Secondary battery and electric device

Abstract

The invention discloses an electrolyte, a secondary battery and a power utilization device, and belongs to the technical field of batteries, a lithium supplementing material is of a core-shell structure, a core is a lithium supplementing agent, a shell has heat sensitivity, the lithium supplementing agent cannot be released during normal operation of the secondary battery, and when lithium supplementing is needed, heating is conducted to enable the shell to be dissolved, so that the lithium supplementing effect is achieved. The lithium supplement agent can be uniformly released, non-uniform distribution is avoided, lithium supplement is carried out in the subsequent charging and discharging process, the cycle life of the secondary battery is effectively prolonged, and the DCR (Direct Current Ratio) is reduced.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a secondary battery and an electrical device. Background Technology

[0002] The emergence of portable electronic devices and electric vehicles has created a significant demand for high-energy-density lithium-ion batteries. Furthermore, the energy storage industry, characterized by high growth potential and high certainty, is developing rapidly. With the increasing installed capacity, the market is placing higher demands on the safety and economic efficiency of rechargeable batteries. The formation of the negative electrode solid electrolyte membrane (SEI membrane) during the first cycle irreversibly consumes a large amount of active lithium ions from the positive electrode, and the loss of lithium reduces the battery's energy density and cycle life.

[0003] Therefore, this application is submitted. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of the existing technology and provide a secondary battery and power device that can effectively improve the cycle life of the secondary battery and reduce the DCR.

[0005] To achieve the above objectives, a first aspect of this application provides an electrolyte comprising a lithium replenishing material, the lithium replenishing material comprising a lithium replenishing agent and a coating layer located on the outer surface of the lithium replenishing agent; The lithium replenishing agent includes at least one of LiSO2CF3, LiSO2C2H5, LiSO2C6H4CH3, LiSO2C6H4Cl, LiSO2NC5H4, LiSO2CH3, LiSO2C6H5, LiSO2C6H4F, LiSO2SC4H3, and LiSO2C2F5. The melting point of the coating layer is 50~90℃.

[0006] As an embodiment of this application, the coating layer includes at least one of paraffin wax, polycaprolactone, ethylene-vinyl acetate copolymer, polyurethane, and polyethylene glycol.

[0007] As an embodiment of this application, the thickness of the coating layer is 10~1000nm.

[0008] As an embodiment of this application, the lithium replenishing material has a mass percentage content of 0.1-5% in the electrolyte.

[0009] As an embodiment of this application, the electrolyte further includes additives, which include at least one of vinylene carbonate, fluoroethylene carbonate, and tris(trimethylsilane) phosphate.

[0010] As an embodiment of this application, the additive has a mass percentage content of 0.5-5% in the electrolyte.

[0011] As an embodiment of this application, the electrolyte further includes an organic solvent, which includes cyclic carbonates and chain carbonates; The cyclic carbonate includes at least one of propylene carbonate and ethylene carbonate; The chain carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0012] As an embodiment of this application, the organic solvent further includes a carboxylic acid ester, which includes at least one of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0013] As an implementation scheme of this application, at least one of the following (a) to (c) is satisfied: (a) The cyclic carbonate accounts for 20-40% of the mass of the organic solvent; (b) The chain carbonate accounts for 30-70% of the mass percentage of the organic solvent; (c) The carboxylic acid ester accounts for 0 to 50% of the mass percentage of the organic solvent.

[0014] A second aspect of this application provides a secondary battery comprising the electrolyte described above.

[0015] A third aspect of this application provides an electrical device including the aforementioned secondary battery, wherein the secondary battery serves as the power supply for the electrical device.

