A composite lithium supplement and a preparation method thereof, a positive electrode sheet, and a lithium ion battery

Abstract

The application provides a composite lithium supplement agent, a preparation method thereof, a positive pole piece and a lithium ion battery. The composite lithium supplement agent comprises Li2C2O4, B element and a conductive carrier, wherein the B element is dispersed in the crystal lattice of the Li2C2O4 in a nanoscale. The preparation method comprises the following steps: mixing metal lithium powder and LiB(C2O4)2 according to a molar ratio of (2.8-3.2):1, performing first mechanical ball milling treatment under the protection of inert gas, and making the two react in situ to generate a nanocomposite of Li2C2O4 and B element; mixing the obtained nanocomposite with the conductive carrier, and performing second mechanical ball milling treatment to form the composite lithium supplement agent dispersed in a nanoscale. The application realizes the atomic / nanoscale dispersion of the B element in the crystal lattice of the Li2C2O4 through in-situ reaction, obtains a unique microstructure, and makes the composite lithium supplement agent have the characteristics of low decomposition voltage (<4.3V), high lithium supplement capacity (>400mAh / g), no gas production and excellent cycle stability, and the particle size D90 is less than or equal to 1 microns, which is more suitable for the existing electrode production line.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a lithium-ion battery positive electrode lithium replenishment material and its preparation method, positive electrode sheet and lithium-ion battery, and particularly to a Li2C2O4-B nanocomposite lithium replenishment agent prepared by in-situ chemical reaction and its application in lithium-ion batteries. Background Technology

[0002] During the initial charge and discharge cycle of a lithium-ion battery, the organic electrolyte undergoes reduction and decomposition on the surface of the negative electrode material, such as graphite, forming a solid electrolyte interphase (SEI) film. The formation of the SEI film consumes approximately 10%-30% of the active lithium, leading to irreversible capacity loss and resulting in an initial coulombic efficiency of less than 90%. To compensate for lithium loss, pre-lithiation technology has become one of the key methods to improve the energy density of lithium-ion batteries. Among these technologies, positive electrode lithium replenishment agents have attracted considerable attention due to their high compatibility with existing battery manufacturing processes and ease of operation.

[0003] Existing cathode lithium replenishers are mainly divided into three categories: ternary lithium-containing compounds (such as Li₂NiO₂ and Li₅FeO₄), binary lithium-containing compounds (such as Li₂O and Li₂O₂), and organic lithium salts (such as Li₂C₂O₄). Among them, the organic lithium salt Li₂C₂O₄ (lithium oxalate) has potential application value due to its low delithiation voltage (<4.5V). However, Li₂C₂O₄ as a lithium replenisher has two inherent drawbacks: firstly, its theoretical lithium replenishment capacity is relatively limited; secondly, the residual oxalate and other organic matter after the electrochemical reaction accelerates electrolyte oxidation, adversely affecting battery cycle life. These drawbacks make it difficult to simultaneously meet the dual requirements of efficient lithium replenishment and battery safety when using Li₂C₂O₄ alone.

[0004] To address the aforementioned issues, existing technologies have attempted to combine lithium compounds with reducing agents, using the reducing agent to drive the decomposition of the lithium compound at a lower potential to release active lithium. For example, Chinese patent document CN115498176A discloses a composite lithium replenisher for lithium-ion batteries based on a chemical reaction, comprising lithium oxide and / or lithium fluoride as lithium compounds, and elemental phosphorus, boron, etc., as reducing agents, prepared through a physical mixing and milling process. This technical solution is only applicable to lithium oxide and lithium fluoride systems and cannot be applied to the composite modification of organic lithium salts such as Li₂C₂O₄.

[0005] For example, Chinese patent document CN120600743A discloses a secondary battery and an electrical device, whose lithium replenishment composition includes a lithium replenishing agent and a reducing agent. The list of lithium replenishing agents includes lithium oxalate, and the list of reducing agents includes elemental boron. This document only provides a very broad list of components and does not disclose any specific technical solutions regarding how lithium oxalate and elemental boron can be effectively combined, nor does it address the microstructural characteristics of the combined components and their impact on electrochemical performance. Based on the disclosure of this document, those skilled in the art cannot obtain a composite lithium replenishing agent that can achieve uniform dispersion and synergistic effect of lithium oxalate and elemental boron.

[0006] For example, Chinese patent document CN112002894A discloses a lithium-supplementing material, its preparation method, and its application. This material includes a lithium-containing compound (such as lithium metasilicate) and an inorganic non-metallic reducing agent (such as sulfides like MoS2), which can be mixed using ball milling. The reducing agent used in this technical solution is a sulfide, which differs fundamentally from the boron element of this invention in terms of reaction mechanism, catalytic activity, and final product. Furthermore, its mixing method is a simple, disordered mixing, which cannot achieve nanoscale uniform dispersion of the reducing agent within the lithium compound lattice.

