Negative pole piece and secondary battery

Abstract

The invention discloses a negative pole piece and a secondary battery, and belongs to the technical field of electrochemical energy storage, the negative pole piece is characterized in that a lithium-loving layer and a framework deposition layer are simultaneously arranged on a current collector, and the conductivity of the framework deposition layer and a lithium-loving included angle of the lithium-loving layer are cooperatively regulated and controlled; according to the present invention, the lithium metal can be uniformly deposited from bottom to top based on the induction effect during the deposition process, the structure stability of the pole piece structure layer during the deposition process is high, the interface stability of the pole piece and the electrolyte is high, the side reaction is reduced, and the pole piece has characteristics of low expansion rate, long cycle life and ideal rapid charging performance when the pole piece is applied to the secondary battery.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, specifically to negative electrode sheets and secondary batteries. Background Technology

[0002] Although lithium metal batteries have a higher relative specific capacity than traditional graphite anode lithium-ion batteries and a lower operating potential during charging and discharging, the disordered deposition of lithium metal during the deposition of lithium metal in traditional lithium metal battery anodes tends to concentrate on the top of the electrode. This not only leads to a large expansion rate of the electrode during cycling, affecting cycle life, but also easily causes lithium dendrite growth, especially under fast charging conditions, which can even lead to safety issues in severe cases. Summary of the Invention

[0003] The purpose of this application is to overcome the shortcomings of the existing technology and provide a negative electrode sheet. By simultaneously setting a lithiophilic layer and a framework deposition layer on the current collector, and synergistically controlling the conductivity of the framework deposition layer and the lithiophilic angle of the lithiophilic layer, not only can lithium metal be uniformly deposited from bottom to top based on the inductive effect during the deposition process, but also the electrode structure layer has high structural stability and high interfacial stability between the electrode and the electrolyte during the deposition process, reducing side reactions. When applied to secondary batteries, the electrode sheet has a low expansion rate, long cycle life, and ideal fast charging performance.

[0004] To achieve the above objectives, in a first aspect of this application, a negative electrode sheet is provided, comprising a current collector, a lithiophilic layer disposed on the current collector, and a framework deposition layer, wherein the lithiophilic layer is disposed between the current collector and the framework deposition layer; the framework deposition layer comprises a porous material. The negative electrode plate satisfies -3.5≤y+6.23lnx≤3.5; Where x is the electrical conductivity of the skeleton deposition layer in S / cm, and y is the lithium affinity angle of the lithium affinity layer.

[0005] In some implementations, the 1×10 -4 S / cm≤x≤2×10 -1 S / cm.

[0006] In some implementations, 11°≤y≤60°.

[0007] In some embodiments, the porosity of the skeleton deposition layer is greater than or equal to 40%.

[0008] In some embodiments, the porous material includes a fibrous material, which includes at least one of glass fiber, ceramic fiber, polymer fiber, natural fiber, metal fiber, and carbon fiber.

[0009] In some embodiments, the lithiophilic layer comprises a lithiophilic material.

[0010] In some embodiments, the lithiophilic layer further includes a conductive material and / or a binder.

[0011] In some embodiments, the negative electrode sheet satisfies: 1≤A / B≤60, where B is the thickness of the lithiophilic layer and A is the thickness of the framework deposition layer.

[0012] In some implementations, 1μm≤B≤10μm.

[0013] In some implementations, 10μm≤A≤60μm.

[0014] In some embodiments, the negative electrode sheet satisfies: 10≤A / d≤120, where d is the resilience of the skeleton deposition layer and A is the thickness of the skeleton deposition layer.

[0015] In some implementations, the 50% ≤ d ≤ 100%.

[0016] In a third aspect, this application provides a secondary battery, including the negative electrode sheet described in this application.

[0017] In a fourth aspect, this application provides an electrical device including the secondary battery, wherein the secondary battery serves as a power supply for the electrical device.

[0018] The beneficial effects of this application are as follows: This application provides a negative electrode sheet that simultaneously sets a lithiophilic layer and a framework deposition layer on the current collector, and synergistically controls the conductivity of the framework deposition layer and the lithiophilic angle of the lithiophilic layer. This not only allows lithium metal to be uniformly deposited from bottom to top based on the inductive effect during the deposition process, but also ensures high structural stability of the electrode structure layer and high interfacial stability between the electrode and the electrolyte during the deposition process, reducing side reactions. When applied to secondary batteries, the electrode sheet has a low expansion rate, long cycle life, and ideal fast charging performance. Attached Figure Description

[0019] Figure 1 This is a cross-sectional schematic diagram of the negative electrode sheet described in Embodiment 1 of this application. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] 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.

[0023] The present application is further illustrated below with specific embodiments: A negative electrode includes a current collector, a lithiophilic layer disposed on the current collector, and a framework deposition layer, wherein the lithiophilic layer is disposed between the current collector and the framework deposition layer; the framework deposition layer comprises a porous material. The negative electrode plate satisfies -3.5≤y+6.23lnx≤3.5; Where x is the electrical conductivity of the skeleton deposition layer in S / cm, and y is the lithium affinity angle of the lithium affinity layer.

