Lithium ion battery

Abstract

The invention relates to the technical field of batteries, in particular to a lithium ion battery. The lithium ion battery comprises an electrolyte, a negative plate and a positive plate, the electrolyte comprises a fluorinated solvent, and the weight content of the fluorinated solvent is f wt% on the basis of the total weight of the electrolyte; the ratio of the width of the negative plate to the width of the positive plate is g, and the lithium ion battery meets the following relational expression: f / g is greater than or equal to 2 and less than or equal to 30. According to the lithium ion battery disclosed by the invention, by controlling the relationship between the weight content of the fluorinated solvent in the electrolyte and the width ratio of the positive plate and the negative plate, the fluorinated solvent can form an SEI film rich in LiF on the surfaces of the positive electrode and the negative electrode and the edge of the negative plate, and the SEI film rich in LiF is relatively thin and relatively high in toughness; the short circuit risk caused by burrs on the edge of the negative plate can be reduced, meanwhile, the diffusion speed of lithium ions in the electrolyte is increased, the lithium precipitation condition is improved, and therefore the safety performance and cycling stability of the battery are improved.

Description

Technical Field

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

[0002] In recent years, lithium-ion batteries have made significant progress in energy density, safety, charging speed, and cycle life, providing better support and assurance for their widespread application in various scenarios. However, the lithium plating problem in lithium-ion batteries hinders their further development due to its impact on cycle performance and safety. Summary of the Invention

[0003] The lithium plating problem in lithium-ion batteries can be addressed by adding functionalized solvents to the electrolyte. These functionalized solvents possess specific functional groups that can improve battery safety and cycle performance. For example, adding fluorinated solvents to organic solvents can enhance the solubility of lithium salts and improve electrolyte stability, thereby reducing lithium plating and improving battery safety and cycle performance. However, burrs are generated at the edges of the negative electrode after slitting. These burrs increase the risk of short circuits, affecting battery safety and cycle performance.

[0004] To overcome the aforementioned technical problems in the prior art, this invention provides a lithium-ion battery. The lithium-ion battery of this invention controls the ratio of the weight content of the fluorinated solvent in the electrolyte to the width of the positive and negative electrode sheets, enabling the fluorinated solvent to form a LiF-rich SEI film on the surfaces of the positive and negative electrodes and at the edges of the negative electrode sheet. This LiF-rich SEI film is relatively thin and has high toughness, reducing the short-circuit risk caused by burrs at the edges of the negative electrode sheet. Simultaneously, it increases the diffusion rate of lithium ions in the electrolyte, improves lithium plating, and thus enhances the battery's safety performance and cycle stability.

[0005] This invention provides a lithium-ion battery, comprising an electrolyte, a negative electrode, and a positive electrode. The electrolyte includes a fluorinated solvent, and the weight content of the fluorinated solvent is f wt% based on the total weight of the electrolyte. The ratio of the width of the negative electrode to the width of the positive electrode is g. The lithium-ion battery then satisfies the following relationships: 2 ≤ f / g ≤ 30, 1.01 ≤ g ≤ 1.08, 3wt% ≤ f wt% ≤ 30wt%. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector includes a single-sided region and a double-sided region. The negative electrode active material layer includes a first negative electrode active material layer, a second negative electrode active material layer, and a third negative electrode active material layer. In the single-sided region, the third negative electrode active material layer is located on one side of the negative electrode current collector. In the double-sided region, the first negative electrode active material layer and the second negative electrode active material layer are located on both sides of the negative electrode current collector. The thickness h of the third negative electrode active material layer in the single-sided region is 30 μm ≤ h μm ≤ 75 μm.

[0006] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: By controlling the weight content (f wt%) of the fluorinated solvent in the electrolyte within the aforementioned range, the viscosity of the electrolyte can be moderate, increasing the transport rate of lithium ions in the electrolyte, increasing the solubility of lithium salts in the electrolyte, improving the conductivity of the electrolyte, and enhancing the cycle stability of the battery. By controlling the ratio g of the width of the negative electrode to the width of the positive electrode to be 1.01 ≤ g ≤ 1.08, the effective surface area of ​​the electrodes can be increased, improving the available capacity of the electrode active material, thereby increasing the energy density of the battery. The lithium-ion battery of the present invention, by controlling the relationship between the weight content of fluorinated solvent in the electrolyte and the width ratio of the positive and negative electrode sheets, can improve the stability of the interface between the positive and negative electrode sheets and the electrolyte, reduce the concentration polarization and electrochemical reaction polarization phenomena of the electrolyte during lithium insertion / extraction. In particular, it can form a tough SEI film around the burrs of the negative electrode sheet, making the current more uniform in the burr part of the negative electrode sheet, reducing the short circuit risk caused by the burrs on the edge of the negative electrode sheet, and improving the cycle performance and safety performance of the battery. At the same time, during the cycle, the fluorinated solvent in the electrolyte can repair the SEI film in time, so that the battery maintains high cycle performance, improves the lithium ion transport rate in the electrolyte, and improves lithium plating.

[0007] Controlling h to 30μm≤hμm≤75μm can avoid increasing the difficulty of lithium insertion / extraction on the surface of the negative electrode due to excessive thickness. At the same time, a moderate thickness can enable the battery to maintain high performance while having high energy density.

