Secondary batteries and electrical devices

Abstract

The present invention relates to a secondary battery and an electric device, which relates to the field of batteries. The secondary battery includes a negative electrode active material and an electrolyte, the mass proportion of a silicon-containing material in the negative electrode active material is W1%, the mass proportion of the fluorinated cyclic carbonate in the electrolyte is W2%, and the mass proportion of the fluorinated cyclic carbonate in the electrolyte is W2, where 0.1W1≦W2≦0.7W1.

Description

[Technical Field]

[0001] This application relates to the technical field of lithium batteries, and in particular to secondary batteries and electrical devices. [Background technology]

[0002] Lithium-ion batteries have attracted attention due to their high specific energy, long cycle life, low self-discharge, and excellent safety performance. Currently, lithium-ion batteries are used in all aspects of daily life, including cameras, laptops, and electric vehicles.

[0003] To improve the energy density of lithium-ion batteries, the current common practice is to increase the nickel content of the positive electrode to increase its gram capacity, and to dope the corresponding negative electrode with silicon to increase its gram capacity. When lithium is inserted into the silicon, its volume increases by 300%. The SEI film on the surface is destroyed, exposing a new interface, where the electrolyte continues to undergo reduction reactions, consuming both the electrolyte and the active lithium, resulting in poor cycle and storage performance. Summary of the Invention [Problem to be solved by the invention]

[0004] The main object of the present application is to provide a secondary battery and an electric device that aim to optimize the cycle performance and storage performance of the secondary battery. [Means for solving the problem]

[0005] In a first aspect, the present application provides a secondary battery comprising a negative electrode active material and an electrolyte, wherein the negative electrode active material comprises a silicon-containing material, the mass proportion of the silicon-containing material in the negative electrode active material is W1%, the electrolyte comprises a fluorinated cyclic carbonate, the mass proportion of the fluorinated cyclic carbonate in the electrolyte is W2%, and 0.1W1≦W2≦0.7W1.

[0006] When a silicon-containing material is added to the negative electrode active material, its volume expands and contracts rapidly, destroying the SEI film on the surface and exposing a new interface. When the fluorinated cyclic carbonate content (W2%) in the electrolyte and the silicon content (0.1W1≦W2≦0.7W1) are satisfied, the fluorinated cyclic carbonate can effectively form a film on the silicon-containing material surface without rupture. When W2 is less than 0.1W1, the W2 content is too low to effectively cover the entire surface of the silicon-containing material. When W2 is greater than 0.7W1, a film can be effectively formed at the silicon-containing material interface, but the excess fluorinated cyclic carbonate not involved in the film formation is likely to be oxidized at the cathode and generate gas. When the content of the fluorinated cyclic carbonate in the electrolyte and the silicon-containing material in the negative electrode satisfy the above specific relationship, a film can be effectively formed on the silicon-containing material surface, preventing interfacial rupture and improving the cycle life and storage life of the battery.

[0007] In some embodiments, 1%≦W1%≦50%. The inventors' research has revealed that if W1% is less than 1%, the contribution of silicon to the negative electrode capacity becomes too small, and if W1% is greater than 50%, the negative electrode's charged volume expands excessively, making it impossible to effectively prevent interfacial breakdown by the electrolyte. Furthermore, 2%≦W1%≦25%. By keeping W1% within the above range, the cycle life and storage life of the battery can be further improved.

[0008] In some embodiments, 0.5%≦W2%≦25%, and further, 1%≦W2%≦20%. When the content W2% of the fluorinated cyclic carbonate in the electrolyte is within the above range, a film can be effectively formed on the surface of the silicon-containing material, interfacial rupture can be suppressed, and the cycle life and storage life of the battery can be improved.

[0009] In some embodiments, the electrolyte further comprises LiPF6 and fluorine-containing lithium sulfonyl imide, wherein the molar concentration of LiPF6 in the electrolyte is C1, the molar concentration of fluorine-containing lithium sulfonyl imide is C2, and 0.25≦C1 / C2≦5. When the concentrations of fluorine-containing lithium sulfonyl imide and LiPF6 in the electrolyte satisfy the above relationship, the generation of HF in the electrolyte can be reduced, the damage to the negative electrode interface caused by HF can be reduced, and the aluminum foil can be prevented from corroding. The cycle life and storage life of the battery can be further improved.

