Secondary battery and device

Abstract

Provided are a secondary battery and a device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte solution, wherein the negative electrode sheet comprises a negative electrode active material layer and a negative electrode solid electrolyte interfacial film on a surface of the negative electrode active material layer. As tested by means of an X-ray photoelectron spectrometer, the mass percentage content of sulfur in the negative electrode solid electrolyte interfacial film is Z%; the negative electrode active material layer comprises a negative electrode active material, and a carbon coating layer is provided on a surface of the negative electrode active material; in correspondence to every 100 g of the negative electrode active material, Y g of the carbon coating layer is contained; the electrolyte solutio comprises vinylene carbonate and a sulfur-containing additive; in correspondence to every 100 g of the negative electrode active material, T g of the vinylene carbonate is added to the electrolyte solution; and the secondary battery satisfies: 0.5≤Y / T+Z / 50≤2.6. By regulating and controlling the corresponding vinylene carbonate content relative to the negative electrode active material per unit, the amount of carbon coating on the surface of the negative electrode active material and the sulfur content of the negative electrode solid electrolyte interfacial film, the film-forming stability of the negative electrode sheet is improved, the impedance of the secondary battery is reduced, the cycle life of the secondary battery is prolonged, and the low-temperature performance of the secondary battery is improved.

Description

Secondary batteries and devices

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 13, 2023, with application number 202311717222.0 and application name “Secondary Batteries and Devices”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of energy storage, and in particular to a secondary battery and device. Background Art

[0003] Lithium-ion batteries are widely used in smartphones, unmanned aerial vehicles, hybrid electric vehicles, etc. However, with the development of society, low-energy-density lithium-ion batteries can no longer meet the demand. The development of high-capacity / high-safety battery systems has become the development direction of high-energy-density lithium-ion batteries.

[0004] Lithium iron phosphate batteries are widely used in power and energy storage batteries due to their excellent thermal stability. However, in high-energy scenarios, the high density of the electrode leads to a significant decline in the kinetic performance of the battery cell, increasing the risk of lithium plating during charge and discharge. This problem limits the application of lithium iron phosphate batteries in high-energy scenarios. Furthermore, the degree of matching between the electrolyte and the negative electrode material also affects the transport of lithium ions at the negative electrode / electrolyte interface. A poor match reduces lithium ion conductivity, increases the risk of lithium plating in the battery cell, and shortens the cycle life of the lithium-ion battery.

[0005] Therefore, in order to meet society's demand for high-energy-density batteries and solve the problems of lithium iron phosphate batteries in high-energy scenarios, it is necessary to develop a new type of battery system, in which the matching of electrolyte and negative electrode materials and their interaction with positive electrode materials need to be deeply studied.

[0006] Summary of the Invention

[0007] In view of the above-mentioned problems in the prior art, this application proposes a secondary battery and device. This application improves the stability of the negative electrode film formation and reduces lithium deposition at the negative electrode by regulating the relationship between the vinylene carbonate content per unit of negative electrode active material, the carbon coating on the surface of the negative electrode active material, and the sulfur content in the negative electrode solid electrolyte interface film. This reduces the overall impedance of the secondary battery and improves the cycle life and low-temperature performance of the secondary battery.

[0008] A first aspect of the present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate and an electrolyte, the negative electrode plate includes a negative electrode active material layer and a negative electrode solid electrolyte interface membrane located on the surface of the negative electrode active material layer; using an X-ray photoelectron spectrometer to test, the mass percentage of sulfur element in the negative electrode solid electrolyte interface membrane is Z%; the negative electrode active material layer includes a negative electrode active material, and the surface of the negative electrode active material has a carbon coating layer; every 100g of the negative electrode active material corresponds to Yg of the carbon coating layer; the electrolyte contains vinylene carbonate and a sulfur-containing additive; every 100g of the negative electrode active material corresponds to Tg of vinylene carbonate added to the electrolyte; the secondary battery satisfies: 0.5≤Y / T+Z / 50≤2.6.