[0024] In existing technologies, lithium metal batteries with lithium-free anodes typically use traditional porous materials as the current collector layer, such as porous carbon materials as storage sites for lithium metal deposition. However, this approach suffers from significant energy level barriers, leading to strong disorder during lithium metal deposition. Lithium metal often deposits only on the top of the electrode, causing increased electrode expansion, decreased stability, and in severe cases, lithium dendrite formation that compromises safety. While reducing the lithium metal deposition rate can alleviate this problem, it also prevents the electrode from being used in fast-charging applications, resulting in poor fast-charging performance. Therefore… In this application, to balance the orderliness of lithium metal deposition and the kinetic performance of the electrode, the negative electrode has a porous framework deposition layer on the current collector as a lithium metal deposition site. Simultaneously, a lithiophilic layer is constructed between this layer and the current collector. The lithiophilic angle of the lithiophilic layer and the conductivity of the framework deposition layer are synergistically controlled. On the one hand, if the conductivity of the framework deposition layer is too high, its attraction to lithium ions is too strong. During deposition, lithium metal will preferentially deposit at the top of the framework deposition layer due to the tip effect, not only failing to effectively utilize the remaining deposition space at the bottom but also causing significant electrode expansion. Furthermore, these deposited... Lithium metal has high dispersion and a large specific surface area, which significantly increases side reactions upon contact with the electrolyte. If the conductivity is too low, during discharge, due to the large local concentration difference between the framework deposit and the electrolyte, lithium metal does not escape in a top-down pattern. Some lithium metal fails to escape from the framework deposit, forming dead lithium, which severely affects subsequent charge / discharge capacity and efficiency. On the other hand, by adding a lithiophilic layer, this structure not only serves as a connecting layer between the current collector and the framework deposit, improving interlayer bonding, but also enhances the overall lithiophilicity of the interlayer structure. Through a strong inductive effect, lithium metal preferentially deposits at the bottom of the deposit layer, uniformly moving upwards. For optimal deposition, a uniform deposition rate is crucial. Insufficient lithiophilicity (i.e., an excessively large lithiophilic angle) results in a lower inductive effect on lithium metal, leading to a lower bottom-up deposition tendency, dispersed initial deposition sites, and high deposition density, which is detrimental to long-term cycling. However, excessive lithiophilicity (i.e., an excessively small lithiophilic angle) causes lithium deposition at an excessively rapid rate, which in turn damages the bond between the lithiophilic layer and the framework deposition layer, also hindering long-term cycling. Therefore, it is necessary to synchronously regulate the conductivity of the framework deposition layer to prevent excessive concentration of lithium metal at the bottom and to disperse deposition pressure.When the conductivity of the framework deposition layer and the lithiophilicity of the lithiophilic layer are adaptively controlled, it can not only ensure that lithium metal can effectively follow the bottom-up deposition method during deposition and the top-down extraction method during extraction, but also ensure that the electrode expansion rate is low, the lithium storage space is fully utilized, the probability of dead lithium formation is low, and the lithium deposition rate is moderate and uniform, which will not affect the interlayer structure stability of the electrode. The interface stability between the electrode and the electrolyte is high, reducing side reactions. This can not only effectively extend the cycle life of the corresponding secondary battery, but also achieve excellent fast charging performance.

[0025] In some implementations, y+6.23lnx can be a range of one or any two of the following: -3.5, -3.2, -3, -2.8, -2.5, -2.2, -2.0, -1.8, -1.5, -1.2, -1.0, -0.8, -0.5, -0.2, 0, 0.2, 0.5, 0.8, 1, 1.5, 1.8, 2, 2.3, 2.8, 3, 3.5.

[0026] More preferably, -2.8≤y+6.23lnx≤2.3.

[0027] In some implementations, the 1×10 -4 S / cm≤x≤1×10 5 S / cm.

[0028] In some implementations, the 1×10 -4 S / cm≤x≤2×10 -1 S / cm.

[0029] In some implementations, x can be 1 × 10 -4 S / cm, 5×10 -4 S / cm, 1×10 -3 S / cm, 5×10 - 3 S / cm, 1×10 -2 S / cm, 5×10 -2 S / cm, 2×10 -1 The range of one or both of S / cm.

[0030] More preferably, the 1×10 -3 S / cm≤x≤1×10 -2 S / cm.

[0031] As mentioned above, the conductivity of the framework deposition layer cannot be too high, otherwise it will affect the single induction effect of the lithiophilic layer and the regularity of lithium metal deposition will be poor. However, if it is too low, it will affect the lithium metal extraction efficiency. Therefore, it is necessary to match and regulate the lithiophilicity of the lithiophilic layer. After regulation, when the conductivity of the framework deposition layer is further optimized within the above range, the negative electrode sheet has better performance and stability during lithium metal deposition.