[0016] The beneficial effects of this application are as follows: The lithium replenishing material described in this application has a core-shell structure, with the core being the lithium replenishing agent and the shell being thermosensitive. During the normal operation of the secondary battery, the lithium replenishing agent will not be released. When lithium replenishment is required, heating is performed to dissolve the shell, thereby releasing the lithium replenishing agent. The lithium replenishing agent can be released uniformly, avoiding uneven distribution. Lithium replenishment is performed during subsequent charge and discharge processes, effectively improving the cycle life of the secondary battery and reducing the DCR. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0019] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0020] The inventors of this application have discovered that an electrolyte interphase (SEI) film at the interface between the electrolyte and the negative electrode is essential for secondary batteries, playing a crucial role in stable cycle performance. Essentially, the SEI film is electrically insulating but ionicly conductive, thus preventing direct contact between the negative electrode and the electrolyte and preventing excessive electrolyte decomposition. However, the formation of the SEI film results in a large irreversible capacity in the first cycle, and lithium loss reduces the battery's energy density and cycle life.

[0021] The irreversible capacity loss in the first cycle can be overcome by increasing the positive electrode active material, but due to the low specific capacity of current positive electrode active materials, this significantly reduces the energy density and reaction kinetics of the secondary battery. The initial irreversible capacity loss in the first cycle mainly affects the cycle life and energy density of the secondary battery. Therefore, in order to maintain the energy density and cycle life of the secondary battery, it is necessary to compensate for the loss of lithium ions.

[0022] In the prior art, the positive electrode lithium replenishment method is one of the commonly used methods to replenish lithium lost in secondary batteries. However, after lithium replenishment, there are often by-products of other transition metals that affect the performance of secondary batteries.

[0023] Therefore, based on the above problems, this application provides an electrolyte including a lithium replenishing material, wherein the lithium replenishing material includes a lithium replenishing agent and a coating layer located on at least a portion of the surface of the lithium replenishing agent; The lithium replenishing agent includes at least one of LiSO2CF3, LiSO2C2H5, LiSO2C6H4CH3, LiSO2C6H4Cl, LiSO2NC5H4, LiSO2CH3, LiSO2C6H5, LiSO2C6H4F, LiSO2SC4H3, and LiSO2C2F5. The melting point of the coating layer is 50~90℃, for example, it can be 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃ or any two of these values.

[0024] The lithium replenishing material described in this application has a core-shell structure. The core is the lithium replenishing agent, and the shell is thermosensitive. It does not release the lithium replenishing agent during the normal operation of the secondary battery. When lithium replenishment is needed, heating is performed to dissolve the shell, thereby releasing the lithium replenishing agent. The lithium replenishing agent can be released evenly, avoiding uneven distribution. Lithium replenishment is performed during subsequent charge and discharge processes, effectively improving the cycle life of the secondary battery and reducing DCR.

[0025] In some embodiments, the coating layer includes at least one of paraffin wax, polycaprolactone, ethylene-vinyl acetate copolymer, polyurethane, and polyethylene glycol. In particular, when the coating layer uses such materials, it has good chemical stability and will not leak during the normal operation of the secondary battery (i.e., it will not leak the lithium replenishing agent), effectively protecting the lithium replenishing agent. Moreover, such materials have certain phase change endothermic and exothermic characteristics, which can reduce the temperature of the secondary battery, delay the decomposition of the electrolyte, and effectively improve the safety and cycle life of the secondary battery.

[0026] In some embodiments, the thickness of the coating layer is 10~1000nm, for example, it can be a range of 10nm, 20nm, 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm or any two of these values. By controlling the thickness of the coating layer within this range, structural stability can be improved, premature release of the lithium replenishing agent can be avoided, and the lithium replenishing agent can be slowly released during the heating and dissolution process, thereby achieving a longer-term lithium replenishment effect and effectively improving the cycle life of the secondary battery.

[0027] In some embodiments, the mass percentage of the lithium replenishing material in the electrolyte is 0.1% to 5%, for example, it can be 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any two of these values. By having the mass percentage of the lithium replenishing material in the electrolyte within this range, the dissolution effect of the lithium replenishing agent in the electrolyte can be effectively improved, thus effectively improving the lithium replenishment effect. At the same time, excessive gas production is avoided, which may have a negative impact on the secondary battery, thereby effectively improving the cycle life of the secondary battery.