[0009] A second aspect of the present application provides a device including the aforementioned secondary battery.

[0010] The technical solution of this application can achieve the following beneficial effects:

[0011] This application regulates the relationship between the vinylene carbonate content corresponding to the unit negative electrode active material, the carbon coating amount on the surface of the negative electrode active material, and the sulfur content in the negative electrode solid electrolyte interface film to meet specific limiting conditions, so as to improve the negative electrode film formation stability, reduce the negative electrode lithium precipitation, and thus reduce the overall impedance of the secondary battery, and improve the cycle life and low temperature performance of the secondary battery. The reason is that the lithium precipitation of the battery core is strongly related to the cycle performance. Within a limited range, by increasing the sulfur content in the negative electrode solid electrolyte interface film (SEI), the interface impedance of the SEI film can be effectively reduced, and the lithium precipitation of the battery core can be reduced; increasing the carbon coating content on the negative electrode surface can increase the ion / electron transfer rate at the electrode / electrolyte interface and reduce the lithium ion diffusion impedance, thereby reducing the high rate lithium precipitation situation; by reducing the ethylene carbonate content in the electrolyte, the thickness and polymer content of the SEI film can be effectively reduced, thereby reducing the lithium ion crossing the SEI energy barrier and reducing the high rate lithium precipitation situation. DETAILED DESCRIPTION

[0012] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of this application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of this application. The embodiments of this application should not be interpreted as limiting this application.

[0013] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0014] In the description herein, unless otherwise specified, “above” and “below” include the number itself.

[0015] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0016] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0017] Primary and secondary batteries

[0018] One or more embodiments of the present application provide a secondary battery, which includes a positive electrode plate, a negative electrode plate and an electrolyte, the negative electrode plate includes a negative electrode active material layer and a negative electrode solid electrolyte interface membrane located on the surface of the negative electrode active material layer; using an X-ray photoelectron spectrometer to test, the mass percentage of sulfur element in the negative electrode solid electrolyte interface membrane is Z%; the negative electrode active material layer includes a negative electrode active material, and the surface of the negative electrode active material has a carbon coating layer; every 100g of the negative electrode active material corresponds to Yg of the carbon coating layer; the electrolyte contains vinylene carbonate and a sulfur-containing additive; every 100g of the negative electrode active material corresponds to Tg of vinylene carbonate added to the electrolyte; the secondary battery satisfies: 0.5≤Y / T+Z / 50≤2.6.

[0019] The present application regulates the relationship between the vinylene carbonate content corresponding to the unit negative electrode active material, the carbon coating amount on the surface of the negative electrode active material, and the sulfur content in the negative electrode solid electrolyte interface film to meet the above conditions, thereby improving the film formation stability of the negative electrode sheet, reducing lithium plating on the negative electrode sheet, and thereby reducing the overall impedance of the secondary battery and improving the cycle life and low-temperature performance of the secondary battery.

[0020] In some embodiments, Y / T+Z / 50 is 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, or a range consisting of any two of the above values.

[0021] In some embodiments, 1.0≤Y / T+Z / 50≤2.2. Within this defined range, the sulfur-containing component in the SEI film replaces the polymer component generated by vinylene carbonate (VC), reducing the SEI film impedance. At the same time, the increased carbon content on the surface of the negative electrode active material can effectively accelerate the lithium ion migration rate, reduce lithium plating in the battery cell, and further improve the cycle life and low-temperature energy retention of the secondary battery.

[0022] In some embodiments, 1.5≤T≤2.5. By limiting the content of vinylene carbonate (VC) corresponding to the unit negative electrode active material, a stable and low-impedance negative electrode solid electrolyte interface film (SEI) is formed on the negative electrode sheet. Reducing the content of vinylene carbonate can improve the low-temperature performance of the secondary battery, but it will affect the cycle life of the secondary battery; and too high a content of vinylene carbonate will lead to the occurrence of lithium plating on the negative electrode sheet, and will seriously reduce the cycle life of the secondary battery. Therefore, in order to take into account the low-temperature performance, cycle life and lithium plating of the secondary battery, this application limits the content of vinylene carbonate (VC) corresponding to the unit negative electrode active material to the above reasonable range, thereby ensuring the cycle life and low-temperature performance of the secondary battery. In some embodiments, T is 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5 or a range consisting of any two of the above values. In some embodiments, 1.5≤T≤2.4.

