Lithium-ion battery and preparation method therefor

Abstract

A lithium-ion battery and a preparation method therefor. The lithium-ion battery comprises a positive electrode sheet, a separator and a negative electrode sheet, which are stacked in sequence, wherein the surface of the negative electrode sheet is provided with a solid electrolyte interface film, and the solid electrolyte interface film comprises a lithium oxide. The solid electrolyte interface film is subjected to a sputtering test by using an X-ray photoelectron spectrometer. Under at least one sputtering depth in the range of 30-70 nm, the atomic percentage of lithium is A, and the atomic percentage of oxygen is B, wherein A≥50%, and B≥20%; and the ratio of the atomic percentage of lithium to that of oxygen is greater than 1.5.

Description

Lithium-ion batteries and their preparation methods

[0001] This application claims priority to Chinese Patent Application No. 202410951051.6, filed on July 15, 2024, entitled "Lithium-ion Battery and Preparation Method Thereof", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, specifically to a lithium-ion battery and its preparation method. Background Technology

[0003] During the initial charging and formation stage of a lithium-ion battery, the electrolyte undergoes a side reaction with the lithium salt on the negative electrode surface, forming a solid electrolyte interface (SEI) film. However, during the charging and discharging process of a lithium-ion battery, a poorly performing SEI film can hinder ion permeability, leading to an increase in battery impedance. Furthermore, once the unstable SEI film is damaged, the electrolyte will continue to decompose on the negative electrode surface, constantly consuming the limited number of lithium ions and thus causing a decline in battery cycle performance. Summary of the Invention

[0004] In view of this, this application provides a lithium-ion battery in which the solid electrolyte interface film on the surface of the negative electrode is composed of lithium-rich and oxygen-rich components, has a stable structure and low impedance.

[0005] The first aspect of this application provides a lithium-ion battery, comprising a positive electrode, a separator, and a negative electrode stacked sequentially; the surface of the negative electrode has a solid electrolyte interface film, the solid electrolyte interface film comprising lithium oxide; the solid electrolyte interface film is sputtered using X-ray photoelectron spectroscopy, and at at least one sputtering depth in the range of 30 nm to 70 nm, the atomic percentage of lithium is A, and the atomic percentage of oxygen is B, wherein A ≥ 50%, B ≥ 20%; and the ratio of the atomic percentage of lithium to the atomic percentage of oxygen is greater than 1.5.

[0006] The negative electrode of the lithium-ion battery provided in this application has a solid electrolyte interface film, and the solid electrolyte interface film includes lithium oxide. Sputtering tests were performed on the negative electrode with the solid electrolyte interface film using X-ray photoelectron spectroscopy. At at least one sputtering depth in the range of 30nm-70nm, the atomic percentage of lithium A ≥ 50%, the atomic percentage of oxygen B ≥ 20%, and the ratio of the atomic percentages of lithium to oxygen is greater than 1.5. This indicates that the surface of the negative electrode of the lithium-ion battery provided in this application has stable lithium oxide, providing excellent ionic conductivity for the lithium-ion battery and reducing battery impedance. Simultaneously, this stable lithium oxide is not easily detached during battery use, alleviating the continuous consumption of electrolyte during battery use, thereby extending the battery's cycle life.

[0007] In this embodiment of the application, at sputtering depths within the range of 30nm-70nm, A≥50% and B≥20% are satisfied; and the ratio of the atomic percentage of lithium to the atomic percentage of oxygen is greater than 1.5.

[0008] In this embodiment of the application, 55% ≤ A ≤ 70%; 22% ≤ B ≤ 30%.

[0009] In this embodiment of the application, the ratio of the atomic percentage of lithium to the atomic percentage of oxygen is (1.8-3):1.

[0010] In this embodiment of the application, the solid electrolyte interface film includes lithium oxide.

[0011] In this embodiment of the application, the positive electrode includes a positive current collector and a positive active layer loaded on at least one side of the positive current collector, the positive active layer including Li 1-x NiO2 (0≤x≤1), Li3FeO 3.5 A combination of one or more of LiFeO2.

[0012] The second aspect of this application provides a method for preparing the lithium-ion battery provided in the first aspect of this application, comprising the following steps:

[0013] A positive electrode slurry is prepared by adding positive electrode active material, lithium supplement, conductive agent and binder to a solvent;

[0014] A negative electrode slurry is prepared by adding negative electrode active material, conductive agent and binder to solvent;

[0015] The positive electrode slurry is coated on at least one side of the positive electrode current collector to obtain the first positive electrode sheet;

[0016] The negative electrode slurry is coated on at least one side of the negative electrode current collector to obtain the first negative electrode sheet;

[0017] The first positive electrode, the separator, and the first negative electrode are stacked in sequence, and then an electrolyte is injected to form a lithium-ion battery.

[0018] The negative electrode of the lithium-ion battery has a solid electrolyte interface film on its surface, the solid electrolyte interface film comprising lithium oxide; the solid electrolyte interface film is sputtered using X-ray photoelectron spectroscopy, and at at least one sputtering depth in the range of 30nm-70nm, the atomic percentage of lithium is A and the atomic percentage of oxygen is B, wherein A≥50% and B≥20%; the ratio of the atomic percentage of lithium to the atomic percentage of oxygen is greater than 1.5.

[0019] In this embodiment of the application, the formation includes: constant voltage charging for 2-5 hours in two voltage ranges: 3.0V to 3.5V and 4.1V to 4.3V, respectively.

[0020] In this embodiment of the application, the temperature of the constant voltage charging is 40℃~60℃.

