Secondary battery and electric device

Abstract

The application discloses a secondary battery and an electric device, the secondary battery comprising an electrolyte, the electrolyte comprising propylene carbonate and a cyclic sulfur ester, the cyclic sulfur ester comprising one or more of compounds represented by formula I, formula II and formula III: wherein M1 and M2 independently comprise at least one of a monocyclic sulfur ester, an H atom, a halogen atom, a substituted or unsubstituted C1-C10 hydrocarbon group, a phenyl group, a carbonyl group, a carboxyl group, an ester group, a nitrile group and an ether group; the mass percentage of the propylene carbonate is 2-50% and the mass percentage of the cyclic sulfur ester is 0.005-5% based on the total mass of the electrolyte. By adjusting the content of the propylene carbonate and the type and content of the cyclic sulfur ester within a suitable range, a stable SEI film can be formed, the peeling of PC solvent from graphite is reduced, the low-temperature performance of the secondary battery is improved, and the cycle performance of the secondary battery is improved.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to secondary batteries and electrical equipment. Background Technology

[0002] Batteries are not only used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of battery applications, market demand is also constantly increasing. Propylene carbonate (PC) in the electrolyte can co-intercalate with lithium ions. The continuous embedding of solvated lithium ions into graphite causes the graphite layered structure to collapse, reducing the lifespan of the secondary battery. Summary of the Invention

[0003] A first aspect of this application provides a secondary battery comprising an electrolyte, the electrolyte comprising propylene carbonate and a cyclic thioester, the cyclic thioester comprising one or more compounds represented by formulas I, II, and III:

[0004]

[0005] Wherein, M1 and M2 independently include at least one of the following: monocyclic thioester, H atom, halogen atom, substituted or unsubstituted C1-C10 hydrocarbon group, phenyl, carbonyl, carboxyl, ester group, nitrile group, and ether group;

[0006] Based on the total mass of the electrolyte, the mass percentage of propylene carbonate is 2%-50%, and the mass percentage of cyclic thioesters is 0.005%-5%. By keeping the content of propylene carbonate, the type and content of cyclic thioesters within appropriate ranges, a stable SEI film can be formed, reducing the stripping of graphite by PC solvent, thereby improving both the low-temperature performance and cycle performance of the secondary battery.

[0007] According to some embodiments of this application, the monocyclic thioester includes one or more compounds represented by formulas IV, V, and VI:

[0008]

[0009] R1, R2, and R3 independently include H atoms, halogen atoms, substituted or unsubstituted C1-C10 hydrocarbon groups, phenyl groups, carbonyl groups, carboxyl groups, ester groups, nitrile groups, and ether groups, respectively. Therefore, binary or ternary cyclic thioesters exhibit higher reactivity than monocyclic thioesters, enabling them to rapidly interact during the initial charge-discharge process and participate in interfacial film formation.

[0010] According to some embodiments of this application, the cyclic thioester comprises:

[0011]

[0012] One or more of these components. Therefore, they participate in the film formation on the negative electrode surface, reducing the stripping of graphite by the PC solvent, thus improving both the low-temperature performance and cycle performance of the secondary battery.

[0013] According to some embodiments of this application, the cyclic thioester accounts for 0.1%-1.5% of the total mass of the electrolyte. This improves the cycle performance of the secondary battery while reducing the thickness of the SEI film, lowering the interfacial impedance, and enhancing the kinetic performance of the secondary battery.

[0014] According to some embodiments of this application, the electrolyte further includes ethylene carbonate (EC), wherein the mass percentage of ethylene carbonate is 0.5%-20% based on the total mass of the electrolyte. The combined use of EC and PC can improve the ionic conductivity of the electrolyte.

[0015] According to some embodiments of this application, the electrolyte further includes fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is 0.5%-20% based on the total mass of the electrolyte. By keeping the EC content within the above range, the ionic conductivity of the electrolyte can be improved while maintaining the low-temperature performance of the secondary battery.