[0032] It should be noted that the conductivity of the framework deposition layer described in this application can be limited by, but is not limited to, the following methods: After freezing the negative electrode sheet with liquid nitrogen, a cutting machine is used to cut it from the plane of the negative electrode sheet to obtain micron-sized slices. After cutting, the slices are screened to separate the framework deposition layer slices; the framework deposition layer slices are soaked in dimethyl carbonate for 2 hours, dried, and then the resistivity of the sample is tested using a volume resistivity tester (ST2811 electrocarbon product resistivity and connection resistance tester from Suzhou Jingge Electronics Co., Ltd.). Before the test, the sample needs to be cut into small circular pieces with a diameter of 16.5 mm. Then, a fixed pressure of 0.1 MPa is applied to the circular pieces using a tablet press. Then, a layer of zinc foil is placed on the upper and lower surfaces of the sample. After applying pressure, the foil fills the uneven areas on the sample surface. Then, the four-probe method is used for testing, and the obtained resistivity ρ is converted: the conductivity of the framework deposition layer σ = 1 / ρ, where the unit of ρ is Ωm and the unit of σ is S / m.

[0033] In some implementations, 11°≤y≤60°.

[0034] In some implementations, y can be a range of one or any two of 11°, 14°, 15°, 18°, 20°, 25°, 30°, 40°, 45°, 50°, 55°, 57°, and 60°.

[0035] More preferably, the 30°≤y≤45°.

[0036] As described above, the negative electrode sheet of this application, based on the setting of a lithiophilic layer and a framework deposition layer, can effectively control the deposition uniformity and deposition rate during lithium metal deposition, thereby ensuring the efficiency and stability of the overall charging and discharging process. When the lithiophilic angle of the lithiophilic layer is further optimized within the above range, the lithiophilic layer can further balance the induction effect and the lithium deposition rate, resulting in a better lithium metal deposition effect and better cycle performance and fast charging performance of the corresponding secondary battery.

[0037] It should be noted that the lithium-affinity angle of the lithium-affinity layer described in this application can be limited in the following ways, but is not limited to: After freezing the negative electrode sheet with liquid nitrogen, it was cut into micron-sized slices from the plane of the negative electrode sheet using a cutting machine. After cutting, the slices were screened to separate the current collector slices containing the lithiophilic layer. The framework deposition layer slices were soaked in dimethyl carbonate for 2 hours, dried, and transferred into an argon-filled glove box. Lithium was melted on a heating stage using a molybdenum crucible, and the temperature was set to 185°C. The molten lithium was transferred using a molybdenum needle and a high-temperature resistant syringe. The molten lithium was transferred and slowly extruded using the syringe, forming a stable droplet on the surface of the slice on the lithiophilic layer side. The side image of the droplet falling onto the sample surface (0-5s) was captured quickly using a camera. The obtained image was analyzed using contact angle analysis software, and the contact angle was calculated using the tangent method.

[0038] In some embodiments, the lithiophilic layer is partially embedded in the framework deposition layer.

[0039] It should be noted that the lithiophilic layer and the framework deposition layer described in this application can be combined in any way, such as hot pressing, sputtering, in-situ generation, etc. Therefore, the lithiophilic layer can be bonded to the framework deposition layer at the contact surface, or a portion of the lithiophilic layer can be embedded in the framework deposition layer at the contact surface. After embedding, the bonding strength between the lithiophilic layer and the framework deposition layer is higher, and the lithiophilic induction effect is stronger. However, it is not limited to this. Based on actual operational requirements, those skilled in the art may also choose not to embed the lithiophilic layer into the framework deposition layer.

[0040] In some embodiments, the porosity of the skeleton deposition layer is greater than or equal to 40%.

[0041] More preferably, the porosity of the skeleton deposition layer is greater than or equal to 40% and less than or equal to 80%.

[0042] It should be noted that the porosity of the skeleton deposition layer described in this application can be confirmed by, but is not limited to, the following methods: The negative electrode sheet was frozen with liquid nitrogen and then cut into micron-sized slices from its plane using a cutting machine. After cutting, the skeletal deposition layer slices were separated by screening. The skeletal deposition layer slices were soaked in dimethyl carbonate for 2 hours, dried, and then the porosity was measured using the BET method. A nitrogen-based surface area and porosity analyzer (BELSORP MAX surface area and porosity analyzer from Microtrac, Japan) was used. 100 mg of sample was weighed, degassed under vacuum at 150°C for 8 hours, with a relative pressure range of 0.01-0.995 and an equilibrium time of 20 s / point. After data processing, the BJH pore size and total pore volume Vp were obtained. The porosity was calculated using the following formula: Porosity = Vp / (Vp + 1 / ρ). skeleton Calculate the porosity, where ρ skeletonThis is the skeleton density of the slice; this parameter is measured using a helium hydrometer. The specific method is as follows: Take 2g of the cut slice sample, dry it at 105℃, fill the sample cell with the sample, evacuate to <10Pa, then inject 100kPa of helium gas into the sample cell. Calculate the volume of helium gas displaced by the sample through pressure change. Repeat this process three times and take the average value. The formula for calculating the skeleton density is as follows: ρ skeleton =m / (V cell -V He ), where m is the sample weight, V cell V is the sample cell volume. He The volume replaced by helium.

