A lithium-ion battery

Abstract

This invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode includes a positive current collector, a positive active layer, and a protective layer. The protective layer is disposed on at least one outer surface of the positive current collector, and the positive active layer is disposed on the surface of the protective layer away from the positive current collector. The protective layer includes conductive particles, each conductive particle comprising a core and a shell disposed on at least a portion of the surface of the core. The core comprises an inorganic material, and the shell comprises a conductive material. The electrolyte includes a fluorinated solvent. The lithium-ion battery satisfies 0.5 ≤ b / k ≤ 15, where b is the average particle size of the conductive particles in μm, and k is the mass content of the fluorinated solvent in the electrolyte in %. This lithium-ion battery exhibits both high safety and high cycle performance.

Description

Technical Field

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

[0002] Currently, higher energy density and thinner lithium-ion batteries are commonly achieved by reducing the thickness of the current collector. However, when lithium-ion batteries are subjected to mechanical forces such as punctures, compression, or impacts from heavy objects, they are prone to failure, fire, explosion, and other safety issues. This is because mechanical damage to the battery not only easily causes the current collector to break, but also greatly increases the probability of internal short circuits. For example, short circuits can occur when the positive electrode active layer and the negative electrode current collector come into direct contact, or when the positive electrode current collector and the negative electrode active layer come into direct contact, or when the positive electrode current collector and the negative electrode current collector come into direct contact. In such cases, a huge current and heat will be generated instantly, leading to battery failure or even combustion and fire.

[0003] Therefore, improving battery safety performance is an urgent problem to be solved in this field. Summary of the Invention

[0004] To address the aforementioned deficiencies, this invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode includes a protective layer, and the electrolyte includes a fluorinated solvent. By ensuring a specific relationship between the average particle size of the conductive particles in the protective layer and the mass content of the fluorinated solvent in the electrolyte, the battery can simultaneously possess both high safety performance and high cycle performance.

[0005] The present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode includes a positive current collector, a positive active layer, and a protective layer. The protective layer is disposed on at least one side surface of the positive current collector, and the positive active layer is disposed on the surface of the protective layer away from the positive current collector.

[0006] The protective layer includes conductive particles, each conductive particle comprising a core and a shell disposed on at least a portion of the surface of the core, the core comprising an inorganic material and the shell comprising a conductive material;

[0007] The electrolyte includes a fluorinated solvent;

[0008] The lithium-ion battery satisfies 0.5≤b / k≤15, where b is the average particle size of the conductive particles in μm, and k is the mass content of the fluorinated solvent in the electrolyte in %.

[0009] Furthermore, the fluorinated solvent includes at least one selected from the following: fluoroethylene carbonate, ethyl monofluoroacetate, methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, monofluorobenzene, 1,2-difluorobenzene, p-difluorobenzene, tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) phosphonate, 1,2-difluoroethylene, monofluoroethylene, and monofluoropropylene.

[0010] And / or, the inorganic material includes at least one of alumina, magnesium oxide, titanium oxide, zinc oxide, silicon oxide, boehmite, and cobalt oxide;

[0011] And / or, the conductive material includes at least one of antimony-doped tin dioxide, fluorine-doped tin dioxide, tin-doped indium oxide, and carbon materials.

[0012] Furthermore, the mass content k of the fluorinated solvent in the electrolyte is 5-30%;

[0013] And / or, the conductive particles in the protective layer have a mass content of 70–98 wt%.

[0014] Furthermore, the average particle size b of the conductive particles is 0.05 to 1 μm.

[0015] Furthermore, the shell layer comprises 2-40% by mass in the conductive particles;

[0016] Preferably, the shell layer has a mass content of 10-30% in the conductive particles.

[0017] Furthermore, the diaphragm includes a substrate, an adhesive layer, and a ceramic layer;

[0018] Preferably, the ceramic layer is disposed on at least one surface of the substrate, and the adhesive layer is disposed on the surface of the ceramic layer away from the substrate;

[0019] Preferably, the areal density p of the ceramic layer is 2-6 g / cm³. 3 .

[0020] Furthermore, the electrolyte also includes lithium salts, including lithium hexafluorophosphate and lithium tetrafluoroborate;

[0021] Preferably, the total mass of the lithium hexafluorophosphate and lithium tetrafluoroborate accounts for 8-20% of the electrolyte;

[0022] Preferably, the mass ratio of lithium hexafluorophosphate to lithium tetrafluoroborate is (10-145):1.

[0023] Furthermore, the thickness h1 of the protective layer is 1 to 10 μm, and / or the thickness h2 of the positive electrode active layer is 30 to 120 μm, and / or the thickness h3 of the positive electrode current collector is 3 to 12 μm.

[0024] Furthermore, the electrolyte also includes additives;

[0025] The additives include at least one of the following: vinylene carbonate, propylene sulfonate lactone, methane disulfonate, 1,3-propane sulfonate lactone, vinyl sulfate, bis(butadiene)nitrile, adiponitrile, glutaronitrile, hexanetrionitrile, ethylene glycol bis(propionitrile) ether, glycerol trinitrile, tetravinylsilane, tri(trimethylsilyl)borate, hexamethyldisilazane, triphenyl phosphite, pentafluoroethoxycyclotriphosphazene, and 1,3,5-hexanetrionitrile;

[0026] Preferably, the additive has a mass content of 0.1% to 20% in the electrolyte.