[0016] According to some embodiments of this application, the electrolyte further includes phosphate ester additives, which include one or two compounds represented by formula VII and formula VIII:

[0017]

[0018] R4, R5, and R6 independently include H atoms, halogen atoms, substituted or unsubstituted C1-C10 hydrocarbon groups, silyl groups, siloxane groups, silazane groups, phenyl groups, carbonyl groups, carboxyl groups, ester groups, nitrile groups, and ether groups, respectively. Phosphate ester additives can reduce the acidity of the system, reduce acid damage to the interfacial film and corrosion of the positive and negative electrode active materials, and improve the life of the secondary battery.

[0019] According to some embodiments of this application, the phosphate ester additive includes:

[0020]

[0021] One or more of the above-mentioned phosphate ester additives can reduce the acidity of the system, reduce acid damage to the interfacial film and corrosion of the positive and negative electrode materials, and improve the life of the secondary battery.

[0022] According to some embodiments of this application, the phosphate ester additive accounts for 0.005%-5% of the total mass of the electrolyte. This reduces acid corrosion of the interface film and positive and negative electrode materials, while also lowering interfacial impedance and minimizing the impact on the kinetic performance of the secondary battery.

[0023] According to some embodiments of this application, the secondary battery further includes a negative electrode sheet, which includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector. The negative active material layer includes a negative active material, which includes a silicon-based material and graphite. This improves the energy density and cycle performance of the secondary battery.

[0024] According to some embodiments of this application, the silicon-based material includes one or more of nano-silicon, micron-silicon, silicon-oxygen materials, and silicon-carbon materials. This improves the energy density of the secondary battery.

[0025] According to some embodiments of this application, the mass ratio of silicon to carbon in the silicon-carbon material is 0.6-1.5. This improves the energy density and cycle performance of the secondary battery.

[0026] According to some embodiments of this application, the silicon-based material includes silicon-carbon material, and the mass percentage of the silicon-carbon material is 1%-90% based on the total mass of the negative electrode active material layer. This improves the energy density of the secondary battery.

[0027] According to some embodiments of this application, the silicon-based material includes silicon-carbon material, and the mass percentage of the silicon-carbon material is 10%-50% based on the total mass of the negative electrode active material layer. This balances the energy density and cycle life of the secondary battery.

[0028] According to some embodiments of this application, the electrolyte further includes an electrolyte salt, which includes one or more of LiPF6, LiFSI, LiTFSI, LiBF4, LiBOB, LiDFOB, LiAsF6, and LiClO4. This improves the ionic conductivity of the electrolyte.

[0029] The second aspect of this application provides an electrical device, including the secondary battery provided in the first aspect of this application.

[0030] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0031] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0032] Figure 1 This is a schematic diagram of a battery according to one embodiment of this application.

[0033] Figure 2 yes Figure 1 An exploded view of a battery according to one embodiment of this application is shown.

[0034] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0035] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0036] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0037] Figure 6 This is a schematic diagram of an electrical device in which a battery is used as a power source according to one embodiment of this application.

[0038] Explanation of reference numerals in the attached figures:

[0039] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0040] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0041] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0042] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0043] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0044] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0045] Currently, judging from market trends, battery applications are becoming increasingly widespread. Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of battery applications, market demand is also constantly increasing.

[0046] Propylene carbonate (PC) in the electrolyte can co-intercalate with lithium ions. As solvated lithium ions continuously intercalate into graphite, the graphite layered structure collapses, and the solvent continues to decompose, reducing the lifespan of the secondary battery.

[0047] This application proposes a secondary battery. Propylene carbonate in the electrolyte can improve the low-temperature charge / discharge and rate performance of the secondary battery. However, due to the easy co-intercalation of Li and PC during charging, the solvated lithium ions intercalating into graphite can cause the graphite structure to collapse, reducing the cycle life of the secondary battery. This application adds cyclic sulfides to the electrolyte. Cyclic sulfides can participate in the film formation at the negative electrode interface, generating interfacial components of sulfates, sulfites, and sulfur-containing organic compounds, which block the contact between the PC solvent and the electrode material, thereby effectively reducing the exfoliation of graphite by PC. The inorganic coating of sulfates and sulfites can improve the lithium-ion conductivity of the electrode interface, reduce interfacial impedance, and improve the fast-charging performance of the battery. By controlling the content of cyclic sulfides, a stable interfacial film can be formed while reducing interfacial impedance, thus reducing the impact on the kinetic performance of the secondary battery.