[0008] Other features and advantages of the present invention will be described in detail in the following detailed description section.

[0009] 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

[0010] Figure 1 The diagram shows a stacked negative electrode and a positive electrode of the present invention.

[0011] Figure 2 The diagram shown is a schematic diagram of the negative electrode sheet of the present invention.

[0012] Figure 3 The diagram shown is a schematic diagram of the positive electrode current collector 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 invention. Unless otherwise specified herein, data ranges include endpoints.

[0014] It should be noted that the numerical designations such as "first" and "second" in this disclosure are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0015] This invention provides a lithium-ion battery, wherein the lithium-ion battery includes an electrolyte, a negative electrode, and a positive electrode. The electrolyte includes a fluorinated solvent, and the weight content of the fluorinated solvent is f wt% based on the total weight of the electrolyte. The ratio of the width of the negative electrode to the width of the positive electrode is g. Then the lithium-ion battery satisfies the following relationship: 2≤f / g≤30.

[0016] Figure 1 The diagram shows stacked negative and positive electrode plates. To illustrate the relative widths of the negative and positive electrode plates, [further details are needed]. Figure 1 The separator is omitted in the text, but it is present in lithium-ion batteries to separate the positive and negative electrodes. For example... Figure 1 As shown, the width b1 of the negative electrode 1 is greater than the width b2 of the positive electrode 2, and the ratio of the width of the negative electrode to the width of the positive electrode is g = b2 / b1. In this invention, the width is the length along the width direction.

[0017] The lithium-ion battery of the present invention can be a wound-cell structure lithium-ion battery or a stacked-cell structure lithium-ion battery. In the wound-cell structure lithium-ion battery, before winding, the positive and negative electrode sheets can be as follows: Figure 1 As shown, the electrodes are stacked and wound to form a core, with a separator between the positive and negative electrodes to isolate them; in a stacked lithium-ion battery, the positive and negative electrodes can also be arranged as shown... Figure 1 As shown, stacked and repeated as follows Figure 1The positive and negative electrodes shown form a stacked cell, wherein a separator is provided between the positive and negative electrodes to isolate them.

[0018] The electrolyte of this invention includes a fluorinated solvent. During the first discharge, the fluorinated solvent forms a solvated sheath layer around the lithium ions. The fluorinated solvent in the sheath layer has a high anion concentration, which increases the LUMO energy level of the anions and promotes the enrichment of LiF in the SEI film. The LiF-rich SEI film has a higher Young's modulus and a more uniform lithium ion flux, which makes lithium dendrites more inclined to grow in a planar manner. This makes the interface between the electrolyte and the positive and negative electrodes more stable and reduces the concentration polarization of the electrolyte and the electrochemical polarization phenomenon of lithium insertion and extraction.

[0019] By controlling the relationship between the weight content of the fluorinated solvent in the electrolyte and the width ratio of the positive and negative electrodes, it is possible to ensure that the fluorinated solvent forms a LiF-rich SEI film at the edge burrs of the negative electrode. This SEI film is thin, tough, and has low impedance, which can promote ion diffusion and transport, improve lithium plating at the interface between the negative electrode and the electrolyte, and, after satisfying a specific relationship, enable the SEI film to continuously repair itself during cycling, ensuring high stability of the SEI film near the negative electrode burrs. This avoids local polarization on the surface of the negative electrode caused by uneven current at the burrs, reduces the risk of short circuits caused by the edge burrs of the negative electrode, and improves the lithium ion transport rate in the electrolyte, thereby enabling the battery to maintain long cycle performance and high safety performance.

[0020] The lithium-ion battery can satisfy the following relationship: 2≤f / g≤30 (e.g., 2, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, or 30). When f / g < 2, the content of fluorinated solvent is low or the ratio of the width of the negative electrode to the width of the positive electrode is too high. If the content of fluorinated solvent in the electrolyte is too low, a LiF-rich SEI film cannot be formed on the surface of the positive and negative electrodes, and the SEI film cannot be repaired in time during cycling. As a result, the polarization and short circuit problems caused by the burrs of the negative electrode cannot be effectively improved. If the ratio of the width of the negative electrode to the width of the positive electrode is too high, the effective surface area of ​​the electrode will be reduced, the burrs of the negative electrode will increase, and the micro-short circuit situation during cycling will be greatly increased. When f / g > 30, the content of fluorinated solvent is high or the ratio of the width of the negative electrode to the width of the positive electrode is too low. If the fluorinated solvent content is too high, the electrolyte viscosity will increase, increasing the risk of lithium plating in the battery. If the ratio of the width of the negative electrode to the width of the positive electrode is too low, the lithium intercalation capacity of the negative electrode will be weaker than that of the positive electrode. At the same time, the higher content of fluorinated solvent will further slow down the rate of lithium ion intercalation into the negative electrode, making the lithium ion intercalation rate of the negative electrode even slower.

[0021] In this invention, by controlling the relationship between the weight content of the fluorinated solvent in the electrolyte and the ratio of the widths of the positive and negative electrodes, the battery can achieve higher safety performance and more stable cycle performance compared to existing technologies. To further improve the effect, one or more of the technical features can be further optimized.