[0023] In some embodiments, 1.5≤Y≤4.0. If the carbon coating layer is too thick, it will lead to a large loss of active lithium during the first cycle of charge and discharge of the battery; if the carbon coating layer is too thin, it will lead to insufficient interface dynamics of the negative electrode plate, and lithium plating will occur at high rates of the battery cell; controlling the amount of carbon coating on the surface of the negative electrode active material within the above range can accelerate the transfer process of lithium ions between the negative electrode particles, maximize the lithium ion conductivity in the battery cell, reduce the occurrence of lithium plating, and improve the cycle life and low temperature performance of the battery cell. In some embodiments, Y is 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0 or a range consisting of any two of the above values. In some embodiments, 2≤Y≤3.5.

[0024] In some embodiments, 0.01≤Z≤15. In the SEI film, if the sulfur content Z is too high, the corresponding polymer component will be reduced, the mechanical properties of the SEI will be reduced, and the long-cycle performance will be affected; if the sulfur content Z is too low, the impedance of the SEI film will increase, the energy barrier for lithium ions to cross the SEI will increase, and the risk of lithium plating in the battery cell will increase; controlling the sulfur content Z within the above range is beneficial to taking into account both excellent SEI film mechanical properties and moderate lithium ion crossing energy barriers, and achieving high-rate long-cycle of the battery cell. In some embodiments, Z is 0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 4, 6, 8, 10, 12, 14, 15 or a range consisting of any two of the above values. In some embodiments, 5≤Z≤10.

[0025] In some embodiments, the sulfur-containing additive includes at least one of a sulfonate, a sulfate, and a sulfite. The sulfur-containing additive can improve the composition and structure of the SEI film, making the SEI film impedance lower and more stable. This can effectively inhibit the contact between the electrolyte and the negative electrode active material, which would cause continuous side reactions and electrolyte consumption, and reduce the energy barrier for lithium ion crossover, thereby extending the cycle life of the secondary battery.

[0026] In some embodiments, the sulfonate ester includes at least one of 1,3-propane sultone (1,3-PS), 1-propylene-1,3-sultone (PST), and 1,4-butane sultone (1,4-BS).

[0027] In some embodiments, the sulfate ester includes at least one of diethyl sulfate (DTD), 4-methylethylene sulfate (PCS), 4-ethylethylene sulfate (PES), 4-propylethylene sulfate (PEGLST), and propylene sulfate (TS).

[0028] In some embodiments, the sulfite includes at least one of ethylene sulfite (DTO), dimethyl sulfite (DMS), and diethyl sulfite (DES).

[0029] In some embodiments, the mass content of the sulfur-containing additive is 0.05% to 5%. In some embodiments, the mass content of the sulfur-containing additive is 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or any value therebetween. In some embodiments, the mass content of the sulfur-containing additive is 0.1% to 3%.

[0030] In some embodiments, the electrolyte further comprises other additives, including at least one of a fluorine-containing cyclic carbonate and a fluorine-containing lithium salt. In some embodiments, the other additives comprise at least one of fluoroethylene carbonate, lithium difluorophosphate, and lithium difluorooxalatoborate. These other additives can synergistically optimize the composition and mechanical properties of the SEI film, thereby improving the long-term cycling stability of the SEI film.

[0031] In some embodiments, the weight content of other additives is 0.05% to 10% based on the weight of the electrolyte. In some embodiments, the weight content of other additives is 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of the above values. In some embodiments, the weight content of other additives is 0.1% to 8%.