[0048] In summary, this application achieves a balance between the cycle performance and storage performance of secondary batteries by keeping the types and contents of propylene carbonate and cyclic thioesters within a suitable range.

[0049] The secondary battery proposed in this application can be used in electrical devices that use secondary batteries as a power source or in various energy storage systems that use secondary batteries as energy storage elements. Electrical devices can include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0050] A first aspect of this application provides a secondary battery comprising an electrolyte, the electrolyte comprising propylene carbonate and a cyclic thioester, the cyclic thioester comprising one or more compounds represented by formulas I, II, and III:

[0051]

[0052] Wherein, M1 and M2 independently include at least one of the following: monocyclic thioester, H atom, halogen atom, substituted or unsubstituted C1-C10 hydrocarbon group, phenyl, carbonyl, carboxyl, ester group, nitrile group, and ether group;

[0053] Based on the total mass of the electrolyte, the mass percentage of propylene carbonate is 2%-50%, and the mass percentage of cyclic thioesters is 0.005%-5%.

[0054] In this application, after disassembling the secondary battery to obtain the electrolyte, the organic components of the electrolyte can be qualitatively analyzed by gas chromatography, referring to GB / T9722-2023 "General Rules for Gas Chromatography of Chemical Reagents". For example, using a GC-MS 3100 organic component gas chromatograph, the diluted electrolyte solution is placed in the instrument for full-scan positioning. After the test, a total ion current chromatogram of each organic compound is obtained. The corresponding organic compound type is identified based on the peak position of the chromatogram, and the corresponding mass percentage of each organic compound is calculated based on the peak area. The calculated mass of propylene carbonate and cyclic thioesters is divided by the mass of the electrolyte sample to obtain the mass percentage. It can be understood that the mass percentage of propylene carbonate and cyclic thioesters in the secondary battery electrolyte is slightly lower than the added mass percentage of propylene carbonate and cyclic thioesters in the secondary battery electrolyte.

[0055] As an example, the mass percentage of propylene carbonate is 2%, 10%, 20%, 30%, 40%, 50%, etc., or can be any range of the above values.

[0056] As an example, the mass percentage of cyclic thioesters can be 0.005%, 0.05%, 0.5%, 1%, 2%, 3%, 4%, 5%, etc., or can be any range of the above values. By keeping the content of cyclic thioesters within the above range, the thickness of the SEI film can be reduced while decreasing the peeling of graphite by PC, thereby reducing the negative electrode interface impedance and improving the kinetic performance of the secondary battery.

[0057] According to some specific embodiments of this application, the mass percentage of the cyclic thioester is 0.1%-1.5% based on the total mass of the electrolyte.

[0058] In this application, the term "halogen atom" includes one or more of fluorine, chlorine, and iodine atoms.

[0059] This application improves the low-temperature charge-discharge and rate performance of secondary batteries by keeping the content of propylene carbonate within the above-mentioned range. At the same time, adding 0.005%-5% cyclic thioester to the electrolyte can reduce the insertion of solvated lithium ions into graphite and the reversible insertion and extraction of lithium ions in the graphite electrode, thereby improving the cycle performance of secondary batteries.

[0060] According to some embodiments of this application, the monocyclic thioester includes one or more compounds represented by formulas IV, V, and VI:

[0061]

[0062] R1, R2, and R3 independently include H atoms, halogen atoms, substituted or unsubstituted C1-C10 hydrocarbon groups, phenyl groups, carbonyl groups, carboxyl groups, ester groups, nitrile groups, and ether groups, respectively. Therefore, binary or ternary cyclic thioesters exhibit higher reactivity, enabling rapid film formation during the first charge-discharge cycle of the secondary battery, further improving interfacial stability, effectively protecting electrode materials, and enhancing the cycle stability of the secondary battery.