[0028] The lithium replenishing material described in this application has a simple reverse method: the electrolyte sample in the secondary battery is centrifuged and dried, and the core-shell structure and thickness of the lithium replenishing material can be observed by energy dispersive X-ray spectroscopy (EDS). The type of lithium replenishing agent and the type of coating layer can be further identified by combining Fourier transform infrared spectroscopy (FTIR) or Raman spectroscopy.

[0029] In some embodiments, the coating layer completely covers the outer surface of the lithium replenishing agent, meaning the coating layer completely covers the outer surface of the lithium replenishing agent. This application, by controlling the coating layer to completely cover the outer surface of the lithium replenishing agent, can improve the stability of the lithium replenishing material and increase the lithium replenishment efficiency.

[0030] In some embodiments, the electrolyte further includes additives, including at least one of vinylene carbonate, fluoroethylene carbonate, and tris(trimethylsilane) phosphate. During formation, the additives undergo single-electron reduction to generate free radical anions, which can be reduced on the electrode surface to generate an SEI rich in organic compounds such as alkyl lithium carbonate. This enhances the flexibility of the SEI, suppresses side reactions of the lithium replenishing agent at the interface, improves the lithium replenishing efficiency of the lithium replenishing agent, and together with the lithium replenishing agent, improves the cycle life of the secondary battery and reduces the volume expansion of the secondary battery.

[0031] In some embodiments, the additive has a mass percentage content of 0.5% to 5% in the electrolyte, for example, it can be 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5% or any two of these values. By controlling the content of the additive within this range, it is possible to promote the formation of a dense SEI film that is ion-conducting and electronically insulating, effectively suppress interfacial side reactions, effectively improve the cycle life of the secondary battery, and reduce DCR.

[0032] The additive has a simple reverse method; the type and content of the additive can be determined by testing and analyzing the electrolyte sample in the secondary battery using gas chromatography-mass spectrometry.

[0033] In some embodiments, the electrolyte further includes an organic solvent, which includes cyclic carbonates and chain carbonates; The cyclic carbonate includes at least one of propylene carbonate and ethylene carbonate; The chain carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0034] In some embodiments, the organic solvent further includes a carboxylic acid ester, which includes at least one of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0035] In some embodiments, the cyclic carbonate accounts for 20-40% of the organic solvent by mass, for example, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, or any two of these values.

[0036] In some embodiments, the chain carbonate accounts for 30-70% of the organic solvent by mass, for example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any two of these values.

[0037] By controlling the mass percentage of the chain carbonate and cyclic carbonate in the organic solvent within the above-mentioned range, the dissolution effect of the lithium supplement material can be improved, the ionic conductivity can be increased, the viscosity of the electrolyte can be kept within a suitable range, the lithium salt dissociation effect can be improved, and the conductivity can be increased.

[0038] In some embodiments, the carboxylic acid ester accounts for 0 to 50% of the organic solvent by mass, for example, it can be a range of 0, 10%, 20%, 30%, 35%, 40%, 45%, 50%, or any two of these values.

[0039] The organic solvent described in this application can effectively improve the solubility of lithium-supplementing materials, enhance the wetting performance of the electrolyte on the electrode, provide better electron conduction and ion diffusion channels, reduce internal resistance, and improve cycle performance.

[0040] In some embodiments, the electrolyte further includes a lithium salt, which includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium perchlorate, lithium difluorophosphate, and lithium tetrafluorophosphate.

[0041] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.5~2M, for example, it can be a range of 0.5M, 0.6M, 0.8M, 1M, 1.2M, 1.5M, 1.8M, 2M or any two of these values. By controlling the concentration of the lithium salt within the above range, the transference number of lithium ions and the antioxidant performance can be improved.

[0042] In some embodiments, the method for preparing the lithium supplement material includes the following steps: S1. The coating material and lithium supplement are heated in a water bath to obtain a mixture; S2. Mix the surfactant and deionized water evenly, preheat the resulting mixture to 80~90℃, add the mixed solution from step S1 to the preheated mixture, stir evenly to obtain an emulsion. S3. Add deionized water at 0~5℃ to the emulsion in S2 to form solidified microspheres, rinse, and vacuum dry to obtain the lithium supplement material.