[0010] In some embodiments, 0.2 mol / L≦C1≦1 mol / L and / or 0.2 mol / L≦C2≦0.9 mol / L. When C1 and C2 are within the above ranges, the generation of HF in the electrolyte can be reduced, damage to the negative electrode interface caused by HF can be alleviated, the aluminum foil can be prevented from corroding, and the cycle life and storage life of the battery can be further improved.

[0011] In some embodiments, the fluorine-containing lithium sulfonyl imide includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium fluoro(trifluoromethylsulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide. The use of such substances can reduce the generation of HF in the electrolyte, mitigate damage to the negative electrode interface caused by HF, and prevent corrosion of the aluminum foil, thereby further improving the cycle life and storage life of the battery.

[0012] In some embodiments, the fluorinated cyclic carbonate contains at least one of fluoroethylene carbonate and bisfluoroethylene carbonate, which allows for effective film formation on silicon surfaces, suppresses interfacial rupture, and improves the lifespan of secondary batteries.Furthermore, the fluorinated cyclic carbonate contains fluoroethylene carbonate, which further improves the lifespan of secondary batteries.

[0013] In some embodiments, the silicon-containing material includes at least one of silicon dioxide, silicon, and silicon monoxide, which can effectively form a film on the silicon surface, suppress interfacial rupture, and improve the life of the secondary battery.

[0014] In some embodiments, the electrolyte solution further comprises a solvent, and the solvent comprises at least one of ethylene carbonate, propylene carbonate, fluorobenzene, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl acetate, and methyl formate. The above materials are excellent organic solvents, and the use of at least one of the above organic solvents can improve the cycle life and storage life of the battery.

[0015] In some embodiments, the electrolyte further comprises a solvent, and the mass ratio of the solvent in the electrolyte is 20% to 60%, which can improve the cycle life and storage life of the battery.

[0016] In some embodiments, the electrolyte solution further comprises an additive, the additive comprising at least one of vinylene carbonate, ethylene sulfate, 1,3-propane sultone, lithium difluorooxalatoborate, lithium bisoxalatoborate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, and lithium difluorophosphate, which has the effect of assisting film formation.

[0017] In some embodiments, the negative electrode active material further comprises at least one of natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, and soft carbon. By doping the carbon-based materials with silicon, the energy density of the secondary battery can be effectively improved.

[0018] In a second aspect, the present application provides an electrical device comprising the secondary battery described in the above examples. DETAILED DESCRIPTION OF THE INVENTION

[0019] In order to make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following provides a clear and complete description of the technical solutions in the embodiments of the present invention.

[0020] It should be noted that unless specific conditions are specified in the examples, the experiments are carried out according to standard conditions or manufacturer-recommended conditions. Reagents or equipment used without a manufacturer's name are all commercially available products. The meaning of "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solutions A, B, or both A and B. Furthermore, the technical solutions in each example may be combined with each other to the extent feasible by those skilled in the art. If a combination of technical solutions is mutually inconsistent or unfeasible, such a combination of technical solutions does not exist and is not considered to be within the scope of protection claimed by the present invention. Based on the examples of the present invention, all other examples that can be derived by those skilled in the art without any creative effort are within the scope of protection of the present invention.

[0021] Lithium-ion batteries have attracted attention due to their high specific energy, long cycle life, low self-discharge, and excellent safety performance. Currently, lithium-ion batteries are used in all aspects of daily life, including cameras, laptops, and electric vehicles.

[0022] To improve the energy density of lithium-ion batteries, the current common practice is to increase the nickel content of the positive electrode to increase its gram capacity, and to dope the corresponding negative electrode with silicon to increase its gram capacity. When lithium is inserted into the silicon, its volume increases by 300%. The SEI film on the surface is destroyed, exposing a new interface, where the electrolyte continues to undergo reduction reactions, consuming both the electrolyte and the active lithium, resulting in poor cycle and storage performance.