[0063] For binary and ternary cyclic thioesters, a greater number of active sites are beneficial for the formation of cross-linked polymer structures. When the negative electrode active material includes silicon-based materials, it can better cope with the volume expansion and contraction of the negative electrode and improve the cycle performance of the secondary battery.

[0064] As an example, the cyclic thioesters include:

[0065]

[0066] One or more of them.

[0067] The aforementioned types of monocyclic sulfides, binary cyclic sulfides, and ternary cyclic sulfides can effectively reduce the stripping of graphite by PC and improve the cycle performance of secondary batteries.

[0068] According to some specific embodiments of this application, the electrolyte further includes ethylene carbonate (EC), and the mass percentage of ethylene carbonate is 0.5%-20% based on the total mass of the electrolyte. Ethylene carbonate can improve the ionic conductivity of the electrolyte, and when used in combination with PC, it can further reduce the stripping of graphite by PC. By keeping the EC content within the above range, the viscosity of the electrolyte can be reduced, and the low-temperature performance of the secondary battery can be improved.

[0069] As an example, the mass percentage of EC can be 0.5%, 10%, 15%, 20%, etc., or a range of any of the above values.

[0070] According to some embodiments of this application, the electrolyte further includes fluoroethylene carbonate (FEC), and the mass percentage of FEC is 0.5%-20% based on the total mass of the electrolyte. FEC can form an inorganic SEI film containing lithium fluoride and a cross-linked polymer, effectively repairing the SEI film during secondary battery cycling. By keeping the FEC content within the above range, the risk of FEC reacting with lithium hexafluorophosphate to generate acidic substances and damaging the SEI film can be reduced.

[0071] As an example, the mass percentage of FEC can be 0.5%, 1%, 5%, 10%, 15%, 20%, etc., or a range of any of the above values.

[0072] According to some embodiments of this application, the electrolyte further includes phosphate ester additives, which include one or two compounds represented by formula VII and formula VIII:

[0073]

[0074] R4, R5, and R6 independently include H atoms, halogen atoms, substituted or unsubstituted C1-C10 hydrocarbon groups, silyl groups, siloxane groups, silazane groups, phenyl groups, carbonyl groups, carboxyl groups, ester groups, nitrile groups, and ether groups, respectively. Phosphate ester additives can effectively complex hydrogen atoms in HF and H2O while participating in film formation, reducing electrolyte acidity, minimizing damage to the SEI film, and improving the cycle life of the secondary battery.

[0075] In this application, the substituted C1-C10 hydrocarbon groups can be substituted by halogen atoms.

[0076] According to some embodiments of this application, the phosphate ester additive includes:

[0077]

[0078] One or more of them.

[0079] According to some embodiments of this application, the mass percentage of the phosphate ester additive is 0.005%-5% based on the total mass of the electrolyte. For example, it can be 0.005%, 0.05%, 0.5%, 1%, 2%, 3%, 4%, 5%, etc., or it can be a range of any of the above values.

[0080] In this application, the test methods for organic components in the electrolyte can all refer to the qualitative and quantitative detection methods for propylene carbonate and cyclic thioesters, and will not be repeated here.

[0081] The electrolyte also includes an electrolyte salt, which comprises one or more of LiPF6, LiFSI, LiTFSI, LiBF4, LiBOB, LiDFOB, LiAsF6, and LiClO4. This improves the ionic conductivity of the electrolyte.

[0082] The secondary battery also includes a negative electrode sheet, which includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector. The negative active material layer includes a negative active material, which includes silicon-based material and graphite. The combination of silicon-based material and graphite as the active material of the negative electrode can improve the cycle performance and energy density of the secondary battery.