[0043] In some embodiments, the porous material includes a fibrous material, which includes at least one of glass fiber, ceramic fiber, polymer fiber, natural fiber, metal fiber, and carbon fiber.

[0044] Specifically, the polymer fiber can be polypropylene fiber, polyethylene terephthalate fiber, aramid fiber, acrylic fiber, or composite polymer fiber, and can be a conductive polymer or a non-conductive polymer. The natural fiber can be wool fiber, cotton fiber, etc., and there is no specific limitation. Based on different fiber compositions or structures, the porosity of the skeleton deposition layer can also be different. When a porous material containing a fiber structure is used, lithium ions can achieve better conduction by relying on the fiber structure during the conduction process, resulting in higher lithium ion conduction efficiency and better performance of the corresponding secondary battery.

[0045] In some embodiments, the lithiophilic layer comprises a lithiophilic material.

[0046] In some embodiments, the lithiophilic material includes at least one of elemental gold or its alloys, elemental silver or its alloys, elemental zinc or its alloys, elemental magnesium or its alloys, and elemental antimony or its alloys.

[0047] In some embodiments, the particle size D of the lithiophilic material v50 The range is 20~2000nm.

[0048] In some embodiments, the lithiophilic layer further includes a conductive material and / or a binder.

[0049] In some embodiments, the lithiophilic layer includes a lithiophilic material, a conductive material, and a binder.

[0050] When setting the lithiophilic layer, the inductive effect of the lithiophilic layer is further enhanced by the conductive material. At the same time, the conductive material, the lithiophilic layer, and the current collector and framework deposition layer are connected by the binder, which can ensure the interlayer stability of the electrode.

[0051] In some embodiments, the conductive material includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0052] In some embodiments, the adhesive includes at least one of polyacrylic acid, styrene-butadiene rubber, carboxymethyl cellulose, polyurethane, polydopamine, polyvinylidene fluoride, polyvinyl butyral, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, and polyvinyl alcohol.

[0053] In some embodiments, the mass ratio of the lithiophilic material, the conductive material, and the binder in the lithiophilic layer is (5~15):(0.5~1.5):(1~3).

[0054] In some embodiments, the negative electrode sheet satisfies: 1≤A / B≤60, where B is the thickness of the lithiophilic layer and A is the thickness of the framework deposition layer.

[0055] In some implementations, A / B can be a range of one or both of the following: 1, 3, 5, 7, 7.5, 10, 15, 18, 20, 30, 50, 60.

[0056] More preferably, the negative electrode sheet satisfies: 7.5≤A / B≤20.

[0057] In the process of setting up the lithiophilic layer and the framework deposition layer, the main function of the lithiophilic layer is to serve as an ideal connection between the current collector and the framework deposition layer, as well as to induce lithium metal. If the thickness is small, the degree of connection and induction effect is low, but its contribution to the deposition and accommodation of lithium metal is low, and it will actually bring a certain resistance to the transport of lithium ions. The greater the thickness, the greater the resistance. On the other hand, the greater the thickness of the framework deposition layer, the more space there is for lithium metal, the greater the capacity, and the smaller the expansion rate of the electrode after deposition, and the lower the resistance to lithium metal deposition. However, relatively speaking, an excessively thick framework deposition layer will lead to an increase in the overall porosity of the electrode, and the side reactions will be enhanced after wetting with the electrolyte. When the thickness of these two layers is optimized and controlled, not only can the low resistance of lithium metal deposition and the better kinetic performance be achieved, but the stability of the interlayer structure can also be ensured and the side reactions with the electrolyte reduced, further improving the cycle stability and fast charging performance of the corresponding secondary battery.

[0058] In some implementations, 1μm≤B≤10μm.

[0059] In some implementations, B can be a range of one or any two of 1μm, 2μm, 3μm, 4μm, 5μm, 8μm, and 10μm.

[0060] More preferably, the 2μm≤B≤4μm In some implementations, 10μm≤A≤60μm.

[0061] In some implementations, A can be a range of one or any two of the following: 10μm, 12μm, 15μm, 20μm, 22μm, 25μm, 28μm, 30μm, 32μm, 35μm, 38μm, 40μm, 45μm, 50μm, 55μm, and 60μm.

[0062] More preferably, the 30μm≤A≤40μm.

[0063] As mentioned above, the thickness of the framework deposition layer directly affects the total amount of lithium metal deposited and the interface stability of the negative electrode sheet. When the thickness is further preferably within the above range, the interface stability of the corresponding negative electrode sheet is higher, and lithium metal can be fully deposited in the deposition layer gaps.