[0022] In one example, the lithium-ion battery satisfies the following relationship: 6 ≤ f / g ≤ 15.

[0023] In one example, 3wt% ≤ f wt% ≤ 30wt% (e.g., 3wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, or 30wt%). Controlling the weight content of the fluorinated solvent in the electrolyte within this range allows for appropriate electrolyte viscosity, increases the lithium-ion transport rate in the electrolyte, increases the solubility of lithium salts in the electrolyte, improves the electrolyte conductivity, and enhances the cycle stability of the battery.

[0024] In one instance, 5wt% ≤ f wt% ≤ 20wt%.

[0025] In one example, the fluorinated solvent includes one or more of fluorinated carboxylic esters, fluorinated ethers, fluorinated benzenes, fluorinated phosphates, and fluorinated alkenes. Fluorinated solvents have a high dielectric constant, which is beneficial for the dissolution and dissociation of lithium salts, thereby improving the cycle performance of the battery. At the same time, they can also form a protective film on the surface of the positive electrode current collector, inhibiting the corrosion of the positive electrode current collector (aluminum foil).

[0026] In one example, the fluorinated solvent is selected from one or more of fluorocarboxylic esters, fluoroethers, fluorobenzenes, fluorophosphates, and fluoroolefins.

[0027] In one example, the number of fluorine substitutions in the fluorinated solvent is ≤2 (e.g., 1 or 2). When the number of fluorine substitutions in the fluorinated solvent is higher than 2, the viscosity of the electrolyte increases, making the electrolyte prone to lithium deposition. Furthermore, the structure of the fluorinated solvent is unstable, and during cycling, the fluorine elements in the fluorinated solvent are prone to break bonds, forming HF that corrodes the positive electrode. Therefore, it is necessary to control the number of fluorine substitutions in the fluorinated solvent to ≤2.

[0028] In one example, the fluorocarboxylic acid ester includes one or more of ethyl monofluoroacetate, dimethyl difluoroacetate, ethyl difluoroacetate (DFEA), and vinyl difluoroacetate.

[0029] In one example, the fluoroether comprises one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane ether (DTDL), and octafluoropentyl-tetrafluoroethyl ether.

[0030] In one example, the fluorobenzene includes one or more of fluorobenzene and 1,2-difluorobenzene.

[0031] In one example, the fluorophosphate ester includes one or more of tris(2,2,2-trifluoroethyl) phosphate and bis(2,2,2-trifluoroethyl)-ethyl phosphate.

[0032] In one example, the fluoroolefin includes one or more of 1,2-difluoroethylene, monofluoroethylene, and monofluoropropylene.

[0033] In one example, 1.01 ≤ g ≤ 1.08 (e.g., 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08). By controlling the ratio of the width of the negative electrode to the width of the positive electrode, the effective surface area of ​​the electrode can be increased, the available capacity of the electrode active material can be improved, and thus the energy density of the battery can be increased.

[0034] In one instance, 1.03 ≤ g ≤ 1.06.

[0035] In one example, the area ratio n of the negative electrode to the area of ​​the positive electrode is (1.01-1.12):1 (e.g., 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, or 1.12). By controlling the area ratio of the negative electrode to the positive electrode, the effective surface area of ​​the electrode can be increased, the available capacity of the electrode active material can be improved, and thus the energy density of the battery can be increased.

[0036] In one instance, n is (1.03-1.08):1.

[0037] In one example, 1.01 ≤ g ≤ 1.08 and n is (1.01 - 1.12):1. The values ​​of g and n can be the same or different. When the values ​​of g and n are the same, it means that the ratio of the width of the negative electrode to the width of the positive electrode and the ratio of the area of ​​the negative electrode to the area of ​​the positive electrode are the same, and the lengths of the positive and negative electrodes are the same. When the values ​​of g and n are different, it means that the ratio of the width of the negative electrode to the width of the positive electrode and the ratio of the area of ​​the negative electrode to the area of ​​the positive electrode are different, and the lengths of the positive and negative electrodes are different.

[0038] In one instance, 1.03 ≤ g ≤ 1.06 and n is (1.03 - 1.08): 1.

[0039] like Figure 2As shown, the negative electrode sheet 1 includes a negative electrode current collector 11 and a negative electrode active material layer. The negative electrode current collector 11 includes a single-sided region 111 and a double-sided region 112. The negative electrode active material layer includes a first negative electrode active material layer 121, a second negative electrode active material layer 122 and a third negative electrode active material layer 123. In the single-sided region 111, the third negative electrode active material layer 123 is located on the surface of the negative electrode current collector on one side. In the double-sided region 112, the first negative electrode active material layer 121 and the second negative electrode active material layer 122 are located on the surfaces of the negative electrode current collector 11 on both sides.

[0040] In one example, the thickness of the third negative electrode active material layer in the single-sided region is h, in μm, and the lithium-ion battery satisfies the following relationship: 0.1≤f / h≤0.7 (e.g., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 or 0.7).