[0007] A comprehensive analysis of existing technologies reveals that, although there are technical approaches to improving lithium replenishment performance by combining lithium compounds with reducing agents, no mature technical solutions exist. In particular, for the composite system of Li₂C₂O₄ and elemental boron, existing technologies exhibit the following gaps and deficiencies: First, there is a lack of targeted composite methods. Existing technologies generally employ physical mixing methods to directly mix lithium compounds with reducing agents, such as sand milling and stirring. For the composite of Li₂C₂O₄ and elemental B, physical mixing makes it difficult to achieve uniform dispersion of elemental B in Li₂C₂O₄. Elemental B tends to agglomerate into micron-sized particles, leading to reduced catalytic efficiency and failing to fully leverage the synergistic effect of elemental B in driving the decomposition of Li₂C₂O₄.

[0008] Second, the microstructure is uncontrollable. Current technology cannot achieve precise control over the dispersion state of elemental boron in Li₂C₂O₄. Elemental boron and Li₂C₂O₄ only form physical contact, resulting in a large interfacial impedance. Furthermore, elemental boron is prone to further agglomeration during electrochemical cycling, leading to a decline in lithium replenishment performance.

[0009] Third, the possibility of in-situ reaction pathways has not been recognized. Existing technologies all follow the preparation approach of "directly mixing the desired final component," that is, directly mixing Li₂C₂O₄ with elemental B. This approach ignores the possibility of "in-situ generation" of the target component through chemical reactions, and also fails to recognize the crucial role of in-situ generation in achieving atomic / nanoscale dispersion.

[0010] To address the shortcomings of existing technologies, this invention proposes a novel approach: instead of directly mixing Li₂C₂O₄ and elemental B, it utilizes an in-situ chemical reaction between lithium metal powder and LiB(C₂O₄)₂ to simultaneously generate Li₂C₂O₄ and elemental B under mechanical ball milling assistance. Furthermore, elemental B is instantly captured by the Li₂C₂O₄ lattice during generation, achieving atomic / nanometer-level uniform dispersion of elemental B within Li₂C₂O₄. This approach fundamentally alters the existing preparation path, potentially overcoming the dispersion limits of physical mixing methods and yielding novel composite lithium supplements with unique microstructures and superior electrochemical performance. Summary of the Invention

[0011] The present invention aims to solve the aforementioned problems and defects in the prior art. Specifically, the technical problems to be solved by the present invention include: First, there is a lack of effective preparation methods for the Li₂C₂O₄-B composite system. While existing technologies recognize that combining lithium compounds with reducing agents can improve lithium replenishment performance, for the Li₂C₂O₄-B composite system, they only provide broad component listings and fail to offer specific technical solutions for achieving effective combination. Physical mixing methods struggle to achieve uniform dispersion of B in Li₂C₂O₄, leading to B agglomeration, low catalytic efficiency, and an inability to fully leverage the synergistic effect of the two.

[0012] Second, there is the problem of uncontrollable dispersion of elemental boron in Li₂C₂O₄. Existing physical mixing methods cannot achieve precise control over the dispersion scale of elemental boron. Elemental boron and Li₂C₂O₄ only form physical contact, resulting in a large interfacial impedance. Furthermore, elemental boron is prone to further agglomeration during electrochemical cycling, leading to a rapid decline in lithium replenishment performance.

[0013] Third, there is a lack of high-performance Li2C2O4-B composite lithium replenishers with unique microstructures. Due to limitations in preparation methods, existing technologies cannot obtain composite lithium replenishers in which elemental B is uniformly dispersed in the Li2C2O4 lattice at the nanoscale / atomic level. Consequently, it is also impossible to achieve the comprehensive performance of low decomposition voltage, high lithium replenishment capacity, no gas generation, and excellent cycle stability.

[0014] Fourth, there is the problem of poor compatibility between existing preparation processes and existing electrode production lines. The lithium replenishing agents prepared by existing technologies are usually in the micrometer range (20μm-200μm), which is difficult to adapt to the requirements of existing high-precision coating processes for nano-sized lithium replenishing agents, thus limiting their industrial application.

[0015] To achieve the above objectives, this invention provides a composite lithium replenishing agent and its preparation method, a positive electrode sheet, and a lithium-ion battery. The core of this invention lies in abandoning the traditional "direct physical mixing" approach and adopting an "in-situ chemical reaction" pathway. Using lithium metal powder and LiB(C2O4)2 as raw materials, an in-situ reaction is initiated through mechanical ball milling to simultaneously generate Li2C2O4 and elemental B. Furthermore, elemental B is captured by the Li2C2O4 lattice at the moment of generation, thereby achieving atomic / nanometer-level uniform dispersion of elemental B in Li2C2O4.

[0016] Based on the above-described inventive concept, a first aspect of the present invention provides a composite lithium supplement agent, comprising: Lithium compound, wherein the lithium compound is lithium oxalate (Li2C2O4). The driving substance is element B; and Conductive carrier; The elemental B is dispersed in the Li2C2O4 lattice at the nanoscale.

[0017] The elemental boron is uniformly distributed within the Li₂C₂O₄ crystal lattice and at grain boundaries in the form of nanodomains with a diameter of 1 nm to 50 nm. This unique microstructure is one of the key features of this invention, ensuring sufficient contact and efficient catalytic effect between elemental boron and Li₂C₂O₄.

[0018] The conductive carrier accounts for 5%-30% of the total mass.