[0021] In the embodiments of this application, the lithium supplement includes one or more combinations of Li2CO3, Li2C2O4, Li6CoO4, Li2NiO2, Li2Se, Li3N, Li2O2, Li2O, Li2S, Li2S2, Li5FeO4, lithium borate, and lithium thioborate.

[0022] In this embodiment of the application, the mass of the lithium supplement is 0.5%-6% of the mass of the positive electrode active material.

[0023] In this embodiment of the application, the mass of the lithium replenishing agent is 1%-5% of the mass of the positive electrode active material.

[0024] The third aspect of this application provides an electrical device, including the lithium-ion battery provided in the first aspect of this application, or a lithium-ion battery prepared by the preparation method of the second aspect of this application. Attached Figure Description

[0025] Figure 1 is a schematic diagram of the structure of a lithium-ion battery provided in an embodiment of this application;

[0026] Figure 2 shows the XPS spectra of the negative electrode sheet provided in Embodiment 5 of this application at sputtering depths of 30 nm, 50 nm, and 70 nm.

[0027] Figure 3 shows the XPS spectra of the negative electrode sheet provided in Embodiment 9 of this application at sputtering depths of 30 nm, 50 nm, and 70 nm;

[0028] Figure 4 shows the XPS spectra of the negative electrode provided in Comparative Example 1 of this application at sputtering depths of 30 nm, 50 nm, and 70 nm.

[0029] Explanation of icon numbers:

[0030] 20 - Lithium-ion battery; 21 - Positive electrode sheet; 211 - Positive active layer; 212 - Positive current collector; 22 - Separator; 23 - Negative electrode sheet; 231 - Negative active layer. Detailed Implementation

[0031] The present application will be further described in detail below with reference to preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0032] In this application, all technical terms have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this application.

[0033] During the initial charging formation stage of a lithium-ion battery, the electrolyte undergoes side reactions with the lithium salt on the surface of the negative electrode (mainly the surface of the negative electrode active material particles and the conductive agent particles), forming a solid electrolyte interface (SEI) film on the surface of the negative electrode. The SEI is a passivation film with the properties of a solid electrolyte. The SEI film typically consists of a dense inorganic inner layer and a loose organic outer layer. On one hand, the SEI is a good lithium-ion conductor, allowing lithium ions to be transported and enter the surface of the negative electrode active material for lithium insertion / extraction. On the other hand, the SEI is also a good electronic insulator, significantly reducing ongoing side reactions within the battery and improving cycle performance and lifespan. However, conventional SEI films are thermodynamically unstable and undergo dissolution and regeneration during battery cycling and high-temperature storage. In particular, the dissolution of organic components into the electrolyte leads to a porous structure in the SEI, causing continuous electrolyte decomposition, persistent side reactions, and ultimately, battery capacity decay. The dissolution and regeneration of the solid electrolyte interface film can also lead to a decrease in the uniformity of the solid electrolyte interface film. The local thickening areas hinder the passage of lithium ions, which increases the impedance of the battery during cycling.

[0034] In view of this, the first aspect of this application provides a lithium-ion battery, including a positive electrode, a separator, and a negative electrode stacked sequentially; the surface of the negative electrode has a solid electrolyte interface film, the solid electrolyte interface film including lithium oxide; the solid electrolyte interface film is sputtered using an X-ray photoelectron spectroscopy instrument, and at at least one sputtering depth in the range of 30nm-70nm, the atomic percentage of lithium is A and the atomic percentage of oxygen is B, wherein A≥50%; B≥20%; and the ratio of the atomic percentage of lithium to the atomic percentage of oxygen is greater than 1.5.

[0035] In this embodiment, XPS (X-ray Photoelectron Spectroscopy) is used to perform sputtering tests on the surface of the negative electrode with a solid electrolyte interface film. At at least one sputtering depth within the range of 30 nm to 70 nm, the atomic percentage of lithium is A, and the atomic percentage of oxygen is B, where A ≥ 50% and B ≥ 20%; and the ratio of the atomic percentage of lithium to the atomic percentage of oxygen is greater than 1.5. This can be understood as satisfying the following conditions at one sputtering depth within the 30 nm to 70 nm range: the atomic percentage of lithium A ≥ 50%, the atomic percentage of oxygen B ≥ 20%, and the ratio of the atomic percentage of lithium to the atomic percentage of oxygen can be 1.55, 1.6, 1.7, 1.8, 2.0, 2.1, 2.2, 2.3, 2.5, 2.7, 2.9, 3.0, or 3.1. In some specific embodiments of this application, the atomic percentage of lithium at a sputtering depth of 30 nm can be, for example, 50%, 55%, 60%, 65%, 70%, or 75%; the atomic percentage of oxygen can be, for example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 28%, 29%, 30%, or 32%; and the ratio of the atomic percentage of lithium to the atomic percentage of oxygen can be 1.55, 1.6, 1.7, 1.8, 2.0, 2.1, 2.2, 2.3, 2.5, 2.7, 2.9, 3.0, or 3.1. In some specific embodiments of this application, the atomic percentage of lithium at a sputtering depth of 40 nm can be, for example, 50%, 55%, 60%, 65%, 70%, or 75%; the atomic percentage of oxygen can be, for example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 28%, 29%, 30%, or 32%; and the ratio of the atomic percentage of lithium to the atomic percentage of oxygen can be 1.55, 1.6, 1.7, 1.8, 2.0, 2.1, 2.2, 2.3, 2.5, 2.7, 2.9, 3.0, or 3.1. In some specific embodiments of this application, the atomic percentage of lithium at a sputtering depth of 60 nm can be, for example, 50%, 55%, 60%, 65%, 70%, or 75%; the atomic percentage of oxygen can be, for example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 28%, 29%, 30%, or 32%; and the ratio of the atomic percentage of lithium to the atomic percentage of oxygen can be 1.55, 1.6, 1.7, 1.8, 2.0, 2.1, 2.2, 2.3, 2.5, 2.7, 2.9, 3.0, or 3.1.In some specific embodiments of this application, the atomic percentage of lithium at a sputtering depth of 70 nm can be, for example, 50%, 55%, 60%, 65%, 70%, or 75%; the atomic percentage of oxygen can be, for example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 28%, 29%, 30%, or 32%; and the ratio of the atomic percentage of lithium to the atomic percentage of oxygen can be 1.55, 1.6, 1.7, 1.8, 2.0, 2.1, 2.2, 2.3, 2.5, 2.7, 2.9, 3.0, or 3.1.

