Electrochemical device and electronic device

Abstract

The present application discloses an electrochemical device and an electronic device. The electrochemical device comprises a positive electrode sheet and a negative electrode sheet. The positive electrode sheet comprises a positive electrode material; the positive electrode material comprises a sodium element and a lithium element; and on the basis of the mass of the positive electrode sheet, the mass ratio of the sodium element ranges from 0.2% to 3%. The negative electrode sheet comprises a negative electrode material; the negative electrode material comprises a sodium element; and on the basis of the mass of the negative electrode sheet, the mass ratio of the sodium element ranges from 0.05% to 1.2%. The electrochemical device of the present application has good low-temperature cycle performance and kinetic performance.

Description

Electrochemical devices and electronic devices Technical Field

[0001] This application relates to the field of electrochemistry, and more particularly to an electrochemical device and an electronic device. Background Technology

[0002] Lithium-ion batteries are currently widely used in consumer electronics, electric vehicles, and aerospace. Low-temperature performance and rate performance are key factors affecting battery applications. However, traditional lithium-ion batteries are prone to capacity decay, increased internal resistance, low efficiency, and high heat generation in low-temperature environments.

[0003] To address these issues, extensive research has been conducted at the positive and negative electrode material levels. For positive electrode materials, multivalent metal ion doping is employed to enhance conductivity and ion mobility, thereby improving battery performance. For negative electrode materials, a protective layer is coated onto the material surface to improve interfacial stability and suppress side reactions. However, these methods still face many challenges, such as insufficient uniformity of doped elements, limited coating stability, and complex fabrication processes.

[0004] Summary of the Invention

[0005] In view of this, this application provides an electrochemical device and an electronic device.

[0006] The first aspect of this application provides an electrochemical device, including a positive electrode and a negative electrode. The positive electrode includes a positive electrode material, which includes sodium and lithium elements, and the sodium element accounts for 0.2% to 3% of the total mass based on the mass of the positive electrode. The negative electrode includes a negative electrode material, which includes sodium elements, and the sodium element accounts for 0.05% to 1.2% of the total mass based on the mass of the negative electrode.

[0007] This application adds sodium to the cathode material. Since sodium ions have a larger radius than lithium ions, when sodium ions enter the lithium layer, they expand the interlayer spacing of the lithium layer, which is conducive to the diffusion of lithium ions and improves the diffusion kinetics of lithium ions in the cathode material. This results in the electrochemical device having good low-temperature cycling performance and kinetic performance (such as charge / discharge rate).

[0008] This application adds sodium to the negative electrode material, which undergoes reversible dissolution and deposition during the charge and discharge process of the electrochemical device, providing additional capacity to the electrochemical device. Sodium can also form more inorganic components on the surface of the negative electrode material, making the SEI film denser and more uniform, and improving the stability of the negative electrode material surface. Due to the presence of sodium, the desolvation process of lithium ions on the surface of the negative electrode material can be promoted, especially the desolvation capability at low temperature, thereby improving the low-temperature cycling performance and kinetic performance of the electrochemical device.

[0009] Based on the first aspect, in some possible implementations, the positive electrode material also includes boron, with the boron content ranging from 0.01% to 0.3% based on the mass of the positive electrode sheet.

[0010] This application adds boron to the cathode material and controls the mass ratio of boron to meet the above-mentioned range. Since boron forms on the surface of the cathode material, it reduces the side reactions between the cathode material and the electrolyte, improves the stability of the cathode material surface, and further enhances the low-temperature cycling performance of the electrochemical device.

[0011] Based on the first aspect, in some possible implementations, when the positive electrode is in a fully discharged state, the mass percentage of sodium is A% and the mass percentage of lithium is B%, based on the mass of the positive electrode, and the B / A ratio is 1.83 to 40.

[0012] This application further improves the low-temperature cycling performance and kinetic performance of the electrochemical device by controlling the mass ratio of lithium and sodium elements in the cathode material to meet the above-mentioned range.

