Lithium supplementing additive, preparation method and application thereof

Abstract

This application provides a lithium replenishing additive, its preparation method, and its application. The lithium replenishing additive has a fibrous structure and includes a linear core material and a coating layer covering the linear core material. The linear core material includes multiple lithium replenishing particles, and the coating layer includes a polymer containing a metallo-oxime groups. This fibrous lithium replenishing additive can not only quickly extract active lithium to replenish lithium loss during the first charge, but also, because the coating layer of the additive is a polymer containing metallo-oxime groups, this polymer has a strong chelating ability for transition metal ions, thereby greatly reducing the risk of transition metal element dissolution and giving the battery good cycle performance, rate performance, and safety performance.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, specifically to a lithium supplement additive, its preparation method, and its application. Background Technology

[0002] During the first charge of a battery, a surface solid electrolyte membrane (SEI membrane) forms on the surfaces of the positive and negative electrodes. The formation of the SEI membrane consumes lithium in the battery and converts it into inactive lithium compounds, resulting in reversible lithium loss, reduced initial efficiency, and reduced battery discharge capacity.

[0003] To compensate for lithium loss caused by the formation of the SEI film during the first charge, lithium replenishment additives can be added to the positive electrode to compensate for the loss of active lithium. However, the transition metal elements in existing positive electrode lithium replenishment additives are prone to dissolution, causing side reactions in the electrolyte under the catalysis of transition metal ions, resulting in gas production and cracks in the electrode, reducing the structural stability of the electrode and limiting the battery capacity. In addition, transition metal ions can also damage the SEI film, thereby reducing the battery's cycle performance, rate performance, and safety performance. Summary of the Invention

[0004] In view of this, this application provides a fibrous lithium replenishment additive, which can not only quickly extract active lithium to replenish the lithium loss during the first charge, but also has a coating layer containing a polymer containing a amine oxime group. This polymer has a strong chelating ability for transition metal ions, which can greatly reduce the risk of transition metal element dissolution, so that the battery has high capacity and good cycle performance, rate performance and safety performance.

[0005] The first aspect of this application provides a lithium replenishing additive, which has a fibrous structure and includes a linear core and a skin covering the linear core. The linear core includes a plurality of lithium replenishing particles, and the skin includes a polymer containing a amine oxime group.

[0006] The lithium replenishing additive of this application has a fibrous structure. The fibrous structure of the lithium replenishing additive has a large specific surface area, which is beneficial to the wetting of the electrolyte and thus promotes the decomposition of the lithium replenishing particles. The lithium replenishing particles are encapsulated in a polymer containing a metallo-oxime groups. On the one hand, the metallo-oxime groups have a strong chelating ability for transition metal ions, which can quickly complex the transition metal ions generated by the decomposition of the lithium replenishing particles and inhibit the diffusion of transition metal ions in the electrolyte. On the other hand, the polymer coating layer makes the lithium replenishing additive easy to be wetted by the electrolyte, ensuring that the lithium replenishing particles have a fast decomposition rate, thereby achieving sufficient and effective lithium replenishment.

[0007] Optionally, the oximation rate of the polymer containing the amylopyridine oxime group is 45% to 60%.

[0008] Optionally, in the radial cross-section of the fibrous lithium supplement additive, the ratio of the radius R1 of the linear core material to the thickness R2 of the skin layer is (1~2.2):1.

[0009] Optionally, the mass ratio of the linear core material to the polymer containing the amylopyridine group is 1:(0.05-0.15).

[0010] Optionally, in the radial cross-section of the fibrous lithium supplement additive, the radius R1 of the linear core material is 5μm to 10μm, and the thickness R2 of the skin layer is 1μm to 6μm.

[0011] Optionally, the skin layer has a porous structure with an average pore size of 50 nm to 100 nm.

[0012] Optionally, the average particle size of the lithium replenishing particles is 0.5 μm to 1.5 μm.

[0013] Optionally, the polymer containing a methylamine oxime group has an electrical conductivity of 3 S / m to 3.6 S / m.

[0014] Optionally, the molecular weight of the polymer containing the amine oxime group is 50,000 to 150,000.

[0015] Optionally, the polymer containing a metallo-oxime group includes polyacrylonitrile containing a metallo-oxime group.

[0016] Secondly, this application provides a method for preparing a lithium supplement additive, comprising: obtaining a lithium supplement fiber with polymer-coated lithium supplement particles by electrospinning, wherein the polymer contains cyano groups;

[0017] The lithium-replenishing fiber is reacted with an oxime agent to obtain a fibrous lithium-replenishing additive, wherein the oxime agent is a compound having hydroxyl and amino groups; the fibrous lithium-replenishing additive includes a linear core material and a skin layer covering the linear core material, wherein the linear core material includes a plurality of lithium-replenishing particles, and the skin layer includes a polymer containing a hydroxylamine oxime group.

[0018] Optionally, the mass ratio of the oxime agent to the lithium-supplemented fiber is 1:(5-20).

[0019] Optionally, the oxime agent includes one or more of hydroxylamine, hydroxylamine hydrochloride, hydroxyurea sulfate, and 2-amino-3-hydroxypyridine.

[0020] Optionally, the electrospinning method includes: electrospinning with a polymer solution and a lithium-supplemented particle solution as electrospinning solutions, wherein the flow rate ratio of the lithium-supplemented particle solution to the polymer solution is 1:(0.25-4).

[0021] Optionally, the electrospinning process conditions are: voltage less than or equal to 30kV, injection speed less than or equal to 10mL / h, humidity 30% to 70%, and the diameter of the spinning needle is 0.5mm to 1mm.

[0022] Optionally, the step of reacting the lithium-replenishing fiber with an oxime agent to obtain a fibrous lithium-replenishing additive includes: placing the lithium-replenishing fiber in a solution containing an oxime agent, adding an alkaline substance, and mixing to obtain a fibrous lithium-replenishing additive.

[0023] Thirdly, this application provides a positive electrode sheet, which includes an active material and a lithium supplementation additive as described in the first aspect.

[0024] Fourthly, this application provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte includes a fibrous lithium-replenishing additive as described in the third aspect of this application.

[0025] Fifthly, this application provides an electronic device comprising a secondary battery as described in the fourth aspect. Attached Figure Description

[0026] Figure 1 A schematic diagram illustrating the principle of positive electrode lithium replenishment provided in an embodiment of this application;

[0027] Figure 2 A schematic diagram illustrating the reaction between a polymer containing a amine oxime group and transition metal ions, provided in one embodiment of this application.