[0023] Based on this, researchers in this field have made improvements. For example, in the prior art, there is a method of improving film formation by adding an additive to the electrolyte. In this method, for example, the negative electrode is a silicon-based negative electrode, the electrolyte contains LiFSI and LiPF6 (at a content ratio of 1:1 to 1:3 (mol / mol)), and the solvent in the electrolyte is DEC (diethyl carbonate):FEC (fluoroethylene carbonate) = 70:30 to 95:5. However, in this method, a silicon-based negative electrode is used, and while FEC can improve film formation to some extent, VC (vinylene carbonate) produced by decomposition of FEC is susceptible to oxidation and is prone to oxidization, particularly at the positive electrode, generating gas, which causes the cell to swell with gas.

[0024] Based on this, in response to the above problems, the present inventors have, through a large amount of experimentation and innovative thinking, developed a novel electrolyte that can significantly improve the cycle life and storage life of a battery, and a battery containing the electrolyte.

[0025] Specifically, the present application provides a secondary battery comprising a negative electrode active material and an electrolyte, wherein the negative electrode active material comprises a silicon-containing material, the mass percentage of the silicon-containing material in the negative electrode active material is W1%, and the electrolyte comprises a fluorinated cyclic carbonate, the mass percentage of the fluorinated cyclic carbonate in the electrolyte is W2%, and 0.1W1≦W2≦0.7W1. The secondary battery provided in the present application has the following beneficial effects:

[0026] When a silicon-containing material is added to the negative electrode active material, its volume expands and contracts rapidly, destroying the SEI film on the surface and exposing a new interface. When the fluorinated cyclic carbonate content (W2%) in the electrolyte and the silicon content (W2%) in the negative electrode satisfy the relationship 0.1W1≦W2≦0.7W1, the fluorinated cyclic carbonate can effectively form a film on the surface of the silicon-containing material without rupture. When W2 is less than 0.1W1, the W2 content is too low to effectively cover the entire surface of the silicon-containing material. When W2 is greater than 0.7W1, the fluorinated cyclic carbonate effectively forms a film on the silicon-containing material interface, but the excess fluorinated cyclic carbonate not involved in the film formation is likely to be oxidized at the cathode and generate gas. When the content of the fluorinated cyclic carbonate in the electrolyte and the silicon-containing material in the negative electrode satisfy the above specific relationship, the film can be effectively formed on the surface of the silicon-containing material, preventing interfacial rupture and improving the cycle life and storage life of the battery.

[0027] In addition, in the present application, the fluorinated cyclic carbonate in the electrolyte can significantly improve the stability of the metallic lithium negative electrode.

[0028] It is understood that in the present application, the type of the silicon-containing material is not limited, and all are within the scope of protection of the present application, as long as they contain silicon element. In the embodiments of the present application, the silicon-containing material may be silicon element, silicon dioxide, silicon monoxide, etc., which can effectively form a film on the silicon surface, suppress interfacial rupture, and improve the service life of the secondary battery.

[0029] In some embodiments, 1%≦W1%≦50%, for example, W1% can be 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc. The inventors' research has found that when the amount of silicon doped in the negative electrode is less than 1%, the contribution of silicon to the negative electrode capacity becomes too small, and when the amount is more than 50%, the charged volume of the negative electrode expands excessively, and the electrolyte cannot effectively prevent interfacial breakdown.

[0030] Furthermore, 2%≦W1%≦25%, and for example, W1% may be 2%, 5%, 8%, 10%, 12%, 16%, 18%, 21%, 23%, 24%, 25%, etc. By being within the above range, the cycle life and storage life of the battery can be further improved.

[0031] In some embodiments, 0.5%≦W2%≦25%, for example, W2 may be 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, etc., or 1%≦W2%≦20%, for example, W2 may be 1%, 2%, 4%, 9%, 12%, 17%, 22%, 25%, etc. When the content W2% of the fluorinated cyclic carbonate in the electrolyte is within the above range, a film can be effectively formed on the surface of the silicon-containing material, interfacial rupture can be suppressed, and the cycle life and storage life of the battery can be improved.