[0036] The negative electrode of the lithium-ion battery provided in this application has a solid electrolyte interface film, and the solid electrolyte interface film includes lithium oxide. Sputtering tests were performed on the negative electrode with the solid electrolyte interface film using X-ray photoelectron spectroscopy. At at least one sputtering depth in the range of 30nm-70nm, the atomic percentage of lithium A ≥ 50%, the atomic percentage of oxygen B ≥ 20%, and the ratio of the atomic percentages of lithium to oxygen is greater than 1.5. This indicates that the surface of the negative electrode of the lithium-ion battery provided in this application has stable lithium oxide, providing excellent ionic conductivity for the lithium-ion battery and reducing battery impedance. Simultaneously, this stable lithium oxide is not easily detached during battery use, alleviating the continuous consumption of electrolyte during battery use, thereby extending the battery's cycle life.

[0037] In the embodiments of this application, lithium oxide refers to a compound composed only of lithium and oxygen elements, and is an important component of the solid electrolyte interface film on the surface of the negative electrode.

[0038] In this application, the atomic percentages of lithium and oxygen are measured using an XPS (X-ray Photoelectron Spectroscopy) instrument equipped with an argon-ion sputtering gun to sputter the surface of the negative electrode with a solid electrolyte interface film. During the sputtering test, the sputtering depth of the argon-ion sputtering gun on the negative electrode is controlled by the sputtering time to determine the atomic percentages of lithium and oxygen at different sputtering depths. However, the negative electrode in the lithium-ion battery provided in this application has a solid electrolyte interface film, which includes lithium oxide. Because the composition of the solid electrolyte interface film on the surface of the negative electrode is complex, it is difficult to determine accurate parameters of the argon-ion sputtering gun. Therefore, this application uses structurally and performance-stable silicon dioxide as a reference, and calibrates the sputtering depth on the surface of the negative electrode with a solid electrolyte interface film by controlling the sputtering thickness of the silicon dioxide by the argon-ion sputtering gun. In some embodiments of this application, the X-ray photoelectron spectrometer is a PHI GENESIS 500, the target material is an Al target, the energy range is 0-1100 eV, the sputtering rate is 5 nm / min-10 nm / min, the sputtering direction is from the surface of the negative electrode to the inside of the negative electrode, i.e., the current collector side, and the testing software is PHI Multipak.

[0039] The analytical methods for XPS atomic ratios are divided into the standard method, the first-principles model method, and the elemental sensitivity factor method. The standard method requires the preparation of a certain amount of standard samples as a reference, and is difficult to use stably for a long time due to the influence of surface structure. It also cannot simulate complex SEI mixture models, so this method is generally not used in research. The first-principles model method considers the observed spectral line intensities, excitation source, properties of the sample to be tested, and spectrometer detection conditions to form a certain physical model. However, because the model involves many elements, there is currently a lack of precise experimental data, so the first-principles model method has not been truly used. The method used in this application is the most commonly used elemental sensitivity factor method. This method uses the spectral line intensity of a specific element as a reference standard, measures the relative spectral line intensities of other elements, and uses the atomic sensitivity factor S. i (Sensitivity factor S) i This method, using existing technology (which allows for the determination of the relative abundance of each element by consulting tables), is a semi-empirical, relative quantitative method. The method for calculating atomic percentages is as follows:

[0040] As shown in Equation 1, the normalized area (N) A ) by peak area (I A Calculate: N A =I A / S i Formula 1

[0041] As shown in Equation 2, the relative atomic percentage of any element in the sample is calculated:

[0042] In some embodiments of this application, within a sputtering depth range of 30nm-70nm, the following conditions are met: A≥50%, B≥20%; and the atomic percentage of lithium to the atomic percentage of oxygen is greater than 1.5. The negative electrode sheet meeting these characteristics exhibits a more uniform and stable distribution of lithium oxide on its surface, providing better ionic conductivity for lithium-ion batteries and extending their cycle life.

[0043] In some embodiments of this application, 55% ≤ A ≤ 70%; 22% ≤ B ≤ 30%. By controlling the atomic percentages of lithium and oxygen within the above ranges, the lithium oxide is uniformly distributed in the solid electrolyte interface film, which can further reduce the interface impedance and improve the cycling performance of lithium ions.

[0044] In this application, at at least one sputtering depth within the range of 30nm-70nm, the atomic percentage ratio of lithium to oxygen is (1.8-3):1. In some embodiments of this application, the atomic percentage ratio of lithium to oxygen can be, for example, 1.8:1, 2:1, 2.2:1, 2.4:1, 2.5:1, 2.8:1, or 3:1. By controlling the atomic ratio of lithium to oxygen within a suitable range, this application is more conducive to reducing impedance and increasing battery cycle life.