[0028] Figure 3 A schematic radial cross-section of a fibrous lithium-replenishing additive provided in an embodiment of this application;

[0029] Figure 4 This is a schematic diagram of an electrospinning apparatus provided in an embodiment of this application;

[0030] Figure 5 This is a schematic cross-sectional view of a spinning needle provided in an embodiment of this application;

[0031] Figure 6 This is a schematic diagram of the structure of a lithium-supplementing fiber provided in an embodiment of this application. Figure 6 (a) in the figure is a schematic cross-section of the lithium-supplemented fiber in the fiber extension direction. Figure 6 (b) is a schematic diagram of the cross-section of the lithium-supplemented fiber perpendicular to the fiber extension direction;

[0032] Figure 7 This is a schematic diagram of the structure of a fibrous lithium supplementary additive provided in one embodiment of this application. Figure 7 (a) in the figure is a schematic cross-section of the fibrous lithium supplementation additive in the fiber extension direction. Figure 7(b) is a schematic diagram of a cross-section of the fibrous lithium supplementation additive perpendicular to the fiber extension direction;

[0033] Figure 8 This is a scanning electron microscope image of the fibrous lithium supplementation additive provided in Example 1 of this application;

[0034] Figure 9 This is a scanning electron microscope image of the fibrous lithium supplementation additive provided in Example 1 of this application. Detailed Implementation

[0035] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0036] The core components of a lithium-ion rechargeable battery include the positive electrode, negative electrode, electrolyte, separator, and corresponding connecting components and circuits. During charging, lithium ions are released from the positive electrode lattice, transported through the electrolyte, and then inserted into or react with the negative electrode. During discharging, lithium ions are released from the negative electrode, transported through the electrolyte, and then inserted into the positive electrode lattice. However, during the first charge of a lithium-ion rechargeable battery, some electrolyte undergoes a reduction reaction on the surface of the negative electrode, simultaneously combining with the lithium ions released from the positive electrode to form a solid electrolyte interphase (SEI) film. The formation of the SEI film consumes active lithium in the battery, converting it into inactive lithium compounds, resulting in reversible lithium loss and reducing the battery's initial efficiency and discharge capacity. To compensate for the lithium loss during the first charge, active lithium needs to be replenished to the battery. Positive electrode lithium replenishment has advantages such as simple process, low cost, and high safety. Please refer to [link to relevant documentation]. Figure 1 , Figure 1 This is a schematic diagram illustrating the principle of positive electrode lithium replenishment according to an embodiment of this application. Figure 1In this lithium-ion battery, A1 is the negative electrode, S1 is the solid electrolyte interphase (SEI) film on the negative electrode surface, and C1 is the positive electrode. The positive electrode contains a lithium-replenishing additive. During the operation of the lithium-ion secondary battery, the lithium-replenishing additive in the positive electrode decomposes and provides active lithium, thereby compensating for the active lithium ions consumed when the SEI film is formed on the negative electrode surface and restoring the irreversible capacity lost in the first cycle. However, existing positive electrode lithium-replenishing additives contain transition metal elements. These transition metal elements can leach out during battery cycling and accumulate on the negative electrode side. Free transition metal elements in the electrolyte not only catalyze the decomposition of the electrolyte but also damage the SEI film, leading to a decrease in the battery's cycle performance, rate performance, and safety performance. To address this, this application provides a fibrous lithium-replenishing additive. The polymer coating layer in this additive can inhibit the diffusion of transition metal ions in the electrolyte, achieving efficient lithium replenishment while reducing the risk of transition metal dissolution, ensuring that the battery has high capacity and good cycle performance, rate performance, and safety performance.

[0037] In this embodiment, the fibrous lithium-replenishing additive includes a core material and a skin layer covering the core material. The core material includes multiple lithium-replenishing particles arranged and stacked linearly to form a linear core material. The skin layer includes a polymer containing a amine oxime group. The polymer containing a amine oxime group refers to a polymer containing the functional group amine oxime. In some embodiments of this application, the structural formula of the polymer containing a amine oxime group is shown in formula (I):

[0038]

[0039] In formula (I), R1 and R2 are independently selected from substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted cycloalkyl, and substituted or unsubstituted aryl groups. Modifying the polymer in the skin layer with a metallo-oxime group (—C(NOH)NH2) in this application can enable the lithium-supplementing additive to complex transition metal ions. Please refer to [link to relevant documentation]. Figure 2 , Figure 2 This is a schematic diagram illustrating the reaction principle of a polymer containing a metallo-oxime group with transition metal ions according to an embodiment of this application. The metallo-oxime group has a chelating effect and can react with transition metal ions to form a complex, thereby inhibiting the release of transition metal ions into the electrolyte.

[0040] In this application, the amylopyxime group in the polymer is obtained by oximation treatment of the cyano group in the raw material polymer. The oximation rate refers to the conversion rate of the cyano group to the amylopyxime group, that is, the molar ratio of the amylopyxime group in the polymer after the reaction to the cyano group in the polymer before the reaction. In the embodiments of this application, the oximation rate of the polymer containing the amylopyxime group is 45% to 60%, and the specific oximation rate of the polymer containing the amylopyxime group can be, but is not limited to, 45%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, or 60%. When the content of amine oxime groups in the polymer is controlled between 45% and 60%, the lithium-replenishing additive can fully complex the transition metal elements dissolved from the positive electrode active material after phase transition during charging and discharging, inhibiting the transfer of transition metal elements to the negative electrode side and ensuring that the battery has a high capacity. Furthermore, the polymer containing amine oxime groups has good conductivity, ensuring the complete decomposition of the lithium-replenishing additive. In some embodiments of this application, the adsorption amount of metal elements by the polymer containing amine oxime groups is greater than or equal to 80 ppm.

[0041] In some embodiments of this application, the polymer containing a metallo-oxime group includes polyacrylonitrile containing a metallo-oxime group. Polyacrylonitrile has a stable long-chain structure and good conductivity. When used as a coating layer, the metallo-oxime-containing polyacrylonitrile can act as an electron transfer medium to promote electron transfer between the electrolyte and the lithium replenishment particles, thereby ensuring that the lithium replenishment particles can decompose quickly and fully to provide active lithium. Moreover, polyacrylonitrile contains cyano groups, so the cyano groups can be directly converted into metallo-oxime groups through oximation treatment, making the preparation method simpler. In addition, polyacrylonitrile is abundant, inexpensive, and environmentally friendly, not only having the advantages of environmental friendliness but also achieving uniform coating of the lithium replenishment particle surface at a low cost. In some embodiments of this application, the average molecular weight of the metallo-oxime-containing polyacrylonitrile is 50,000 to 150,000. The average molecular weight of the metallo-oxime-containing polyacrylonitrile can specifically be, but is not limited to, 50,000, 80,000, 100,000, 120,000, or 150,000. In some embodiments of this application, the polymer containing a metallo-oxime group has an electrical conductivity of 3 S / m to 3.6 S / m. Specifically, but not limited to, the electrical conductivity of the polymer containing a metallo-oxime group may be 3 S / m, 3.2 S / m, 3.3 S / m, 3.5 S / m, or 3.6 S / m. The higher electrical conductivity of the polymer containing a metallo-oxime group in the coating layer is beneficial for promoting the decomposition of lithium-supplementing particles.