[0019] The composite lithium replenishing agent has a particle size distribution D90 ≤ 1 μm. Alternatively, the composite lithium replenishing agent may have a particle size distribution D90 ≤ 0.5 μm. This nanoscale particle size allows the lithium replenishing agent of this invention to be perfectly compatible with the coating process of existing electrode production lines.

[0020] A second aspect of the present invention provides a method for preparing the above-mentioned composite lithium supplement, comprising the following steps: Step S1, in-situ reaction preparation of nanocomposite: In step S1, lithium metal powder and LiB(C2O4)2 are mixed in a predetermined molar ratio and subjected to a first mechanical ball milling treatment under inert gas protection, so that lithium metal and LiB(C2O4)2 undergo an in-situ chemical reaction to generate a nanocomposite of Li2C2O4 and elemental B. Step S2, conductive carrier composite: The nanocomposite obtained in step S1 is mixed with the conductive carrier and subjected to a second mechanical ball milling process to form a nanoscale dispersed composite lithium supplement.

[0021] The core innovation of the preparation method of this invention lies in the in-situ reaction process of step S1. This reaction follows the chemical equation: 3Li + LiB(C₂O₄)₂ → 2Li₂C₂O₄ + B In this reaction, lithium metal powder (0 valence) acts as a strong reducing agent, reducing the +3 valence boron in LiB(C2O4)2 to elemental boron, while simultaneously being oxidized to Li⁺ and combining with oxalate to form Li₂C₂O₄. This in-situ reaction process has the following unique advantages: (1) Atomic-level dispersion: B element is generated synchronously during the formation of Li2C2O4 lattice. B atoms are "captured" and "frozen" by the newly formed Li2C2O4 lattice at the moment of formation, and cannot migrate and aggregate, thus achieving atomic-level / nanoscale dispersion; (2) Chemical bonding interface: The in-situ generated B forms a chemical bond or strong interaction interface with Li2C2O4, rather than a simple physical contact, which can significantly reduce the interface impedance and improve the kinetic performance of the electrochemical reaction. (3) High reactivity: The in-situ generated elemental B is in a highly active state, and its catalytic effect on the decomposition of Li2C2O4 is more efficient.

[0022] In step S1, the molar ratio of lithium metal powder to LiB(C2O4)2 is (2.8-3.2):1, more preferably 3:1. This molar ratio strictly follows the stoichiometric ratio of the chemical reaction to ensure that the reaction proceeds completely and to avoid the presence of unreacted lithium metal or LiB(C2O4)2.

[0023] The ball milling speeds for the first and second mechanical ball milling processes are independently 400 rpm to 1200 rpm, the ball-to-material ratio is 10:1 to 50:1, and the ball milling time is 5 hours to 20 hours. These process parameter ranges were obtained through extensive experimental optimization, and the best dispersion effect and product performance can be achieved within these ranges.

[0024] The inert gas is at least one of argon, nitrogen, or helium. Inert gas protection is crucial to prevent oxidation of lithium metal powder and contamination of elemental B generated in situ.

[0025] In step S2, the conductive carrier is selected from at least one of carbon nanotubes, graphene, acetylene black, Ketjen black, or metal oxides; the mixing can be carried out by mechanical stirring or ball milling.

[0026] A third aspect of the present invention provides a positive electrode sheet comprising a current collector and a positive electrode material layer coated on at least one surface of the current collector, the positive electrode material layer comprising the composite lithium supplement agent described in the first aspect of the present invention.

[0027] The positive electrode material layer comprises, by weight, 70-90 parts of positive electrode active material, 2-15 parts of composite lithium supplement, 4-7.5 parts of conductive agent, and 4-7.5 parts of binder, based on 100 parts by weight.

[0028] A fourth aspect of the present invention provides a lithium-ion battery comprising the positive electrode sheet described in the third aspect of the present invention.

[0029] The fifth aspect of the present invention provides a battery module including the lithium-ion battery described in the fourth aspect of the present invention.

[0030] A sixth aspect of the present invention provides an electrical device comprising a lithium-ion battery or the battery module described in the fifth aspect of the present invention.

[0031] Compared with the prior art, the present invention has the following beneficial effects: First, this invention achieves atomic / nanoscale dispersion of elemental boron (B) in Li₂C₂O₄, resulting in a unique microstructure. The invention utilizes an "in-situ chemical reaction + two-step ball milling" method, enabling elemental boron to be simultaneously generated and trapped within the Li₂C₂O₄ lattice during its formation. This results in a unique microstructure where elemental boron is uniformly distributed in the form of 1-50 nm nanodomains within and at the grain boundaries of the Li₂C₂O₄ lattice. This structural feature is completely unattainable by existing physical mixing methods (such as CN115498176A and CN112002894A). XRD analysis shows that the characteristic diffraction peaks of elemental boron in the composite lithium supplement of this invention are significantly broadened or shifted compared to standard elemental boron, confirming a strong interaction between boron and the Li₂C₂O₄ lattice.

