposition". If black spots appeared, the copper content was further tested by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) to scan the black spot area (in backscatter mode, black spots on the negative electrode appear as bright spots in the SEM image). When the copper content in the black spot area is not higher than 0.5wt%, it is recorded as "slight copper precipitation"; when the copper content is greater than 0.5wt% and less than 2wt%, it is recorded as copper precipitation; when the copper content is greater than or equal to 2wt%, it is recorded as severe copper precipitation; among them, no copper precipitation and slight copper precipitation do not affect the normal use of the battery, and the results are recorded in Table 1.

[0119] (2) Cyclic performance test at 25℃ The lithium-ion batteries prepared in the examples and comparative examples were discharged at 25°C with a current of 0.5C to 3.0V. They were then charged at a constant current of 1C to a voltage of 4.55V, and then charged at a constant voltage of 4.55V to a current of 0.05C. After resting for 5 minutes, they were discharged at a constant current of 0.7C to a voltage of 3.0V. This constitutes one charge-discharge cycle. The discharge capacity of the first week was measured as x mAh, and the discharge capacity of the Nth week was measured as y mAh. The capacity of the Nth week was divided by the capacity of the first week to obtain the cycle capacity retention rate R = y / x. The number of cycles when the capacity retention rate was 80% was recorded, and the results are shown in Table 1.

[0120] (3) K-value test The lithium-ion batteries prepared in the examples and comparative examples were charged at 25°C with a constant current of 0.5C to a voltage of 4.55V, and then charged at 4.55V with a constant voltage to a current of 0.025C. The batteries were tested continuously for 5 days using a six-and-a-half-digit test voltage. The K value was calculated using the voltage (V1) on the third day and the voltage (V2) on the fifth day: K = (V1-V2) / (2×24). The results are recorded in Table 1.

[0121] Table 1 As can be seen from Table 1, the lithium-ion battery of the present invention can significantly improve the copper plating problem compared with the comparative example, and has a lower K value and a longer cycle life.

[0122] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes a negative electrode and an electrolyte; The negative electrode sheet includes a negative electrode current collector and a negative electrode active coating located on at least one side of the surface of the negative electrode current collector; the negative electrode current collector includes a copper foil and a protective layer located on at least one side of the copper foil, the protective layer containing a first element, the first element including chromium and / or nickel; the negative electrode active coating includes a silicon-carbon material, the mass content c of element Si in the negative electrode active coating is 2%-50%; the silicon-carbon material has pores, and the pore volume v per unit mass of the silicon-carbon material is 0.5 mm. 3 / g-30.5mm 3 / g; The electrolyte includes a first additive, the first additive comprising: , , , , , , , and At least one of the following; the mass content c1 of the first additive in the electrolyte is 0.1%-6%; c, v, and c1 satisfy: 0.0005 ≤ c1 / (v×c) ≤ 5.5, where v is in mm. 3 / g.

2. The lithium-ion battery according to claim 1, wherein, v is 0.8mm 3 / g-25mm 3 / g; And / or, c1 is 0.5%-5%; And / or, 0.001≤c1 / (v×c)≤0.

65.

3. The lithium-ion battery according to claim 1 or 2, wherein, The thickness of the copper foil is 2μm-16μm; And / or, the thickness 'a' of the protective layer is 0.02 μm-0.1 μm; And / or, the protective layer comprises chromium oxide; And / or, the mass content of the first element in the negative electrode current collector is 40ppm-650ppm.

4. The lithium-ion battery according to claim 3, wherein, a is 0.04μm-0.1μm; And / or, the thickness a of the protective layer and the mass content c1 of the first additive in the electrolyte satisfy: 0.3≤a / c1≤50.

5. The lithium-ion battery according to claim 1 or 2, wherein, After the silicon-carbon material reacts with deionized water in a sealed container, the volume percentage of hydrogen in the sealed container is 30%-90%. The mass ratio of the silicon-carbon material to the deionized water is 1:5, and the volume of the sealed container is twice the volume of the deionized water; the reaction condition is to store the container in a 60°C oven for 12 hours.

6. The lithium-ion battery according to claim 1 or 2, wherein, The sphericity of the silicon-carbon material is 0.8-0.99; And / or, the mass content of element Si in the silicon-carbon material is 20%-80%; And / or, the silicon-carbon material includes a porous carbon matrix and silicon particles located within the porous carbon matrix.

7. The lithium-ion battery according to claim 6, wherein, The silicon-carbon material contains 35%-60% by mass of element Si. And / or, the compaction density of the negative electrode is 1.2 g / cm³. 3 -1.95g / cm 3 .

8. The lithium-ion battery according to claim 1 or 2, wherein, The electrolyte includes a second additive, which includes at least one of butadionitrile, adiponitrile, trans-butadionitrile, malononitrile, o-phthalonitrile, iso-phthalonitrile, ethylene glycol bis(propionitrile) ether, glutaronitrile, and terephthalonitrile; And / or, the mass content c2 of the second additive in the electrolyte is 0.1%-3.9%.

9. The lithium-ion battery according to claim 8, wherein, c2 is 1%-3.5%; The electrolyte also includes lithium hexafluorophosphate, the mass content of lithium hexafluorophosphate in the electrolyte c3 is 7%-22%; and / or, the mass content of c2 and lithium hexafluorophosphate in the electrolyte c3 satisfies: 0.005≤c2 / c3≤0.

5.

10. The lithium-ion battery according to claim 9, wherein, c3 is 8%-16%; And / or, 0.05≤c2 / c3≤0.4.

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