[0042] In some embodiments of this application, the lithium replenishing particles in the core material can specifically be one or more of Li6CoO4, Li5FeO4, Li2NiO2, Li2CuO2, Li3N, Li2O, and Li2C2O4. The lithium replenishing specific capacity of these compounds can reach 500mAh / g to 900mAh / g, far exceeding the specific capacity of the cathode material. Therefore, they can fully compensate for the irreversible capacity loss of lithium secondary batteries and have excellent lithium replenishing capabilities. In some embodiments, the lithium replenishing particles include Li5FeO4, whose metallo-oxime groups have good complexing properties for iron ions, thus more effectively suppressing the dissolution of iron ions from the lithium replenishing particles. In some embodiments of this application, the average particle size of the lithium replenishing particles is 0.5μm to 1.5μm. The average particle size of the lithium replenishing particles can specifically be, but is not limited to, 0.5μm, 0.8μm, 1μm, 1.2μm, or 1.5μm. Lithium-replenishing particles within this particle size range can be more evenly distributed in the core material, making them less prone to agglomeration. Furthermore, the polymer in the skin layer can fully coat the lithium-replenishing particles, ensuring that the lithium-replenishing additive has good structural stability.

[0043] Please see Figure 3 , Figure 3 This is a schematic diagram of the radial cross-section of a fibrous lithium-replenishing additive provided in an embodiment of this application. The radial cross-section of the fibrous lithium-replenishing additive refers to the cross-section perpendicular to the fiber extension direction. Figure 3 In this embodiment, the core material 20 is encased within the lithium-supplementing additive by the skin layer 10. R1 represents the radius of the core material 20, and R2 represents the thickness of the skin layer 10. In this application, the radial cross-section of the core material includes a circular, elliptical, or irregular shape, and the radius R1 of the core material refers to the radius of the circumcircle of the radial cross-section. In some embodiments of this application, the average radius R1 of the core material is 5 μm to 10 μm, and the average thickness R2 of the skin layer is 1 μm to 6 μm. The average radius R1 of the core material can specifically be, but is not limited to, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, and the average thickness R2 of the skin layer can specifically be, but is not limited to, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or 6 μm. In some embodiments of this application, the ratio of the average radius R1 of the core material to the average thickness R2 of the skin layer is (1 to 2.2):1. The ratio of the average radius R1 of the core material to the average thickness R2 of the skin layer can be, but is not limited to, 1:1, 1.2:1, 1.5:1, 1.7:1, 2:1, or 2.2:1. Controlling the ratio of the core material radius to the skin layer thickness R2 ensures that the lithium-replenishing additive has a fast decomposition rate, enabling rapid decomposition to provide active lithium, and the skin layer can effectively inhibit the dissolution of transition metals in the lithium-replenishing particles. In some embodiments of this application, the mass ratio of the core material to the polymer containing a metallo-oxime group is 1:(0.05~0.15). The mass ratio of the core material to the polymer containing a metallo-oxime group can be, but is not limited to, 1:0.05, 1:0.08, 1:0.1, or 1:0.15.

[0044] In some embodiments of this application, the area ratio of multiple lithium-replenishing particles in the radial cross-section of the fibrous lithium-replenishing additive is 80% to 90%. This area ratio can be understood as the ratio of the total area of ​​multiple lithium-replenishing particles to the area of ​​the radial cross-section of the lithium-replenishing additive. A higher area ratio of lithium-replenishing particles in the lithium-replenishing additive ensures that the lithium-replenishing additive has a higher lithium-replenishing capacity.

[0045] In this application, the lithium replenishing additive has a fibrous structure. In some embodiments, the average length of the fibrous lithium replenishing additive is 2000 μm to 5000 μm, and the average diameter is 10 μm to 15 μm. In some embodiments, the aspect ratio of the fibrous lithium replenishing additive is 1:(130 to 500). The fibrous structure of the lithium replenishing additive has a large specific surface area, which is beneficial for the electrolyte to fully wet the lithium replenishing additive, thereby promoting the decomposition of the lithium replenishing particles and enabling the lithium replenishing particles to fully release active lithium. In some embodiments, the skin layer has a porous structure, which can further increase the specific surface area, thereby promoting electrolyte wetting. In some embodiments, the average pore size of the porous structure is 50 nm to 100 nm, and the average pore size of the porous structure can be, but is not limited to, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm. The average pore size of the porous structure of the skin layer can be obtained by BET specific surface area testing.

[0046] In the lithium replenishment additive provided in this application, the lithium replenishment particles are coated with a conductive polymer, which greatly improves the conductivity of the material and also enhances the wettability of the electrolyte to the material. The polymer is modified with a amine oxime group, which gives the lithium replenishment additive a strong chelating ability for transition metal ions, thereby inhibiting the dissolution of transition metal ions and ensuring that the battery has excellent cycle performance, rate performance and safety performance.

[0047] This application also provides a method for preparing the above-mentioned fibrous lithium supplementation additive, comprising the following steps:

[0048] Step 100: Prepare lithium-replenishing particle solution and polymer solution respectively, wherein the polymer in the polymer solution contains cyano groups;

[0049] Step 200: Electrospinning is performed using the lithium-supplemented particle solution and the polymer solution as electrospinning solutions to obtain lithium-supplemented fibers;

[0050] Step 300: React lithium-supplementing fibers with an oxime agent to obtain fibrous lithium-supplementing additives. The oxime agent is a compound with hydroxyl and amino groups.

[0051] In step 100 of this application, the particle size of the lithium-replenishing particles in the lithium-replenishing particle solution is 0.5 μm to 1.5 μm. This particle size range is beneficial for the uniform distribution of lithium-replenishing particles in the fiber and for the polymer to uniformly coat the particle surface. In some embodiments of this application, the original lithium-replenishing particles are ball-milled to refine the size of the lithium-replenishing particles and optimize their morphological regularity. In some embodiments of this application, the ball-milling process includes: placing the lithium-replenishing particles in a ball mill jar and adding ethanol. The addition of ethanol can inhibit the adhesion of raw materials to the inner wall of the ball mill jar, thereby improving the quality and efficiency of the ball milling process. The ball-milled lithium-replenishing particles are dried in a vacuum oven at 80°C, pulverized, and then passed through a 300-400 mesh sieve to remove larger particles or other impurities, thus obtaining lithium-replenishing particles. The obtained lithium-replenishing particles are added to an organic solvent, which includes at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide (DMAC). In some embodiments of this application, the temperature for mixing the lithium replenishing particles with the organic solvent is 50°C to 80°C, the mixing time is 1h to 5h, and the mass percentage of lithium replenishing particles in the mixed solution is 2% to 20%.