[0013] Based on the first aspect, in some possible implementations, when the positive electrode is in a fully discharged state, the positive electrode material also includes lithium, and the mass percentage of lithium is 5.5% to 8% based on the mass of the positive electrode.

[0014] This application improves the low-temperature cycling performance and kinetic performance of the electrochemical device by controlling the mass ratio of lithium in the cathode material to meet the above range.

[0015] Based on the first aspect, in some possible implementations, when the positive electrode is in a fully discharged state, the positive electrode material also includes manganese, and the mass percentage of manganese is 24.43% to 30% based on the mass of the positive electrode.

[0016] This application improves the stability of the electrochemical device by adding manganese to the cathode material and controlling the mass ratio of manganese to meet the above-mentioned range. The added manganese maintains a stable +4 valence state and will not react with the electrolyte. This further enhances the low-temperature cycling performance of the electrochemical device.

[0017] Based on the first aspect, in some possible implementations, when the positive electrode is in a fully discharged state, the positive electrode material also includes nickel, and the mass percentage of nickel is 26.2% to 32% based on the mass of the positive electrode.

[0018] This application further improves the low-temperature cycling performance and kinetic performance of the electrochemical device by adding nickel to the cathode material and controlling the mass ratio of nickel to meet the above-mentioned range.

[0019] Based on the first aspect, in some possible embodiments, the negative electrode material includes graphite or silicon-based materials. This application uses graphite or silicon-based negative electrode materials, enabling the electrochemical device to have both high energy density and good low-temperature cycling performance.

[0020] Based on the first aspect, in some possible implementations, the negative electrode material also includes boron, with the boron content ranging from 0.02% to 0.1% by mass, depending on the mass of the negative electrode sheet.

[0021] This application further improves the low-temperature cycling performance and kinetic performance of the electrochemical device by adding boron to the negative electrode material and controlling the mass ratio of boron to meet the above-mentioned range.

[0022] Based on the first aspect, in some possible implementations, when the negative electrode is in a charged state, the mass percentage of sodium is 0.5% to 1.2% based on the mass of the negative electrode. This further improves the low-temperature cycling performance and kinetic performance of the electrochemical device.

[0023] Based on the first aspect, in some possible implementations, when the negative electrode is in the discharged state, the mass percentage of sodium is 0.07% to 0.4% based on the mass of the negative electrode. This further improves the low-temperature cycling performance and kinetic performance of the electrochemical device.

[0024] Based on the first aspect, in some possible implementations, when the negative electrode is in a fully discharged state, the mass percentage of sodium is X% based on the mass of the negative electrode; when the negative electrode is in a fully charged state, the mass percentage of sodium is Y% based on the mass of the negative electrode, wherein X / Y is 0.1 to 0.8.

[0025] Based on the first aspect, in some possible implementations, the negative electrode material also includes manganese, with the manganese content ranging from 0.001% to 0.04% by mass, depending on the mass of the negative electrode sheet.

[0026] This application further improves the low-temperature cycling performance and kinetic performance of the electrochemical device by adding manganese to the negative electrode material and controlling the mass ratio of manganese to meet the above-mentioned range.

[0027] Based on the first aspect, in some possible implementations, the negative electrode material also includes nickel, with the nickel content being 0.002% to 0.02% by mass, depending on the mass of the negative electrode sheet.

[0028] This application further improves the low-temperature cycling performance and kinetic performance of the electrochemical device by adding nickel to the negative electrode material and controlling the mass ratio of nickel to meet the above-mentioned range.

[0029] Based on the first aspect, in some possible implementations, an electrolyte is also included, comprising adiponitrile, fluoroethylene carbonate, and vinylene carbonate.

[0030] This application further improves the low-temperature cycling performance and kinetic performance of the electrochemical device by adding adiponitrile, fluoroethylene carbonate and vinylene carbonate to the electrolyte.

[0031] A second aspect of this application provides an electronic device including the aforementioned electrochemical device, which has good low-temperature cycling performance and kinetic performance, thus improving the service life of the electronic device. Detailed Implementation

[0032] The embodiments of this application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. The reagents and materials described in the following embodiments are all commercially available.