[0032] In some embodiments, the electrolyte further comprises LiPF and a fluorine-containing lithium sulfonyl imide, wherein the molar concentration of LiPF is C1 and the molar concentration of the fluorine-containing lithium sulfonyl imide is C2, and the molar concentration of the LiPF is C2, where C1 / C2 is 0.25≦C1 / C2≦5. For example, C1 / C2 may be 0.25, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, etc. When the lithium salt in the electrolyte is LiPF, moisture released from the electrode sheet reacts with LiPF, and the resulting HF and PF (Lewis acid) further damage the SEI film. Therefore, in the present application, by replacing a portion of LiPF with a fluorine-containing lithium sulfonyl imide, the probability of HF and PF formation is reduced. When the concentrations of the fluorine-containing lithium sulfonyl imide and LiPF in the electrolyte satisfy the above relationship, the generation of HF in the electrolyte can be reduced, which can mitigate damage to the negative electrode interface caused by HF and prevent corrosion of the aluminum foil. This can further improve the cycle life and storage life of the battery.

[0033] In some embodiments, 0.2 mol / L≦C1≦1 mol / L and / or 0.2 mol / L≦C2≦0.9 mol / L, for example, C1 may be 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, etc., and C2 may be 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, etc. When C1 and C2 are within the above ranges, the generation of HF in the electrolyte can be reduced, and damage to the negative electrode interface caused by HF can be mitigated. In addition, the aluminum foil is not corroded, and the cycle life and storage life of the battery can be further improved.

[0034] In some embodiments, the fluorine-containing lithium sulfonyl imide includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium fluoro(trifluoromethylsulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide. The use of such substances can reduce the generation of HF in the electrolyte, mitigate damage to the negative electrode interface caused by HF, and prevent corrosion of the aluminum foil, thereby further improving the cycle life and storage life of the battery.

[0035] In some embodiments, the fluorinated cyclic carbonate includes at least one of fluoroethylene carbonate and bisfluoroethylene carbonate, which can effectively form a film on a silicon surface, suppress interfacial rupture, and improve the life of the secondary battery.

[0036] Furthermore, the fluorinated cyclic carbonate includes fluoroethylene carbonate, which is a chemical substance that forms a better-performing SEI film and a dense structure layer without increasing impedance, and can prevent further decomposition of the electrolyte and improve the low-temperature properties of the electrolyte, thereby further improving the life of the secondary battery.

[0037] In some embodiments, the electrolyte solution further comprises a solvent, and the solvent comprises at least one of ethylene carbonate, propylene carbonate, fluorobenzene, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl acetate, and methyl formate. The above materials are excellent organic solvents, and the use of at least one of the above organic solvents can improve the cycle life and storage life of the battery.

[0038] Ethylene carbonate (EC) is an organic solvent with excellent dissolving properties for various polymers and is used in lithium battery electrolytes. Propylene carbonate is an excellent medium for high-energy batteries and capacitors, and has stable properties. Dimethyl carbonate, abbreviated as DMC, is a colorless, transparent liquid with a pungent odor at room temperature. It has a relative density (d204) of 1.0694, a melting point of 4°C, a boiling point of 90.3°C, a flash point of 21.7°C (open cup) and 16.7°C (closed cup), and a refractive index of 1.3687. It is flammable and non-toxic. It is miscible with almost all organic solvents, including alcohols, ketones, and esters, in any ratio and is slightly soluble in water. Compared to other methylation reagents, dimethyl carbonate is less toxic and biodegradable. Ethyl methyl carbonate, also known as ethyl methyl carbonate, is a colorless, transparent liquid that is insoluble in water and can be used in organic synthesis. It is also an excellent solvent for lithium-ion battery electrolytes.

[0039] In some embodiments, the electrolyte solution further comprises a solvent, and the weight ratio of the solvent in the electrolyte solution is 20% to 60%, such as 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc. The above weight ratios can improve the cycle life and storage life of the battery.