[0032] In some embodiments, the electrolyte further includes a lithium salt, the lithium salt including at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0033] In some embodiments, the electrolyte further includes a non-aqueous solvent, and the non-aqueous solvent includes at least one of a chain carbonate compound, a cyclic carbonate compound, and a carboxylate compound.

[0034] In some embodiments, the linear carbonate compound includes, but is not limited to, one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), or ethylmethyl carbonate (MEC).

[0035] In some embodiments, the cyclic carbonate compound includes, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC).

[0036] In some embodiments, the carboxylate compound includes, but is not limited to, one or more of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerolactone, or caprolactone.

[0037] In some embodiments, the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, carbon nanotubes, graphene, silicon, silicon alloys, silicon oxides, silicon carbon compounds, metallic lithium, and lithium titanate.

[0038] In some embodiments, the negative electrode active material layer further includes a binder and a conductive agent. The binder includes, but is not limited to: at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon. The conductive agent includes, but is not limited to: at least one of carbon-based materials, metal-based materials, conductive polymers and mixtures thereof. In some embodiments, the carbon-based material includes natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber or any combination thereof. In some embodiments, the metal-based material includes metal powder, metal fiber, copper, nickel, aluminum or silver. In some embodiments, the conductive polymer includes a polyphenylene derivative.

[0039] In some embodiments, the negative electrode plate further includes a negative electrode current collector, which includes at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0040] In some embodiments, the positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material. The positive electrode active material includes at least one of a lithium iron phosphate material, a lithium cobalt oxide material, and a nickel cobalt material. In some embodiments, the lithium iron phosphate material includes Li x Fe y R (1-y) At least one of PO4 materials, wherein R includes at least one of Mn, Co, Ti, Mg, Ca, Cr, Cu, Ni, V, Mo, Zn, Al, B and Nb, 0.05≤x≤1.2, 0<y≤1. In some embodiments, the lithium cobalt oxide material includes Li 1+z Co 1-j-k Maj Mb k At least one of the O2 materials, wherein Ma is at least one of Al, Ga, Hf, Mg, Sn, Zn, and Zr; Mb is at least one of Ni, Mn, V, Mo, Nb, Cu, Fe, In, W, and Cr, 0≤j≤0.01, 0≤k≤0.01, -0.05≤z≤0.08. In some embodiments, the nickel-cobalt material includes Li a Ni m Co n A (1-m-n) At least one of the O2 materials, wherein A comprises at least one of Mn, Al, Mg, Cr, Ca, Zr, Mo, Ag or Nb, 0.9≤a≤1.2, 0.5≤m≤1, 0≤n≤0.5, and m+n≤1.

[0041] In some embodiments, the positive electrode active material is preferably a lithium iron phosphate material, such as LiFePO4. When the positive electrode active material is a lithium iron phosphate material, better negative electrode sheet film formation characteristics can be achieved by adapting the relationship between the vinylene carbonate content per unit of negative electrode active material in the electrolyte of the system, the carbon coating amount on the surface of the negative electrode active material, and the sulfur content in the negative electrode solid electrolyte interface film.

[0042] In some embodiments, the positive electrode active material layer further includes a binder, and optionally a conductive material. The binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector.

[0043] In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.

[0044] In some embodiments, the conductive material includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0045] In some embodiments, the positive electrode sheet further includes a positive electrode current collector, which can be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0046] In some embodiments, a separator is provided between the positive and negative electrode sheets to prevent short circuits. The material and shape of the separator used in the embodiments of the present application are not particularly limited and may be any known prior art material. In some embodiments, the separator comprises a polymer or inorganic material, for example, formed from a material that is stable to the electrolyte of the present application.

[0047] In some embodiments, the isolation film includes a base film and a coating disposed on the base film. The base film includes at least one of a polyethylene film, a polypropylene film, a PP / PE / PP composite film, a polyimide film, an aramid film, a polyethylene terephthalate film, or a non-woven fabric. In some embodiments, the coating includes at least one of a polymer layer, an inorganic ceramic layer, or a hybrid layer of a polymer and an inorganic ceramic layer.