[0033] Electrochemical device

[0034] One embodiment of this application provides an electrochemical device, including a housing (such as a packaging bag) for accommodating a positive electrode, a separator, a negative electrode, and an electrolyte, as well as other components known in the field of electrochemistry. This application does not limit the scope of these other components. This application does not impose any particular limitation on the housing; it can be a housing known in the art, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag can be used. This application does not impose any particular limitation on the type of electrochemical device; it can include any device that performs an electrochemical reaction. The electrochemical device of this application exhibits excellent low-temperature cycling performance and kinetic performance.

[0035] Positive electrode sheet

[0036] The positive electrode includes a positive current collector and a positive electrode material layer disposed on the positive current collector. The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, including, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The positive electrode material layer includes a positive electrode material comprising sodium and lithium elements, wherein the mass percentage of sodium is 0.2% to 3% based on the mass of the positive electrode. For example, the mass percentage of sodium can be any value within the range of 0.2%, 1%, 1.02%, 1.04%, 1.08%, 1.09%, 1.1%, 1.17%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, or any value above.

[0037] This application adds sodium to the cathode material. Since sodium ions have a larger radius than lithium ions, when sodium ions enter the lithium layer, they expand the interlayer spacing of the lithium layer, which is conducive to the diffusion of lithium ions and improves the diffusion kinetics of lithium ions in the cathode material. This results in the electrochemical device having good low-temperature cycling performance and kinetic performance (such as charge / discharge rate).

[0038] In some embodiments, the positive electrode material further includes boron, with the boron content ranging from 0.01% to 0.3% by mass, based on the mass of the positive electrode sheet. For example, the boron content can be any value within the range of 0.01%, 0.03%, 0.05%, 0.07%, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.26%, 0.28%, 0.3%, or any of the above values.

[0039] This application adds boron to the cathode material and controls the mass ratio of boron to meet the above-mentioned range. Since boron forms on the surface of the cathode material, it reduces the side reactions between the cathode material and the electrolyte, improves the stability of the cathode material surface, and further enhances the low-temperature cycling performance of the electrochemical device.

[0040] In some embodiments, when the positive electrode is in a fully discharged state, the mass percentage of sodium is A%, the mass percentage of lithium is B%, and the B / A ratio is 1.83 to 40, based on the mass of the positive electrode. For example, B / A can be any value within the range of 1.83, 2, 5, 8, 10, 14, 16, 20, 24, 28, 30, 34, 36, 40, or any of the above values.

[0041] This application further improves the low-temperature cycling performance and kinetic performance of the electrochemical device by controlling the mass ratio of lithium and sodium elements in the cathode material to meet the above-mentioned range.

[0042] In some embodiments, when the positive electrode is in a fully discharged state, the positive electrode material further includes lithium, and the mass percentage of lithium is 5.5% to 8% based on the mass of the positive electrode. For example, the mass percentage of lithium can be any value within the range of 5.5%, 5.7%, 5.9%, 6%, 6.1%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.4%, 7.5%, 7.6%, 7.8%, 8%, or any value above.

[0043] This application improves the low-temperature cycling performance and kinetic performance of the electrochemical device by controlling the mass ratio of lithium in the cathode material to meet the above range.

[0044] In some embodiments, when the positive electrode is in a fully discharged state, the positive electrode material further includes manganese, and the mass percentage of manganese is 24.43% to 30% based on the mass of the positive electrode. For example, the mass percentage of manganese can be any value within the range of 24.43%, 25%, 26%, 27%, 28%, 29%, 30%, or any higher.

[0045] This application improves the stability of the electrochemical device by adding manganese to the cathode material and controlling the mass ratio of manganese to meet the above-mentioned range. The added manganese maintains a stable +4 valence state and will not react with the electrolyte. This further enhances the low-temperature cycling performance of the electrochemical device.