[0041] In the single-sided region of the negative electrode, since the negative electrode active material layer is coated only on one side of the negative electrode current collector, the current density is high, which easily causes local overheating of the negative electrode and exacerbates lithium deposition on the surface of the negative electrode. The inventors of this invention have discovered that by controlling the relationship between the weight content of the fluorinated solvent in the electrolyte and the thickness of the third negative electrode active material layer in the single-sided region, a LiF-rich SEI film with low impedance can be formed on the surface of the single-sided region. This can alleviate the lithium deposition on the surface of the negative electrode caused by local overheating. Simultaneously, the fluorinated solvent accelerates the desolvation of lithium ions, thus speeding up the lithium ion intercalation / deintercalation process and avoiding the deposition of transition metals and side reactions of electrolyte decomposition.

[0042] In one example, the lithium-ion battery satisfies the following relationship: 0.23 ≤ f / h ≤ 0.5.

[0043] In one example, 30μm ≤ h μm ≤ 75μm. Controlling h within this range avoids increasing the difficulty of lithium insertion / extraction on the negative electrode surface due to excessive thickness. At the same time, a moderate thickness allows the battery to maintain high performance while having high energy density.

[0044] In one instance, 40 μm ≤ h μm ≤ 68 μm.

[0045] In one example, the second and third negative electrode active material layers are located on the same side of the negative electrode current collector. The thickness of the first and second negative electrode active material layers may be the same or different, and the ratio of the thickness of the first to the third negative electrode active material layer is 1:(0.8-0.99). By controlling the ratio of the thickness of the first to the third negative electrode active material layer, the overall thickness of the negative electrode active material layers in the negative electrode sheet can be kept within a suitable range, while the thickness of the third negative electrode active material layer is kept relatively thin. This helps to reduce the electron and ion transport paths, improve the electronic conductivity and ion conductivity of the battery, thereby reducing the internal impedance of the battery and improving lithium plating, thus enhancing the charge-discharge efficiency and cycle performance of the battery.

[0046] In one example, the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer is 1:(0.86-0.96).

[0047] In one example, the components and weight content of each component in the first negative electrode active material layer, the second negative electrode active material layer, and the third negative electrode active material layer may be the same or different.

[0048] In one example, the second negative electrode active material layer and the third negative electrode active material layer have the same composition and the same weight content of each component.

[0049] In one example, the components and weight content of each component in the first negative electrode active material layer and the second negative electrode active material layer are different.

[0050] In one example, the negative electrode active material layer includes a negative electrode active substance, which includes carbon-based materials and / or silicon-based materials.

[0051] In one example, the carbon-based material includes at least one of natural graphite, artificial graphite, mesophase carbon microspheres, soft carbon, and hard carbon.

[0052] In one example, the silicon-based material may include at least one of silicon, silicon oxide, silicon carbon, and silicon alloys.

[0053] In one example, the negative electrode active material layer includes a negative electrode conductive agent and a negative electrode binder.

[0054] In one example, the negative electrode conductive agent includes at least one of conductive carbon black (Super P), acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, and metal powder.

[0055] In one example, the negative electrode binder includes at least one of styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, and polyvinylidene fluoride.

[0056] In one example, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode active material is 96wt%-98wt% (e.g., 96wt%, 96.5wt%, 97wt%, 97.5wt%, or 98wt%), the weight content of the negative electrode conductive agent is 0.5wt%-2wt% (e.g., 0.5wt%, 1wt%, 1.5wt%, or 2wt%), and the weight content of the negative electrode binder is 1wt%-2wt% (e.g., 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, or 2wt%).

[0057] In one example, the negative electrode current collector includes a polymer layer and copper foil layers located on both sides of the polymer layer, the polymer layer comprising PP and / or PE.

[0058] To further improve battery safety, the negative electrode current collector of this invention adopts a composite current collector, such as... Figure 3 As shown, the negative electrode current collector 11 includes a polymer layer 113 and copper foil layers 114 located on both sides of the polymer layer.

[0059] In one example, the polymer layer comprises PP and / or PE.

[0060] Studies have shown that the stronger the polarity of the solvent in the electrolyte, the greater the corrosion of the copper foil. The electrolyte of this invention includes a weakly polar fluorinated solvent. After the fluorinated solvent undergoes a passivation reaction on the surface of the copper foil, it can form a protective film. This protective film can improve the stability of the copper foil in the electrolyte environment and further reduce the corrosion of the negative electrode current collector by the electrolyte. That is, through the synergistic effect of the negative electrode composite current collector and the fluorinated solvent in the electrolyte, the corrosion of the negative electrode current collector by the electrolyte can be further reduced, and the corrosion resistance of the negative electrode current collector can be improved.

[0061] In one example, the copper foil layer is copper foil.

[0062] In one example, the thickness of the copper foil layer is 0.3 μm-1.5 μm (e.g., 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, or 1.5 μm). The thickness of the copper foil layer is a single-sided thickness. If both surfaces of the polymer layer have copper foil layers with the same thickness, then the thickness of the copper foil layer is the thickness of the copper foil layer on either side.

[0063] In one example, the thickness of the polymer layer is 4 μm to 8 μm (e.g., 4 μm, 5 μm, 6 μm, 7 μm or 8 μm).