[0027] Furthermore, the protective layer also includes an adhesive;

[0028] The adhesive includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, and polyethylene oxide;

[0029] Preferably, the adhesive content in the protective layer is 2-30 wt%.

[0030] The lithium-ion battery of this invention, by setting a protective layer on the surface of the positive electrode active layer, adding a fluorinated solvent to the electrolyte, and controlling the average particle size b of the conductive particles in the protective layer and the mass content k of the fluorinated solvent in the electrolyte to satisfy 0.5≤b / k≤15, can enable the conductive particles in the protective layer and the fluorinated solvent in the electrolyte to work together synergistically and effectively improve the safety and cycle performance of the lithium-ion battery. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet of the present invention in one embodiment;

[0032] Figure 2 This is a schematic diagram of the structure of the positive electrode sheet of the present invention in another embodiment.

[0033] Explanation of reference numerals in the attached figures:

[0034] 1-Protective layer;

[0035] 2- Positive electrode active layer;

[0036] 3-Positive current collector. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0038] The first aspect of the present invention provides a lithium-ion battery, including a positive electrode, a negative electrode, an electrolyte and a separator. The positive electrode includes a positive current collector, a positive active layer and a protective layer. The protective layer is disposed on at least one side surface of the positive current collector, and the positive active layer is disposed on the surface of the protective layer away from the positive current collector.

[0039] The protective layer includes conductive particles, each conductive particle including a core and a shell disposed on at least a portion of the surface of the core, the core including an inorganic material and the shell including a conductive material;

[0040] The electrolyte includes fluorinated solvents;

[0041] Lithium-ion batteries satisfy the condition 0.5 ≤ b / k ≤ 15, where b is the average particle size of the conductive particles in μm, and k is the mass content of the fluorinated solvent in the electrolyte in %.

[0042] For example, when k is 15% and b is 0.2 μm, b / k = 0.15 / 0.2 = 0.75.

[0043] For example, b / k is 0.5, 1, 2, 4, 6, 8, 10, 12, 14 or 15.

[0044] Figure 1 This is a schematic diagram of the structure of the positive electrode in one embodiment. Figure 1 In the process, the protective layer 1 is disposed on one side surface of the positive current collector 3, and the positive active layer 2 is disposed on the surface of the protective layer 1 away from the positive current collector 3.

[0045] Figure 2 This is a schematic diagram of the positive electrode sheet in another embodiment. Figure 2 In the process, the protective layer 1 is disposed on both sides of the positive current collector 3, and the positive active layer 2 is disposed on the surface of the protective layer 1 away from the positive current collector 3.

[0046] The lithium-ion battery of this invention exhibits high safety and cycle performance. This is primarily because, when the lithium-ion battery is subjected to external mechanical forces, the protective layer 1, located between the positive electrode active layer 2 and the positive electrode current collector 3, increases the mechanical strength of the battery structure, especially protecting it from external physical impacts and preventing breakage or damage. Simultaneously, the special structure of the conductive particles in the protective layer 1 not only ensures battery safety but also provides sufficient conductivity, effectively reducing internal resistance and resulting in high cycle performance. However, the poor bonding between the shell and core of the conductive particles makes them prone to detachment and separation, negatively impacting battery safety and cycle performance. By adding a fluorinated solvent to the electrolyte, the solvent can penetrate between the shell and core of the conductive particles. The strong electronegativity of fluorine allows it to form strong hydrogen bonds with the core and shell, enhancing the adhesion between them. This effectively improves the bonding strength between the shell and core, ensuring the connectivity of the conductive network, enhancing the overall conductivity of the material, and eliminating the negative impacts caused by the instability of the core-shell structure of the conductive particles.

[0047] Furthermore, the inventors' analysis revealed that the average particle size of the conductive particles and the mass content of the fluorinated solvent in the electrolyte also significantly impact the battery's cycle performance and safety. An excessively large average particle size results in an excessively thick protective layer 1, affecting the battery's cycle performance; while a too-small average particle size, although beneficial for achieving a thin coating of the protective layer 1 on the positive electrode current collector 3 and ensuring battery cycle performance, will decrease safety performance. An excessively high mass content of the fluorinated solvent in the electrolyte will also enhance the activity of the binder in the positive electrode active layer 2, making lithium-ion insertion / extraction difficult and degrading the cycle; an excessively low mass content will prevent the formation of sufficient hydrogen bonds between the core and shell, thus failing to enhance the bonding strength between the core and shell.

[0048] Therefore, by controlling the average particle size of conductive particles and the mass content of fluorinated solvent in the electrolyte to satisfy a specific relationship of 0.5≤b / k≤15, the conductive particles and fluorinated solvent can work synergistically to comprehensively improve the safety and cycle performance of the battery.

[0049] In this invention, the average particle size of the conductive particles can be obtained by scanning electron microscopy (SEM). Specifically, SEM testing is performed on the conductive particles, and the conductive particles in three arbitrary 50μm*50μm regions are tested. The particle size of the conductive particles in the three regions is measured, and the average value is taken as the average particle size of the conductive particles.