[0043] In some embodiments, the water bath heating temperature is 80~90°C, for example, it can be 80°C, 82°C, 85°C, 88°C, 90°C or any two of these values.

[0044] In some embodiments, the water bath heating time is 5 to 30 minutes, for example, it can be 5 minutes, 8 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes or any two of these values.

[0045] In some embodiments, the surfactant includes at least one of polyvinyl alcohol, sodium dodecylbenzenesulfonate, and hexadecyltrimethylammonium chloride.

[0046] In some embodiments, the stirring speed in step S2 is 500~1200 rpm, for example, it can be 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm or any two of these values.

[0047] In some embodiments, the stirring time in step S2 is 1 to 10 minutes, for example, it can be 1 minute, 2 minutes, 4 minutes, 5 minutes, 6 minutes, 8 minutes, 10 minutes or any two of these values.

[0048] In some embodiments, the mass ratio of the coating material to the lithium replenishing agent is 1:(0.1~10), for example, it can be 1:0.1, 1:0.5, 1:1, 1:2, 1:4, 1:5, 1:6, 1:8, 1:10 or any two of these values.

[0049] In some embodiments, the mass ratio of the surfactant to deionized water is 1:(1~10), for example, it can be 1:1, 1:2, 1:4, 1:5, 1:6, 1:8, 1:10 or any two of these values.

[0050] In some embodiments, the mass ratio of the mixture to the preheated mixture is 1:4 to 100, for example, it can be 1:4, 1:5, 1:10, 1:20, 1:40, 1:50, 1:80, 1:100 or any two of these values.

[0051] In some embodiments, the volume ratio of the deionized water to the emulsion is 1:(0.1~10), for example, it can be 1:0.1, 1:0.5, 1:1, 1:2, 1:4, 1:5, 1:6, 1:8, 1:10 or any two of these values.

[0052] A second aspect of this application provides a secondary battery comprising the electrolyte described above.

[0053] In some embodiments, the secondary battery further includes a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active material.

[0054] In some embodiments, the positive electrode active material may be a known positive electrode active material for secondary batteries. As a non-limiting example, the positive electrode active material may include lithium phosphate, lithium transition metal oxide, and their respective modified compounds. However, this application is not limited to these materials or substances, and other conventional materials or substances that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Non-limiting examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds.

[0055] In some embodiments, the positive electrode active material includes materials with the general chemical formula Li. a Fe 1-b M b Compounds of PO4, wherein 0.8 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.9, and M is selected from at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, and Ti.

[0056] In some of these embodiments, the type of positive current collector is not particularly limited, and it may be any material known to be suitable for use as a positive current collector.

[0057] In some embodiments, the positive current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper.

[0058] There are no particular restrictions on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, it can be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, it can be in the form of carbon plate, carbon film, carbon cylinder, etc.

[0059] In some embodiments, the positive electrode active material layer also includes a conductive agent and a binder.

[0060] In some embodiments, 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 surface of the negative current collector, the negative active material layer including a negative active material.

[0061] In this application, there are no particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collector, etc.

[0062] In some embodiments, the negative electrode active material includes graphite, silicon-based materials, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, and spinel-structured lithium titanate Li4Ti5O. 12 At least one of Li-Al alloys and metallic lithium.

[0063] In some embodiments, the negative electrode active material layer further includes a conductive agent and a binder.

[0064] In some embodiments, the types of conductive agents mentioned in this application are not limited, and known conductive agents can be used.

[0065] In some embodiments, the conductive agent includes at least one of carbon materials such as acetylene black, needle coke, carbon nanotubes, and graphene.

[0066] In some embodiments, the type of adhesive mentioned in this application is not limited, and known adhesives can be used.

[0067] In some embodiments, the adhesives mentioned include at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer or its hydrogenation, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer.

[0068] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and electrolyte.