[0045] In some embodiments of this application, the solid electrolyte interface film includes lithium oxide. As an inorganic material in the solid electrolyte interface film, lithium oxide supports the internal structure of the film, enhancing its stability and lithium-ion transport capability. Particularly at sputtering depths of 3 nm or more in XPS, lithium oxide remains stable, further increasing the stability of the solid electrolyte interface film and its lithium-ion transport characteristics, and also increasing battery cycle life.

[0046] Figure 1 is a schematic diagram of the structure of a lithium-ion battery according to an embodiment of this application. As shown in Figure 1, the lithium-ion battery 20 includes a positive electrode 21, a separator 22, and a negative electrode 23 stacked sequentially. The positive electrode 21 includes a positive current collector 212 and a positive active layer 211 loaded on at least one side of the positive current collector 212. The positive active layer 211 includes Li 1-x NiO2 (0≤x≤1), Li3FeO 3.5 A combination of one or more of LiFeO2.

[0047] In the embodiments of this application, Li 1-xNiO2 (0≤x≤1), Li3FeO 3.5 LiFeO2 can be the residual material left in the positive electrode active layer after the positive electrode lithium replenishing agent undergoes an irreversible delithiation reaction.

[0048] In some embodiments of this application, the positive electrode active material includes one or more combinations of phosphate-based positive electrode active materials and transition metal oxide positive electrode active materials. In these embodiments, the positive electrode active material can be any positive electrode active material known in the art for use in lithium-ion batteries, including but not limited to one or more of phosphate-based and transition metal oxide positive electrode active materials. In some embodiments, the phosphate-based positive electrode active material can be, for example, one or more of lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate, lithium nickel phosphate, and lithium manganese iron phosphate; the transition metal oxide positive electrode active material can be, for example, one or more of ternary positive electrode materials and lithium-rich layered oxides.

[0049] In some embodiments, the positive electrode active material includes, but is not limited to, a positive electrode active material that has been doped and / or coated and modified; or a positive electrode active material that has not been doped and / or coated and modified. In embodiments of this application, the positive electrode active material includes, but is not limited to, the examples described above. In some embodiments of this application, the positive electrode active material includes lithium iron phosphate material.

[0050] The negative electrode of the lithium-ion battery provided in this application has a solid electrolyte interface film, and the solid electrolyte interface film includes lithium oxide. X-ray photoelectron spectroscopy is used to perform sputtering tests on the negative electrode with the solid electrolyte interface film. At at least one sputtering depth in the range of 30nm-70nm, the atomic percentage of lithium A ≥ 50%, the atomic percentage of oxygen B ≥ 20%, and the ratio of the atomic percentages of lithium to oxygen is greater than 1.5. The surface of the negative electrode of the lithium-ion battery provided in this application has stable lithium oxide, providing excellent ionic conductivity for the lithium-ion battery and reducing battery impedance. Simultaneously, this stable lithium oxide is not easily detached during battery use, alleviating the continuous consumption of electrolyte during battery use, thereby extending the battery's cycle life.

[0051] The second aspect of this application provides a method for preparing a lithium-ion battery, comprising the following steps:

[0052] A positive electrode slurry is prepared by adding positive electrode active material, lithium supplement, conductive agent and binder to a solvent;

[0053] A negative electrode slurry is prepared by adding negative electrode active material, conductive agent and binder to solvent;

[0054] A positive electrode slurry is coated on at least one side of the positive electrode current collector to obtain a first positive electrode sheet;

[0055] The negative electrode slurry is coated on at least one side of the negative electrode current collector to obtain the first negative electrode sheet;

[0056] After stacking the first positive electrode, the separator, and the first negative electrode in sequence, an electrolyte is injected, and a lithium-ion battery is obtained through formation.

[0057] The surface of the negative electrode of a lithium-ion battery has a solid electrolyte interface film, which includes lithium oxide. The solid electrolyte interface film is sputtered using X-ray photoelectron spectroscopy. At at least one sputtering depth in the range of 30 nm to 70 nm, the atomic percentage of lithium is A and the atomic percentage of oxygen is B, wherein A ≥ 50% and B ≥ 20%; and the ratio of the atomic percentage of lithium to the atomic percentage of oxygen is greater than 1.5.

[0058] This application improves the solid electrolyte interface film structure on the surface of the negative electrode of a lithium-ion battery by supplementing lithium to the positive electrode and combining it with a formation method. The lithium supplementing agent can release lithium ions during formation and battery cycling, thereby accelerating the reaction kinetics of solid electrolyte interface film formation and promoting the formation of stable lithium oxide. X-ray photoelectron spectroscopy is used to sputter the negative electrode with the solid electrolyte interface film. At at least one sputtering depth in the range of 30nm-70nm, the atomic percentage of lithium A ≥ 50%, the atomic percentage of oxygen B ≥ 20%, and the ratio of the atomic percentage of lithium to oxygen is greater than 1.5. The negative electrode surface of the lithium-ion battery provided by this application has stable lithium oxide, providing excellent ionic conductivity and reducing battery impedance. Simultaneously, this stable lithium oxide is not easily detached during battery use, alleviating the continuous consumption of electrolyte during battery use and thus extending the battery's cycle life.