[0052] In this application, the polymer in the polymer solution is a cyano-containing polymer. In some embodiments, the polymer includes polyacrylonitrile (PAN). The cyano group in PAN allows for direct subsequent oxime treatment, simplifying the preparation process. PAN contains polymer chains, exhibiting good conductivity and good solubility in organic solvents, which facilitates uniform coating of lithium-supplementing particles. Furthermore, PAN has a lower cost, reducing production costs. In some embodiments of this application, the polymer mass percentage in the polymer solution is 10%–30%, specifically, but not limited to, 10%, 15%, 20%, 25%, or 30%. In some embodiments of this application, the preparation of the polymer solution includes: drying the organic solvent in an oven to remove water, then mixing the polymer with the organic solvent and performing ultrasonic defoaming to obtain the polymer solution. The organic solvent includes at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide (DMAC).

[0053] In step 200 of this application, the lithium-added particles are encapsulated inside the polymer using electrospinning. (See [link to application]). Figure 4 , Figure 4 This is a schematic diagram of an electrospinning apparatus provided in an embodiment of this application. Figure 4In this diagram, 1 represents a DC positive high-voltage power supply with a voltage range of 0–30 kV; 2 represents the wires and electrodes; 3 represents the spinning needle; 4 represents the jet of polymer-coated lithium-replenishing particles; and 5 represents the grounded receiving screen. In some embodiments of this application, the polymer solution and the lithium-replenishing particle solution are injected into the spinning needle through different channels; please refer to [reference needed]. Figure 5 , Figure 5 This is a schematic cross-sectional view of a spinning needle provided in an embodiment of this application. 31 is the inlet for the lithium replenishment particle solution, and 32 is the inlet for the polymer solution. The polymer solution channel covers the outside of the lithium replenishment particle solution channel. A spinning needle with this structure can form lithium-replenishing fibers with polymer-coated lithium replenishment particles. Please refer to... Figure 6 , Figure 6 This is a schematic diagram of the structure of a lithium-supplementing fiber provided in an embodiment of this application. Figure 6 (a) in the figure is a schematic cross-section of the lithium-supplemented fiber in the fiber extension direction. Figure 6 (b) is a schematic diagram of the cross-section of the lithium-supplemented fiber perpendicular to the fiber extension direction.

[0054] In some embodiments of this application, the electrospinning steps include: using a polymer solution and a lithium-supplemented particle solution as the electrospinning solution; loading the electrospinning solution into a syringe and placing it on a micro-injection pump; connecting the syringe to a spinning needle via a tubing; connecting the positive terminals of different high-voltage electrostatic transmitters to the spinning needle and the cylindrical auxiliary electrode, respectively; and grounding the receiving device. Before starting electrospinning, the spinning distance is adjusted to push the spinning solution to the spinning needle to form a suspended droplet. After setting the pushing rate, the high-voltage electrostatic transmitter is turned on, the cylindrical voltage is set to 10kV to 15kV, and the spinning needle voltage is adjusted to perform electrospinning. Specifically, the spinning voltage is less than or equal to 30V, the injection speed is less than or equal to 10mL / h, the spinning distance is 8cm to 25cm, the diameter of the spinning needle is 0.5mm to 1mm, the ambient temperature is 15℃ to 30℃, and the ambient humidity is 30% to 70%. In some embodiments of this application, the flow ratio of the lithium-replenishing particle solution to the polymer solution is 1:(0.25-4). Specifically, but not limited to, the flow ratio can be 1:0.25, 1:0.5, 1:0.7, 1:0.1, 1:2, 1:3, or 1:4. By adjusting the flow ratio of the lithium-replenishing particle solution to the polymer solution, the diameter of the lithium-replenishing fiber and the thickness of the polymer coating can be controlled, resulting in good structural stability of the lithium-replenishing additive.

[0055] In step 300 of this application, the lithium-supplementing fiber is reacted with an oxime agent to react the cyano groups in the polymer to generate a metallo-oxime group, thereby obtaining a fibrous lithium-supplementing additive. The oxime agent is a compound having hydroxyl and amino groups. In some embodiments of this application, the oxime agent includes one or more of hydroxylamine, hydroxylamine hydrochloride, hydroxyurea sulfate, and 2-amino-3-hydroxypyridine. In some embodiments of this application, the mass ratio of the oxime agent to the lithium-supplementing fiber is 1:(5-20), and the specific mass ratio may be, but is not limited to, 1:5, 1:8, 1:10, 1:12, 1:15, or 1:20. Please refer to [link to previous application]. Figure 7 , Figure 7 This is a schematic diagram of the structure of a fibrous lithium supplementary additive provided in one embodiment of this application. Figure 7 (a) in the figure is a schematic cross-section of the fibrous lithium supplementation additive in the fiber extension direction. Figure 7 (b) is a schematic diagram of a cross-section of the fibrous lithium supplementation additive perpendicular to the fiber extension direction. Figure 7 In (b), the polymer is modified with a amine oxime group (—C(NOH)NH2).

[0056] In some embodiments of this application, the reaction between the lithium-supplementing fiber and the oxime agent includes: dissolving the oxime agent in an organic solvent to obtain an oxime agent solution, wherein the organic solvent includes one or more of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide; placing the lithium-supplementing fiber in the oxime agent solution; adding sodium bicarbonate and sodium hydroxide; reacting at 55°C-65°C while stirring and mixing simultaneously; and centrifuging and drying the mixture after the reaction to obtain a fibrous lithium-supplementing additive. In some embodiments of this application, hydroxylamine hydrochloride is used as the oxime agent, and the reaction equation between the polymer and hydroxylamine hydrochloride is shown in formula (II):

[0057]

[0058] The method for preparing the fibrous lithium-replenishing additive provided in this application involves coating the surface of lithium-replenishing particles with a polymer using electrospinning and then subjecting the polymer to oxime treatment to modify it with a metallo-oxime group (general formula RC(NOH)NH2). This structure not only provides excellent conductivity but also effectively inhibits the dissolution of transition metal elements in the lithium-replenishing agent. This preparation method is highly compatible with existing lithium-replenishing additive production lines, requiring only the addition of an electrospinning treatment line to the end of the existing lithium-replenishing agent production line without significant changes to the original production line architecture, making the solution easy to implement. The processing environment of this method is ambient temperature and pressure, eliminating the need for an additional closed system and resulting in lower production costs. Furthermore, the electrospinning technology used in this preparation method allows for rapid coating of lithium-replenishing particles, with uniform and controllable coating thickness, resulting in a lithium-replenishing additive with a large specific surface area and a high product yield.