[0083] When the negative electrode active material contains silicon-based materials, the silicon-based materials have a large volume effect. This application improves the stability of the SEI film by simultaneously adding propylene carbonate and cyclic sulfides to the electrolyte and keeping the content of cyclic sulfides within a suitable range, thereby reducing the risk of the SEI film cracking due to silicon expansion and improving the cycle performance of the secondary battery.

[0084] According to some embodiments of this application, the silicon-based material includes one or more of nano-silicon, micron-silicon, silicon-oxygen materials, and silicon-carbon materials. This improves the energy density of the secondary battery.

[0085] According to some embodiments of this application, the silicon-based material includes silicon-carbon material to reduce the volume expansion of the negative electrode and improve the cycle performance of the secondary battery.

[0086] In this application, the silicon-carbon material includes porous carbon and nano-silicon deposited in the pores of the porous carbon, wherein the number of mesopores in the porous carbon accounts for more than or equal to 50%, and the number of micropores accounts for less than 50%.

[0087] Mesopores refer to pores with a diameter of 2nm-10nm, while micropores refer to pores with a diameter of 0.2nm-2nm.

[0088] According to some embodiments of this application, the mass ratio of silicon to carbon in the silicon-carbon material is 0.6-1.5. This improves the energy density of the secondary battery while reducing the volume expansion of the negative electrode and minimizing damage to the SEI film.

[0089] As an example, the mass ratio of silicon to carbon can be 0.6, 0.8, 1, 1.3, 1.5, or any range of the above values.

[0090] In this application, the negative electrode sheet is obtained by disassembling a single battery cell. The ratio of silicon-carbon to graphite in the negative electrode sheet is tested as follows: First, the negative electrode sheet is cut into 6mm × 6mm pieces and attached to an ion polishing machine. It is then cut at 7.5kV for 30 minutes, perpendicular to the large surface of the electrode sheet. The sheet is then tested and observed using a Sigma300 scanning electron microscope with energy dispersive spectroscopy (EDS) according to the JY / T010-1996 testing standard. The images show that the dark particles are graphite and the bright particles are silicon. The elemental content ratio of silicon-carbon is obtained by selecting a single silicon particle for testing. Then, a large area is selected (the selection area size is defined) for whole-area elemental testing to obtain the ratio of (graphite + carbon) to silicon. The final calculation yields the mass ratio of graphite to silicon-carbon.

[0091] According to some embodiments of this application, the silicon-based material includes silicon-carbon material, and the mass percentage of the silicon-carbon material is 1%-90% based on the total mass of the negative electrode active material layer. Specifically, this can be adjusted to balance the energy density and cycle performance of the secondary battery.

[0092] As an example, the mass percentage of the silicon-carbon material can be 1%, 10%, 30%, 60%, 90%, etc., or can be any range of the above values.

[0093] According to some embodiments of this application, the silicon-based material includes silicon-carbon material, and the mass percentage of the silicon-carbon material is 10%-50% based on the total mass of the negative electrode active material layer.

[0094] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0095] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0096] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0097] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0099] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0100] Secondary batteries also include a positive electrode.

[0101] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes the positive active material of the first aspect of this application.

[0102] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0103] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0104] In some embodiments, when the battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0105] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0106] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0107] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0108] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0109] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0110] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0111] In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0112] In some implementations, the battery's outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The battery's outer packaging can also be a soft pack, such as a pouch. The soft pack can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0113] This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0114] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0115] In some implementations, the batteries can be assembled into battery modules, and the number of batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0116] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0117] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0118] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0119] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0120] In addition, this application also provides an electrical device, which includes at least one of the battery, battery module, or battery pack provided in this application. The battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0121] As the electrical equipment, batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0122] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density batteries, a battery pack or battery module can be used.

[0123] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can be powered by a battery.

[0124] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0125] Example 1

[0126] 1. Preparation of positive electrode sheet

[0127] An 8μm thick aluminum foil was used as the positive electrode current collector. The positive electrode active material, LiNi, was used. 0.8 Co 0.1 Mn 0.1O2 (NCM811), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are dissolved in solvent N-methylpyrrolidone (NMP) at a weight ratio of 93:2:5. After thorough stirring and mixing, a positive electrode slurry is obtained. The positive electrode slurry is then uniformly coated onto the positive electrode current collector, and after drying, cold pressing, and slitting, a positive electrode sheet is obtained.