[0032] Second, the lithium replenishment capacity is significantly improved, and the decomposition voltage is further reduced. Thanks to the atomic-level dispersion of elemental boron, each boron atom can effectively catalyze the decomposition of Li₂C₂O₄, greatly improving the utilization rate of the active material in the lithium replenishment agent. Half-cell test results show that the specific capacity of the composite lithium replenishment agent of this invention in the first charge cycle can reach over 400 mAh / g, far exceeding existing technologies (e.g., 190.2 mAh / g in Example 1 of patent CN115498176A, and 412 mAh / g in this invention). Simultaneously, thanks to the close chemical contact between boron and Li₂C₂O₄, the catalytic reaction can occur at a lower potential (<4.3V), reducing the decomposition voltage by more than 0.2V compared to existing technologies.

[0033] Third, it achieves the superior characteristics of "no gas production" or "controlled gas production". In this invention, elemental boron drives the decomposition of Li₂C₂O₄ to generate LiB(C₂O₄)₂. This product itself is an excellent electrolyte additive, which helps to form a high-quality CEI film on the positive electrode surface. The small amount of CO₂ that may be generated during the reaction is utilized in situ and participates in the formation of the CEI film, rather than being simply released and causing the battery to swell. This "waste-to-treasure" effect is not available in existing technologies (such as the gas production from the decomposition of LiF in patent CN115498176A).

[0034] Fourth, the residue exhibits excellent compatibility with the electrolyte, preventing an increase in battery impedance. After decomposition, the residual conductive carrier of the composite lithium supplement of this invention can form a stable interface with the electrolyte, preventing an increase in battery impedance. Simultaneously, the generated lithium salts, such as LiB(C2O4)2, can dissolve in the electrolyte, improving the lithium-ion conductivity of the electrolyte and positively impacting the overall battery performance.

[0035] In summary, this invention successfully prepared a Li2C2O4-B nanocomposite lithium replenisher with a unique microstructure through a disruptive "in-situ chemical reaction" pathway (using lithium metal powder and LiB(C2O4)2 as raw materials, simultaneously generating Li2C2O4 and elemental B under mechanical ball milling assistance). For a long time, the art has sought to widely apply Li2C2O4 as a lithium replenisher, but its inherent defects of low capacity and significant residue hazards have remained unresolved. This invention, through a novel reaction pathway, fundamentally solves the dispersion and reactivity problems of Li2C2O4 lithium replenishers. Simultaneously, after decomposition during charging, the residual B is converted into a beneficial LiB(C2O4)2 electrolyte component, which can participate in the formation of stable CEI and SEI films, extending battery cycle life. This lithium replenisher combines low decomposition voltage, high lithium replenishment capacity, and process compatibility, achieving unexpected technical effects and possessing outstanding substantive characteristics and significant progress. Attached Figure Description

[0036] Figure 1 This is a flowchart of the preparation method of the composite lithium supplement provided in Example 1 of the present invention.

[0037] Figure 2 XRD comparison diagrams of composite lithium supplements prepared by different methods.

[0038] Figure 3 This is a TEM image of the composite lithium supplement of the present invention.

[0039] Figure 4 TEM images of comparative physical mixtures of lithium supplementation agents.

[0040] Figure 5 This is a comparison chart of the particle size distribution of different lithium supplements.

[0041] Figure 6 The first charge-discharge curves of half-cells with different lithium replenishment agents.

[0042] Figure 7 Cycle performance curves for full cells with different lithium replenishers. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0044] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components.

[0045] The core of this invention lies in the preparation of Li2C2O4-B nanocomposite lithium supplement through in-situ chemical reaction, the specific reaction of which is as follows: 3Li + LiB(C₂O₄)₂ → 2Li₂C₂O₄ + B The reaction was carried out with the assistance of mechanical ball milling, in which lithium metal powder reduced B³⁺ in LiB(C₂O₄)₂ to B. 0 The element B simultaneously oxidizes to Li⁺ and combines with oxalate to form Li₂C₂O₄. The element B is immediately captured by the newly formed Li₂C₂O₄ lattice, thus achieving atomic / nanoscale dispersion.

[0046] In the following examples, all raw materials used were commercially available analytical grade reagents, wherein: Lithium metal powder: purity ≥ 99.9%, particle size D50 ≤ 50 μm; LiB(C2O4)2 (lithium dioxalatoborate): Purity ≥ 99.5%; Conductive carrier: carbon nanotubes (CNTs), diameter 10-20nm, length 5-15μm, purity ≥95%; graphene, number of layers ≤3, specific surface area ≥500m² / g; Milling media: Zirconia balls, 3-10 mm in diameter; Positive electrode active material: LiCoO2, particle size D50=10μm; Conductive agent: SuperP; Adhesive: Polyvinylidene fluoride (PVDF); Solvent: N-methylpyrrolidone (NMP).

[0047] In the following embodiments, the performance testing method is as follows: 1. Structural characterization XRD testing: A Bruker D8 Advance X-ray diffractometer was used with Cu Kα radiation, a scanning range of 10°-80°, and a scanning rate of 2° / min.

[0048] SEM / TEM testing: The morphology and microstructure of the samples were observed using a Hitachi S-4800 scanning electron microscope and a JEOL JEM-2100F transmission electron microscope.