[0059] This application also provides a positive electrode sheet comprising an active material and the fibrous lithium-supplementing additive of this application. In some embodiments of this application, the active material comprises one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, ternary materials, lithium manganese phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, lithium vanadium oxide, and lithium-rich manganese-based materials.

[0060] In some embodiments of this application, the mass ratio of the fibrous lithium-replenishing additive to the active material is 1:(10-100), meaning the amount of the fibrous lithium-replenishing additive relative to the active material is 1%-10%. Specifically, the mass ratio can be, but is not limited to, 1:10, 1:15, 1:20, 1:50, 1:80, or 1:100. In some embodiments of this application, the mass ratio of the fibrous lithium-replenishing additive to the active material is 1:(20-50), meaning the amount of the fibrous lithium-replenishing additive relative to the active material is 2%-5%. Controlling the amount of fibrous lithium-replenishing additive ensures sufficient lithium replenishment to the battery, improves the battery's initial efficiency, and helps control the formation process time, reducing the occurrence of side reactions.

[0061] In some embodiments of this application, the positive electrode includes a current collector and an active material layer disposed on the current collector. The active material layer includes an active material and a fibrous lithium-supplementing additive. In some embodiments of this application, the active material layer further includes a conductive agent and a binder. The conductive agent may be one or more of graphite, carbon fiber, carbon black, acetylene black, carbon nanotubes, activated carbon, graphene, metal powder, and metal oxide. The binder may be one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polyamide, polyacrylonitrile, and polyacrylate.

[0062] In some embodiments of this application, the active material comprises 80%-99% by mass in the active material layer. Specifically, but not limited to, 80%, 85%, 89%, 90%, 93%, 95%, 98%, or 99% by mass. In some embodiments of this application, the fibrous lithium-supplementing additive comprises 0.1%-15% by mass in the active material layer. Specifically, but not limited to, 0.1%, 1%, 3%, 5%, 10%, or 15% by mass. In some embodiments of this application, the binder comprises 0.1%-15% by mass in the active material layer; in some embodiments, the binder comprises 1%-7% by mass. In some embodiments of this application, the conductive agent comprises 0.1%-20% by mass in the active material layer; in some embodiments, the conductive agent comprises 1%-10% by mass.

[0063] This application also provides a method for preparing the above-mentioned positive electrode sheet. In some embodiments, the method for preparing the positive electrode sheet includes a direct mixing method, which includes: mixing fibrous lithium-supplementing additives, positive electrode materials, conductive agents, binders, and solvents to form a positive electrode slurry; coating the positive electrode slurry onto the surface of a current collector; and drying to obtain the positive electrode sheet. The solvent can be any solvent available in the prior art, such as one or more selected from N-methylpyrrolidone (NMP), dimethylformamide (DMF), diethylformamide (DEF), dimethyl sulfoxide (DMSO), and tetrahydrofuran (THF). The amount of solvent used is such that the content of active material in the slurry is 20-90 wt%, and further, the amount of solvent used is such that the content of active material in the slurry is 40-85 wt%. In some embodiments of this application, the drying temperature of the positive electrode sheet is 60°C to 150°C, preferably 80°C to 130°C, and the drying time is 0.5 h to 5 h.

[0064] In some embodiments of this application, the positive electrode sheet includes a current collector, a positive electrode material layer, and a lithium replenishment layer sequentially disposed therefrom. The positive electrode material layer includes an active material, and the lithium replenishment layer includes a fibrous lithium replenishment additive. In some embodiments of this application, the positive electrode material layer includes an active material, a conductive agent, and a binder, and the lithium replenishment layer includes a fibrous lithium replenishment additive, a conductive agent, and a binder. In some embodiments, the preparation method of the positive electrode sheet includes a coating method, which includes: mixing the positive electrode material, the conductive agent, the binder, and a solvent to form a positive electrode slurry; coating the positive electrode slurry onto the surface of the current collector to form a positive electrode material layer; and then applying the fibrous lithium replenishment additive, the conductive agent, and the binder onto the surface of the positive electrode material layer to form a lithium replenishment layer, thereby obtaining the positive electrode sheet.

[0065] This application also provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode includes the positive electrode sheet provided in this application. The secondary battery provided in this application has higher capacity and cycle performance due to the use of the positive electrode sheet of this application. In some embodiments of this application, the secondary battery includes a lithium secondary battery.

[0066] In this application, the negative electrode of the secondary battery can be any negative electrode known in the art. In the embodiments of this application, the negative electrode may include one or more of carbon-based, silicon-based, tin-based, and lithium-based negative electrodes. Specifically, the carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, etc.; the silicon-based negative electrode may include silicon, silicon-carbon, silicon-oxygen, silicon metal compounds, or a mixture of these silicon-containing materials with non-silicon-containing materials such as graphite; the tin-based negative electrode may include tin, tin-carbon, tin-oxygen, tin metal compounds, or a mixture of these tin-containing materials with non-tin-containing materials such as graphite; the lithium-based negative electrode may include metallic lithium or a lithium alloy. Specifically, the lithium alloy may be at least one of lithium-silicon alloy, lithium-sodium alloy, lithium-potassium alloy, lithium-aluminum alloy, lithium-tin alloy, and lithium-indium alloy. In some embodiments of this application, the current collector of the negative electrode is copper foil, and the negative electrode active material includes one or more of natural graphite, artificial graphite, hard carbon, soft carbon, lithium titanate, iron oxide, lithium titanium phosphate, titanium dioxide, silicon, silicon suboxide, tin and its oxides, and antimony and its oxides; the binder includes one or more of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), and styrene-butadiene latex (SBR); the conductive agent includes one or more of acetylene black, Ketjen carbon black, Super-P, carbon nanotubes, carbon nanofibers, activated carbon, and graphene. In this application, the negative electrode can be prepared using any method known in the art.

[0067] In this application, the separator of the secondary battery can be any separator known to those skilled in the art. For example, the separator can be one or more of polyolefin microporous membrane, polyethylene terephthalate, polyethylene felt, glass fiber felt or ultrafine glass fiber paper.