[0069] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0070] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or other shapes.

[0071] One embodiment of this application provides an electrical device including the secondary battery described above, wherein the secondary battery serves as the power supply for the electrical device.

[0072] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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., but are not limited thereto.

[0073] The present application is further illustrated below with specific embodiments: Example 1 A method for preparing a secondary battery includes the following steps: (1) Preparation of lithium supplementation materials: S1. Mix paraffin (0.2g) and lithium supplement (0.2g) evenly and seal them in the same small bottle. Then immerse the small bottle in an 82°C water bath.

[0074] S2. In another vial, polyvinyl alcohol (5 mL) and deionized water (12.5 mL) are mixed evenly at 82°C to obtain a surfactant / water mixture. The mixture of paraffin and lithium supplement is added to the surfactant / water mixture that is preheated in an 82°C water bath. The mixture is emulsified for 2 minutes by mechanical stirring at 1000 rpm to obtain an emulsion.

[0075] S3. Add 50 mL of deionized ice water (0°C) to the above emulsion and mechanically stir at 1000 rpm for 5 min. Rinse with deionized water to remove excess surfactant and dry under vacuum to obtain the lithium-supplementing material.

[0076] (2) At room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed uniformly in a mass ratio of 30:40:30. Water was removed using a 4Å molecular sieve to obtain a mixed solvent. Mixed lithium salts (0.8M LiPF6 / 0.2M LiFSI) were added to the obtained mixed solvent in turn. The mixture was stirred continuously and cooled with dry ice to ensure that the electrolyte temperature rise did not exceed 2°C. Finally, a colorless and transparent liquid was obtained. Then, vinylene carbonate (VC) was added and stirred uniformly to obtain a batch of electrolyte, wherein the mass percentage of vinylene carbonate in the batch of electrolyte was 2.5%. At room temperature, in an argon-filled glove box (H2O < 1 ppm, O2 < 1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed uniformly at a mass ratio of 30:40:30. Water was removed using a 4 Å molecular sieve to obtain a mixed solvent. A mixed lithium salt (0.8 M LiPF6 / 0.2 M LiFSI) was added sequentially to the obtained mixed solvent, with continuous stirring and cooling using dry ice to ensure the electrolyte temperature did not rise by more than 2 °C. A colorless and transparent liquid was finally obtained. Then, vinylene carbonate was added and stirred uniformly. Next, lithium supplementation material was added and stirred uniformly to obtain a second-phase electrolyte, in which the mass percentage of vinylene carbonate in the second-phase electrolyte was 2.5%, and the mass percentage of the lithium supplementation material in the second-phase electrolyte was 2%.

[0077] The parameters of the electrolyte are shown in Table 1.

[0078] (2) Preparation of the positive electrode sheet: LiFePO4, conductive agent SP, and binder PVDF were mixed in a mass ratio of 96:2:2. NMP was added, and the mixture was stirred under vacuum until homogeneous to obtain the positive electrode slurry. The positive electrode slurry was then uniformly coated onto both sides of the positive electrode current collector aluminum foil, dried in an oven, and then cold-pressed to obtain the positive electrode sheet. The compacted density of the positive electrode sheet was 2.45 g / cm³. 3.

[0079] (3) Preparation of negative electrode sheet The negative electrode active material graphite, conductive agent acetylene black (Super P) and binder SBR are mixed evenly in a mass ratio of graphite:SuperP:SBR=94:3:3, and then evenly dispersed in deionized water to form a uniform black slurry. The mixed slurry is coated on both sides of copper foil, and then baked, rolled, and cut into sheets to obtain the negative electrode sheet.

[0080] (4) Separator: A polyethylene (PE) film with a thickness of 6 μm is used as the substrate; ceramic particles boehmite and adhesive PVDF are mixed evenly in an appropriate amount of solvent deionized water at a weight ratio of 7:1 to obtain a ceramic slurry with a solid content of 60%; the ceramic slurry is coated on both surfaces of the substrate using a coating machine and dried to form a ceramic coating with a single-sided thickness of 2 μm.