[0064] In one example, the thickness t1 of the copper foil layer is 0.3 μm-1.5 μm, and the thickness of the polymer layer is 4 μm-8 μm. Controlling the thicknesses of the copper foil layer and the polymer layer within these ranges ensures that the copper foil layer is thinner, thereby accelerating the electron transport rate. The moderate thickness of the polymer layer, located in the middle, enhances the mechanical strength of the negative electrode current collector, improving the structural stability of the battery. Furthermore, the polymer layer exhibits excellent corrosion resistance and high-temperature resistance, maintaining stable performance even under extreme operating conditions. Compared to conventional current collectors, such as pure copper foil current collectors, the negative electrode current collector of this invention is thinner, has superior conductivity, stronger heat dissipation capacity, and moderate weight, thus improving the gravimetric energy density of the battery.

[0065] In one example, the positive electrode sheet includes a positive current collector and a positive active material layer located on one or both surfaces of the positive current collector, the positive active material layer including a positive active substance, a positive conductive agent and a positive binder.

[0066] In one example, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, and lithium-rich manganese.

[0067] In one example, the positive electrode conductive agent includes at least one of conductive carbon black (Super P), acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, and metal powder.

[0068] In one example, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

[0069] In one example, based on the total weight of the positive electrode active material layer, the weight content of the positive electrode active site is 96wt%-98.5wt%, the weight content of the positive electrode conductive agent is 0.5wt%-2wt%, and the weight content of the positive electrode binder is 0.5wt%-2wt%.

[0070] In one example, the electrolyte further includes lithium salt, ethylene carbonate (EC), propylene carbonate (PC), organic solvent, and additives.

[0071] In one example, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium bis(fluorosulfonyl)imide (LiTFSI), lithium bis(trifluoromethanesulfonyl)imide, lithium difluorobis(oxalate phosphate), lithium tetrafluoroborate, lithium bis(oxalate borate), lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(trifluoromethanesulfonyl)imide, lithium di(pentafluoroethylsulfonyl)imide, lithium tri(trifluoromethanesulfonyl)methyl, and lithium di(trifluoromethanesulfonyl)imide. The lithium salt can affect the basic physicochemical properties of the electrolyte and is a crucial component in the electrolyte that significantly influences the characteristics of lithium-ion batteries. Lithium salts play a role in conducting lithium ions and can improve the conductivity of the electrolyte.

[0072] During the first charge and discharge process, the ethylene carbonate (EC) can form an SEI film on the negative electrode, which improves the efficiency of subsequent lithium ion insertion / extraction at the negative electrode and reduces the occurrence of side reactions.

[0073] The propylene carbonate (PC) has a high dielectric constant, which can promote the dissociation of lithium salts and significantly improve the conductivity of ions in the electrolyte.

[0074] In one example, the organic solvent includes one or more of propyl propionate (PP), ethyl propionate (EP), ethyl butyrate (EB), ethyl acetate (EA), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC).

[0075] In one example, the additive includes one or more of 1,3-propanesulfonyl lactone (PS), 1,3-acrylonitrile lactone (PST), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), adiponitrile (ADN), succinate (SN), fluoroethylene carbonate (FEC), and 1,3,6-hexanetrionitrile (HTCN). Succinate (SN) and HTCN primarily complex with cobalt ions in the positive electrode, protecting the positive electrode material from dissolution and release under high voltage; VC and PS preferentially form films on the surface of the negative electrode, making the SEI film more robust.

[0076] In one example, based on the total weight of the electrolyte, the lithium salt has a weight content of 10-21 wt%, the EC has a weight content of 0-15 wt%, the PC has a weight content of 7-15 wt%, the organic solvent has a weight content of 30-60 wt%, and the additive has a weight content of 15-25 wt%.

[0077] 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.

[0078] The following examples illustrate the lithium-ion battery of the present invention.

[0079] Example 1 (1) Preparation of positive electrode The positive electrode active material (lithium cobalt oxide), positive electrode conductive agent (Super P), and positive electrode binder (polyvinylidene fluoride (PVDF)) are dispersed in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 98:1.2:0.8. The mixture is thoroughly stirred to form a uniform positive electrode slurry. This slurry is then coated onto both sides of the positive electrode current collector (conventional aluminum foil). After drying, rolling, and cutting (to a size of 6.5cm × 120cm), the material is cleaned (the cleaned area is 3 × 5mm). Adhesive tabs are then attached to obtain the positive electrode sheet, which has a width of 118mm and an area of ​​104481mm². 2 .

[0080] (2) Preparation of negative electrode The negative electrode active material (graphite) and the negative electrode conductive material (Super) P) A negative electrode binder (1.5 parts by weight of styrene-butadiene rubber (SBR) and 0.5 parts by weight of thickener sodium carboxymethyl cellulose (CMC)) is dispersed in an appropriate amount of deionized water at a weight ratio of 97:1:2 and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is coated on the surface of the negative electrode current collector (conventional copper foil) to form a negative electrode active material layer. A first negative electrode active material layer and a second negative electrode active material layer are coated on both sides of the negative electrode current collector. The thickness of the first negative electrode active material layer is 51.2 μm, and the thickness of the second negative electrode active material layer is 51.2 μm. A third negative electrode active material layer is coated on one side of the single-sided area of ​​the negative electrode current collector (located on the same side as the second negative electrode active material layer). The thickness of the third negative electrode active material layer is 49.1 μm. Then, after drying, rolling, cutting (cut size 6.8 cm × 120.5 cm), cleaning, and attaching tab adhesive, a negative electrode sheet is obtained.