[0046] In some embodiments, when the positive electrode is in a fully discharged state, the positive electrode material further includes nickel, and the mass percentage of nickel is between 26.2% and 32% based on the mass of the positive electrode. For example, the mass percentage of nickel can be any value within the range of 26.2%, 27%, 27.5%, 28%, 28.5%, 29%, 29.5%, 30%, 30.5%, 31%, 31.5%, 32%, or any value above.

[0047] This application further improves the low-temperature cycling performance and kinetic performance of the electrochemical device by adding nickel to the cathode material and controlling the mass ratio of nickel to meet the above-mentioned range.

[0048] In some embodiments, the positive electrode material layer further includes an adhesive for bonding the positive electrode active material particles to facilitate the formation of the film layer, and also to improve the bonding force between the positive electrode active layer and the positive electrode current collector. In some embodiments, the adhesive may include, but is not limited to, at least one of polyvinylidene fluoride, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0049] In some embodiments, the positive electrode material layer further comprises a conductive material, which includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, synthetic graphite, conductive carbon black (Super P), acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0050] Negative electrode sheet

[0051] The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, including, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode material layer includes a negative electrode material, and optionally a conductive agent, binder, and thickener. The negative electrode material includes sodium, and the mass percentage of sodium is from 0.05% to 1.2% based on the mass of the negative electrode sheet. For example, the mass percentage of sodium can be any value within the range of 0.05%, 0.06%, 0.07%, 0.3%, 0.39%, 0.4%, 0.41%, 0.47%, 0.5%, 0.56%, 0.6%, 0.65%, 1.2%, or any value above.

[0052] This application adds sodium to the negative electrode material, which undergoes reversible dissolution and deposition during the charge and discharge process of the electrochemical device, providing additional capacity to the electrochemical device. Sodium can also form more inorganic components on the surface of the negative electrode material, making the SEI film denser and more uniform, and improving the stability of the negative electrode material surface. Due to the presence of sodium, the desolvation process of lithium ions on the surface of the negative electrode material can be promoted, especially the desolvation capability at low temperature, thereby improving the low-temperature cycling performance and kinetic performance of the electrochemical device.

[0053] In some embodiments, the negative electrode material includes graphite or silicon-based materials. Specifically, the silicon-based negative electrode material is a silicon-carbon composite material. The use of graphite or silicon-based negative electrode materials in this application enables the electrochemical device to possess both high energy density and good low-temperature cycling performance.

[0054] In some embodiments, the negative electrode material further includes boron, with the boron content ranging from 0.02% to 0.1% by mass, based on the mass of the negative electrode sheet. For example, the boron content can be any value within the range of 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, or any of the above values.

[0055] This application further improves the low-temperature cycling performance and kinetic performance of the electrochemical device by adding boron to the negative electrode material and controlling the mass ratio of boron to meet the above-mentioned range.

[0056] In some embodiments, when the negative electrode is in a charged state, the mass percentage of sodium is 0.5% to 1.2% based on the mass of the negative electrode. This further improves the low-temperature cycling performance and kinetic performance of the electrochemical device.

[0057] In some embodiments, when the negative electrode is in the discharged state, the mass percentage of sodium is 0.07% to 0.4% based on the mass of the negative electrode. This further improves the low-temperature cycling performance and kinetic performance of the electrochemical device.

[0058] In some embodiments, when the negative electrode is in a fully discharged state, the mass percentage of sodium is X% based on the mass of the negative electrode; when the negative electrode is in a fully charged state, the mass percentage of sodium is Y% based on the mass of the negative electrode, where X / Y is from 0.1 to 0.8. For example, X / Y can be any value within the range of 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.55, 0.65, 0.7, 0.75, 0.8, or any of the above values.

[0059] In some embodiments, the negative electrode material further includes manganese, with the manganese content ranging from 0.001% to 0.04% by mass, based on the mass of the negative electrode sheet. For example, the manganese content can be any value within the range of 0.001%, 0.003%, 0.005%, 0.008%, 0.01%, 0.015%, 0.002%, 0.025%, 0.03%, 0.035%, 0.04%, or any of the above values.

[0060] This application further improves the low-temperature cycling performance and kinetic performance of the electrochemical device by adding manganese to the negative electrode material and controlling the mass ratio of manganese to meet the above-mentioned range.