[0064] In some embodiments, the negative electrode sheet satisfies: 10≤A / d≤120, where d is the resilience of the skeleton deposition layer and B is the thickness of the skeleton deposition layer.

[0065] In some implementations, A / d can be a range of one or both of the following: 10, 20, 30, 40, 45, 50, 60, 80, 100, and 120.

[0066] Furthermore, the negative electrode sheet satisfies: 20≤A / d≤70.

[0067] More preferably, the negative electrode sheet satisfies: 45≤A / d≤60.

[0068] The resilience of the skeleton deposition layer is mainly related to its recoverability after deformation under external force. As lithium metal is continuously deposited and extracted, the skeleton deposition layer is constantly deformed. When the resilience of the skeleton deposition layer is high, it can ensure that the electrode is always in close contact with the separator and there will be no electrolyte vacuum area. At this time, further optimizing the thickness of the negative electrode and making the ratio of the two preferably within the above range can shorten the lithium ion transport path, improve the lithium metal deposition efficiency, and ultimately achieve better fast charging performance.

[0069] In some implementations, the 50% ≤ d ≤ 100%.

[0070] Further, d can be a range of one or any two of 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%.

[0071] Furthermore, the 50%≤d≤90%.

[0072] It should be noted that the resilience of the skeleton deposition layer described in this application can be confirmed by, but is not limited to, the following methods: After freezing the negative electrode sheet with liquid nitrogen, it was cut into micron-sized slices from the plane of the negative electrode sheet using a cutting machine. After cutting, the skeletal deposition layer slices were separated by screening. The slices were cut into 50mm × 50mm squares, and a thickness gauge (Chengli Instruments' PPG battery thickness gauge, with weights for counterweight) was used to apply a pressure of 300g to the sample. The thickness at this point was recorded as the initial thickness T0 of the sample. After the sample was allowed to stand for 10 minutes, it was placed on the platform of a universal testing machine (S2 series electronic universal testing machine from Stema Instruments Group). The program was started, and the sample was compressed to 75% strain at a speed of 0.01mm / min, held under compression for 1 minute, and then unloaded at the same speed until the load was zero. This compression-unloading cycle was repeated 5 times. After the final unloading, the sample was allowed to stand for 10 minutes, and the residual thickness T of the sample was measured using a thickness gauge. f The thickness T of the sample in the compressed state. c =T0×(1-compressive strain)Then the resilience of the skeleton deposited layer =(T f -T c ) / (T0 / T c ).

[0073] In some embodiments, the current collector includes at least one of a metal current collector, an alloy current collector, a polymer current collector, and a polymer / metal composite current collector.

[0074] In the solution described in this application, the selection of the current collector is not specifically limited. Those skilled in the art can select a suitable type of current collector based on actual needs, such as a metal current collector like copper foil, an alloy current collector like lithium silver alloy, or a polymer current collector with conductive function, etc.

[0075] In some embodiments, the negative electrode sheet can be prepared by, but is not limited to, the following methods: A lithiophilic layer is deposited on the current collector, and a framework deposition layer is deposited on the lithiophilic layer.

[0076] In some embodiments, the formation of the lithiophilic layer on the current collector can be carried out in the following manner: A slurry is prepared by dispersing a lithiophilic substance, a conductive substance, and a binder in a solvent, and then coating it onto the surface of the current collector.

[0077] In some embodiments, the formation of the framework deposition layer on the lithiophilic layer can be performed in the following manner: After the slurry of the lithiophilic layer is coated on the surface of the current collector, the shaped skeleton deposition layer is placed on the slurry, then pressed and heated to dry, thus obtaining the negative electrode sheet.

[0078] It should be noted that the negative electrode sheet described in this application is not limited to the above-described operations during preparation. Those skilled in the art can also use other common methods based on actual conditions, and can also adjust some details of the above operation steps. For example, after the slurry is coated, it can be heated and dried first, and then the skeleton deposition layer can be placed and pressed. This is not limited.

[0079] In some embodiments, the solvent includes an aqueous solvent and / or an oil-based solvent. Specifically, the aqueous solvent includes deionized water, and the oil-based solvent includes N-methylpyrrolidone.

[0080] In some embodiments, the solid content of the slurry is 2 to 20 wt%.

[0081] In the technical solution of this application, the lithium affinity angle of the lithium affinity layer can be controlled by the solid content of the slurry during the preparation of the lithium affinity layer. The lower the solid content of the slurry, the smaller the lithium affinity angle. However, it is not limited to this. Those skilled in the art can also control it by other means, such as selecting different lithium affinity substances, or selecting different proportions of binders and conductive substances when coating the slurry (the higher the proportion of lithium affinity substances, the better the lithium affinity and the smaller the lithium affinity angle). There is no limitation on this.