[0050] The present invention does not specifically limit the type of positive current collector 3, and commonly used materials in the art, such as aluminum foil, can be used.

[0051] This invention does not specifically limit the types and sources of inorganic materials, conductive materials, and fluorinated solvents; products prepared using commercially available products or conventional preparation methods well known to those skilled in the art are acceptable.

[0052] This invention does not specifically limit the manufacturing method of lithium-ion batteries; common methods in the field can be used for manufacturing.

[0053] In one specific embodiment, the fluorinated solvent includes at least one selected from fluoroethylene carbonate, ethyl monofluoroacetate, methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, monofluorobenzene, 1,2-difluorobenzene, p-difluorobenzene, tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) phosphonate, 1,2-difluoroethylene, monofluoroethylene, and monofluoropropylene.

[0054] When the fluorinated solvent is at least one of the aforementioned specific compounds, the bonding strength between the shell and the core can be further improved, thereby enhancing the cycle performance and safety performance of the battery.

[0055] When the fluorinated solvent is a mixture of the aforementioned specific compounds, the present invention does not impose specific limitations on the proportions between the various specific compounds.

[0056] In one specific embodiment, the inorganic material includes at least one selected from aluminum oxide, magnesium oxide, titanium oxide, zinc oxide, silicon oxide, boehmite, and cobalt oxide. This allows for better protection and improves battery safety.

[0057] When the inorganic material is a mixture of the aforementioned specific compounds, the present invention does not impose specific limitations on the proportions between the various specific compounds.

[0058] In one specific embodiment, the conductive material includes at least one selected from antimony-doped tin dioxide (ATO), fluorine-doped tin dioxide (FTO), tin-doped indium oxide (ITO), and carbon materials. When the conductive material includes at least one of the aforementioned substances, it can better synergize and cooperate with fluorinated solvents, further improving the conductivity of the protective layer, thereby enabling the lithium-ion battery to have higher cycle performance.

[0059] The carbon material used in this invention is preferably at least one of conductive carbon black, graphite, conductive polymer, multi-walled carbon nanotubes, graphene, and carbon fiber; wherein the conductive polymer is preferably polyaniline and / or polypyrrole.

[0060] This invention does not specifically limit the type of conductive polymer; any commonly chosen polymer in the field can be used. This invention also does not specifically limit the molecular weight of the conductive polymer.

[0061] When the conductive material is a mixture of the aforementioned specific substances, the present invention does not impose specific limitations on the proportions between the various specific substances.

[0062] In one specific embodiment, the mass content k of the fluorinated solvent in the electrolyte is 5-30%. Within this range, it can better cooperate with the conductive particles, resulting in better bonding strength between the shell and core of the conductive particles. At the same time, it can avoid the difficulty of lithium-ion insertion / extraction caused by excessive fluorinated solvent content, thus giving the lithium-ion battery higher safety and cycle performance.

[0063] For example, k is 5%, 10%, 15%, 20%, 25%, or 30%.

[0064] In one specific embodiment, the mass content of conductive particles in the protective layer 1 is 70–98 wt%. Within this range, not only can the insulating effect of the protective layer 1 be guaranteed, improving the safety of the battery, but it can also give the positive electrode sheet higher conductivity, effectively reducing the internal resistance of the battery and giving the battery higher safety and cycle performance.

[0065] For example, the mass content of conductive particles in the protective layer 1 is 70 wt%, 74 wt%, 78 wt%, 82 wt%, 86 wt%, 90 wt%, 94 wt%, or 98 wt%.

[0066] In one specific embodiment, the average particle size b of the conductive particles is 0.05–1 μm. Within this range, the average particle size of the conductive particles is moderate, avoiding energy loss due to excessively large particle size and ensuring safety performance is not compromised due to excessively small particle size.

[0067] For example, b is 0.05μm, 0.2μm, 0.4, 0.6μm, 0.8μm or 1μm.

[0068] In one specific embodiment, the shell layer comprises 2-40% by mass in the conductive particles; preferably, the shell layer comprises 10-30% by mass in the conductive particles. Within this range, not only can the conductivity of the conductive particles be guaranteed, but also the increase in internal resistance of the battery due to excessive shell layer thickness can be avoided, thereby reducing energy loss during energy transfer.

[0069] For example, the shell layer has a mass content of 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40% in the conductive particles.

[0070] The mass content of the shell in the conductive particles in this invention can be obtained by inductively coupled plasma (ICP) testing.

[0071] In one embodiment, the diaphragm includes a substrate, an adhesive layer, and a ceramic layer; preferably, the ceramic layer is disposed on at least one side surface of the substrate, and the adhesive layer is disposed on the surface of the ceramic layer away from the substrate.

[0072] Preferably, the areal density ρ of the ceramic layer is 2–6 g / cm³. 3 .

[0073] Ceramic layers typically have high melting points and good thermal conductivity. When a ceramic layer is included in the separator, it can work in conjunction with the protective layer 1 in the positive electrode to provide dual protection for the battery. This effectively isolates the electrode materials under high-temperature conditions, reduces short circuits and thermal runaway caused by overheating, and further improves the safety performance of lithium-ion batteries.