[0068] In this application, the electrolyte of the secondary battery comprises a solution of an electrolyte lithium salt in a non-aqueous solvent. In embodiments of this application, the electrolyte lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluorosilicate (Li2SiF6), lithium tetraphenylborate (LiB(C6H5)4), lithium chloride (LiCl), lithium bromide (LiBr), lithium chloroaluminate (LiAlCl4), lithium fluorocarbon sulfonate (LiC(SO2CF3)3), LiCH3SO3, LiN(SO2CF3)2, and LiN(SO2C2F5)2. In some embodiments of this application, the non-aqueous solvent includes one or more of chain esters and cyclic esters. In some embodiments of this application, the chain ester includes one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), and dipropyl carbonate (DPC). In some embodiments of this application, the chain esters include fluorinated, sulfur-containing, or unsaturated chain organic esters. In some embodiments of this application, the cyclic esters include one or more of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), γ-butyrolactone (γ-BL), and sulpholactone. In some embodiments of this application, the cyclic esters include fluorinated, sulfur-containing, or unsaturated cyclic organic esters. In some embodiments of this application, the non-aqueous solvent includes one or more of chain ethers and cyclic ether solutions. In some embodiments of this application, the cyclic ethers include one or more of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL), and 4-methyl-1,3-dioxolane (4-MeDOL). In some embodiments of this application, the cyclic ethers include fluorinated, sulfur-containing, or unsaturated cyclic organic ethers. In some embodiments of this application, the chain ether includes one or more of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), 1,2-dimethoxypropane (DMP), and diethylene glycol dimethyl ether (DG). In some embodiments of this application, the chain ether includes fluorine-containing, sulfur-containing, or unsaturated chain organic ethers. In some embodiments of this application, the concentration of the electrolyte lithium salt in the electrolyte is 0.1 mol / L to 15 mol / L. In some embodiments of this application, the concentration of the electrolyte lithium salt is 1 mol / L to 10 mol / L.

[0069] In the embodiments of this application, the battery can be fabricated using either a lamination process or a winding process. In some embodiments of this application, the battery is fabricated using a lamination process.

[0070] This application also provides an electronic device that includes a secondary battery provided in this application, which powers the electronic device.

[0071] The technical solution of this application will be further described below with reference to several embodiments.

[0072] Example 1

[0073] 1) Preparation of fibrous lithium-supplementing additives

[0074] Preparation of lithium-replenishing particle solution: Li5FeO4 was ball-milled to obtain lithium-replenishing particles with an average particle size of 1μm. After vacuum drying at 80℃, the Li5FeO4 particles were added to DMAc solvent at 60℃, heated and stirred for 3h, and cooled to room temperature to obtain a lithium-replenishing particle solution with a mass fraction of 10%.

[0075] Preparation of lithium-supplemented fibers: A 15% (w / w) PAN solution was prepared by mixing polyacrylonitrile (PAN, conductivity 20 S / m) and methylacetamide (DMAc). The electrospinning solution was loaded into a medical syringe and placed on a micro-injection pump. A spinning needle was connected via a tubing. Different high-voltage electrostatic emitters were connected to the positive electrodes of the spinning needle and the cylindrical auxiliary electrode, respectively. The spinning voltage was 25 kV, the flow rate of the lithium-supplemented particle solution was 4 mL / h, the flow rate of the polymer solution was 6 mL / h, the spinning distance was 15 cm, the spinning needle diameter was 0.8 mm, the ambient temperature was 25 °C, and the ambient humidity was 30%.

[0076] Oximation treatment: 10g of hydroxylamine hydrochloride was added to 100mL of N,N dimethylformamide, heated to 45℃ and stirred for 30min to obtain a hydroxylamine hydrochloride solution. 5g of sodium bicarbonate and 2g of sodium hydroxide were added, and the mixture was stirred at 60℃ for 1h. Then, 100g of lithium-supplementing fiber was added to the reaction vessel, dispersed, and heated to 80℃ for 12h. 2.5g of sodium bicarbonate and 1g of sodium hydroxide were added and reacted for 6h. After cooling, the oximated fiber was obtained by centrifugation at 8000rpm and baked in a vacuum oven to obtain a fibrous lithium-supplementing additive.

[0077] 2) Preparation of lithium secondary batteries

[0078] Lithium cobalt oxide, fibrous lithium supplementation additive, conductive agent (Super P), and binder (polyvinylidene fluoride, PVDF) were mixed in a weight ratio of 93:3:2:2. N-methylpyrrolidone was added and stirred into a homogeneous slurry. The slurry was coated on aluminum foil, dried at 100°C for 4 hours, and then rolled and slit to obtain the positive electrode sheet.

[0079] A negative electrode slurry is prepared by mixing carbon-coated silicon suboxide, conductive agent (Super P), and binder (sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR)) in a weight ratio of 90:5:5. The slurry is then coated onto a copper foil current collector, and after drying, rolling, and slitting, a negative electrode sheet is obtained.

[0080] Preparation of the full cell: The positive electrode, separator, and negative electrode prepared above were sequentially stacked to form a cell. The cell was housed in a battery casing, and an electrolyte (a 1 mol / L LiPF6 EC+DEC mixture (EC:DEC volume ratio 1:1)) was injected. The battery casing was then sealed to obtain the full cell. The cycle life and energy density of the full cell were tested.

[0081] Preparation of half-cell: The positive electrode sheet prepared above is assembled with a lithium metal sheet to form a coin cell.

[0082] Example 2

[0083] Example 2 uses the same method as Example 1 to prepare lithium-replenishing particle solution and polymer solution. The difference between Example 2 and Example 1 is that in Example 2, when preparing lithium-replenishing fibers, the flow rate of lithium-replenishing particle solution is 1.5 mL / h and the flow rate of polymer solution is 8.5 mL / h. The same method as Example 1 is used to prepare fibrous lithium-replenishing additive and lithium secondary battery.

[0084] Example 3

[0085] Example 3 uses the same method as Example 1 to prepare lithium-replenishing particle solution and polymer solution. The difference between Example 3 and Example 1 is that in Example 2, when preparing lithium-replenishing fibers, the flow rate of lithium-replenishing particle solution is 8.5 mL / h and the flow rate of polymer solution is 1.5 mL / h. Fibrous lithium-replenishing additive and lithium secondary battery are prepared using the same method as Example 1.

[0086] Example 4

[0087] Example 4 uses the same method as Example 1 to prepare lithium-supplementing fibers. The difference between Example 4 and Example 1 is that Example 4 undergoes oxime treatment: 4g of hydroxylamine hydrochloride is added to 100mL of N,N dimethylformamide, that is, the mass of hydroxylamine hydrochloride is different from that in Example 1. After the reaction, fibrous lithium-supplementing additives are obtained, and lithium secondary batteries are prepared using the same method as in Example 1.

[0088] Example 5

[0089] Example 5 uses the same method as Example 1 to prepare lithium-supplementing fibers. The difference between Example 5 and Example 1 is that Example 5 undergoes oxime treatment: 25g of hydroxylamine hydrochloride is added to 100mL of N,N dimethylformamide, that is, the mass of hydroxylamine hydrochloride is different from that in Example 1. After the reaction, fibrous lithium-supplementing additives are obtained, and lithium secondary batteries are prepared using the same method as in Example 1.

[0090] Example 6

[0091] The difference between Example 6 and Example 1 is that the polymer used is polyphenylene nitrile with a conductivity of 5 S / m, the mass fraction of the polymer solution is 15%, and the fibrous lithium supplementation additive and lithium secondary battery are prepared using the same method as in Example 1.