[0049] Particle size distribution: Tested using a Malvern Mastersizer 3000 laser particle size analyzer, with deionized water as the dispersion medium.

[0050] 2. Electrochemical performance testing Lithium-replenished half-cell: Lithium replenisher, Super P, and PVDF were mixed in a mass ratio of 7:2:1. A slurry was prepared using NMP as a solvent, coated onto aluminum foil, dried, and punched into a 12mm diameter disc as the working electrode; a lithium metal sheet was used as the counter electrode; the electrolyte was 1 M LiPF6 / (EC+DMC) (volume ratio 1:1); CR2032 button cells were assembled in an argon-filled glove box. Charge-discharge test voltage range: 2.0-4.5V, current density: 0.1C.

[0051] Full cell: The positive electrode sheet was prepared according to the formulation described in the example; the negative electrode was a graphite electrode; the separator was Celgard 2325; the electrolyte was the same as above. CR2032 button cells were assembled, and the charge / discharge test voltage range was 3.0-4.5V, and the cycle performance test current density was 0.3C.

[0052] To clearly illustrate the implementation methods and specific implementation details based on the embodiments provided by this invention, the following sections provide a detailed description: I. Preparation Examples of Composite Lithium Supplements Example 1 (In-situ Reaction Method, Optimal Ratio) This embodiment provides a composite lithium supplement (denoted as S1), the preparation method of which includes the following steps: Step S1, in-situ reaction preparation of nanocomposite: In an argon-filled glove box, 0.21 g (0.03 mol) of lithium metal powder and 2.79 g (0.01 mol) of LiB(C2O4)2 were weighed, ensuring a molar ratio of 3:1. The raw materials were transferred to a zirconia ball mill jar in a planetary ball mill, with a ball-to-material ratio of 20:1, and zirconia balls (a mixture of 5 mm and 10 mm diameter balls) were added. After sealing, the mixture was removed from the glove box and subjected to a first mechanical ball milling process under argon protection at 600 rpm for 12 hours. After ball milling, the jar was opened in the glove box, yielding Li2C2O4-B nanocomposite (theoretical yield: approximately 2.04 g of Li2C2O4 and approximately 0.11 g of elemental B).

[0053] Step S2, conductive carrier composite: All the nanocomposite obtained in step S1 was mixed with 0.34 g of carbon nanotubes (CNTs) (the conductive carrier accounted for approximately 15% of the total mass), and added to a ball mill jar at a ball-to-material ratio of 20:1. A second mechanical ball milling treatment was performed under argon protection at a speed of 600 rpm for 6 hours. After ball milling, the product was removed from a glove box to obtain composite lithium supplement S1.

[0054] Tests showed that the particle size distribution of S1 was D50 of 0.42 μm and D90 of 0.68 μm.

[0055] Example 2 (Different conductive carrier contents) This embodiment is basically the same as Embodiment 1, except that the mass of carbon nanotubes added in step S2 is 0.11g (the conductive carrier accounts for about 5% of the total mass), denoted as S2. Testing showed that the particle size distribution of S2 is D50 of 0.48μm and D90 of 0.75μm.

[0056] Example 3 (Different conductive carrier contents) This embodiment is basically the same as Embodiment 1, except that the mass of carbon nanotubes added in step S2 is 0.92g (the conductive carrier accounts for about 30% of the total mass), denoted as S3. Testing showed that the particle size distribution of S3 is D50 of 0.51μm and D90 of 0.82μm.

[0057] Example 4 (Different ball milling conditions) This embodiment is basically the same as Embodiment 1, except that: the ball milling speed in step S1 is 400 rpm and the ball milling time is 20 h; the ball milling speed in step S2 is 400 rpm and the ball milling time is 10 h. This is denoted as S4. Testing showed that the particle size distribution of S4 has a D50 of 0.58 μm and a D90 of 0.95 μm.

[0058] Example 5 (Different ball milling conditions) This embodiment is basically the same as Embodiment 1, except that: the ball milling speed in step S1 is 1200 rpm and the ball milling time is 5 hours; the ball milling speed in step S2 is 1200 rpm and the ball milling time is 3 hours. This is denoted as S5. Testing showed that the particle size distribution of S5 is D50 of 0.44 μm and D90 of 0.71 μm.

[0059] Example 6 (Different conductive carriers) This embodiment is basically the same as Embodiment 1, except that in step S2, carbon nanotubes are replaced with an equal mass of graphene, denoted as S6. Testing showed that the particle size distribution of S6 is D50 of 0.45 μm and D90 of 0.72 μm.

[0060] Example 7 (Different molar ratios) This embodiment is basically the same as Embodiment 1, except that the molar ratio of lithium metal powder to LiB(C2O4)2 in step S1 is 2.8:1 (0.196g of lithium metal powder and 2.79g of LiB(C2O4)2), which is denoted as S7.

[0061] Example 8 (Different molar ratios) This embodiment is basically the same as Embodiment 1, except that the molar ratio of lithium metal powder to LiB(C2O4)2 in step S1 is 3.2:1 (0.224g of lithium metal powder and 2.79g of LiB(C2O4)2), denoted as S8.