[0074] This invention does not specifically limit the materials of the substrate, adhesive layer, and ceramic layer, and commonly used materials in the art can be used. For example, the substrate can be at least one of polypropylene, polyethylene, and polypropylene / polyethylene composite materials; the adhesive layer includes a polymer material, which includes at least one of oil-based polyvinylidene fluoride, water-based polyvinylidene fluoride, oil-based polymethyl methacrylate, and water-based polymethyl methacrylate; the ceramic layer includes an inorganic material and an adhesive; wherein the inorganic material includes at least one of boehmite (γ-AlOOH), alumina (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), titanium oxide (TiO2), zinc oxide (ZnO), cobalt oxide (CoO), magnesium hydroxide (Mg(OH)2), and silicon dioxide (SiO2); the adhesive can be the same as the adhesive in protective layer 1, and will not be described in detail here.

[0075] Furthermore, when the areal density p of the ceramic layer is 2–6 g / cm³ 3 This can further improve the thermal stability of the battery, provide stronger protection, and reduce the risk of internal short circuits caused by physical damage such as impact and compression during battery use.

[0076] For example, p is 2 g / cm³ 3 3g / cm 3 4g / cm 3 5g / cm 3 Or 6g / cm 3 .

[0077] In one specific embodiment, the electrolyte also includes lithium salts, including lithium hexafluorophosphate and lithium tetrafluoroborate;

[0078] Preferably, the total mass of lithium hexafluorophosphate and lithium tetrafluoroborate accounts for 8-20% of the electrolyte.

[0079] When mechanical abuse occurs, and the electrolyte comes into contact with the negative electrode current collector, the lithium hexafluorophosphate in the electrolyte reacts with the aluminum foil to form a dense, protective passivation film composed of aluminum fluoride on its surface. This passivation film has good chemical stability and can effectively isolate the aluminum foil from the external environment, preventing further direct contact between the aluminum foil and the electrolyte, acidic or alkaline substances, and other substances that may cause corrosion. This improves the stability and corrosion resistance of the aluminum foil, thereby improving the cycle performance of the battery. Simultaneously, lithium tetrafluoroborate can be adsorbed on the aluminum foil surface, altering its surface charge state and potential distribution, reducing the reactivity of the aluminum foil surface, and further reducing corrosion.

[0080] Therefore, when a lithium-ion battery is subjected to external mechanical forces such as heavy impact or puncture, the current collector may break or develop microcracks, resulting in a fresh fracture surface. The lithium hexafluorophosphate and lithium tetrafluoroborate in the electrolyte can quickly passivate the fracture surface, reducing corrosion and thus improving the battery's safety and cycle performance.

[0081] Furthermore, when the mass content of lithium hexafluorophosphate and lithium tetrafluoroborate in the electrolyte is within the aforementioned range, they can work together more effectively, further reducing corrosion during mechanical abuse and giving the battery higher cycle performance and safety performance.

[0082] For example, the total mass of lithium hexafluorophosphate and lithium tetrafluoroborate accounts for 8%, 10%, 12%, 14%, 16%, 18%, or 20% of the electrolyte.

[0083] In one specific embodiment, the mass ratio of lithium hexafluorophosphate to lithium tetrafluoroborate is (10–145):1. When the mass ratio is within the aforementioned range, the two components can work together more effectively, further improving the battery's safety and cycle performance.

[0084] For example, the mass ratio is 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, 110:1, 120:1, 130:1, 140:1 or 145:1.

[0085] Furthermore, the thickness of the current collector, the thickness of the positive electrode active layer 2, and the thickness of the protective layer 1 in a lithium-ion battery have a significant impact on the battery's energy density, safety performance, and cycle performance.

[0086] While excessively thick current collectors can reduce the risk of puncture or breakage during punctures, compressions, or impacts from heavy objects, thus improving battery safety, they also increase internal resistance, affecting discharge and cycle performance. Furthermore, they can raise internal pressure, increasing the risk of fire or even explosion, thus compromising battery safety. Conversely, excessively thin current collectors significantly reduce the mechanical strength of the electrodes and also increase internal resistance, further compromising battery safety.

[0087] When the thickness of the positive electrode active layer 2 is too thick, it will increase the internal resistance of the battery, affecting the battery's output power and cycle life. At the same time, it will also cause excessive heat to be generated inside the battery during charging and discharging, which may lead to thermal runaway. If it is too thin, it will result in a significant decrease in battery capacity and make the battery more susceptible to stress during charging and discharging, affecting the battery's cycle performance.

[0088] If the protective layer 1 is too thick, it will significantly reduce the energy density of the battery and increase the internal resistance of the battery, thus reducing the charging and discharging efficiency; if it is too thin, it will fail to provide protection and reduce the safety performance of the battery.

[0089] Therefore, it is necessary to control the thickness of the protective layer 1, the positive electrode active layer 2, and the positive electrode current collector 3 in the electrode sheet in order to achieve a balanced improvement in the electrochemical performance and safety performance of lithium-ion batteries.

[0090] In one specific embodiment, the thickness h1 of the protective layer 1 is 1–10 μm. Within this range, the safety performance of the lithium-ion battery can be correspondingly improved, and the loss in volumetric energy density is relatively small.

[0091] For example, the thickness h1 of the protective layer 1 is 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm.