[0040] In some embodiments, the electrolyte solution further comprises an additive, the additive comprising at least one of vinylene carbonate, ethylene sulfate, 1,3-propane sultone, lithium difluorooxalatoborate, lithium bisoxalatoborate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, and lithium difluorophosphate, which has the effect of assisting film formation.

[0041] In some embodiments, the negative electrode active material further comprises at least one of natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, and soft carbon. By doping the carbon-based materials with silicon, the energy density of the secondary battery can be effectively improved.

[0042] The above-mentioned negative electrode active material, conductive agent, thickener, and binder are dissolved in water and mixed uniformly to obtain a negative electrode slurry. The negative electrode slurry is then coated onto a negative electrode current collector, baked, cold-pressed, edge-cut, thinly sliced, and slit, and then baked under vacuum conditions to produce a negative electrode sheet.

[0043] The electrolyte solution can be prepared by the following method. In an argon-filled glove box (water content <10 ppm, oxygen content <1 ppm), the fluorinated cyclic carbonate and additives are added to an organic solvent (e.g., ethylene carbonate:ethyl methyl carbonate = 3:7 W% / W%) and mixed uniformly. After that, an appropriate amount of LiPF6 and fluorine-containing lithium sulfonylimide (LiFSI) are slowly added to the non-aqueous organic solvent until the lithium salt is completely dissolved, and the target electrolyte solution is obtained.

[0044] In some embodiments, the secondary battery further includes a positive electrode sheet containing a positive electrode material, the positive electrode material further includes a positive electrode active material, and the active material contained in the positive electrode independently is 1) LiNi x Co y N z M 1-x-y-z O2 (where N is selected from Mn and Al, M is any one selected from Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, 0 ≦ x < 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, and x + y + z ≦ 1), 2) LiMn2O4, Li2MnO3·(1 - a)LiPO2 (P = Ni, Co, Mn) (where 0 < a < 1), and may be at least one of them, or may be a positive electrode material obtained by mixing the above two materials in any ratio. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector.

[0045] As an example, the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is provided on either one or both of the two opposing surfaces of the positive electrode current collector.

[0046] In some embodiments, a metal foil or a composite current collector can be used as the positive electrode current collector. For example, an aluminum foil can be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material base (such as a base of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0047] In some embodiments, the positive electrode sheet can be manufactured as follows: The components for manufacturing the positive electrode sheet described above, such as the positive electrode active material, conductive agent, binder, and other optional components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, which is then coated onto a positive electrode current collector, followed by baking, cold pressing, and other processes to obtain the positive electrode sheet.

[0048] The secondary battery further includes a separator. Specifically, the separator includes a base film and a coating layer coated on the base film. The coating layer may further include an adhesive layer, a ceramic layer, or the like.

[0049] During charging and discharging, active ions are inserted and removed between the positive and negative electrode sheets. The electrolyte serves to conduct ions between the positive and negative electrode sheets. The separator, located between the positive and negative electrode sheets, primarily serves to prevent short-circuiting between the positive and negative electrodes while allowing ions to pass through.

[0050] The battery cell can be manufactured by a method commonly used in this field. For example, a battery cell can be produced by forming a positive electrode sheet, a negative electrode sheet, and a separator into an electrode assembly by a winding process or a lamination process, and then injecting an electrolyte into the electrode assembly and sealing it.

[0051] In some embodiments, the battery cell may include an outer casing, which can be used to package the electrode assembly and electrolyte.

[0052] In some embodiments, the battery cell exterior may be a hard case, such as a hard plastic case, an aluminum case, or a steel case. The battery cell exterior may be a soft pack, such as a soft bag. The soft pack may be made of plastic, such as polypropylene, polybutylene terephthalate, or polybutylene succinate.

[0053] In the present application, the shape of the battery cell is not particularly limited, and may be cylindrical, rectangular, or any other shape.

[0054] The battery may be specifically expressed in the form of a battery module or a battery pack, and the number of battery cells included in the battery module may be one or more, and the specific number can be selected by those skilled in the art depending on the application and capacity of the battery module.