[0061] In some embodiments, the negative electrode material further includes nickel, with the nickel content ranging from 0.002% to 0.02% by mass, based on the mass of the negative electrode sheet. For example, the nickel content can be any value within the range of 0.002%, 0.003%, 0.005%, 0.008%, 0.01%, 0.015%, 0.016%, 0.017%, 0.018%, 0.02%, or any of the above values.

[0062] This application further improves the low-temperature cycling performance and kinetic performance of the electrochemical device by adding nickel to the negative electrode material and controlling the mass ratio of nickel to meet the above-mentioned range.

[0063] The specific type of conductive agent is not limited and can be selected according to requirements. For example, conductive agents include, but are not limited to, conductive graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and at least one of the following:

[0064] The specific type of adhesive is not limited and can be selected according to requirements. As an example, adhesives include, but are not limited to, at least one of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, and carboxymethyl cellulose.

[0065] The specific type of thickener is not limited and can be selected according to needs. As an example, thickeners include, but are not limited to, sodium carboxymethyl cellulose (CMC).

[0066] electrolyte

[0067] According to some embodiments of this application, the electrolyte includes an organic solvent, a lithium salt, and optional additives.

[0068] In some embodiments, the additives include adiponitrile, fluoroethylene carbonate, and vinylene carbonate: the additives selected in this application are adiponitrile, fluoroethylene carbonate, and vinylene carbonate, which further improve the low-temperature cycling performance and kinetic performance of the electrochemical device.

[0069] In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalateborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalateborate LiBF2(C2O4) (LiDFOB).

[0070] In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, or ethyl propionate.

[0071] Separating membrane

[0072] The material and shape of the separator used in the electrochemical device of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0073] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0074] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, 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, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0075] Electronic devices

[0076] The aforementioned electrochemical device is applied to electronic devices to power loads within them. Furthermore, this electrochemical device exhibits excellent low-temperature cycling and kinetic performance, which helps extend the lifespan of the electronic devices. These electronic devices may include, but are not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0077] Example 1

[0078] <Preparation of cathode materials>

[0079] 1. Prepare a mixed solution containing NiSO4 and MnSO4 according to the elemental molar ratio Ni:Mn = 50:50. Mix this solution with the precipitant NaOH solution and the complexing agent ammonia solution. By controlling the reaction time, ammonia concentration, and pH value, the precursor Ni is obtained. 0.5 Mn 0.5 (OH)2.

[0080] 2. The above-mentioned precursor Ni 0.5 Mn 0.5 (OH)2, lithium hydroxide and sodium hydroxide are ground and mixed evenly in a certain proportion, and calcined at 850℃ in air atmosphere for 48h at a heating rate of 1℃ / min. Then, the mixture is cooled to room temperature at a rate of 3℃ / min in a mixed atmosphere of Ar and H2. Finally, the cathode material is obtained by crushing and sieving.

[0081] <Preparation of the positive electrode>

[0082] Polyvinylidene fluoride (PVDF) binder, conductive carbon black (Super P) conductive agent, and positive electrode material were mixed uniformly at a weight ratio of 1.5:1.5:97. N-methylpyrrolidone (NMP) was added as a solvent to obtain a positive electrode slurry with a viscosity of 3000 mPas to 6000 mPas. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil current collector and dried at 120°C for 1 hour to obtain a positive electrode sheet with a single-sided coating of a 60 μm thick positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material layer. The sheet was dried under vacuum at 120°C for 1 hour, and then cold-pressed, cut, and had tabs welded to obtain a positive electrode sheet with dimensions of 74 mm × 867 mm.

[0083] <Preparation of Anode Materials>

[0084] Graphite was thoroughly mixed with a certain amount of sodium fluoride, and then heated to 1050°C at 10°C in a N2 atmosphere. The temperature was held at 1050°C for 12 hours. After the holding time was completed, the temperature was lowered to room temperature at a rate of 3°C / min to obtain the negative electrode material of this application.