[0092] In one specific embodiment, the thickness h2 of the positive electrode active layer 2 is 30–120 μm. Within this range, the battery energy density can be maximized while ensuring battery safety performance.

[0093] For example, the thickness h2 of the positive electrode active layer 2 is 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm or 120μm.

[0094] In one specific embodiment, the thickness h3 of the positive electrode current collector 3 is 3–12 μm. Within this range, it is beneficial to improve the toughness of the electrode and the corrosion resistance of the current collector, which helps to improve the safety performance of the battery.

[0095] For example, the thickness h3 of the positive current collector 3 is 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm or 12μm.

[0096] It should be noted that the thickness h1 of the protective layer 1 and the thickness h2 of the positive electrode active layer 2 in this invention refer to the thickness on one side of the positive electrode current collector 3.

[0097] In one specific embodiment, the electrolyte further includes additives; the additives include at least one of the following: vinylene carbonate, propylene sulfonate lactone, methane disulfonate, 1,3-propane sulfonate lactone, vinyl sulfate, dibutylnitrile, adiponitrile, glutaronitrile, hexanetrionitrile, ethylene glycol bis(propionitrile) ether, glycerol trinitrile, tetravinylsilane, tri(trimethylsilyl)borate, hexamethyldisilazane, triphenyl phosphite, pentafluoroethoxycyclotriphosphazene, and 1,3,5-hexanetrionitrile;

[0098] Preferably, the mass content of the additive in the electrolyte is 0.1% to 20%.

[0099] When the electrolyte contains the above-mentioned additives, it helps to form SEI and CEI films in the positive and negative electrodes, thereby improving the cycle performance of the battery.

[0100] When the additive is a mixture of the aforementioned compounds, the present invention does not impose specific limitations on the proportions between the individual compounds.

[0101] Furthermore, when the mass content of the additive in the electrolyte is within the above range, it can not only promote the formation of the interfacial film, but also avoid the increase in gas production and impedance caused by excessive content, thus enabling the battery to have higher cycle performance.

[0102] For example, the mass content of the additive in the electrolyte is 0.1%, 1%, 5%, 10%, 15%, or 20%.

[0103] In one specific embodiment, the protective layer 1 further includes an adhesive;

[0104] The adhesive includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, and polyethylene oxide;

[0105] Preferably, the adhesive content in the protective layer 1 is 2-30 wt%.

[0106] When the protective layer 1 includes the aforementioned binder, and the mass content of the binder in the protective layer 1 is within the aforementioned range, the bonding force between the protective layer 1 and the positive electrode current collector 3 and the positive electrode active layer 2 can be guaranteed, effectively preventing the protective layer 1 from falling off, which is beneficial to improving the safety performance of the battery.

[0107] For example, the adhesive content in the protective layer 1 is 2 wt%, 6 wt%, 10 wt%, 14 wt%, 18 wt%, 22 wt%, 26 wt%, or 30 wt%.

[0108] When the binder is a mixture of the aforementioned specific compounds, the present invention does not impose specific limitations on the proportions between the various specific compounds.

[0109] In one specific embodiment, the electrolyte further includes an organic solvent, preferably, the organic solvent includes carbonate solvents and / or carboxylic acid ester solvents; preferably, the carbonate solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); the carboxylic acid ester solvent includes at least one of ethyl acetate, ethyl propionate, propyl propionate, methyl propionate, methyl butyrate, and ethyl butyrate.

[0110] In one specific embodiment, the lithium salt may further include at least one of lithium difluorophosphate (LiPO2F2), lithium hexafluoroantimony oxide (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate, lithium di(trifluoromethanesulfonyl)imide, lithium di(pentafluoroethylsulfonyl)imide, lithium tri(trifluoromethanesulfonyl)methyl, lithium difluorooxalateborate (LiDFOB), lithium difluorobis(oxalate)phosphate, lithium di(difluorophosphoryloxy)difluoroborate, and lithium tetra(difluorophosphoryloxy)borate.

[0111] In one specific embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active layer including a negative electrode active material.

[0112] The negative electrode current collector and negative electrode active material in this invention are not specifically limited and can be materials commonly used in the field. For example, the negative electrode current collector can be copper foil and the negative electrode active material can be artificial graphite.

[0113] The lithium-ion battery of the present invention will be described in detail below through specific embodiments.

[0114] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0115] Example 1

[0116] 1) Preparation of positive electrode sheet: The positive electrode active material lithium cobalt oxide (LiCoO2), conductive agent carbon black and carbon nanotubes (CNT), and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97.2:1:1:0.8. Then, an appropriate amount of N-methylpyrrolidone (NMP) is added and stirred thoroughly until a uniform positive electrode active slurry is formed.

[0117] 95 wt% conductive particles and 5 wt% PVDF were mixed, NMP was added, and the mixture was stirred to obtain a protective layer slurry with a solid content of 40%. The conductive particles had an average particle size of 0.5 μm, a shell of fluorine-doped tin dioxide, and an alumina core. The shell accounted for 20% of the mass of the conductive particles.

[0118] A protective layer slurry is coated on two functional surfaces of an aluminum foil (9 μm thick) and dried to obtain an electrode sheet coated with a protective layer. A positive electrode active slurry is then coated on the outer surface of the protective layer. After drying, rolling, and slitting, positive electrode tabs are welded and protective adhesive paper is attached to obtain a positive electrode sheet. The thickness of the protective layer on one side is 3 μm, and the thickness of the positive electrode active layer on one side is 30 μm.