[0128] 2. Preparation of negative electrode sheet

[0129] The negative electrode active material, conductive carbon black, and binder polyacrylic acid are mixed in a mass ratio of 8:1:1. The negative electrode active material includes silicon-carbon composite material and graphite. Based on the total mass of the negative electrode active material, the mass ratio of silicon-carbon composite material is 30% and the mass ratio of graphite is 70%. Deionized water is added and the mixture is stirred thoroughly to form a negative electrode slurry. The negative electrode slurry is uniformly coated on one surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0130] 3. Separating membrane

[0131] Polyethylene film is used as the separator.

[0132] 4. Preparation of electrolyte

[0133] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed evenly. Then, cyclic thioester type I-1, phosphate ester additive type VII-2, fluoroethylene carbonate (FEC), and electrolyte salt lithium hexafluorophosphate (LiPF6) are added and mixed evenly. Finally, fully dried electrolyte salt LiPF6 is added.

[0134] Based on the total mass of the electrolyte, PC accounts for 2%, EC accounts for 23%, EMC accounts for 16.5%, DMC accounts for 32.5%, cyclic thioester type I-1 accounts for 1%, phosphate ester additive type VII-2 accounts for 0.5%, FEC accounts for 12%, and LiPF6 accounts for 12.5%.

[0135] 5. Assembly of secondary batteries

[0136] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a barrier between the positive and negative electrodes. They are then wound to obtain a bare cell. Tabs are welded onto the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product.

[0137] The preparation methods of the secondary batteries in Examples 2-25 and Comparative Examples 1-4 are the same as those in Example 1, with the differences detailed in Table 1.

[0138]

[0139]

[0140] Performance testing

[0141] 1. Cyclic performance

[0142] At 25°C, the secondary batteries (full cells) prepared in the examples and comparative examples were charged to 4.25V at 0.33C and then discharged to 2.5V at 0.5C. This constitutes one charge-discharge cycle, and the discharge capacity at this point is recorded as the initial discharge capacity. The secondary batteries were then subjected to the same charge-discharge cycle test, and the discharge capacity after each cycle was recorded until the discharge capacity of the secondary battery decreased to 80% of the initial discharge capacity. The number of cycles at this point was recorded.

[0143] 2.60℃ storage life

[0144] At 25°C, the secondary batteries prepared in each embodiment and comparative example were charged at a constant current rate of 0.33C to the charging cutoff voltage of 4.25V, then charged at a constant voltage rate until the current ≤0.05C, and allowed to stand for 5 minutes. They were then discharged at a constant current rate of 0.33C to the discharging cutoff voltage of 2.5V, and allowed to stand for 5 minutes. This constituted one charge-discharge cycle. The batteries were then charged at a constant current rate of 0.33C to the charging cutoff voltage of 4.25V, then charged at a constant voltage rate until the current ≤0.05C. After storing the batteries at 60°C for 100 days, cyclic charge-discharge tests were conducted on the batteries according to the above method, and the capacity retention rate of the lithium-ion batteries after 100 days of storage was calculated.

[0145] 3. Internal resistance test

[0146] At 25°C, the shipped lithium-ion batteries were charged to 4.25V at a constant current of 0.33C. Then, they were charged at a constant voltage of 4.25V until the current was less than 0.05C, and then discharged at 0.33C for 60 minutes, adjusting the battery capacity to 50% SOC. Next, the batteries were placed in a -20°C constant temperature chamber for 30 minutes. The positive and negative probes of a TH2523A AC internal resistance tester were connected to the positive and negative terminals of the battery, respectively, and the internal resistance value was read and recorded as the initial battery internal resistance (mΩ).

[0147] The test results of the secondary batteries in Examples 1-25 and Comparative Examples 1-4 are shown in Table 2.