[0062] II. Preparation of the Comparative Example Comparative example (physical mixing method, no in-situ reaction) This comparative example provides a composite lithium supplement (denoted as D1), which is prepared using a traditional physical mixing method. The specific steps are as follows: 2.04 g of Li₂C₂O₄ (commercially available, purity ≥ 99%), 0.11 g of elemental B (commercially available, particle size D50 = 5 μm), and 0.34 g of carbon nanotubes were weighed and directly mixed. The mixture was then placed in a planetary ball mill and ball-milled under argon protection at a speed of 600 rpm, a ball-to-material ratio of 20:1, and a milling time of 18 h (consistent with the total milling time in Example 1). After milling, composite lithium supplement D1 was obtained.

[0063] Tests showed that the particle size distribution of D1 was D50 of 1.8 μm and D90 of 3.5 μm.

[0064] Comparative Example 2 (simulating the LiF-B system of prior art 1) This comparative example simulates the technical solution of prior art 1 (CN115498176A) to prepare a LiF-B composite lithium supplement, denoted as D2. The specific steps are as described in Example 2 of prior art 1: LiF and B elements were mixed at a mass ratio of 3:1 (LiF 3.0 g, B 1.0 g), and the mixture was ground in ethanol as a medium. The mixture was then sand-milled for 5 hours and spray-dried under a nitrogen atmosphere to obtain composite lithium supplement D2. The particle size distribution of D2 was tested to be D50 of 15 μm and D90 of 32 μm.

[0065] Comparative Example 3 (simulating the sulfide reducing agent system of prior art 3) This comparative example simulates the technical solution of prior art 3 (CN112002894A) to prepare a Li2C2O4-MoS2 composite lithium supplement, denoted as D3. The specific steps are as described in Example 8 of prior art 3: 2.0 g of Li₂C₂O₄ and 0.2 g of MoS₂ were mixed, and appropriate amounts of NMP and PVDF were added. The mixture was ball-milled and then dried to obtain composite lithium supplement D3. The particle size distribution of D3 was tested to be D50 of 2.2 μm and D90 of 4.1 μm.

[0066] Comparative Example 4 (without conductive carrier) This comparative example is basically the same as Example 1, except that a conductive carrier is not added in step S2, and it is denoted as D4. Testing showed that the particle size distribution of D4 is D50 of 0.45 μm and D90 of 0.73 μm.

[0067] Comparative Example 5 (Excess Conductive Carrier) This comparative example is basically the same as Example 1, except that 1.53g of carbon nanotubes (conductive carrier accounting for about 40% of the total mass) were added in step S2, denoted as D5. The particle size distribution of D5 was tested to be D50 = 0.60μm and D90 = 0.98μm.

[0068] Comparative Example 6 (One-step mixing) This comparative example provides a composite lithium supplement (denoted as D6) prepared using a one-step mixing method. Lithium metal powder, LiB(C2O4)2, and carbon nanotubes are added to a ball mill jar and ball-milled simultaneously, with other conditions identical to those in Example 1. Testing revealed that D6 has a particle size distribution of D50 of 0.55 μm and D90 of 0.88 μm.

[0069] III. Examples of the Preparation of Positive Electrode Sheets and Lithium-ion Batteries Example 9 (Positive electrode and lithium-ion battery) This embodiment provides a positive electrode and a lithium-ion battery comprising the composite lithium supplement S1 prepared in Example 1.

[0070] The preparation method of the positive electrode sheet is as follows: LiCoO2 (positive electrode active material), S1 (composite lithium supplementer), Super P (conductive agent), and PVDF (binder) were added to NMP solvent in a mass ratio of 88:4:4:4 and thoroughly mixed to obtain a positive electrode slurry. This slurry was then coated onto an aluminum foil current collector, dried at 100°C, and rolled to obtain the positive electrode sheet. The mass fraction of the composite lithium supplementer in the positive electrode material layer was 4%.

[0071] Preparation of lithium-ion batteries: Using the positive electrode sheet prepared above as the positive electrode, the graphite electrode as the negative electrode, the Celgard 2325 polypropylene three-layer composite membrane as the separator, and 1 M LiPF6 / (EC+DMC) (volume ratio 1:1) as the electrolyte, a CR2032 button cell was assembled in an argon-filled glove box and denoted as B1.

[0072] Examples 10-16 (Positive electrode sheets and lithium-ion batteries with different lithium replenishing agents) Examples 10-16 are basically the same as Example 9, except that they use the composite lithium replenishing agents S2-S8 prepared in Examples 2-8 respectively, and the corresponding lithium-ion batteries are denoted as B2-B8 respectively.

[0073] IV. Preparation of Comparative Cells Comparative Example 7 (without lithium supplement) This comparative example provides a positive electrode and a lithium-ion battery without the addition of a lithium replenishing agent, denoted as BD1. In the preparation of the positive electrode, LiCoO2, Super P, and PVDF are mixed in a mass ratio of 92:4:4, and the remaining preparation conditions are consistent with those of Example 9.