[0092] Example 7

[0093] The difference between Example 7 and Example 1 is that Li5FeO4 was ball-milled to obtain lithium-replenishing particles with an average particle size of 0.2 μm. Then, a lithium-replenishing particle solution was prepared, and fibrous lithium-replenishing additives and lithium secondary batteries were prepared using the same method as in Example 1.

[0094] Example 8

[0095] The difference between Example 8 and Example 1 is that Li5FeO4 was ball-milled to obtain lithium-replenishing particles with an average particle size of 3μm. Then, a lithium-replenishing particle solution was prepared, and fibrous lithium-replenishing additives and lithium secondary batteries were prepared using the same method as in Example 1.

[0096] To highlight the beneficial effects of this application, the following comparative examples are provided.

[0097] Comparative Example 1

[0098] Lithium cobalt oxide, a conductive agent (Super P), and a binder (polyvinylidene fluoride, PVDF) were mixed in a weight ratio of 94:3:3. N-methylpyrrolidone was added and stirred to form a homogeneous slurry. The slurry was coated onto aluminum foil and dried at 100°C for 4 hours. The resulting positive electrode sheet was obtained by rolling and slitting. A lithium secondary battery was prepared using the same method as in Example 1.

[0099] Comparative Example 2

[0100] Comparative Example 2 prepared a lithium-replenishing particle solution and a polymer solution using the same method as in Example 1. The polymer solution and the lithium-replenishing particle solution were directly mixed and centrifuged at 8000 rpm to obtain polymer-coated lithium-replenishing particles. These particles were then baked in a vacuum oven to obtain granular lithium-replenishing additives. A lithium secondary battery was then prepared using the same method as in Example 1.

[0101] Comparative Example 3

[0102] Comparative Example 3 prepared lithium-supplemented fibers using the same method as Example 1, but without oxime treatment. The lithium-supplemented fibers were directly added to the positive electrode. The preparation process of the positive electrode sheet was as follows: lithium cobalt oxide, lithium-supplemented fibers, conductive agent (Super P), and binder (polyvinylidene fluoride, PVDF) were mixed in a weight ratio of 93:3:2:2. N-methylpyrrolidone was added and stirred to form a homogeneous slurry. The slurry was coated onto aluminum foil, dried at 100°C for 4 hours, and then rolled and slit to obtain the positive electrode sheet. A lithium secondary battery was prepared using the same method as in Example 1.

[0103] Effect Example

[0104] To strongly support the beneficial effects of the technical solutions in the embodiments of this application, the following tests are provided:

[0105] 1) The morphology of the fibrous lithium-supplementing additive prepared in Example 1 was characterized. Please refer to [link to relevant documentation]. Figure 8 and Figure 7 , Figure 8 and Figure 9 This is a scanning electron microscope (SEM) image of the fibrous lithium-replenishing additive provided in Example 1 of this application. The SEM image shows that the lithium-replenishing additive of this application has a fibrous structure with a diameter of 17.8 μm and a coating thickness of 3.6 μm, resulting in a calculated core radius of 5.3 μm. The morphology of the lithium-replenishing additives in Examples 1-8 and Comparative Examples 2-3 were characterized using the same method, and the test results are shown in Table 1.

[0106] Table 1. Structural parameters of lithium supplementation additives in Examples 1-8 and Comparative Examples 2-3

[0107]

[0108] As can be seen from Table 1, the lithium-replenishing additive prepared in the embodiments of this application has a fibrous structure, and the polymer coats the lithium-replenishing particles inside the fibers; Comparative Example 2 uses a method of directly mixing polymer solution and lithium-replenishing particle solution to prepare a polymer coating layer, and the resulting lithium-replenishing additive has a granular structure.

[0109] 2) The oxime effect of the fibrous lithium-supplementing additives prepared in Examples 1-8 was tested. The test method was as follows: the fibrous lithium-supplementing additives were characterized by Fourier transform infrared spectroscopy (FT-IR). As can be seen from the infrared spectrum, at 2242 cm⁻¹... -1 The characteristic absorption peak at 1647 cm⁻¹ is a cyano group (-CN), indicating that the fibrous lithium-supplementing additive contains polyacrylonitrile (PAN); -1 and 937cm -1The absorption peak appearing at this point is a characteristic absorption peak of the C=N, N-O bond in the oxime group, which proves the success of the oxime reaction, that is, the polyacrylonitrile contains a geminal oxime group.

[0110] 3) The oximation rate of the fibrous lithium supplementation additives prepared in Examples 1-8 was tested. The test method was as follows: the content of Fe, N and O elements in the sample was tested by ICP. The content of Fe element was used to determine the oxygen element content in the lithium supplementation particles. The oxygen element content in the polymer was obtained by subtracting the oxygen element content in the lithium supplementation particles from the total oxygen element content in the sample. The mass ratio of N element to O element in the polymer was calculated, and then the molar ratio of N and O atoms in the polymer was calculated. Since the N:O ratio in the ammonium oxime group is 2:1 and there is no O element in the cyano group, the oximation treatment introduces the same number of N and O atoms. Therefore, the number of O atoms is the number of ammonium oxime groups. The N atoms in the ammonium oxime group that are proportional to O were subtracted from the total number of N atoms. The remaining N atoms are the N atoms in the cyano group. The number of oximated and unoximated cyano groups in the polypropylene was calculated. Oxidation rate = number of moles of oximated cyano groups / total number of moles of cyano groups. The experimental results are shown in Table 2.

[0111] Table 2. Oximation rate parameters of fibrous lithium-supplementing additives in Examples 1-8 and Comparative Examples 1-3.

[0112]

[0113]

[0114] As shown in Table 2, the oximation rate of the fibrous lithium-replenishing additive obtained in Example 4 of this application is 40%, which is relatively low. This is because the content of added hydroxylamine hydrochloride is small, and the oximation reaction is insufficient. The oximation rate of the fibrous lithium-replenishing additive obtained in Example 5 is 68%, which is relatively high. This is because the content of added hydroxylamine hydrochloride is too large, and the cyano group can be fully oximated. However, the excessively high oximation rate will reduce the conductivity of the coating layer on the surface of the lithium-replenishing particles and affect the overall conductivity of the lithium-replenishing additive. Example 6 uses polyphenylene nitrile as the coating layer. The cyano group in polyphenylene nitrile is located in the side chain. The content of cyano group is small and it is not easy to undergo oximation reaction, so the oximation rate is low.