[0082] In some embodiments, the framework deposition layer can be a commercially available product, a self-made product, or a further processed product of a commercially available product; there is no limitation on this. For example, the preparation steps of the framework deposition layer described in this application can be: After the plastic fiber film is impregnated and bonded with organic resin, it is pre-oxidized at 250~300℃ for 6~10h.

[0083] In some embodiments, the atmosphere during pre-oxidation is an oxygen-containing inert atmosphere, and the oxygen volume content in the atmosphere is 30-50%.

[0084] In some embodiments, the plastic fiber is a polyacrylonitrile-based fiber.

[0085] In some embodiments, the pressure during pressing is 0.1~0.6 MPa.

[0086] It should be noted that the electrical conductivity of the framework deposition layer described in this application can be controlled by the temperature and time during the pre-oxidation process. The higher the temperature and the longer the time, the higher the degree of oxidation and the higher the electrical conductivity. The resilience of the framework deposition layer is mainly achieved by selecting raw materials or by controlling the density of the framework deposition layer through the magnitude of the pressing pressure. However, it is not limited to this. Those skilled in the art can also control the electrical conductivity in other ways, such as introducing a certain amount of conductive material into the framework deposition layer to improve the overall electrical conductivity of the framework deposition layer.

[0087] In a second aspect, this application provides a secondary battery, including the negative electrode sheet described in this application.

[0088] In some embodiments, the secondary battery further includes an electrolyte comprising a solvent and a lithium salt.

[0089] In some embodiments, the solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents.

[0090] Exemplary examples include, but are not limited to, at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and fluoroethylene carbonate; carboxylic acid ester solvents include, but are not limited to, at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone; ether solvents include, at least one of dimethyltetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane; sulfone solvents include, at least one of methyl sulfone and dimethyl sulfoxide; nitrile solvents include, at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, and 1,3,6-hexanetrionitrile; and phosphate ester solvents include, at least one of trimethyl triphosphate and triethyl phosphate.

[0091] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium difluoromethanesulfonylimide, lithium ditrifluoromethanesulfonylimide, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0092] In some embodiments, the concentration of lithium salt in the electrolyte is 0.8~2 mol / L.

[0093] After selecting the negative electrode material described in this application for constructing a secondary battery, further adjusting the lithium salt content of the electrolyte based on the coating thickness of the graphite particle coating layer can effectively reduce the consumption of lithium salt and electrolyte in the SEI film formation and subsequent reversible lithium insertion / extraction process of the battery negative electrode sheet, which is beneficial to improving the cycle performance and float charge performance of the secondary battery.

[0094] In some embodiments, the secondary battery further includes a separator located between the positive electrode and the negative electrode.

[0095] It should be noted that the separator can be any of the battery separator materials available in the art. For example, the separator may include, but is not limited to, at least one of polypropylene and polyethylene.

[0096] In some embodiments, the secondary battery further includes a positive electrode sheet, which includes a current collector and a positive active material layer, the positive active material layer including a positive electrode material.

[0097] In some embodiments, the cathode material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium iron phosphate.

[0098] In some embodiments, the positive electrode active material layer further includes a binder and a conductive agent.

[0099] In some embodiments, the mass ratio of the positive electrode material, binder, and conductive agent is (70~90):(5~10):(5~10).

[0100] In some embodiments, the adhesive includes at least one selected from polyvinylidene fluoride, polyvinyl butyral, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, and polyvinyl alcohol.

[0101] In some embodiments, the conductive agent includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0102] In some embodiments, this application provides an electrical device including the secondary battery, which serves as the power supply for the electrical device.

[0103] The present invention is further illustrated below with specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention: Example 1 An embodiment of a negative electrode sheet and a secondary battery, wherein the preparation method of the secondary battery includes the following steps: Preparation of the negative electrode: A lithiophilic layer slurry is coated onto an 8μm thick copper foil current collector. The lithiophilic layer slurry has a particle size D. v500.2 μm elemental silver powder was used as the lithiophilic material, mixed with conductive material graphite and binder polyacrylic acid in a mass ratio of 10:1:9 in N-methylpyrrolidone to obtain a composite material (solid content 12 wt%). The framework deposition layer was then placed on the slurry coating of the lithiophilic layer and pressed under 0.2 MPa pressure. It was then heated to 80°C and dried for 5 min to obtain the negative electrode sheet. The framework deposition layer was obtained by shaving commercially available polyacrylonitrile-based fibers with an average fiber diameter of 6 μm, mixing them with 2 wt% carboxymethyl cellulose, and adding water to adjust the slurry. The slurry was then placed in a headbox and sent to a forming screen with a fine filter for natural dehydration and deposition, resulting in a wet film. Subsequently, it was impregnated with styrene-butadiene rubber (BASF SD417ap) and heated in a hot air box at 120°C for 3 min, then dried. Finally, it was heated to 275°C and held for 8 h in an argon atmosphere with 40% oxygen content to obtain the framework deposition layer. The cross-section of the negative electrode sheet was cut and observed under an electron microscope. Figure 1 As shown, the framework deposition layer and the lithiophilic layer have good bonding, and each structure is well preserved; Preparation of the positive electrode: Commercially available lithium nickel cobalt manganese oxide (LiNi) with an average particle size of 10 μm was used. 0.8 Co 0.1 Mn 0.1 O2), conductive carbon black SP (a conductive agent), and PVDF (a binder) are mixed in N-methylpyrrolidone at a mass ratio of 8:1:1 to prepare a slurry. This slurry is then coated onto an aluminum current collector foil and dried to obtain the positive electrode sheet. The areal density of the positive electrode sheet is 0.212 g / 1540.25 mm². 2 The compacted density is 4.25 g / cm³. 3 ; Preparation of electrolyte: Dimethyl carbonate and fluoroethylene carbonate are mixed at a volume ratio of 4:1 as solvent, and then lithium hexafluorophosphate (LiPF6) is added and mixed evenly to obtain the electrolyte, wherein the concentration of lithium hexafluorophosphate is 1 mol / L.