[0059] In some embodiments of this application, the formation step includes constant voltage charging for 2-5 hours within two voltage ranges: 3.0V–3.5V and 4.1V–4.3V, respectively. Different lithium replenishing agents correspond to different delithiation potentials, and their effects on the formation and stabilization of lithium-rich and oxygen-rich lithium compounds in the solid electrolyte interface film vary. Different electrochemical systems and formation processes can be combined. However, regardless of the formation process, constant voltage charging within the above two voltage ranges is beneficial for the slow release of lithium ions from the lithium replenishing agent, resulting in the formation of a stable solid electrolyte interface film.

[0060] In some embodiments of this application, the constant voltage charging temperature is 40°C to 60°C. A suitable constant voltage charging temperature is beneficial for accelerating the formation kinetics of the solid electrolyte interface film and forming a stable lithium-rich and oxygen-rich substance.

[0061] In this application, the positive electrode active material can be any positive electrode active material known in the art for use in lithium-ion batteries, including but not limited to one or more of phosphate-based positive electrode active materials and transition metal oxide positive electrode active materials. In some embodiments, the phosphate-based positive electrode active material can be, for example, one or more of lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate, lithium nickel phosphate, and lithium manganese iron phosphate; the transition metal oxide positive electrode active material can be, for example, one or more of ternary positive electrode materials and lithium-rich layered oxides. In some embodiments, the positive electrode active material includes, but is not limited to, a doped or coated positive electrode active material, or an undoped or uncoated positive electrode active material. In this application, the positive electrode active material includes, but is not limited to, the examples described above.

[0062] In this application, the negative electrode active material can be any negative electrode active material known in the art for use in lithium-ion batteries, including but not limited to one or more of carbon-based, silicon-based, tin-based, and lithium metal negative electrode active materials. In some embodiments, the carbon-based negative electrode can be, for example, one or more of materials including but not limited to natural graphite, artificial graphite, hard carbon, soft carbon, and graphene; the silicon-based negative electrode can be, for example, one or more of materials including but not limited to silicon, silicon-carbon, silicon-oxygen, and silicon metal compounds; and the tin-based negative electrode can be, for example, one or more of materials including but not limited to tin, tin-carbon, tin-oxygen, and tin metal compounds. In this application, the negative electrode active material includes, but is not limited to, the examples described above.

[0063] In some embodiments of this application, the lithium supplementer added to the positive electrode slurry includes one or more combinations of Li₂CO₃, Li₂C₂O₄, Li₆CoO₄, Li₂NiO₂, Li₂Se, Li₃N, Li₂O₂, Li₂O, Li₂S, Li₂S₂, Li₅FeO₄, lithium borate, and lithium thioborate. Different lithium supplementers correspond to different delithiation potentials and have different effects on the formation and stabilization of lithium-rich and oxygen-rich lithium compounds in the solid electrolyte interface film. They can be selected in conjunction with different electrochemical systems and formation processes.

[0064] In this embodiment, the mass of the lithium replenishing agent added to the positive electrode slurry is 0.5%-6% of the mass of the positive electrode active material, preferably 1%-5%. In some specific embodiments, the mass of the lithium replenishing agent can be, for example, 0.5%, 1%, 1.2%, 1.5%, 1.8%, 2.0%, 2.3%, 2.5%, 2.8%, 3.0%, 3.5%, 4%, 4.5%, 5%, 5.5%, or 6% of the mass of the positive electrode active material. A lithium replenishing agent content within a suitable range is beneficial for improving the overall electrochemical performance of the battery. If the lithium replenishing agent content is less than 1%, the lithium and oxygen content and their percentages in the inner layer of the solid electrolyte interfacial film are low, and the solid electrolyte interfacial film is unstable, resulting in poor battery cycle performance. If the lithium replenishing agent content is higher than 5%, the formation process takes longer, reducing production cycle time; and the effect on reducing ion diffusion resistance and improving cycle performance is not significant.

[0065] In this application, the positive current collector can be any positive current collector known in the art. In some embodiments of this application, the positive current collector can be, for example, aluminum foil. In this application, the negative current collector can be any negative current collector known in the art. In some embodiments of this application, the negative current collector can be, for example, copper foil.

[0066] In the embodiments of this application, the conductive agent can be any conductive agent known in the art. In some embodiments of this application, the conductive agent can be one or more of Super P, acetylene black, graphene, and carbon nanotubes.

[0067] In this application, the adhesive can be any adhesive known in the art. In some embodiments of this application, the adhesive can be one or more of sodium hydroxycellulose, polyvinylidene fluoride, and styrene-butadiene rubber.

[0068] In this application, the positive electrode slurry and / or negative electrode slurry further include the addition of a dispersant, which can be any dispersant known in the art. In some embodiments of this application, the dispersant may be, for example, polyvinylpyrrolidone.

[0069] In this embodiment, the electrolyte is a conventional electrolyte, and its preparation process can be as follows: In an argon-filled glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and vinylene carbonate (VC) are weighed out as electrolyte solvents at mass percentages of 30 wt%, 40 wt%, 14 wt%, and 2% of the total electrolyte mass. Lithium hexafluorophosphate (LiPF6) is weighed out as the electrolyte lithium salt at a mass percentage of 14 wt% of the total electrolyte mass, and the mixture is stirred continuously until dissolved.

[0070] The lithium-ion battery preparation method provided in this application involves adding a lithium supplementer during the preparation of the positive electrode slurry and supplementing the negative electrode with lithium. After the lithium-ion battery is formed, a solid electrolyte interface film with extremely high lithium oxide content is generated on the surface of the negative electrode, resulting in a lithium-rich and oxygen-rich solid electrolyte interface film. The lithium-ion battery prepared by this method has low impedance, good cycle stability, and long service life.