[0048] In some embodiments, the inorganic ceramic layer includes inorganic particles and a binder, wherein the inorganic particles include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.

[0049] The polymer layer includes a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0050] In some embodiments, a method for preparing a secondary battery includes providing an electrode assembly, injecting a solution, encapsulating, and forming a battery. In some embodiments, the forming temperature is 40° C. to 50° C., for example, 40° C., 41° C., 42° C., 43° C., 44° C., 45° C., 46° C., 47° C., 48° C., 49° C., 50° C., or a range consisting of any two of the foregoing values.

[0051] In some embodiments, the formation includes: charging at a constant current of 0.05C for 120 minutes, charging at a constant current and constant voltage of 0.1C to 3.8V, and discharging at 0.2C to 2.3V at a temperature of 40°C-50°C, for example, 45°C, and a pressure of 130kgf-300kgf, for example, 210kgf.

[0052] In some embodiments, the secondary battery is a lithium secondary battery or a sodium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0053] In some embodiments, the secondary battery may include an outer packaging, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0054] In some embodiments, the shape of the secondary battery is not particularly limited and can be cylindrical, square, or any other shape.

[0055] In some embodiments, the present application also provides a battery module. The battery module includes the aforementioned secondary battery. The battery module of the present application utilizes the aforementioned secondary battery and therefore has at least the same advantages as the secondary battery. The battery module of the present application may include multiple secondary batteries, the specific number of which can be adjusted based on the application and capacity of the battery module.

[0056] In some embodiments, the present application further provides a battery pack comprising the aforementioned battery module. The number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0057] 2. Device

[0058] The present application also provides a device comprising at least one of the above-mentioned secondary battery, battery module or battery pack.

[0059] In some embodiments, the device includes, but is not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, etc. To meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0060] In other embodiments, the device may be a mobile phone, a tablet computer, a laptop computer, etc. The device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0061] Hereinafter, the secondary battery of the present application will be further described in combination with specific embodiments and comparative examples.

[0062] Examples and Comparative Examples

[0063] Hereinafter, the present application will be described in more detail with reference to Examples and Comparative Examples. However, the present application is not limited to these Examples unless departing from the gist of the present application.

[0064] The materials and solvents used in the following examples were all commercially available.

[0065] Example 1

[0066] Preparation of positive electrode sheet: The positive electrode active material LiFePO4, conductive agent conductive carbon black (superP), and binder polyvinylidene fluoride (PVDF) are fully slurried in an N-methylpyrrolidone (NMP) solvent system in a weight ratio of LiFePO4:SuperP:PVDF = 97:1.5:1.5, and then evenly coated on both surfaces of a positive electrode current collector aluminum foil with a thickness of 12 μm, dried, and roll-pressed to obtain a positive electrode sheet.

[0067] Preparation of negative electrode sheet: The negative electrode active material artificial graphite, conductive agent superP, CMC, and PAA are fully homogenized in deionized water in a weight ratio of artificial graphite:superP:CMC:PAA=96:2:1:1, and then coated on both surfaces of the negative electrode current collector copper foil with a thickness of 8μm. After drying, rolling, and striping, the negative electrode sheet is obtained.

[0068] Preparation of electrolyte: In a nitrogen-protected glove box (water <1 ppm, oxygen <1 ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC:DMC:EMC = 20:15:49.5, and lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L (mass percentage of 12.5%). Based on the total mass of the electrolyte, 1.5% of vinylene carbonate (VC), 0.5% of vinyl sulfate (DTD), and 1% of fluoroethylene carbonate (FEC) were added, and the mixture was stirred evenly to obtain the electrolyte.

[0069] Separator: A PE porous polymer film with a thickness of 11 μm was used as the separator.