[0119] 2) Preparation of negative electrode sheet: The negative electrode active materials artificial graphite, conductive carbon black, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) are dispersed in an appropriate amount of deionized water at a mass fraction of 96.8:1.6:0.8:0.8. After stirring thoroughly to form a uniform negative electrode slurry, the negative electrode slurry is uniformly coated onto the negative electrode current collector copper foil using a coating machine. Then, after drying, rolling, and cutting, the negative electrode sheet is obtained.

[0120] 3) Electrolyte preparation: In a glove box filled with argon gas and with water and oxygen content less than 0.1 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP) were mixed evenly in a mass ratio of 10:20:20:20:30 to obtain a mixed organic solvent. Subsequently, 14.5 wt% of lithium hexafluorophosphate (LiPF6) and 0.5 wt% of lithium tetrafluoroborate were added based on the total mass of the electrolyte. Then, 10 wt% of fluoroethylene carbonate (FEC), 3 wt% of 1,3-propanesulfonate lactone (PS), 1 wt% of 1,3,5-hexanetrionitrile (HTCN), 1 wt% of adiponitrile (AND), and 1.5 wt% of succinate (SN) based on the total mass of the electrolyte were added. After being mixed evenly, the electrolyte was obtained after passing the moisture and color tests.

[0121] 4) Preparation of the diaphragm: The diaphragm consists of a substrate, an adhesive layer, and a ceramic layer. The adhesive layer is located on one functional surface of the substrate, and the ceramic layer is located on the other functional surface. The substrate is polypropylene / polyethylene, the adhesive layer is oil-based polyvinylidene fluoride, and the ceramic layer comprises inorganic alumina particles and polytetrafluoroethylene binder (mass ratio 10:1). The areal density of the ceramic layer is 5 g / cm³. 3 ;

[0122] 5) The prepared positive electrode sheet, separator and negative electrode sheet are stacked in sequence and wound into a core; then the core is packaged with aluminum-plastic film and injected with the electrolyte. After encapsulation, aging, formation and secondary sealing processes, the lithium-ion battery of this embodiment is obtained.

[0123] Example 2

[0124] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that in step 3), the mass content of the fluorinated solvent in the electrolyte is 5%, and correspondingly, the mass content of the mixed organic solvent in the electrolyte is increased.

[0125] Example 3

[0126] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that in step 3), the fluorinated solvent also includes ethyl difluorocarbonate. The total mass content of ethyl difluorocarbonate and fluoroethylene carbonate in the electrolyte is 30%, and the mass ratio of ethyl difluorocarbonate to fluoroethylene carbonate is 1:1. Correspondingly, the mass content of the mixed organic solvent in the electrolyte is reduced.

[0127] Example 4

[0128] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that in step 1), the average particle size of the conductive particles is 0.05 μm.

[0129] Example 5

[0130] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that in step 1), the average particle size of the conductive particles is 1 μm.

[0131] Example 6

[0132] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that in step 1), the shell layer accounts for 10% of the mass content of the conductive particles.

[0133] Example 7

[0134] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that in step 1), the shell layer accounts for 30% of the mass content of the conductive particles.

[0135] Example 8

[0136] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that in step 1), the shell layer accounts for 2% of the mass content of the conductive particles.

[0137] Example 9

[0138] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that in step 1), the shell layer accounts for 40% of the mass content of the conductive particles.

[0139] Example 10

[0140] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in embodiment 1. The difference is that in step 1), the core of the conductive particles is zinc oxide and the shell is antimony-doped tin dioxide.

[0141] In step 3), fluoroethylene carbonate is replaced with ethyl difluorocarbonate.

[0142] Example 11

[0143] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that in step 1), the core of the conductive particles is boehmite and the shell is tin-doped indium oxide.

[0144] In step 3), fluoroethylene carbonate is replaced with methyltrifluoroethyl carbonate.

[0145] Example 12

[0146] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that in step 1), the core of the conductive particles is cobalt oxide and the shell is graphite.

[0147] In step 3), fluoroethylene carbonate is replaced with p-difluorobenzene.

[0148] Example 13

[0149] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in embodiment 1, except that in step 1), the shell is composed of antimony-doped tin dioxide and fluorine-doped tin dioxide in a mass ratio of 1:1.

[0150] In step 4), the areal density of the ceramic layer is 2 g / cm³. 3 .

[0151] Example 14

[0152] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that in step 4), the areal density of the ceramic layer is 6 g / cm³. 3 .

[0153] Example 15

[0154] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that in step 3), the mass content of lithium hexafluorophosphate in the electrolyte is 7.5% and the mass content of lithium tetrafluoroborate is 0.5%. Correspondingly, the mass content of the mixed organic solvent in the electrolyte is increased.

[0155] Example 16

[0156] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that in step 3), the mass content of lithium hexafluorophosphate in the electrolyte is 19.5% and the mass content of lithium tetrafluoroborate is 0.15%. Correspondingly, the mass content of the mixed organic solvent in the electrolyte is reduced.