[0055] A battery module is formed by electrically connecting a certain number of secondary batteries and setting them in a frame to protect the battery cells from external shock, heat, vibration, etc. A typical battery module generally includes two end plates, with multiple battery cells (lithium-ion batteries) arranged between the two end plates. The end plate provided with the output electrode of the battery module is also called the output electrode end plate, and the end plate not provided with the output electrode of the battery module is also called the non-output electrode end plate.

[0056] In some battery production and processing techniques, multiple battery cells are first integrated into a battery module, and then the battery module is packaged in a battery box to form a battery pack. A battery pack may include multiple battery modules packaged in a single row, or multiple battery modules packaged in multiple rows. The arrangement of the multiple battery modules in multiple rows may be two rows and multiple columns, multiple rows and two columns, multiple rows and multiple columns, etc. Taking a battery pack with two rows and multiple columns of battery modules as an example, the first end plate in each column is generally the top output end plate, the two adjacent end plates between the two rows of battery modules are middle non-output end plates, and the last end plate in each column is the rear non-output end plate. The top output end plate and one of the middle non-output end plates belong to the battery modules in the first row, and one of the middle non-output end plates and the rear output end plate belong to the battery modules in the second row.

[0057] In a second aspect, the present application provides an electrical device comprising the secondary battery described in the above examples.

[0058] The electric devices provided in the present application include, but are not limited to, mobile phones, portable devices, laptops, battery cars, electric vehicles, ships, aircraft, electric toys, and power tools. For example, aircraft include airplanes, rockets, space shuttles, and spaceships, and electric toys include stationary or portable electric toys such as game consoles, electric vehicle toys, electric ship toys, and electric plane toys, and power tools include metal cutting power tools, polishing power tools, assembly power tools, and railroad power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact power drills, concrete vibrators, and electric planers.

[0059] The electric device provided in the present application includes the secondary battery in the above embodiment and has all the beneficial effects of the above secondary battery, which will not be described here one by one. [Example]

[0060] The technical solution of the present invention will be described in more detail below with reference to specific examples. It should be understood that the following examples are only used to explain the present invention, and are not intended to limit the present invention.

[0061] The parameter settings for the secondary batteries in the examples and comparative examples are as shown in Table 1 below.

[0062] [Table 1]

[0063] The manufacturing process of the lithium ion batteries of the Examples and Comparative Examples is as follows.

[0064] [Electrolyte production] In a glove box filled with argon (water content <10 ppm, oxygen content <1 ppm), fluoroethylene carbonate and lithium difluorophosphate were added to an organic solvent (ethylene carbonate:ethyl methyl carbonate = 3:7 W% / W%) and mixed uniformly. After that, an appropriate amount of LiPF6 and LiFSI were slowly added to the non-aqueous organic solvent until the lithium salts were completely dissolved, and the target electrolyte solution was obtained.

[0065] [Production of positive electrode sheets] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, the conductive agent Super P, and the binder polyvinylidene fluoride (PVDF) were mixed in N-methylpyrrolidone (NMP) to form a positive electrode slurry. The solid content of the positive electrode slurry was 50 wt%, and the LiNi 0.5 Co 0.2 Mn 0.3 The mass ratio of O2, Super P, and PVDF was 8:1:1. The positive electrode slurry was applied to an aluminum foil current collector, baked at 85°C, cold-pressed, then edged, sliced, and slit, and baked at 85°C under vacuum for 4 hours to produce a positive electrode sheet.

[0066] [Manufacturing of negative electrode sheets] The negative electrode slurry was prepared by uniformly mixing graphite (as the negative electrode active material), silicon, the conductive agent Super P, the thickener CMC, and the binder styrene-butadiene rubber (SBR) with deionized water. The solid content of the negative electrode slurry was 30 wt%, and the mass ratio of graphite, Super P, CMC, and the binder styrene-butadiene rubber (SBR) in the solids was 80:15:3:2. The negative electrode slurry was applied to a copper foil current collector, baked at 85°C, cold-pressed, edge-cut, sliced, and slit, and then baked at 120°C under vacuum for 12 hours to prepare a negative electrode sheet.