[0070] Preparation of lithium-ion batteries: The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator located between the positive and negative electrode sheets, and then wound to obtain a bare cell; the bare cell is placed in an aluminum-plastic film outer package, vacuum-baked at 75°C for 48 hours, and after being fully dried, the prepared lithium-ion battery electrolyte is injected. The battery is vacuum-sealed, left to stand at room temperature for 12 hours and at 45°C for 12 hours, and then subjected to a capacity-composition step to obtain a lithium-ion battery. Among them, the formation and capacity separation steps include: charging at a constant current of 0.05C for 120 minutes at a temperature of 45°C and a pressure of 147kgf, charging at a constant current of 0.1C for 60 minutes, and charging at a constant current of 0.33C for 54 minutes. After the formation is completed, standing at 45°C for 24 hours, charging at a constant current and constant voltage of 0.5C to 3.8V, discharging at a constant current of 0.33C to 2.3V, charging at a constant current and constant voltage of 0.5C to 3.8V, and discharging at 0.33C to 2.3V, and cycling twice to complete the capacity separation.

[0071] Example 2-10

[0072] Examples 2-10 were achieved based on Example 1 by adjusting the type of positive electrode active material, the type and content of the sulfur-containing additive in the electrolyte, the content of vinylene carbonate, the type and content of other additives, the carbon coating amount of the negative electrode active material, and the sulfur content in the SEI solid electrolyte membrane. Specific adjustment measures and detailed data are shown in Table 1. The rest of the preparation method is the same as that of Example 1.

[0073] Comparative Example 1

[0074] Comparative Example 1 differs from Example 1 in the preparation of the electrolyte: in a nitrogen-protected glove box (moisture <1 ppm, oxygen <1 ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC:DMC:EMC = 20:15:46.25, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L (mass percentage of 12.5%), and based on the total mass of the electrolyte, 5% vinylene carbonate (VC), 0.25% vinyl sulfate (DTD), and 1% fluoroethylene carbonate (FEC) were added, and the mixture was stirred to obtain an electrolyte. The other preparation methods were the same as those in Example 1.

[0075] Comparative Examples 2-7

[0076] Comparative Examples 2-7 were achieved based on Comparative Example 1 by adjusting the type of positive electrode active material, the type and content of the sulfur-containing additive in the electrolyte, the content of vinylene carbonate, the type and content of other additives, the carbon coating amount of the negative electrode active material, and the sulfur content in the SEI solid electrolyte membrane. Specific adjustment measures and detailed data are shown in Table 1. The other preparation methods are the same as those in Example 1.

[0077] Test Method

[0078] 1. X-ray photoelectron spectrometer (XPS) test

[0079] The lithium-ion battery was discharged at a current of 0.1C to 2.3V and then disassembled in an argon-filled glove box to obtain the electrode sheet. The resulting electrode sheet was cut into 8mm×8mm test samples and soaked and cleaned in a low-boiling-point dimethyl carbonate (DMC) solvent for half an hour. After complete drying, it was attached to the XPS sample stage with the surface of the negative electrode active material layer facing away from the current collector facing upward. Measurements were performed without exposure to the atmosphere.

[0080] The specific test conditions and steps are as follows: single crystal spectroscopy AlKα rays are used, as for the X-ray point, an elliptical form of 1000×1750 μm with an output of 10 KV and 22 mA is used, 284.8 eV is used for neutral carbon C1s, and as for data processing such as peak differentiation, 3-point smoothing, peak area measurement, background subtraction and peak synthesis are used to calculate the atoms of each component.

[0081] 2. -20℃ energy retention test

[0082] At room temperature (25°C), the lithium-ion battery was charged to 3.8V at 0.1C constant current and constant voltage, then discharged to 2.3V at 0.1C constant current for three cycles. The average discharge energy data was recorded as the room temperature discharge energy S1. The battery was then placed at -20°C, charged to 3.8V at 0.1C constant current and constant voltage, then discharged to 2.3V at 0.1C constant current. The low temperature discharge energy S2 was recorded, and the energy retention rate was calculated as S2 / S1.