[0085] <Preparation of Negative Electrode Sheets>

[0086] The negative electrode material, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber (SBR) of this application were mixed in a weight ratio of 96:2:2, and deionized water was added. The mixture was stirred and stirred until homogeneous to obtain a negative electrode slurry with a solid content of 75 wt%. The negative electrode slurry was uniformly coated onto one surface of a 12 μm thick copper foil current collector and dried at 120 °C to obtain a negative electrode sheet with a single-sided coating of negative electrode material layer with a coating thickness of 80 μm. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material layer. The sheet was dried under vacuum at 120 °C for 1 hour, and then cold-pressed, cut, and slit to obtain a negative electrode sheet with a size of 78 mm × 875 mm.

[0087] <Preparation of Electrolyte>

[0088] In an argon-atmosphere glove box with a water content of <10 ppm, propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) were mixed in a 1:1:1 mass ratio. Thoroughly dried lithium salt LiPF6 was then dissolved in the above non-aqueous solvent, and 2% 1,3-propanesulfonate lactone was added to prepare the electrolyte used in the examples. Based on the mass of the electrolyte, the mass percentage of LiPF6 was 13%.

[0089] <Preparation of the separating membrane>

[0090] A porous polyethylene (PE) film with a thickness of 7 μm was used as the separator.

[0091] <Preparation of Lithium-ion Pouch Batteries>

[0092] The positive electrode, separator, and negative electrode prepared above are stacked, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound up. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. Following vacuum sealing, settling, formation (with an upper limit voltage of 4.35V, a formation temperature of 85℃, and a settling time of 2 hours), degassing, and edge trimming, a lithium-ion soft-pack battery is obtained.

[0093] Examples 2 to 8

[0094] The difference between Examples 2 to 8 and Example 1 is that the contents of manganese and nickel in the precursor in step 1 of the <Preparation of Cathode Material> are adjusted, the amount of lithium hydroxide and sodium hydroxide added in step 2 is adjusted, and the amount of sodium fluoride added in the <Preparation of Anode Material> is adjusted. The other conditions / preparation methods are the same as in Example 1. The specific preparation parameters mentioned above can be adjusted accordingly according to Tables 1 and 2.

[0095] Examples 9 to 12

[0096] The difference between Examples 9 to 12 and Example 6 is that, after step 2 of the <Preparation of Cathode Material>, the cathode material is thoroughly mixed with boric acid in an air atmosphere and heat-treated at 500°C for 10 hours. The remaining conditions / preparation methods are the same as in Example 6. The specific preparation parameters mentioned above can be adjusted accordingly according to Tables 1 and 2.

[0097] Example 13

[0098] The difference between Example 13 and Example 6 is that adiponitrile, fluoroethylene carbonate, and vinylene carbonate are added to the electrolyte. The other conditions / preparation methods are the same as in Example 6. The specific preparation parameters can be adjusted accordingly according to Tables 1 and 2.

[0099] Examples 14 and 15

[0100] The difference between Examples 14 and 15 and Example 6 is that in the <Preparation of Anode Material>, the anode material is thoroughly mixed with B2O3 under a nitrogen atmosphere and heat-treated at 500°C for 5 hours. The other conditions / preparation methods are the same as in Example 6. The specific preparation parameters mentioned above can be adjusted accordingly according to Tables 1 and 2.

[0101] Comparative Example 1 and Comparative Example 2

[0102] The difference between Comparative Examples 1 and 2 and Example 6 is that the amount of lithium hydroxide and sodium hydroxide added in step 2 of the <Preparation of Positive Electrode Material> and the amount of sodium fluoride added in the <Preparation of Negative Electrode Material> are adjusted. The other conditions / preparation methods are the same as those in Example 6. The specific preparation parameters mentioned above can be adjusted accordingly according to Tables 1 and 2.

[0103] Comparative Example 3

[0104] The difference between Comparative Example 3 and Example 6 is that sodium hydroxide is not added in step 2 of the <Preparation of Cathode Material>. The other conditions / preparation methods are the same as in Example 6. The specific preparation parameters mentioned above can be adjusted accordingly according to Tables 1 and 2.