[0104] The negative electrode, separator, and positive electrode are stacked in sequence, the tabs are welded, and after hot pressing, they are sealed with aluminum-plastic film, liquid is injected, and then sealed again. Under these conditions, the battery is cyclically charged at 0.1C / 1C for two weeks to obtain the secondary battery.

[0105] Examples 2-15 An embodiment of a negative electrode sheet and a secondary battery differs from Embodiment 1 only in that the parameters during the preparation of the negative electrode sheet of the secondary battery are different, and the parameters of the negative electrode sheet are also different, as shown in Tables 1 and 2.

[0106] Example 16 An embodiment of a negative electrode sheet and a secondary battery differs from Embodiment 1 only in that the preparation method of the secondary battery includes the following steps: Preparation of the negative electrode: A lithiophilic layer slurry is coated onto an 8μm thick copper foil current collector. The lithiophilic layer slurry has a particle size D. v50 0.5 μm elemental gold powder was used as a lithiophilic material, and mixed with conductive acetylene black and binder styrene-butadiene rubber in a mass ratio of 10:1:9 in N-methylpyrrolidone to obtain the negative electrode sheet. The skeleton deposition layer was then placed on the slurry coating of the lithiophilic layer and pressed under a pressure of 0.2 MPa. The mixture was then heated to 80 °C and dried for 5 min to obtain the negative electrode sheet. The skeleton deposition layer is a graphene oxide film. The film is prepared by filtering a single-layer graphene oxide dispersion (item number 100056) purchased from Xianfeng Nano using a 0.1 μm filter membrane until the solid and liquid are completely separated, forming a porous film containing some graphene oxide. The film is then irradiated with ultraviolet light at a wavelength of 254 nm at a distance of 15 cm from the light source for 5 min.

[0107] Example 17 An embodiment of a negative electrode sheet and a secondary battery differs from Embodiment 1 only in that the preparation method of the secondary battery includes the following steps: Preparation of the negative electrode: A lithiophilic layer slurry is coated onto an 8μm thick copper foil current collector. The lithiophilic layer slurry has a particle size D. v50 Elemental indium powder with a thickness of 0.8 μm was used as a lithiophilic material and mixed with conductive material acetylene black and binder styrene-butadiene rubber in a mass ratio of 10:1:9 in N-methylpyrrolidone to obtain the negative electrode sheet. The skeleton deposition layer was then placed on the slurry coating of the lithiophilic layer and pressed under a pressure of 0.2 MPa. The mixture was then heated to 80 °C and dried for 5 min to obtain the negative electrode sheet. The skeleton deposition layer is a poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate fiber membrane. The membrane was prepared by coating an aqueous dispersion of PEDOT:PSS (Yingxin Laboratory product number TX80803) onto a separate substrate and drying it at 80 °C for 24 h to obtain a membrane containing poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate fiber.

[0108] Comparative Examples 1-4 A negative electrode sheet and a secondary battery are disclosed, which differ from Example 1 only in the parameters of the negative electrode sheet during its preparation, as shown in Table 1. The parameters of the negative electrode sheet are shown in Table 2.

[0109] Table 1 Continued from Table 1 Continued from Table 1 Table 2 Subsequently, the electrochemical performance of the secondary batteries obtained in each embodiment and comparative example was tested: (1) Cyclic performance test: The test was conducted at 25±3℃. Each secondary battery was charged to 4.25V at a constant current and constant voltage of 0.5C under a pressure of 0.3MPa, and the cut-off current was 0.02C. After standing for 5 minutes, it was discharged to 3V at a constant current of 1C and stood for 5 minutes. The above charge and discharge cycle was repeated until the capacity retention rate was less than 80%. The number of cycles was recorded. The more cycles, the better the cycle stability. (2) Fast charging performance test: The test was conducted at 25±3℃. Each secondary battery was charged to 4.25V with a constant current and constant voltage of 0.1C under a pressure of 0.3MPa, and the cutoff current was 0.02C. The battery was left to stand for 5 minutes, and then discharged to 3V with a constant current of 0.1C. The battery was left to stand for 5 minutes. The above charging and discharging cycle was repeated twice for activation. Then the battery was charged to 4.25V with a constant current and constant voltage of 1.5C, and the cutoff current was 0.02C. The ratio of the constant current charging capacity to the full charge charging capacity was recorded. The larger the ratio, the better the fast charging performance.