[0083] 3. Normal temperature cycle life test

[0084] At room temperature (25°C), the lithium-ion battery was charged to 3.8 V at 1 C constant current and constant voltage, and then discharged to 2.3 V at 1 C constant current. When the capacity was less than 80% of the initial capacity, the cycle was stopped and the number of cycles was recorded.

[0085] 4. Battery cell DC resistance DCR test

[0086] The lithium-ion battery that has been cycled 100 times in the cycle capacity retention test is adjusted to the target SOC with a current of 0.33C and left to rest for 30 minutes. The voltage V0 at this time is recorded as the OCV of the corresponding SOC. The battery is discharged with a discharge current I1 for t seconds, and the voltage V1 at the tth second is recorded. The DCR is calculated using the calculation formula for the discharge DC internal resistance, which is DCR = (V0-V1) / I1.

[0087] 5. Negative electrode lithium plating test

[0088] After 300 cycles, the lithium-ion battery was charged to 3.8V at 1C constant current and constant voltage, and then the fully charged cell was disassembled to observe the lithium deposition at the negative electrode.

[0089] Please see Table 1 below for test data.

[0090] Table 1

[0091] It can be seen from the data comparison results of Examples 1-10 and Comparative Examples 1-7 in Table 1 that the present application regulates the relationship between the vinylene carbonate content (T) corresponding to the unit negative electrode active material, the carbon coating amount (Y) on the surface of the negative electrode active material, and the sulfur content (Z%) in the negative electrode solid electrolyte interface film to satisfy 0.5≤Y / T+Z / 50≤2.6. Within this limited range, there is no lithium deposition or slight lithium deposition on the negative electrode plate, the overall impedance of the secondary battery is significantly reduced, the number of cycles is more than 1700 cycles, and the energy retention rate at low temperature is significantly improved. The reason is that the lithium plating of the battery cell is strongly correlated with the cycle performance. Within a limited range, by increasing the sulfur content (Z%) in the solid electrolyte interface (SEI) of the negative electrode, the interface impedance of the SEI film can be effectively reduced, and the lithium plating of the battery cell can be reduced; increasing the carbon coating content (Y) on the surface of the negative electrode plate can increase the ion / electron transfer rate at the electrode / electrolyte interface, reduce the lithium ion diffusion impedance, and thus alleviate the high-rate lithium plating; by reducing the ethylene carbonate content (T) in the electrolyte, the thickness and polymer content of the SEI film can be effectively reduced, thereby reducing the energy barrier for lithium ions to cross the SEI and alleviating the high-rate lithium plating.

[0092] It can be seen from Examples 1-5 and 6-10 that the present application regulates the relationship between the vinylene carbonate content (T) corresponding to the unit negative electrode active material, the carbon coating amount (Y) on the surface of the negative electrode active material, and the sulfur content (Z%) in the negative electrode solid electrolyte interface film to satisfy 1.0≤Y / T+Z / 50≤2.2. Within this limited range, there is no lithium plating on the negative electrode pole piece, the overall impedance of the secondary battery is further reduced, the number of cycles is above 2100, and the energy retention rate at low temperature is further improved. The reason is that, within the limited range, the sulfur-containing component in the SEI film replaces the polymer component produced by vinylene carbonate (VC), reducing the SEI film impedance. At the same time, the increase in the carbon content on the surface of the negative electrode active material can effectively accelerate the lithium ion migration rate, reduce lithium plating of the battery cell, and further improve the cycle life and low-temperature energy retention rate of the secondary battery.

[0093] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that some modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. A secondary battery, characterized in that: The secondary battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a negative electrode active material layer and a negative electrode solid electrolyte interface film located on the surface of the negative electrode active material layer; and the mass percentage of sulfur element in the negative electrode solid electrolyte interface film is Z% as measured by an X-ray photoelectron spectrometer; The negative electrode active material layer comprises a negative electrode active material, and a carbon coating layer is provided on the surface of the negative electrode active material; and every 100g of the negative electrode active material corresponds to Yg of the carbon coating layer; The electrolyte comprises vinylene carbonate and a sulfur-containing additive; Tg vinylene carbonate is added to the electrolyte for every 100g of negative electrode active material; The secondary battery satisfies: 0.5≤Y / T+Z / 50≤2.