[0074] Comparative Examples 8-13 (Comparative Lithium-Added Batteries) The preparation processes of Comparative Examples 8-13 are consistent with those of Example 9, except that the composite lithium replenishing agents D1-D6 prepared by Comparative Examples 1-6 are used respectively, and the corresponding lithium-ion batteries are denoted as BD2-BD7 respectively.

[0075] V. Structural Characterization Results 1. XRD Analysis The composite lithium supplement S1 prepared in Example 1 was subjected to XRD testing, and the results are as follows: Figure 2 As shown. For comparison, XRD tests were simultaneously performed on D1 prepared by the physical mixing method and D2 of Comparative Example 2 LiF-B system.

[0076] Depend on Figure 2 It can be known that: In the XRD pattern of S1, the characteristic diffraction peaks of Li2C2O4 (2θ≈22.5°, 30.2°, 35.8°) are clearly distinguishable, indicating that the Li2C2O4 crystal phase is fully formed.

[0077] The key difference lies in the characteristic peaks of elemental B: the characteristic diffraction peaks of elemental B in S1 (2θ≈20.1°, 27.3°) are significantly broadened relative to the standard spectral lines of elemental B, and the peak positions are slightly shifted. This phenomenon indicates that elemental B does not exist in the form of large particles, but rather as nanodomains dispersed within the Li₂C₂O₄ lattice. There is a strong interaction between B and the Li₂C₂O₄ lattice, leading to lattice distortion.

[0078] In contrast, the XRD pattern of D1 (prepared by physical mixing method) shows that the characteristic peaks of elemental B are sharp and have high intensity, which are in high agreement with the standard spectral lines of elemental B, indicating that B mainly exists in the form of micron-sized particles and does not interact with the Li2C2O4 lattice.

[0079] The XRD pattern of D2 (LiF-B system) shows characteristic peaks of LiF and B, which exist independently without peak broadening or shift.

[0080] 2. TEM analysis The composite lithium supplement S1 prepared in Example 1 was observed by TEM, and the results are as follows: Figure 3 As shown.

[0081] from Figure 3 It can be clearly seen that: The Li2C2O4 lattice stripes are clearly visible, and the interplanar spacing is about 0.35 nm, corresponding to the (201) crystal plane of Li2C2O4.

[0082] Elemental boron is uniformly distributed within the Li₂C₂O₄ lattice and at grain boundaries in the form of nanodomains with a diameter of approximately 3–8 nm, with no obvious boron agglomerates observed.

[0083] High-resolution images show that there is a transition interface between the B nanodomains and the Li2C2O4 lattice, and lattice distortion can be observed in some areas, which is consistent with the peak broadening phenomenon observed by XRD.

[0084] EDS elemental surface scan results show that element B, C, and O are uniformly distributed at the nanoscale, with no elemental segregation.

[0085] In contrast, TEM images (not shown) of D1 (prepared by physical mixing method) show that B exists as particles of hundreds of nanometers in size, with a clear interface between it and the Li2C2O4 matrix, and no nanoscale dispersion was achieved.

[0086] 3. Particle size distribution analysis The particle size distribution of the lithium supplements in Example 1 and Comparative Example 1 was tested, and the results are shown in Table 1.

[0087] Table 1 Comparison of particle size distribution of lithium supplements obtained by different preparation methods

[0088] S1 (Example 1) 0.21 0.42 0.68 D1 (Comparative Example 1, Physical Mixture) 0.85 1.8 3.5 D2 (Comparative Example 2, spray dried) 8.5 15 32 As shown in Table 1, the lithium replenishing agent S1 prepared by the in-situ reaction method of the present invention has a particle size that is significantly smaller than that of the lithium replenishing agents prepared by the physical mixing method and the spray drying method. Its D90 is less than 1 μm, which can be well adapted to the existing high-precision coating process.

[0089] VI. Electrochemical Performance Test Results 1. Lithium-replenished half-cell performance Half-cell tests were conducted on the lithium replenishing agents prepared in Examples 1-8 and Comparative Examples 1-6. The first charge-discharge curves are shown below. Figure 6 As shown (taking S1 and D1 as examples), the test results are summarized in Table 2.

[0090] Table 2 Comparison of half-cell performance with lithium supplementation S1 (Example 1) In-situ reaction + two-step method 412 28 93.2 4.25 S2 (Example 2) In-situ reaction + two-step method (5% conductive carrier) 385 31 92.0 4.28 S3 (Example 3) In-situ reaction + two-step method (30% conductive carrier) 398 29 92.7 4.26 S4 (Example 4) In-situ reaction + two-step method (400 rpm) 376 33 91.2 4.31 S5 (Example 5) In-situ reaction + two-step method (1200 rpm) 405 30 92.6 4.27 S6 (Example 6) In-situ reaction + two-step method (graphene) 408 28 93.1 4.26 S7 (Example 7) In-situ reaction + two-step method (Li:LiB=2.8:1) 394 32 91.9 4.29 S8 (Example 8) In-situ reaction + two-step method (Li:LiB=3.2:1) 387 34 91.2 4.3 D1 (Comparative Example 1) Physical mixing 312 45 85.6 4.45 D2 (Comparative Example 2) LiF-B system 189 22 87.2 4.6 D3 (Comparative Example 3) Li2C2O4 - MoS2 245 38 84.6 4.52 D4 (Comparative Example 4) No conductive carrier 298 41 87.1 4.4 D5 (Comparative Example 5) 40% of conductive carriers 335 39 88.4 4.38 D6 (Comparative Example 6) One-step mixing 356 35 90.2 4.35 The low coulombic efficiency of the first cycle of the lithium-added half-cell is normal. The core reason is that the main function of the lithium-added is to provide irreversible capacity to the battery system, and its discharge capacity mainly comes from the lithium-added components that have not undergone decomposition reaction.