[0081] The width of the negative electrode is 123 mm, and the area of ​​the negative electrode is 109456 mm². 2 The thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer is 1:0.959.

[0082] (3) Preparation of electrolyte Composition preparation: Fluorinated solvent: Ethyl difluoroacetate (DFEA) (wherein, the number of fluorinated substitutions in the fluorinated solvent is 2), 12 parts by weight; EC, 10 parts by weight; PC, 10 parts by weight; Organic solvent: PP, 35 parts by weight; Lithium salt: Lithium hexafluorophosphate, 15 parts by weight; Additives: PS, 3 parts by weight; FEC, 8 parts by weight; SN, 2 parts by weight; HTCN, 3 parts by weight; ADN (2 parts by weight), totaling 18 parts by weight.

[0083] In a glove box (H2O < 0.01 ppm, O2 < 0.01 ppm, Ar atmosphere), EC / PC / PP / DFEA are mixed evenly, then fully dried lithium salt is added, dissolved, and additives are added. After stirring evenly, the desired electrolyte is obtained after passing the moisture and free acid tests.

[0084] (4) Diaphragm The diaphragm consists of a substrate layer and coatings on both sides of the substrate layer. The substrate layer is composed of PP / PE, the coating on one side of the substrate layer is PVDF, and the coating on the other side of the substrate layer is PMMA.

[0085] (5) Preparation of lithium-ion batteries The positive electrode sheet from step (1), the separator from step (4), and the negative electrode sheet from step (2) are wound together to obtain a bare battery without electrolyte injection. The bare battery is placed in an outer packaging foil, and the electrolyte from step (3) is injected into the dried bare battery. After vacuum sealing, standing, formation, shaping, sorting and other processes, the desired lithium-ion battery is obtained.

[0086] Among them, the ratio of the width of the negative electrode to the width of the positive electrode, g, is 1.04, the ratio of the area of ​​the negative electrode to the area of ​​the positive electrode, n, is 1.05, f / g = 12 / 1.04 = 11.51, and f / h = 0.244.

[0087] Example 2 The process was carried out in accordance with Example 1, except that the negative electrode current collector was a composite current collector, which included a polymer layer and copper foil layers located on both sides of the polymer. The polymer layer was made of PP and had a thickness of 6 μm, while the copper foil layer had a thickness of 1 μm.

[0088] Example 3 Group This set of examples illustrates the effects of changes in f / g.

[0089] Example 3a The experiment was conducted in accordance with Example 1, except that the weight content of the fluorinated solvent in the electrolyte was 5% (f%), and correspondingly, f / g = 4.8 and f / h = 0.102.

[0090] Example 3b The experiment was conducted in accordance with Example 1, except that the weight content of the fluorinated solvent in the electrolyte was 18% (f%), and correspondingly, f / g = 17.27 and f / h = 0.367.

[0091] Example 3c The experiment was conducted in accordance with Example 1, except that the weight content of the fluorinated solvent in the electrolyte was 31% (f%), and correspondingly, f / g = 29.81 and f / h = 0.631.

[0092] Example 3d The experiment was conducted in accordance with Example 1, except that the weight content of the fluorinated solvent in the electrolyte was 3% (f%), and correspondingly, f / g = 2.88 and f / h = 0.061.

[0093] Example 3e The procedure was carried out in accordance with Example 1, except that the width of the negative electrode was 126.5 mm and the area of ​​the negative electrode was 112571 mm². 2 The width of the positive electrode is 118.2 mm, and the area of ​​the positive electrode is 104658 mm². 2 Accordingly, g=1.07, n=1.08, f / g=11.21.

[0094] Example 3f The procedure was carried out in accordance with Example 1, except that the width of the negative electrode was 119.5 mm and the area of ​​the negative electrode was 106341 mm². 2 The width of the positive electrode is 118.3 mm, and the area of ​​the positive electrode is 104746 mm². 2 Accordingly, g=1.01, n=1.02, f / g=11.88.

[0095] Example 3g The procedure was carried out in accordance with Example 1, except that the width of the negative electrode was 130.1 mm and the area of ​​the negative electrode was 115774 mm². 2 The width of the positive electrode is 118.3 mm, and the area of ​​the positive electrode is 104746 mm². 2 Accordingly, g=1.1, n=1.11, f / g=10.91.

[0096] Example 4 group This set of examples illustrates the effects of changes in f / h.

[0097] Example 4a The same procedure was followed as in Example 1, except that the thickness h of the third negative electrode active material layer was 41.2 μm. In order to keep the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer basically unchanged, the thickness of the first negative electrode active material layer was adaptively adjusted to 43 μm, so f / h = 0.291.

[0098] Example 4b The same procedure was followed as in Example 1, except that the thickness h of the third negative electrode active material layer was 67.4 μm. In order to keep the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer basically unchanged, the thickness of the first negative electrode active material layer was adaptively adjusted to 70.3 μm, so f / h = 0.178.