[0081] (5) Assembly of secondary battery: The prepared positive electrode, separator and negative electrode are stacked in order, with the separator in the middle of the positive and negative electrode. After winding, hot pressing and shaping, the tabs are welded to obtain the bare cell. The bare cell is placed in the outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. One injection of electrolyte is injected, and the cell is allowed to stand and form. Then, a second injection of electrolyte is injected and the cell is divided to obtain the secondary battery. The mass ratio of the first injection to the first injection is 39:1.

[0082] Examples 2-7 The difference between Examples 2-4 and Example 1 is that the content of the lithium-replenishing material in the electrolyte is controlled by adjusting the ratio of the primary and secondary injection volumes; the mass percentage of the lithium-replenishing material in the secondary electrolyte is 2%. Example 2: The mass ratio of the first injection to the second injection was 19:1.

[0083] Example 3: The mass ratio of the first injection to the second injection is 3:1.

[0084] Example 4: The mass ratio of the first injection to the second injection is 1:1.

[0085] The difference between Examples 5-7 and Example 1 is that the content of lithium-replenishing material in the electrolyte is controlled by adjusting the percentage content of lithium-replenishing material in the second electrolyte injection and by adjusting the ratio of the first injection volume to the second injection volume.

[0086] Example 5: The mass percentage of lithium replenishment material in the secondary electrolyte is 6%; the mass ratio of the primary electrolyte injection to the secondary electrolyte injection is 1:1.

[0087] Example 6: The mass percentage of lithium replenishing material in the secondary electrolyte is 10%; the mass ratio of the primary electrolyte injection to the secondary electrolyte injection is 1:1.

[0088] Example 7: The mass percentage of lithium replenishment material in the secondary electrolyte is 16%; the mass ratio of the primary electrolyte to the secondary electrolyte is 1:1.

[0089] Examples 8-10 The difference between Examples 8-10 and Example 4 is that the type of coating material is changed.

[0090] Examples 11-12, Comparative Example 1 Examples 11-12 and Comparative Example 1 differ from Example 4 in that the type of lithium supplement is changed, as shown in Table 1.

[0091] Examples 13-16 The difference between Examples 13-16 and Example 4 is that the changes are as shown in Table 1.

[0092] Example 13: The mass ratio of paraffin wax to lithium supplement was 1:1.5.

[0093] Example 14: The mass ratio of paraffin wax to lithium supplement is 1:2.

[0094] Example 15: The mass ratio of paraffin wax to lithium supplement is 1:5.

[0095] Example 16: The mass ratio of paraffin wax to lithium supplement is 2:1.

[0096] Examples 17-19 The difference between Examples 17-19 and Example 4 is that the content of VC is changed, as shown in Table 1.

[0097] Example 20 Example 20 differs from Example 4 in that an equal amount of FEC (fluoroethylene carbonate) is used to replace VC, as shown in Table 1.

[0098] Examples 21-25 Examples 21-25 differ from Example 4 in that the mass ratio and / or type of organic solvent are changed.

[0099] The organic solvent in Example 21 includes ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 40:30:30.

[0100] The organic solvent in Example 22 comprises ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and ethyl acetate in a mass ratio of 30:35:25:10. The organic solvent in Example 23 comprises ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and ethyl acetate in a mass ratio of 30:30:20:20.

[0101] The organic solvent in Example 24 comprises ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and ethyl acetate in a mass ratio of 30:20:10:40.

[0102] The organic solvent in Example 25 comprises ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and ethyl acetate in a mass ratio of 20:15:15:50.

[0103] Comparative Example 2 The difference between Comparative Example 2 and Example 4 is that no lithium supplementation material was added, as shown in Table 1.

[0104] Assembly of the secondary battery in this comparative example: The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrode. After winding, hot pressing and shaping, and welding of the tabs, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. One injection of electrolyte is added, and the cell is allowed to stand and form. Another injection of electrolyte is added, and the cell is tested for capacity to obtain the secondary battery.