[0071] A third aspect of this application provides an electrical device comprising the lithium-ion battery provided in the first aspect, or a lithium-ion battery prepared by the method provided in the third aspect. This electrical device may be, for example, an electric vehicle, a mobile phone, a tablet computer, a laptop computer, a wearable device (watch, bracelet), a digital camera, etc.

[0072] The present application will be further described below with reference to several embodiments:

[0073] Example 1

[0074] Lithium iron phosphate, carbon nanotubes, polyvinylidene fluoride, and lithium carbonate (Li2CO3) lithium supplementer were added to N-methylpyrrolidone in a mass ratio of 100:1:3:1 to prepare a lithium supplementing positive electrode slurry. The lithium supplementing positive electrode slurry was then coated on the surface of aluminum foil, and after drying and rolling, a positive electrode sheet was obtained.

[0075] A negative electrode slurry was prepared by adding graphite, conductive agent and binder to deionized water in a mass ratio of 96:2:2. The negative electrode slurry was then coated on the surface of copper foil, and after drying and rolling, a negative electrode sheet was obtained.

[0076] The prepared positive and negative electrode sheets were stacked sequentially in the order of positive electrode sheet, separator, and negative electrode sheet to form a battery cell. After baking at 100℃ for 24 hours, the cell was encapsulated with an aluminum-plastic film and injected with 1g of electrolyte. After aging at 45℃ for 24 hours, the cell underwent formation on a charge-discharge device. It was first charged at a constant current rate of 0.2C to 3.5V, then charged at 3.5V for 2 hours at a charging current of 0.05C (constant voltage charging temperature of 40℃), then charged at 0.5C to 4.3V, and then charged at 4.3V for 2 hours at a charging current of 0.05C (constant voltage charging temperature of 40℃). Following aging and capacity testing, a lithium-ion battery was obtained with a designed capacity of 1.7Ah. The lithium carbonate (Li2CO3) lithium supplement in the positive electrode sheet of this lithium-ion battery was almost completely decomposed.

[0077] Example 2

[0078] The only difference from Example 1 is that the lithium supplement is lithium oxalate (Li₂C₂O₄). The formation process involves first charging at a constant current rate of 0.2C to 3.1V, then charging at a constant voltage of 3.1V for 4 hours with a charging current of 0.05C (constant voltage charging temperature of 40°C), followed by charging at 0.5C to 4.2V, and then charging at a constant voltage of 4.2V for 4 hours with a charging current of 0.05C (constant voltage charging temperature of 40°C). After aging and capacity testing, a lithium-ion battery is obtained. The lithium oxalate (Li₂C₂O₄) supplement in the positive electrode of this lithium-ion battery is almost completely decomposed.

[0079] Example 3

[0080] The only difference from Example 1 is that the lithium supplement is lithium nickel oxide (Li2NiO2). The formation process involves first charging at a constant current rate of 0.2C to 3.3V, then charging at 3.3V for 3 hours at a constant voltage of 0.05C (constant voltage charging temperature of 40°C), followed by charging at 0.5C to 4.3V, and then charging at 4.3V for 3 hours at a constant voltage of 0.05C (constant voltage charging temperature of 40°C). After aging and capacity testing, a lithium-ion battery is obtained. The lithium nickel oxide (Li2NiO2) lithium supplement in the positive electrode of this lithium-ion battery decomposes to generate Li 1-x NiO2 (0≤x≤1), Li3FeO 3.5 And LiFeO2.

[0081] Example 4

[0082] The only difference from Example 1 is that the lithium supplement is lithium ferrite (Li5FeO4). The formation process involves first charging at a constant current rate of 0.2C to 3.2V, then charging at 3.2V for 3 hours at a constant voltage of 0.05C (constant voltage charging temperature of 40°C), followed by charging at 0.5C to 4.3V, and then charging at 4.3V for 3 hours at a constant voltage of 0.05C (constant voltage charging temperature of 40°C). After aging and capacity testing, a lithium-ion battery is obtained. The lithium ferrite (Li5FeO4) supplement in the positive electrode of this lithium-ion battery decomposes to generate 0.73% LiFeO2 (obtained by XRD testing).

[0083] Example 5

[0084] The only difference from Example 4 is that the lithium-replenishing positive electrode slurry consists of lithium iron phosphate, carbon nanotubes, polyvinylidene fluoride, and lithium iron phosphate (Li5FeO4) lithium replenishing agent in a 100:1:3:3 ratio. The lithium iron phosphate (Li5FeO4) lithium replenishing agent in the positive electrode of this lithium-ion battery decomposes to generate 2.2% LiFeO2 (obtained by XRD testing).

[0085] Example 6

[0086] The only difference from Example 4 is that the lithium-replenishing positive electrode slurry consists of lithium iron phosphate, carbon nanotubes, polyvinylidene fluoride, and lithium iron phosphate (Li5FeO4) lithium replenishing agent in a 100:1:3:5 ratio. In this lithium-ion battery positive electrode, the lithium iron phosphate (Li5FeO4) lithium replenishing agent decomposes to generate Li3FeO. 3.5 and LiFeO2, Li3FeO 3.5 The total content of LiFeO2 is 4% (obtained by XRD testing).