[0067] [Lithium-ion battery manufacturing] A 16 μm polyethylene film (PE) was used as the separator. The prepared positive electrode sheet, separator, and negative electrode sheet were stacked in order so that the separator was between the positive electrode sheet and the negative electrode sheet and served to separate the positive and negative electrodes, and then wound to obtain a bare cell. The tabs were welded, the bare cell was set in an outer casing, and the above-prepared electrolyte was injected into the dried cell. After packaging, standing, chemical conversion, molding, and capacity testing, the lithium-ion battery (soft-pack lithium-ion battery: thickness 4.0 mm, width 60 mm, length 140 mm) was completed.

[0068] Here, C1 / C2 in Example 11 was outside the range of the examples of the present application, W2 / W1 and C1 / C2 in Comparative Example 1 were both outside the range of the examples of the present application, and W2 / W1 in Comparative Example 2 was outside the range of the examples of the present application.

[0069] [Battery performance test] (1) Cycle performance test of lithium-ion batteries The ambient temperature was adjusted to 25°C, and the lithium-ion battery was charged at 1C to 4.25V, then charged at a constant voltage of 0.05C, left to stand for 10 minutes, and discharged at 1C to 2.8V. The discharge capacity C0 was recorded, and 300 cycles were performed according to the above charge-discharge process. The discharge capacity at the 300th cycle was C1, and the cycle capacity retention rate of the lithium-ion battery = C1 / C0*100%.

[0070] (2) High-temperature storage life test for lithium-ion batteries At 25°C, the lithium-ion battery was charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 0.05C until the current reached 0.05C. After leaving the battery for 10 minutes, it was discharged at 1C to 2.8V, and the discharge capacity D0 was recorded. The lithium-ion battery was then placed in a 60°C incubator and kept warm for 60 days. The lithium-ion battery was then removed and, after the surface temperature of the lithium-ion battery returned to room temperature, it was discharged at 1C to 2.8V. After that, it was charged at 1C to 4.25V, charged at a constant voltage of 0.05C, left to stand for 10 minutes, and discharged at 1C to 2.8V, and the discharge capacity D1 was recorded. The high temperature storage life of the lithium-ion battery = D1 / D0*100%.

[0071] The measurement results are shown in Table 2.

[0072] [Table 2]

[0073] As can be seen from the test results in Table 2, the overall performance of Examples 1 to 11 was improved compared to the cycle performance and high-temperature storage life obtained in the tests of Comparative Examples 1 and 2. This indicates that the overall performance of the cell is excellent when the content of fluorinated cyclic carbonate in the electrolyte and the silicon content of the negative electrode satisfy a certain relationship, and when the lithium salt in the electrolyte also satisfies a certain relationship.

[0074] In Example 11, the lithium salt content in the electrolyte did not satisfy the corresponding relationship of 0.25≦C1 / C2≦5, so the HF content in the electrolyte was high, further attacking the SEI film. Ultimately, a severe reduction reaction of the electrolyte at the anode interface occurred, resulting in a large consumption of active lithium. As a result, the cycle and storage life were both inferior to those of the Examples. However, the fluorinated cyclic carbonate content and the silicon content of the anode satisfied the specific relationship of 0.1W1≦W2≦0.7W1, so the cycle and storage life were better than those of Comparative Examples 1 and 2.

[0075] In Comparative Example 1, the content of the fluorinated cyclic carbonate and the silicon content of the anode did not satisfy the specific relationship 0.1W1≦W2≦0.7W1, which meant that the anode could not effectively form a film on the surface of the silicon anode, causing the anode to swell and the SEI to rupture during charging. Furthermore, the content of the lithium salt in the electrolyte did not satisfy the corresponding relationship 0.25≦C1 / C2≦5, resulting in a high content of HF generated in the electrolyte, which further attacked the SEI film. Ultimately, the electrolyte caused a violent reduction reaction at the anode interface, resulting in a large consumption of active lithium, resulting in inferior cycle and shelf life compared to the Examples.