[0115] 4) Cycle life and energy density tests were conducted on the full cells prepared in Examples 1-8 and Comparative Examples 1-3. The specific test conditions were as follows: the charge and discharge voltage range was 3V-4.5V; the charge and discharge regime was 0.7C constant current to the upper voltage limit and 0.2C constant current to the lower voltage limit. The initial discharge capacity was recorded. After 400 charge and discharge cycles, the discharge capacity of the 400th cycle was recorded. The capacity retention rate after 400 cycles was calculated. The calculation formula was: capacity retention rate after 400 cycles (%) = discharge capacity of 400 cycles / discharge capacity of the first cycle × 100%. The energy density of the full cell was the initial energy density. The energy density of the full cell = cell capacity (mAh) * voltage plateau (V) / total battery mass (kg). After the cycled full cell was disassembled, the negative electrode was removed, and the content of iron and cobalt in the negative electrode was tested by an inductively coupled plasma (ICP) instrument to obtain the dissolution amount of transition metal elements in the negative electrode. The performance test results of the full cells of Examples 1-8 and Comparative Examples 1-3 are shown in Table 3. In the table, the dissolution amount of transition metal elements "-" indicates that the content of iron and cobalt in the sample is lower than the detection limit.

[0116] Table 3 Performance parameters of the full cells in Examples 1-8 and Comparative Examples 1-3

[0117]

[0118]

[0119] As can be seen from Table 3, compared with Comparative Example 1 without the addition of lithium replenishment additive, the full cells of Examples 1-8 of this application have higher energy density and capacity retention after cycling. This indicates that the lithium replenishment additive of this application can effectively improve the capacity retention of the battery. The polymers in the lithium replenishment additives of Comparative Examples 2 and 3 do not contain amine oxime groups. After cycling, high levels of transition metal elements were detected in the negative electrode of their batteries, and their capacity retention was also low. Moreover, Comparative Example 2 directly mixed the polymer solution with the lithium replenishment particles to obtain lithium replenishment particles coated with polymer. The uniformity of polymer coating was poor, and the decomposition performance of the lithium replenishment particles was poor. Its lithium replenishment effect was worse than that of the fibrous lithium replenishment additive in Comparative Example 3. For each embodiment, the lithium replenishing additive in Embodiment 2 has a larger thickness of the outer layer, resulting in a lower lithium replenishment capacity and a lower battery cycle retention rate. In Embodiment 3, the lithium replenishing additive has a smaller outer layer thickness and a larger core radius. Due to the poor conductivity of the lithium replenishing particles, the active lithium inside the particles is difficult to fully extract, thus resulting in a lower content of replenished active lithium and a lower battery capacity retention rate. In Embodiment 4, the lithium replenishing additive has a lower oxime content during preparation, resulting in a lower oxime rate. Some transition metals in the lithium replenishing additive will be released into the electrolyte, leading to a decrease in battery performance. In Embodiment 5, the lithium replenishing additive contains oxime during preparation. The higher content of the oxidizing agent leads to a higher oxime rate in the lithium replenishing additive, which reduces the conductivity of the lithium replenishing additive and thus reduces battery performance. In Example 6, the polymer in the lithium replenishing additive is polyphenylene nitrile, which has low conductivity, resulting in poor conductivity of the lithium replenishing additive. The active lithium in the lithium replenishing particles is difficult to fully release, thus the battery's energy density and cycle retention rate are low. In Example 7, the lithium replenishing additive has a smaller particle size, obvious agglomeration between lithium replenishing particles, and poor decomposition performance of the lithium replenishing additive. In Example 8, the lithium replenishing additive has a larger particle size, poor uniformity and structural stability of the lithium replenishing fibers, and a slightly lower cycle retention rate of the battery.

[0120] 5) Coulombic efficiency tests were performed on the half-cells prepared in Examples 1-8 and Comparative Examples 1-3. The specific test conditions were as follows: charge / discharge voltage range of 3V-4.5V; charge / discharge regime of 0.02C constant current to the upper voltage limit and 0.02C constant current to the lower voltage limit. The first discharge specific capacity and first-cycle coulombic efficiency of the half-cells were obtained. The performance test results of the lithium secondary batteries of Examples 1-8 and Comparative Examples 1-3 are shown in Table 4.

[0121] Table 4 Performance parameters of the half-cells in Examples 1-8 and Comparative Examples 1-3

[0122]

[0123] As can be seen from Table 4, the half-cell in this embodiment has a higher discharge specific capacity after the first charge than the half-cell in the comparative example. This indicates that the lithium replenishment additive in this application can effectively replenish active lithium. As can be seen from the coulombic efficiency of the half-cell in the first week, the lithium replenishment agent in this application is easy to decompose and can quickly replenish active lithium.

[0124] The above description represents the preferred embodiments of this application, but should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A lithium supplement additive, characterized in that, The lithium-replenishing additive has a fibrous structure, comprising a linear core and a skin covering the linear core. The linear core comprises multiple lithium-replenishing particles, and the skin comprises a polymer containing a methylamine oxime group, wherein the oxime content of the polymer containing the methylamine oxime group is 45% to 60%.

2. The lithium supplement additive as described in claim 1, characterized in that, In the radial cross-section of the fibrous lithium supplement, the ratio of the radius R1 of the linear core material to the thickness R2 of the skin layer is (1~2.2):

1.

3. The lithium supplementation additive as described in claim 1 or 2, characterized in that, The average particle size of the lithium replenishing particles is 0.5 μm to 1.5 μm.

4. The lithium supplementation additive as described in claim 1 or 2, characterized in that, The skin layer has a porous structure with an average pore size of 50 nm to 100 nm.

5. A method for preparing a lithium supplement additive, characterized in that, include: Lithium-supplementing fibers with polymer-coated lithium-supplementing particles were obtained by electrospinning, wherein the polymer contained cyano groups. The lithium-replenishing fiber is reacted with an oxime agent to obtain a fibrous lithium-replenishing additive, wherein the oxime agent is a compound having hydroxyl and amino groups; the fibrous lithium-replenishing additive includes a linear core material and a skin layer covering the linear core material, wherein the linear core material includes a plurality of lithium-replenishing particles, and the skin layer includes a polymer containing a metallo-oxime group, wherein the oxime-ratio of the polymer containing the metallo-oxime group is 45% to 60%.

6. The preparation method according to claim 5, characterized in that, The mass ratio of the oxime agent to the lithium-supplemented fiber is 1:(5-20).

7. The preparation method according to claim 5 or 6, characterized in that, The electrospinning method includes: electrospinning with a polymer solution and a lithium-supplemented particle solution as electrospinning solutions, wherein the flow rate ratio of the lithium-supplemented particle solution to the polymer solution is 1:(0.25-4).

8. A positive electrode sheet, characterized in that, The positive electrode sheet includes an active material and a fibrous lithium supplementation additive as described in any one of claims 1-4.

9. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode includes the positive electrode sheet as described in claim 8.

10. An electronic device, characterized in that, The electronic device includes the secondary battery as described in claim 9.

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