[0087] Example 7

[0088] The only difference from Example 4 is that the lithium-replenishing positive electrode slurry consists of lithium iron phosphate, carbon nanotubes, polyvinylidene fluoride, and lithium iron phosphate (Li5FeO4) lithium replenishing agent in a 100:1:3:6 ratio. In this lithium-ion battery positive electrode, the lithium iron phosphate (Li5FeO4) lithium replenishing agent decomposes to generate Li3FeO. 3.5 and LiFeO2, Li3FeO 3.5 The total content of LiFeO2 was 4.6% (obtained by XRD testing).

[0089] Example 8

[0090] The only difference from Example 1 is that the lithium-added cathode slurry consists of lithium iron phosphate, carbon nanotubes, polyvinylidene fluoride, and lithium iron phosphate (Li5FeO4) lithium supplementer in a ratio of 100:1:3:0.8. It is first charged at a constant current rate of 0.2C to 3.5V, then charged at 3.5V for 2 hours at a constant voltage of 0.05C (constant voltage charging temperature: 25°C), then charged at 0.5C to 4.3V, and then charged at 4.3V for 2 hours at a constant voltage of 0.05C (constant voltage charging temperature: 25°C). After aging and capacity testing, a lithium-ion battery is obtained. The lithium carbonate (Li2CO3) lithium supplementer in the positive electrode of this lithium-ion battery is almost completely decomposed.

[0091] Example 9

[0092] The only difference from Example 1 is that the lithium-added positive electrode slurry consists of lithium iron phosphate, carbon nanotubes, polyvinylidene fluoride, and lithium carbonate (Li2CO3) as a lithium-added agent in a ratio of 100:1:3:0.5. The lithium carbonate (Li2CO3) lithium-added agent in the positive electrode of this lithium-ion battery is almost completely decomposed.

[0093] Comparative Example 1

[0094] The only difference from Example 1 is that no lithium supplementation agent was added to the positive electrode slurry. The composition of the lithium supplementation positive electrode slurry is lithium iron phosphate, carbon nanotubes, and polyvinylidene fluoride in a ratio of 96:1:3.

[0095] Comparative Example 2

[0096] The only difference from Example 1 is that the formation process is different. The lithium-ion battery is obtained by constant current charging at a rate of 0.2C to 4.3V without constant voltage charging, followed by aging and capacity testing.

[0097] The lithium-ion batteries prepared in Examples 1-9 and Comparative Examples 1-2 were fully discharged (to 2.0V) and then the complete negative electrode sheets were disassembled in an argon glove box. The cleaned negative electrode sheets were then immersed in anhydrous dimethyl carbonate (DMC) for 5 minutes and then prepared after the anhydrous DMC had evaporated. The lithium and oxygen content on the cleaned negative electrode sheets was characterized by X-ray photoelectron spectroscopy (XPS) at sputtering depths of 30 nm, 50 nm, and 70 nm. The compositional information of the negative electrode sheets in the depth direction was analyzed by sputtering layer by layer at an etching rate of 5 nm / min. Sputtering depth = sputtering time * sputtering rate, representing the actual depth of the solid electrolyte interface film on the non-negative electrode (the depth of reference silica). Sputtering efficiency is affected by the organic / inorganic composition of the solid electrolyte interface film; organic components are more unstable and easily decompose during sputtering, while inorganic components are relatively stable and easily retained during sputtering. The content of each element can be obtained from the peak positions and corresponding peak areas in the XPS spectrum.

[0098] Specifically, the test data of Examples 5, 9, and Comparative Example 1 are used as examples for illustration. XPS spectra of the negative electrode sheets obtained in Examples 5, 9, and Comparative Example 1 at sputtering depths of 30 nm, 50 nm, and 70 nm were obtained, as shown in Figures 2, 3, and 4. Figure 2 shows the XPS spectra of the negative electrode sheet provided in Example 5 at sputtering depths of 30 nm, 50 nm, and 70 nm; Figure 3 shows the XPS spectra of the negative electrode sheet provided in Example 9 at sputtering depths of 30 nm, 50 nm, and 70 nm; and Figure 4 shows the XPS spectra of the negative electrode sheet provided in Comparative Example 1 at sputtering depths of 30 nm, 50 nm, and 70 nm. Each spectrum contains characteristic peaks corresponding to the Li1s, C1s, O1s, F1s, P2p, and S2p orbitals, i.e., characteristic peaks corresponding to the Li, C, O, F, P, and S elements. The area (I) of each feature was obtained by processing with XPS peak software. A According to formula 1: N A =I A / S i The normalized areas (N) corresponding to Li, C, O, F, P, and S elements were calculated. AThe sensitivity factors for Li, C, O, F, P, and S are 0.025, 0.278, 0.78, 1, 0.486, and 0.668, respectively. The atomic percentages of each element are calculated using Formula 2.

[0099] The results are shown in Tables 1, 2, and 3. Table 1 shows the atomic ratio of each element under sputtering at 30 nm, 50 nm, and 70 nm in Figure 2 (Example 5). Table 2 shows the atomic ratio of each element under sputtering at 30 nm, 50 nm, and 70 nm in Figure 3 (Example 9). Table 3 shows the atomic ratio of each element under sputtering at 30 nm, 50 nm, and 70 nm in Figure 4 (Comparative Example 1).

[0100] Table 1

[0101] Table 2

[0102] Table 3

[0103] Based on the above method, the results of Examples 1-9 and Comparative Examples 1-2 are shown in Table 4.

[0104] Table 4

[0105] The lithium-ion batteries prepared in Examples 1-9 and Comparative Examples 1-2 were tested for DC internal resistance at 50% SOC and room temperature charging at 1C:

[0106] The testing steps are as follows:

[0107] The following charging and discharging cycles were performed: 0.1C charging for 30 seconds, 0.1C charging for 30 seconds, 0.1C discharging ...