[0099] Example 4c The experiment was conducted in accordance with Example 1, except that the weight content of the fluorinated solvent in the electrolyte was 25%, the thickness h of the third negative electrode active material layer was 31.3 μm, and in order to keep the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer basically unchanged, the thickness of the first negative electrode active material layer was adaptively adjusted to 32.6 μm, so f / g=23.98 and f / h=0.799.

[0100] Example 4d The same procedure was followed as in Example 1, except that the thickness h of the third negative electrode active material layer was 74.6 μm. In order to keep the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer basically unchanged, the thickness of the first negative electrode active material layer was adaptively adjusted to 77.8 μm, so f / h = 0.161.

[0101] Example 4e The same procedure was followed as in Example 1, except that the thickness h of the third negative electrode active material layer was 28.5 μm. In order to keep the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer basically unchanged, the thickness of the first negative electrode active material layer was adaptively adjusted to 29.7 μm, so f / h = 0.421.

[0102] Example 4c The experiment was conducted in accordance with Example 1, except that the weight content of the fluorinated solvent in the electrolyte was 3%, the thickness h of the third negative electrode active material layer was 78.8 μm, and in order to keep the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer basically unchanged, the thickness of the first negative electrode active material layer was adaptively adjusted to 82.2 μm, so f / g=2.88 and f / h=0.038.

[0103] Example 5 group This set of embodiments is used to illustrate the effects of changing the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer.

[0104] Example 5a The same procedure was followed as in Example 1, except that the thickness h of the third negative electrode active material layer was 50.4 μm, and the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer was 1:0.984, f / h=0.238.

[0105] Example 5b The same procedure was followed as in Example 1, except that the thickness h of the third negative electrode active material layer was 44.3 μm, and the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer was 1:0.865, f / h=0.271.

[0106] Example 5c The same procedure was followed as in Example 1, except that the thickness h of the third negative electrode active material layer was 41.8 μm, and the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer was 1:0.816, f / h=0.287.

[0107] Example 5d The same procedure was followed as in Example 1, except that the thickness h of the third negative electrode active material layer was 62.1 μm, and the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer was 1:1.213, f / h=0.193.

[0108] Example 5e The same procedure was followed as in Example 1, except that the thickness h of the third negative electrode active material layer was 535.7 μm, and the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer was 1:0.697, f / h=0.336.

[0109] Example 7 group This set of examples illustrates the effects of changes in fluorinated solvents.

[0110] Example 7a The procedure was carried out in accordance with Example 1, except that the fluorinated solvent was monofluorobenzene (the number of fluorinated substitutions in the fluorinated solvent was 1).

[0111] Example 7b The procedure was carried out in accordance with Example 1, except that the fluorinated solvent was octafluoropentyl-tetrafluoroethyl ether (the number of fluorinated substitutions in the fluorinated solvent was 12).

[0112] Example 7c The procedure was carried out in accordance with Example 1, except that the fluorinated solvent was 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (the number of fluorinated substitutions in the fluorinated solvent was 8).

[0113] Comparative Example 1 The experiment was conducted in accordance with Example 1, except that the weight content of the fluorinated solvent in the electrolyte was 33%, so f / g = 31.73 and f / h = 0.672.

[0114] Comparative Example 2 The experiment was conducted in accordance with Example 1, except that the weight content of the fluorinated solvent in the electrolyte was 1.5%, the thickness h of the third negative electrode active material layer was 12 μm, and in order to keep the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer basically unchanged, the thickness of the first negative electrode active material layer was adaptively adjusted to 12.5 μm, so f / g=1.44 and f / h=0.125.

[0115] Comparative Example 3 The procedure was carried out in accordance with Example 1, except that no fluorinated solvent was added to the electrolyte.

[0116] Comparative Example 4 The same procedure was followed as in Example 1, except that the width of the positive electrode was the same as the width of the negative electrode, and the area of ​​the positive electrode was the same as the area of ​​the negative electrode.

[0117] Test case The lithium-ion batteries obtained in the examples and comparative examples were tested as follows: 1. Cyclic performance test The lithium-ion battery was placed at 25℃ and first discharged to 3V at 0.2C, then charged to 4.48V at 0.5C. The capacity and thickness in the fully charged state were recorded. The battery was then discharged to 3V at 0.2C, then charged to 4.48V at a constant current of 1C, then charged to the upper limit voltage (4.53V) at 0.7C, then charged to 0.05C at a constant voltage of 4.53V and allowed to rest for 5 minutes. Finally, it was discharged to 3V at a constant current of 0.7C and allowed to rest for 5 minutes. This constitutes one charge-discharge cycle. This charge / discharge cycle was repeated 1000 times. The performance parameters of the lithium-ion battery, including capacity retention, thickness expansion rate, and any abnormal appearance, were recorded during the cycle. After cycling, the battery was disassembled to observe lithium plating. Capacity retention rate = (1000T capacity / initial capacity) × 100% Thickness expansion % = (Thickness of a 1000T fully charged battery / Initial thickness) × 100% Lithium plating status: Charge the next battery to 4.48V at 0.5C, then disassemble the battery and observe whether there are any grayish-white dots or flakes on the top, bottom, surface, and arc of the negative electrode interface. If there are no grayish-white dots or flakes, it means no lithium plating. If the area of ​​grayish-white dots or flakes is less than 10% of the electrode area, it means slight lithium plating. If the area of ​​grayish-white dots or flakes is ≥10% of the electrode area, it means lithium plating.