[0105] Comparative Example 4

[0106] The difference between Comparative Example 4 and Example 6 is that sodium fluoride is not added in the <Preparation of Anode Material>, while the other conditions / preparation methods are the same as in Example 6. The specific preparation parameters mentioned above can be adjusted accordingly according to Tables 1 and 2.

[0107] Comparative Example 5

[0108] The difference between Comparative Example 5 and Example 6 is that sodium hydroxide is not added in step 2 of the <Preparation of Positive Electrode Material> and sodium fluoride is not added in the <Preparation of Negative Electrode Material>. The other conditions / preparation methods are the same as those in Example 6. The specific preparation parameters mentioned above can be adjusted accordingly according to Tables 1 and 2.

[0109] Test methods

[0110] (1) Element content test

[0111] Element content test of positive electrode material: The positive electrode material was dissolved in aqua regia solution (for example, 0.4g of positive electrode material was dissolved in 10ml of aqua regia solution (the volume ratio of aqua regia to deionized water was 1:1, and the volume ratio of concentrated hydrochloric acid to concentrated nitric acid was 3:1). The positive electrode material was then fully digested in a CEM-Mars5 / Mars6 microwave digester, and the volume was adjusted to 100mL. The mass percentage content of elements such as Li, Na, Ni, Mn and B in the solution was tested using an inductively coupled plasma optical emission spectrometer (ICP-OES) system.

[0112] Anode material element content test: Weigh 0.5g of anode material and add it to 10mL of HNO3 solution. Digest the anode material completely in a CEM-Mars5 / Mars6 microwave digester. After digestion, bring the volume to 50mL and use ICP-OES to test the content of elements such as Li, Na, Mn, and Ni in the solution.

[0113] (2) 5℃ Cyclic Capacity Retention Rate Test (Low Temperature)

[0114] The lithium-ion pouch battery was placed in a 5℃ constant temperature chamber and left to stand for 30 minutes to reach a constant temperature. The battery was then charged at a constant current of 0.5C to 4.35V at 5℃, followed by constant voltage charging at 4.35V to 0.02C. After standing for 5 minutes, it was discharged at a constant current of 0.5C to 2.8V, and then left to stand for another 5 minutes. This discharge capacity was recorded as the first cycle discharge capacity. This charge-discharge cycle was repeated 400 times, and the discharge capacity of the battery in the 400th cycle was recorded as the 400th cycle discharge capacity. The capacity retention rate (%) of the lithium-ion pouch battery after 400 cycles at 5℃ = (400th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0115] (3) 2C / 0.1C test method

[0116] The lithium-ion pouch battery was charged at 25°C with a constant current of 0.7C to 4.35V, then charged at 4.35V with a constant voltage to 0.025C; allowed to rest for 5 minutes, and then discharged at a constant current of 0.1C to 2.8V, and allowed to rest for 5 minutes. The capacity of the 2C constant current discharge was divided by the capacity of the 0.1C constant current discharge; the ratio is the rate factor 2C / 0.1C.

[0117] The test data for Examples 1 to 15 and Comparative Examples 1 to 5 are recorded in Tables 1 and 2.

[0118] Table 1

[0119] Note: " / " in Table 1 indicates that the corresponding substance or parameter does not exist.

[0120] Table 2

[0121] Note: " / " in Table 2 indicates that the corresponding substance or parameter does not exist.

[0122] As can be seen from Tables 1 and 2, compared with Example 1, Examples 2 to 8, by adjusting the content of manganese and nickel in the precursor in step 1 of <Preparation of positive electrode material>, the amount of lithium hydroxide and sodium hydroxide added in step 2, and the amount of sodium fluoride added in <Preparation of negative electrode material>, enable the electrochemical device to have good low-temperature cycling performance and kinetic performance (charge-discharge rate).