[0076] In Comparative Example 2, the content of the fluorinated cyclic carbonate and the silicon content of the negative electrode did not satisfy the specific relationship 0.1W1≦W2≦0.7W1, so they could not effectively participate in film formation on the surface of the silicon anode, causing the negative electrode to expand and the SEI to rupture during charging, resulting in inferior cycle and shelf life compared to the Examples. However, the content of the lithium salt in the electrolyte satisfied the corresponding relationship 0.25≦C1 / C2≦5, resulting in better cycle and shelf life compared to Comparative Example 1.

[0077] In summary, in the secondary battery provided herein, when the content of fluorinated cyclic carbonate in the electrolyte (W2%) and the silicon content in the anode satisfy the relationship 0.1W1≦W2≦0.7W1, a film can be effectively formed on the surface of the silicon-containing material. When W2 is less than 0.1W1, the W2 content is too low to effectively cover the entire surface of the silicon-containing material. When W2 is greater than 0.7W1, a film can be effectively formed at the interface of the silicon-containing material, but the excess fluorinated cyclic carbonate not involved in the film formation is likely to be oxidized at the cathode and produce gas. When the contents of the fluorinated cyclic carbonate in the electrolyte and the silicon-containing material in the anode satisfy the above specific relationship, a film can be effectively formed on the surface of the silicon-containing material, interfacial rupture can be suppressed, and the cycle life and storage life of the battery can be improved.

[0078] The above is merely a preferred embodiment of the present invention, and does not limit the scope of the claims of the present invention. Those skilled in the art can make various modifications and variations to the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the patent protection scope of the present invention.

Claims

1. a negative electrode active material and an electrolyte solution, the negative electrode active material includes a silicon-containing material, The mass proportion of the silicon-containing material in the negative electrode active material is W1%; the electrolyte solution contains a fluorinated cyclic carbonate; The mass proportion of the fluorinated cyclic carbonate in the electrolyte solution is W2%; A secondary battery characterized in that 0.1W1≦W2≦0.7W1.

2. 1%≦W1%≦50%, and / or 2. The secondary battery according to claim 1, wherein 0.5%≦W2%≦25%.

3. 2%≦W1%≦25%; and / or 2. The secondary battery according to claim 1, wherein 1%≦W2%≦20%.

4. The electrolyte is LiPF ６ and further comprising a fluorine-containing lithium sulfonylimide; In the electrolyte, LiPF ６ The molar concentration of is C1, The molar concentration of the fluorine-containing lithium sulfonylimide is C2; 2. The secondary battery according to claim 1, wherein 0.25≦C1 / C2≦5.

5. 0.2 mol / L≦C1≦1 mol / L, and / or 5. The secondary battery according to claim 4, wherein 0.2 mol / L≦C2≦0.9 mol / L.

6. 5. The secondary battery according to claim 4, wherein the fluorine-containing lithium sulfonylimide includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium fluoro(trifluoromethylsulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

7. the fluorinated cyclic carbonate comprises at least one of fluoroethylene carbonate and bisfluoroethylene carbonate; and / or 2. The secondary battery according to claim 1, wherein the silicon-containing material includes at least one of silicon dioxide, silicon, and silicon monoxide.

8. 2. The secondary battery according to claim 1, wherein the electrolyte further comprises a solvent, the solvent comprising at least one of ethylene carbonate, propylene carbonate, fluorobenzene, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl acetate, and methyl formate.

9. 2. The secondary battery according to claim 1, wherein the electrolytic solution further contains a solvent, and the mass ratio of the solvent in the electrolytic solution is 20% to 60%.

10. 2. The secondary battery of claim 1, wherein the electrolyte further contains an additive, and the additive includes at least one of vinylene carbonate, ethylene sulfate, 1,3-propane sultone, lithium difluorooxalatoborate, lithium bisoxalatoborate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, and lithium difluorophosphate.

11. The secondary battery of claim 1 , wherein the negative electrode active material further comprises at least one of natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, and soft carbon.

12. An electrical device comprising the secondary battery according to any one of claims 1 to 11.

Images