[0110] The test results are shown in Table 3.

[0111] Table 3 As can be seen from Table 3, in the technical solution of this application, the negative electrode sheet has a framework deposition layer containing porous material on the current collector as a deposition site for lithium metal. At the same time, a sandwiched lithiophilic layer is constructed between this layer and the current collector. The lithiophilic angle of the lithiophilic layer and the conductivity of the deposition layer are synergistically controlled. This not only effectively extends the cycle life of the corresponding secondary battery, but also achieves more than 70 cycles in the test. It also achieves excellent fast charging performance, with a fast charging capacity ratio of more than 70%, demonstrating excellent overall performance.

[0112] Meanwhile, a comparison of the embodiments shows that when the included angle of the lithiophilic layer and the conductivity of the framework deposition layer are further optimized to satisfy -2.8≤y+6.23lnx≤2.3, or the conductivity of the framework deposition layer is optimized to 1×10 - 3 S / cm ~ 1×10 -2 Alternatively, optimizing the lithium affinity angle of the lithium-affinity layer to 30-45° can further improve the uniformity and efficiency of lithium metal deposition while maintaining superior chemical stability. This can further enhance the fast charging and cycle performance of the secondary battery.

[0113] Furthermore, during the setup of the lithiophilic layer and the framework deposition layer, the main function of the lithiophilic layer is to serve as an ideal connection between the current collector and the framework deposition layer, as well as to induce lithium metal. The thickness of the framework deposition layer is related to the resistance of lithium metal deposition and the side reactions in contact with the electrolyte. When the thickness of these two elements is optimized and controlled so that the thickness ratio of the two elements satisfies 7.5≤A / B≤20, not only can the low resistance of lithium metal deposition and better kinetic performance be achieved, but the stability of the interlayer structure can also be guaranteed and the side reactions reduced, further improving the cycle stability and fast charging performance of the corresponding secondary battery.

[0114] When optimizing the thickness, the resilience of the framework deposition layer can also be further synergistically controlled. When the ratio of the thickness to the resilience of the framework deposition layer is optimized within the range of 45≤A / d≤60, the lithium-ion transport path can be shortened, the lithium metal deposition efficiency can be improved, and ultimately better fast charging performance can be achieved.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. 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 article without departing from the essence and scope of the technical solutions of this article.

Claims

1. A negative electrode sheet, characterized in that, The device includes a current collector, a lithiophilic layer disposed on the current collector, and a framework deposition layer, wherein the lithiophilic layer is disposed between the current collector and the framework deposition layer; the framework deposition layer comprises a porous material. The negative electrode plate satisfies -3.5≤y+6.23lnx≤3.5; Where x is the electrical conductivity of the skeleton deposition layer in S / cm, and y is the lithium affinity angle of the lithium affinity layer.

2. The negative electrode sheet as described in claim 1, characterized in that, The 1×10 -4 S / cm≤x≤2×10 -1 S / cm.

3. The negative electrode sheet as described in claim 1, characterized in that, The value is 11°≤y≤60°.

4. The negative electrode sheet as described in claim 1, characterized in that, The porosity of the skeleton deposition layer is greater than or equal to 40%.

5. The negative electrode sheet as described in claim 1, characterized in that, The porous material includes fibrous materials, which include at least one of glass fiber, ceramic fiber, polymer fiber, natural fiber, metal fiber, and carbon fiber.

6. The negative electrode sheet as described in claim 1, characterized in that, The lithiophilic layer comprises a lithiophilic material.

7. The negative electrode sheet as described in claim 6, characterized in that, The lithiophilic layer also includes conductive materials and / or binders.

8. The negative electrode sheet as described in claim 1, characterized in that, The negative electrode sheet satisfies: 1≤A / B≤60, where B is the thickness of the lithiophilic layer and A is the thickness of the framework deposition layer.

9. The negative electrode sheet as described in claim 8, characterized in that, The value is 1μm≤B≤10μm.

10. The negative electrode sheet as described in claim 8, characterized in that, The value is 10μm≤A≤60μm.

11. The negative electrode sheet as described in claim 10, characterized in that, The negative electrode sheet satisfies: 10≤A / d≤120, where d is the resilience of the skeleton deposition layer and A is the thickness of the skeleton deposition layer.

12. The negative electrode sheet as described in claim 11, characterized in that, The stated 50% ≤ d ≤ 100%.

13. A secondary battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1 to 12.

14. An electrical appliance, characterized in that, Includes the secondary battery of claim 13, wherein the secondary battery serves as the power supply for the electrical device.

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