[0123] Compared with Example 6, in Examples 9 to 12, boric acid was added after step 2 of the <Preparation of Cathode Material>. By comparison, it can be seen that adding boron to the cathode material can further improve the low-temperature cycling performance and kinetic performance of the electrochemical device of this application, and the effect is even better when the amount of boron added meets the scope of this application.

[0124] Compared with Example 6, Example 13 added adiponitrile, fluoroethylene carbonate and vinylene carbonate to the electrolyte, which further improved the low-temperature cycling performance and kinetic performance (charge-discharge rate) of the electrochemical device.

[0125] Compared with Example 6, Examples 14 and 15, in the <Preparation of Anode Material>, added B2O3, and when the amount of boron added met the scope of this application, further improved the low-temperature cycling performance and kinetic performance (charge-discharge rate) of the electrochemical device.

[0126] Furthermore, a comparison of Example 6 with Comparative Examples 1 and 2 shows that when the sodium content in the positive electrode material and the sodium content in the negative electrode material do not meet the scope of this application, the low-temperature cycling performance and kinetic performance (charge-discharge rate) of the electrochemical device are affected to varying degrees.

[0127] As can be seen from the comparison between Example 6 and Comparative Examples 3 to 5, when the positive electrode material or the negative electrode material does not contain sodium, or when neither contains sodium, the low-temperature cycle capacity retention rate and charge-discharge rate of the electrochemical device are lower than when the positive electrode material or the negative electrode material contains sodium. Therefore, it can be concluded that the sodium in the positive electrode material and the sodium in the negative electrode material have a synergistic effect, which makes the electrochemical device have good low-temperature cycle performance and kinetic performance.

[0128] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. An electrochemical device comprising a positive electrode and a negative electrode, characterized in that, The positive electrode sheet includes a positive electrode material, which includes sodium and lithium elements, and the mass percentage of sodium elements is 0.2% to 3% based on the mass of the positive electrode sheet. The negative electrode sheet includes a negative electrode material, which includes sodium. Based on the mass of the negative electrode sheet, the mass percentage of sodium is between 0.05% and 1.2%.

2. The electrochemical device as described in claim 1, characterized in that, The positive electrode material also includes boron, and the mass percentage of boron is 0.01% to 0.3% based on the mass of the positive electrode sheet.

3. The electrochemical device as described in claim 1, characterized in that, Based on the mass of the positive electrode sheet, the mass percentage of sodium is A%, the mass percentage of lithium is B%, and the B / A ratio is 1.83 to 40.

4. The electrochemical device according to claim 1, characterized in that, Based on the mass of the positive electrode sheet, the mass percentage of lithium element is 5.5% to 8%.

5. The electrochemical device according to any one of claims 1 to 4, characterized in that, The positive electrode material also includes manganese, and the mass percentage of manganese is 24.43% to 30% based on the mass of the positive electrode sheet; and / or The positive electrode material also includes nickel, and the mass percentage of nickel is 26.2% to 32% based on the mass of the positive electrode sheet.

6. The electrochemical device according to any one of claims 1 to 4, characterized in that, The negative electrode material includes graphite or silicon-based materials.

7. The electrochemical device according to any one of claims 1 to 4, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The negative electrode material further includes boron, and the mass percentage of boron is 0.02% to 0.1% based on the mass of the negative electrode sheet; (2) Based on the mass of the negative electrode sheet, the mass percentage of sodium element is 0.5% to 1.2%.

8. The electrochemical device according to any one of claims 1 to 4, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The negative electrode material also includes manganese, and the mass percentage of manganese is 0.001% to 0.04% based on the mass of the negative electrode sheet; (2) The negative electrode material also includes nickel, and the mass percentage of nickel is 0.002% to 0.02% based on the mass of the negative electrode sheet; (3) Based on the mass of the negative electrode sheet, the mass percentage of sodium element is 0.07% to 0.4%.

9. The electrochemical device according to any one of claims 1 to 4, characterized in that, It also includes an electrolyte, which comprises adiponitrile, fluoroethylene carbonate, and vinylene carbonate.

10. An electronic device, characterized in that, Includes the electrochemical device as described in any one of claims 1 to 9.

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