6.

2. The secondary battery according to claim 1, characterized in that: The secondary battery further satisfies at least one of the following conditions: (1) 1.0≤Y / T+Z / 50≤2.2; (2)1.5≤T≤2.5； (3)1.5≤Y≤4.0； (4)0.01≤Z≤15。 3. The secondary battery according to any one of claims 1 or 2, characterized in that: The secondary battery further satisfies at least one of the following conditions: (1)1.5≤T≤2.4； (2)2≤Y≤3.5； (3)5≤Z≤10。 4. The secondary battery according to any one of claims 1 or 2, characterized in that: The sulfur-containing additive includes at least one of sulfonate, sulfate and sulfite; based on the mass of the electrolyte, the mass content of the sulfur-containing additive is 0.05% to 5%.

5. The secondary battery according to claim 4, characterized in that: The sulfonate ester includes at least one of methylene methanedisulfonate, 1,3-propane sultone, 1-propylene-1,3-sultone and 1,4-butane sultone; and / or, The sulfate ester includes at least one of vinyl sulfate, 4-methylethylene sulfate, 4-ethylethylene sulfate, 4-propylethylene sulfate and propylene sulfate; and / or, The sulfite includes at least one of ethylene sulfite, dimethyl sulfite and diethyl sulfite.

6. The secondary battery according to any one of claims 1 or 2, characterized in that: The electrolyte further includes other additives, which include at least one of fluorine-containing cyclic carbonate and fluorine-containing lithium salt; based on the mass of the electrolyte, the mass content of the other additives is 0.05% to 10%.

7. The secondary battery according to claim 6, characterized in that: The other additives include at least one of fluoroethylene carbonate, lithium difluorophosphate and lithium difluorooxalatoborate.

8. The secondary battery according to any one of claims 1 or 2, characterized in that: The positive electrode plate includes a positive electrode active material, and the positive electrode active material includes at least one of a lithium iron phosphate material, a lithium cobalt oxide material, and a nickel cobalt material; The lithium iron phosphate material includes Li x Fe y R (1-y) At least one of PO4 materials, wherein R comprises at least one of Mn, Co, Ti, Mg, Ca, Cr, Cu, Ni, V, Mo, Zn, Al, B and Nb elements, 0.05≤x≤1.2, 0<y≤1; and / or, The lithium cobalt oxide material includes Li 1+z Co 1-j-k Ma j Mb k O2 materials, wherein Ma is at least one of Al, Ga, Hf, Mg, Sn, Zn and Zr; Mb is at least one of Ni, Mn, V, Mo, Nb, Cu, Fe, In, W and Cr, 0≤j≤0.01, 0≤k≤0.01, -0.05≤z≤0.08; and / or, The nickel-cobalt material includes Li a Ni m Co n A (1-m-n) At least one of O2 materials, wherein A includes at least one of Mn, Al, Mg, Cr, Ca, Zr, Mo, Ag or Nb, 0.9≤a≤1.2, 0.5≤m≤1, 0≤n≤0.5, m+n≤1.

9. The secondary battery according to any one of claims 1 or 2, characterized in that: The negative electrode active material includes at least one of graphite, soft carbon, hard carbon, carbon nanotubes, graphene, silicon, silicon alloys, silicon oxides, silicon carbon compounds, metallic lithium and lithium titanate; and / or, The electrolyte also includes a non-aqueous solvent and a lithium salt, wherein the non-aqueous solvent includes at least one of a chain carbonate compound, a cyclic carbonate compound and a carboxylate compound; and the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

10. A device, characterized in that: The device includes the secondary battery according to any one of claims 1 to 9.

Images