[0105] Table 1 Electrolyte Parameters Performance testing 1. Room temperature DCR test: At 25±2℃, the secondary batteries obtained from each implementation case and comparative example were charged to 3.65V at 1C, then discharged at 1C capacity for 30 minutes. After adjusting to 50% SOC, a 10C constant current pulse discharge was performed for 10 seconds. The SOC was then adjusted to 50% using the same method, and charged for another 10 seconds. The DCR was calculated as (voltage before pulse discharge - voltage after pulse discharge) / discharge current * 100%. After 500 cycles, the DCR was tested again. The DCR change rate was calculated as (DCR after 500 cycles - initial DCR) / initial DCR * 100%. The results are shown in Table 2.

[0106] 2. Room Temperature Cycling Performance Test: At 25±2℃, the secondary batteries obtained from each implementation case and comparative example were subjected to charge-discharge cycle tests within the range of 2.5~3.65V at a charge-discharge rate of 1C / 1C. The discharge specific capacity of the secondary batteries in the first cycle and the discharge specific capacity after 500 cycles were recorded. The capacity retention rate after 500 cycles = discharge specific capacity after 500 cycles / discharge specific capacity in the first cycle * 100%. The recorded data are shown in Table 2.

[0107] Table 2 Performance Test Results As can be seen from Table 2, the lithium replenishing material described in this application has a core-shell structure. The core is the lithium replenishing agent, and the shell is thermosensitive. It does not release the lithium replenishing agent during the normal operation of the secondary battery. When lithium replenishment is needed, heating is performed to dissolve the shell, thereby releasing the lithium replenishing agent. The lithium replenishing agent can be released evenly, avoiding uneven distribution. Lithium replenishment is performed during subsequent charge and discharge processes, effectively improving the cycle life of the secondary battery and reducing DCR.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. An electrolyte, characterized in that, The material includes a lithium replenishing agent and a coating layer on the outer surface of the lithium replenishing agent. The lithium replenishing agent includes at least one of LiSO2CF3, LiSO2C2H5, LiSO2C6H4CH3, LiSO2C6H4Cl, LiSO2NC5H4, LiSO2CH3, LiSO2C6H5, LiSO2C6H4F, LiSO2SC4H3, and LiSO2C2F5. The melting point of the coating layer is 50~90℃.

2. The electrolyte according to claim 1, characterized in that, The coating layer includes at least one of paraffin, polycaprolactone, ethylene-vinyl acetate copolymer, polyurethane, and polyethylene glycol.

3. The electrolyte according to claim 1, characterized in that, The thickness of the coating layer is 10~1000nm.

4. The electrolyte according to claim 1, characterized in that, The lithium replenishing material has a mass percentage of 0.1-5% in the electrolyte.

5. The electrolyte according to claim 1, characterized in that, The electrolyte also includes additives, which include at least one of vinylene carbonate, fluoroethylene carbonate, and tris(trimethylsilane) phosphate.

6. The electrolyte according to claim 5, characterized in that, The additive has a mass percentage of 0.5-5% in the electrolyte.

7. The electrolyte according to claim 1, characterized in that, The electrolyte also includes an organic solvent, which includes cyclic carbonates and chain carbonates; The cyclic carbonate includes at least one of propylene carbonate and ethylene carbonate; The chain carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

8. The electrolyte according to claim 7, characterized in that, The organic solvent also includes carboxylic acid esters, which include at least one of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

9. The electrolyte according to any one of claims 7-8, characterized in that, Satisfy at least one of the following conditions (a) to (c): (a) The cyclic carbonate accounts for 20-40% of the mass of the organic solvent; (b) The chain carbonate accounts for 30-70% of the mass percentage of the organic solvent; (c) The carboxylic acid ester accounts for 0 to 50% of the mass percentage of the organic solvent.

10. A secondary battery, characterized in that, Includes the electrolyte as described in any one of claims 1 to 9.

11. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 10, wherein the secondary battery serves as the power supply for the electrical device.

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