[0108] High-temperature cycling capacity retention after 500 cycles: The battery was charged and discharged once at 0.5C / 0.5C to obtain the discharge capacity C1. Then, the battery was placed in a 45℃ constant temperature chamber for 0.5C / 0.5C charge and discharge tests, and the discharge capacity C after the 500th cycle was recorded. 500 500-cycle capacity retention rate = C 500 / C1*100%. The test results are shown in Table 5.

[0109] Table 5

[0110] As can be seen from the data in Tables 4 and 5, the atomic content of lithium and oxygen elements on the negative electrode surface of the lithium-ion battery provided in this application embodiment is much higher than that of the lithium-ion batteries of Comparative Example 1 and Comparative Example 2 within the sputtering depth range of 30nm-70nm. That is, the solid electrolyte interface film of the lithium-ion battery provided in this application has stable lithium oxide, and while achieving the effect of reducing the impedance of the lithium-ion battery, it also improves the cycle performance. At the same time, the lithium-oxygen ratio of the negative electrode surface in this application embodiment is greater than 1.5 within the sputtering depth range of 30nm-70nm, while the lithium-oxygen ratio of Comparative Example 1 and Comparative Example 2 is less than 1.5. The stable lithium oxide lithium-oxygen ratio can further improve the stability of the solid electrolyte interface film, reduce the impedance of the lithium-ion battery, and improve the cycle performance of the battery.

[0111] The preferred embodiments have been described in detail above, but this application is not limited to the specific implementation methods described above. Those skilled in the art can make various specific modifications under the guidance of this application without departing from the protection scope of this application, and these modifications all fall within the protection scope of this application.

Claims

1. A lithium-ion battery, wherein, The negative electrode sheet has a surface with a solid electrolyte interface film, the solid electrolyte interface film includes lithium oxide; the negative electrode sheet is subjected to sputtering test by X-ray photoelectron spectrometer, the atomic percentage of lithium element is A and the atomic percentage of oxygen element is B at at least one sputtering depth in the range of 30nm-70nm, wherein A≥50%, B≥20%; and the ratio of the atomic percentage of lithium element to the atomic percentage of oxygen element is greater than 1.

5.

2. The lithium-ion battery of claim 1, wherein, The atomic percentage of lithium element is A and the atomic percentage of oxygen element is B at at least one sputtering depth in the range of 30nm-70nm, wherein A≥50%, B≥20%; and the ratio of the atomic percentage of lithium element to the atomic percentage of oxygen element is greater than 1.

5.

3. The lithium-ion battery of claim 1 or 2, wherein, 55%≤A≤70%; 22%≤B≤30%.

4. The lithium-ion battery of any one of claims 1-3, wherein, The ratio of the atomic percentage of lithium element to the atomic percentage of oxygen element is (1.8-3):

1.

5. The lithium-ion battery of any one of claims 1-4, wherein, The solid electrolyte interface film includes lithium oxide.

6. The lithium-ion battery of any one of claims 1-5, wherein, The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer loaded on at least one side of the positive electrode current collector, the positive electrode active layer including Li 1-x NiO2(0≤x≤1), Li3FeO 3.5 and LiFeO2one or more combinations thereof.

7. A method of making a lithium-ion battery, wherein, The method comprises the following steps: adding positive electrode active material, lithium supplementing agent, conductive agent and binder into solvent to prepare positive electrode slurry; adding negative electrode active material, conductive agent and binder into solvent to prepare negative electrode slurry; coating the positive electrode slurry on at least one side of positive electrode current collector to obtain first positive electrode sheet; coating the negative electrode slurry on at least one side of negative electrode current collector to obtain first negative electrode sheet; stacking the first positive electrode sheet, separator and the first negative electrode sheet in sequence, injecting electrolyte, and forming lithium ion battery through formation; The negative electrode sheet has a surface with a solid electrolyte interface film, the solid electrolyte interface film includes lithium oxide; the solid electrolyte interface film is subjected to sputtering test by X-ray photoelectron spectrometer, the atomic percentage of lithium element is A and the atomic percentage of oxygen element is B at at least one sputtering depth in the range of 30nm-70nm, wherein A≥50%, B≥20%; The ratio of the atomic percentage of lithium element to the atomic percentage of oxygen element is greater than 1.

5.

8. The method of producing a lithium-ion battery as claimed in claim 7, wherein, The formation comprises: constant voltage charging in two voltage intervals of 3.0V-3.5V and 4.1V-4.3V respectively for 2-5h.

9. The method of producing a lithium-ion battery as claimed in claim 8, wherein, The temperature of the constant voltage charging is 40℃-60℃.

10. The method of producing a lithium-ion battery as claimed in any one of claims 7 to 9, wherein, The lithium supplementing agent includes one or more of the following: Li2CO3, Li2C2O4, Li6CoO4, Li2NiO2, Li2Se, Li3N, Li2O2, Li2O, Li2S, Li2S2, Li5FeO4, lithium borate and lithium thio borate.

11. The method of producing a lithium-ion battery as claimed in any one of claims 7 to 10, wherein, The mass of the lithium supplementing agent is 0.5%-6% of the mass of the positive electrode active material.

12. The method of making a lithium-ion battery of claim 11, wherein, The mass of the lithium supplementing agent is 1%-5% of the mass of the positive electrode active material.

13. An electrical device, comprising: The electric device includes the lithium ion battery of any one of claims 1-6, or the lithium ion battery prepared by the preparation method of any one of claims 7-12.

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