[0148] Table 2

[0149]

[0150]

[0151] As can be seen from Examples 1-25 and Comparative Examples 1-4, the secondary battery proposed in this application has a smaller DC impedance, better cycle performance and storage life. This indicates that by controlling the content of propylene carbonate, the type and content of cyclic thioesters in the electrolyte, this application can block the contact between PC solvent and electrode material, thereby effectively reducing the peeling of graphite by PC and improving the cycle performance of the battery. In addition, it can also improve the lithium-ion conductivity of the electrode interface and reduce the interface impedance.

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, characterized in that, The electrolyte includes propylene carbonate and cyclic thioesters, the cyclic thioesters comprising one or more compounds represented by formulas I, II, and III: Wherein, M1 and M2 independently include at least one of the following: monocyclic thioester, H atom, halogen atom, substituted or unsubstituted C1-C10 hydrocarbon group, phenyl, carbonyl, carboxyl, ester group, nitrile group, and ether group; Based on the total mass of the electrolyte, the mass percentage of propylene carbonate is 2%-50%, and the mass percentage of cyclic thioesters is 0.005%-5%.

2. The secondary battery according to claim 1, characterized in that, The monocyclic thioesters include one or more compounds represented by formulas IV, V, and VI: Among them, R1, R2, and R3 independently include H atoms, halogen atoms, substituted or unsubstituted C1-C10 hydrocarbon groups, phenyl groups, carbonyl groups, carboxyl groups, ester groups, nitrile groups, and ether groups, respectively.

3. The secondary battery according to claim 1 or 2, characterized in that, The cyclic thioesters include: One or more of them.

4. The secondary battery according to any one of claims 1-3, characterized in that, Based on the total mass of the electrolyte, the cyclic thioester accounts for 0.1%-1.5% of the total mass.

5. The secondary battery according to any one of claims 1-4, characterized in that, The electrolyte also includes ethylene carbonate, and the mass percentage of ethylene carbonate is 0.5%-20% based on the total mass of the electrolyte.

6. The secondary battery according to any one of claims 1-5, characterized in that, The electrolyte also includes fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is 0.5%-20% based on the total mass of the electrolyte.

7. The secondary battery according to any one of claims 1-6, characterized in that, The electrolyte further includes phosphate ester additives, which include one or two compounds represented by formula VII and formula VIII: Among them, R4, R5, and R6 independently include H atoms, halogen atoms, substituted or unsubstituted C1-C10 hydrocarbon groups, silyl groups, siloxane groups, silazane groups, phenyl groups, carbonyl groups, carboxyl groups, ester groups, nitrile groups, and ether groups.

8. The secondary battery according to claim 7, characterized in that, The phosphate ester additives include: One or more of them.

9. The secondary battery according to claim 7 or 8, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the phosphate ester additive is 0.005%-5%.

10. The secondary battery according to any one of claims 1-9, characterized in that, The secondary battery further includes a negative electrode sheet, which includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector. The negative active material layer includes a negative active material, which includes silicon-based materials and graphite.

11. The secondary battery according to claim 10, characterized in that, The silicon-based material includes one or more of nano-silicon, micro-silicon, silicon-oxygen materials, and silicon-carbon materials.

12. The secondary battery according to claim 11, characterized in that, The mass ratio of silicon to carbon in the silicon-carbon material is 0.6-1.

5.

13. The secondary battery according to any one of claims 10-12, characterized in that, The silicon-based material includes silicon-carbon material, and the mass percentage of the silicon-carbon material is 1%-90% based on the total mass of the negative electrode active material layer.

14. The secondary battery according to any one of claims 10-13, characterized in that, The silicon-based material includes silicon-carbon material, and the mass percentage of the silicon-carbon material is 10%-50% based on the total mass of the negative electrode active material layer.

15. The secondary battery according to any one of claims 1-14, characterized in that, The electrolyte also includes an electrolyte salt, which includes one or more of LiPF6, LiFSI, LiTFSI, LiBF4, LiBOB, LiDFOB, LiAsF6, and LiClO4.

16. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1-15.

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