[0118] 2. Safety performance test -25℃ external short circuit The battery was fully charged at 0.5C (100% SOC), then stopped at 0.05C and left to stand for 10 minutes. The voltage, internal resistance, and thickness at full charge (100% SOC) were tested at 25±5℃. The battery cell was placed in an environment of 25℃±5℃ for another 30 minutes, with the positive and negative terminals short-circuited. The short-circuit resistance was ≤50mΩ. The voltage and cell temperature rise were monitored. The test was terminated when the battery temperature dropped below 20% of the peak temperature, or when the test duration exceeded 24 hours. A battery explosion or fire was considered a failure. A total of 10 battery samples were tested, and the results were expressed as "Pass / 10". For example, "8 / 10" means 8 out of 10 tests passed.

[0119] The results are recorded in Table 1.

[0120] Table 1 As can be seen from Table 1, through the comparative examples and embodiments, the lithium-ion batteries of the embodiments show a significant improvement in capacity retention, a significant reduction in thickness expansion rate, and a significant improvement in safety performance. This indicates that by controlling the relationship between the weight content of fluorinated solvent in the electrolyte and the ratio of the width of the positive and negative electrodes, the safety performance and cycle stability of the battery can be improved.

[0121] 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 an electrolyte, a negative electrode, and a positive electrode. The electrolyte includes a fluorinated solvent, and the weight content of the fluorinated solvent is fwt% based on the total weight of the electrolyte. The ratio of the width of the negative electrode to the width of the positive electrode is g. Therefore, the lithium-ion battery satisfies the following relationships: 2≤f / g≤30, 1.01≤g≤1.08, 3wt%≤fwt%≤30wt%. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector includes a single-sided region and a double-sided region. The negative electrode active material layer includes a first negative electrode active material layer, a second negative electrode active material layer, and a third negative electrode active material layer. In the single-sided region, the third negative electrode active material layer is located on one side of the negative electrode current collector. In the double-sided region, the first negative electrode active material layer and the second negative electrode active material layer are located on both sides of the negative electrode current collector. The thickness h of the third negative electrode active material layer in the single-sided region is 30 μm ≤ h μm ≤ 75 μm.

2. The lithium-ion battery according to claim 1, wherein, The lithium-ion battery satisfies the following relationship: 6≤f / g≤15; And / or, the fluorinated solvent includes one or more of fluorocarboxylic acid esters, fluoroethers, fluorobenzenes, fluorophosphates and fluoroolefins; And / or, 1.03≤g≤1.06; And / or, 5wt%≤fwt%≤20wt%; And / or, the ratio n of the area of ​​the negative electrode to the area of ​​the positive electrode is (1.01-1.12):

1.

3. The lithium-ion battery according to claim 2, wherein, n is (1.03-1.08):

1.

4. The lithium-ion battery according to claim 1, wherein, The lithium-ion battery satisfies the following relationship: 0.04≤f / h≤0.

9.

5. The lithium-ion battery according to claim 2 or 3, wherein, The fluorocarboxylic acid esters include one or more of ethyl monofluoroacetate, dimethyl difluoroacetate, ethyl difluoroacetate, and vinyl difluoroacetate; And / or, the fluoroether comprises one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane ether, and octafluoropentyl-tetrafluoroethyl ether; And / or, the fluorobenzene includes one or more of monofluorobenzene and 1,2-difluorobenzene; And / or, the fluorophosphate esters include one or more of tris(2,2,2-trifluoroethyl) phosphate and bis(2,2,2-trifluoroethyl)-ethyl phosphate; And / or, the fluoroolefins include one or more of 1,2-difluoroethylene, monofluoroethylene, and monofluoropropylene; And / or, the number of fluorinated substitutions in the fluorinated solvent is ≤2.

6. The lithium-ion battery according to claim 4, wherein, The lithium-ion battery satisfies the following relationship: 0.1 ≤ f / h ≤ 0.7; And / or, 40μm≤h μm≤68μm; And / or, the thickness of the first negative electrode active material layer is the same as or different from the thickness of the second negative electrode active material layer.

7. The lithium-ion battery according to claim 6, wherein, The lithium-ion battery satisfies the following relationship: 0.23≤f / h≤0.

5.

8. The lithium-ion battery according to claim 4, wherein, The negative electrode current collector includes a polymer layer and copper foil layers located on both sides of the polymer layer, wherein the polymer layer includes PP and / or PE.

9. The lithium-ion battery according to claim 8, wherein, The thickness of the copper foil layer is 0.3μm-1.5μm; And / or, the thickness of the polymer layer is 4μm-8μm.

10. The lithium-ion battery according to claim 4, wherein, The negative electrode active material layer includes a negative electrode active material, which includes carbon-based materials and / or silicon-based materials; the carbon-based material includes at least one of natural graphite, artificial graphite, mesophase carbon microspheres, soft carbon, and hard carbon; the silicon-based material includes at least one of silicon, silicon oxide, silicon carbon, and silicon alloy.

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