[0157] Example 17

[0158] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that the thickness of the protective layer on one side is 1 μm in step 1).

[0159] Example 18

[0160] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that the thickness of the protective layer on one side is 10 μm in step 1).

[0161] Example 19

[0162] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in embodiment 1. The difference is that in step 1), the mass content of conductive particles in the protective layer is 70 wt%, and the mass content of PVDF is 5 wt%.

[0163] Example 20

[0164] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in embodiment 1. The difference is that in step 1), the mass content of conductive particles in the protective layer is 98 wt%, and the mass content of PVDF is 2 wt%.

[0165] Example 21

[0166] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that in step 3), the mass content of the additives 1,3-propanesulfonic acid lactone in the electrolyte is 4%, the mass content of 1,3,5-hexanetrionitrile is 4%, the mass content of adiponitrile is 2%, and the mass content of succinic anhydride is 2%. Correspondingly, the mass content of the mixed organic solvent in the electrolyte is reduced.

[0167] Example 22

[0168] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that in step 3), the mass content of the additives 1,3-propanesulfonic acid lactone in the electrolyte is 6%, the mass content of 1,3,5-hexanetrionitrile is 5%, the mass content of adiponitrile is 4%, and the mass content of succinic acid is 4%. Correspondingly, the mass content of the mixed organic solvent in the electrolyte is reduced.

[0169] Example 23

[0170] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that in step 3), the mass content of fluoroethylene carbonate in the electrolyte is 4%, and correspondingly, the mass content of the mixed organic solvent in the electrolyte is increased.

[0171] Example 24

[0172] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that in step 1), the average particle size of the conductive agent is 1.5 μm.

[0173] Example 25

[0174] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that in step 4), the areal density of the ceramic layer is 7 g / cm³. 3 .

[0175] Example 26

[0176] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that in step 4), the separator does not include a ceramic layer.

[0177] Example 27

[0178] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that in step 3), the electrolyte does not include lithium tetrafluoroborate, so the mass content of lithium hexafluorophosphate in the electrolyte is 15%.

[0179] Example 28

[0180] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that in step 3), the mass content of lithium hexafluorophosphate in the electrolyte is 21.3% and the mass content of lithium tetrafluoroborate is 0.7%.

[0181] Example 29

[0182] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that in step 3), the mass content of lithium hexafluorophosphate in the electrolyte is 14% and the mass content of lithium tetrafluoroborate is 1%.

[0183] Example 30

[0184] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that the thickness of the protective layer in step 1) is 12 μm.

[0185] Example 31

[0186] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that in step 3), the electrolyte does not include additives 1,3-propanesulfonic acid lactone, 1,3,5-hexanetrionitrile, adiponitrile and succinic acid. Correspondingly, the mass content of the mixed organic solvent in the electrolyte is increased.

[0187] Example 32

[0188] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that in step 3), the mass content of the additives 1,3-propanesulfonic acid lactone in the electrolyte is 8%, the mass content of 1,3,5-hexanetrionitrile is 5%, the mass content of adiponitrile is 4%, and the mass content of succinic anhydride is 4%. Correspondingly, the mass content of the mixed organic solvent in the electrolyte is increased.

[0189] Example 33

[0190] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that in step 1), the mass content of conductive particles in the protective layer is 65% and the mass content of PVDF is 35%.

[0191] Comparative Example 1

[0192] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 3, except that in step 1), the average particle size of the conductive particles is 0.05 μm.

[0193] Comparative Example 2

[0194] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 5, except that in step 3), the mass content of fluoroethylene carbonate in the electrolyte is 6%.

[0195] Comparative Example 3

[0196] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 5. The difference is that in step 3), the electrolyte does not contain fluoroethylene carbonate, and the mass content of the mixed organic solvent in the electrolyte is increased accordingly.

[0197] Comparative Example 4

[0198] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in embodiment 5, except that in step 1), the positive electrode does not contain a protective layer.

[0199] Test case

[0200] The lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to cycle performance and safety performance tests:

[0201] 1) Cyclic performance

[0202] At an ambient temperature of 25°C, the lithium-ion battery was charged to 4.45V at a constant current of 1C, then charged at a constant voltage of the rated voltage until the cutoff current was 0.05C, and then discharged to 3.0V at 0.5C. The initial discharge capacity was recorded as C0. After 1000 cycles of the aforementioned charge-discharge mechanism, the discharge capacity after the cycle was recorded as C1. The cycle capacity retention rate (%) = (C1 / C0) × 100%, and the calculation results are shown in Table 1.

[0203] 2) Impact of heavy objects

[0204] At an ambient temperature of 25℃, the cells were charged to the upper limit voltage of 4.45V using a constant current and constant voltage at 0.5C, with a cutoff current of 0.02C. The cells were placed on a platform surface, and a metal rod with a diameter of 15.8mm ± 0.2mm was placed horizontally on the upper surface of the cell's geometric center. A weight of 9.1kg ± 0.1kg was dropped from a height of 610mm ± 25mm to impact the surface of the cell with the metal rod, and the results were observed for 6 hours. Ten cells were tested in each group. The test was considered passed if the cells did not catch fire or explode; otherwise, it was considered failed. The number of cells that passed out of 10 was recorded, for example, 8 out of 10 cells passed was recorded as 8 / 10PSS. The test results are shown in Table 1.

[0205] 3) Compression test

[0206] At an ambient temperature of 25℃, the cells were charged at a constant current and voltage of 0.5C to the upper limit voltage of 4.45V, with a cutoff current of 0.02C, at which point they were considered fully charged. The wide side of the fully charged cell was placed between two flat plates, and a compressive force of 13.0kN ± 0.78kN was applied between the plates. The test was stopped once the pressure reached its maximum value. Ten cells were tested in each group. The test was considered passed if the cells did not catch fire or explode; otherwise, it was considered failed. The number of cells that passed out of ten was recorded. For example, if eight out of ten cells passed, it was recorded as 8 / 10PSS. The test results are shown in Table 1.

[0207] Table 1

[0208]

[0209]

[0210] As shown in Table 1:

[0211] Compared to Comparative Examples 1-4, the lithium-ion batteries in Examples 1-33 exhibit higher cycle performance and safety performance. Specifically, the lithium-ion battery in Example 3 achieves a capacity retention rate of 83.0% after 1000 cycles, and its pass rate under heavy impact and compression is as high as 10 / 10. Therefore, the lithium-ion battery of this invention can possess both high safety and high cycle performance.

[0212] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that, The positive electrode includes a positive current collector, a positive active layer, and a protective layer. The protective layer is disposed on at least one side surface of the positive current collector, and the positive active layer is disposed on the surface of the protective layer away from the positive current collector. The protective layer includes conductive particles, each conductive particle comprising a core and a shell disposed on at least a portion of the surface of the core, the core comprising an inorganic material and the shell comprising a conductive material; The electrolyte includes a fluorinated solvent; The lithium-ion battery satisfies 0.5≤b / k≤15, where b is the average particle size of the conductive particles in μm, and k is the mass content of the fluorinated solvent in the electrolyte in μm.

2. The lithium-ion battery according to claim 1, characterized in that, The fluorinated solvent includes at least one of the following: fluoroethylene carbonate, ethyl monofluoroacetate, methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, monofluorobenzene, 1,2-difluorobenzene, p-difluorobenzene, tris(2,2,2-trifluoroethyl) phosphate, and bis(2,2,2-trifluoroethyl) phosphonate. And / or, the inorganic material includes at least one of alumina, magnesium oxide, titanium oxide, zinc oxide, silicon oxide, boehmite, and cobalt oxide; And / or, the conductive material includes at least one of antimony-doped tin dioxide, fluorine-doped tin dioxide, tin-doped indium oxide, and carbon materials.

3. The lithium-ion battery according to claim 1 or 2, characterized in that, The mass content (k) of the fluorinated solvent in the electrolyte is 5-30%; And / or, the mass content of the conductive particles in the protective layer is 70~98wt%.

4. The lithium-ion battery according to claim 1 or 2, characterized in that, The average particle size b of the conductive particles is 0.05~1μm.

5. The lithium-ion battery according to claim 1 or 2, characterized in that, The shell layer has a mass content of 2-40% in the conductive particles.

6. The lithium-ion battery according to claim 5, characterized in that, The shell layer has a mass content of 10-30% in the conductive particles.

7. The lithium-ion battery according to claim 1 or 2, characterized in that, The diaphragm includes a substrate, an adhesive layer, and a ceramic layer.

8. The lithium-ion battery according to any one of claims 7, characterized in that, The ceramic layer is disposed on at least one side surface of the substrate, and the adhesive layer is disposed on the surface of the ceramic layer away from the substrate.

9. The lithium-ion battery according to claim 1 or 2, characterized in that, The electrolyte also includes lithium salts, including lithium hexafluorophosphate and lithium tetrafluoroborate.

10. The lithium-ion battery according to claim 9, characterized in that, The total mass of lithium hexafluorophosphate and lithium tetrafluoroborate accounts for 8-20% of the electrolyte.

11. The lithium-ion battery according to claim 9, characterized in that, The mass ratio of lithium hexafluorophosphate to lithium tetrafluoroborate is (10~145):

1.

12. The lithium-ion battery according to claim 1 or 2, characterized in that, The thickness h1 of the protective layer is 1~10μm, and / or the thickness h2 of the positive electrode active layer is 30~120μm, and / or the thickness h3 of the positive electrode current collector is 3~12μm.

13. The lithium-ion battery according to claim 1 or 2, characterized in that, The electrolyte also includes additives; The additives include at least one of the following: vinylene carbonate, propylene sulfonate lactone, methane disulfonate, 1,3-propane sulfonate lactone, vinyl sulfate, adiponitrile, glutaronitrile, hexanetrionitrile, ethylene glycol bis(propionitrile) ether, glycerol trionitrile, tetravinylsilane, tri(trimethylsilyl)borate, hexamethyldisilazane, triphenyl phosphite, and pentafluoroethoxycyclotriphosphazene.

14. The lithium-ion battery according to claim 13, characterized in that, The additive has a mass content of 0.1-20% in the electrolyte.

15. The lithium-ion battery according to claim 1 or 2, characterized in that, The protective layer also includes an adhesive; The adhesive includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

16. The lithium-ion battery according to claim 15, characterized in that, The adhesive content in the protective layer is 2-30 wt%.

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