[0091] The following conclusions can be drawn from the test data in Table 2: The lithium replenishing agents S1-S8 prepared in the embodiments of the present invention all have a first-cycle charging capacity of over 370 mAh / g, with the highest reaching 412 mAh / g. This has a significant advantage over the lithium replenishing agents prepared in the comparative examples, where the first-cycle charging capacity of comparative example D1 is only 312 mAh / g and the first-cycle charging capacity of comparative example D2 is only 189 mAh / g.

[0092] In the embodiments of the present invention, the decomposition voltage plateau of the lithium supplement is controlled below 4.35V, with a minimum of 4.25V, which is lower than the decomposition voltage plateau of 4.45V and above in the comparative examples.

[0093] When the conductive carrier content is in the range of 5%-30% (corresponding to lithium replenishers S1-S3), the overall performance of the lithium replenisher is optimal. If the conductive carrier content is lower than 5% (corresponding to D4) or higher than 30% (corresponding to D5), key performance indicators such as the first-cycle charging capacity, coulombic efficiency, and decomposition voltage plateau of the lithium replenisher will decrease significantly.

[0094] Although the electrochemical performance of the lithium replenishing agent prepared by the one-step mixing process (corresponding to D6) is better than that of the lithium replenishing agent prepared by the physical mixing process (corresponding to D1), it is still significantly inferior to the lithium replenishing agent prepared by the two-step process of this invention (S1~S8). This further confirms the core and key role of the step sequence of "first generating a complex through in-situ reaction, and then adding a conductive carrier" in the preparation process of the lithium replenishing agent.

[0095] 2. Full battery performance The lithium-ion batteries prepared in Examples 9-16 and Comparative Examples 7-13 were subjected to charge-discharge cycle performance tests, and the test results are summarized in Table 3. The cycle performance curves of the lithium-ion battery prepared in Example 9 (using composite lithium replenishing agent S1) and the comparative group batteries are shown below. Figure 7 As shown.

[0096] Table 3 Comparison of Full Battery Performance B1 (Example 9) S1 212 188 88.7 91.2 B2 (Example 10) S2 208 183 88.0 89.5 B3 (Example 11) S3 210 186 88.6 90.3 B4 (Example 12) S4 205 181 88.3 88.7 B5 (Example 13) S5 211 187 88.6 90.8 B6 (Example 14) S6 209 185 88.5 90.1 B7 (Example 15) S7 207 183 88.4 89.2 B8 (Example 16) S8 206 182 88.3 88.9 BD1 (Comparative Example 7) No lithium supplement 185 148 80.0 72.5 BD2 (Comparative Example 8) D1 (Physical Mixing) 198 168 84.8 81.3 BD3 (Comparative Example 9) D2 (LiF-B) 190 160 84.2 78.5 BD4 (Comparative Example 10) D3 (MoS2) 195 164 84.1 79.8 BD5 (Comparative Example 11) D4 (no conductive carrier) 196 165 84.2 80.2 BD6 (Comparative Example 12) D5 (40% conductive carrier) 200 170 85.0 82.5 BD7 (Comparative Example 13) D6 (One-step method) 203 174 85.7 84.6 As can be seen from Table 3: The lithium-ion batteries B1-B8 prepared using the lithium replenishing agent of this invention all achieved a first-cycle coulombic efficiency of over 88%, with the highest value reaching 88.7%, which is significantly higher than that of BD1 (80.0%) without lithium replenishing agent and the lithium-ion batteries prepared in each comparative example (with a first-cycle coulombic efficiency range of 84%-86%).

[0097] After 200 charge-discharge cycles, the capacity retention rate of the batteries prepared in each embodiment of the present invention reached more than 88%, with the highest value reaching 91.2%, which has a significant advantage compared with the comparative batteries (capacity retention rate range of 72.5%-84.6%).

[0098] Comparing battery B1 (lithium replenisher S1 prepared using the two-step process of this invention) and BD7 (lithium replenisher prepared using a one-step process), it can be seen that even using the same in-situ reaction process, if a one-step mixing of conductive carriers is used (instead of the two-step process of this invention), the cycle performance of the battery still shows a significant difference (91.2% vs 84.6%). This further confirms the indispensability of the "two-step" process of this invention in improving battery performance.

[0099] 3. Gas production behavior analysis Battery B1 prepared in Example 9, battery BD2 prepared in Comparative Example 8 (using a physical mixed lithium supplement agent), and battery BD3 prepared in Comparative Example 9 (using a LiF-B system lithium supplement agent) were selected for formation gas production test. The test results are shown in Table 4.

[0100] Table 4 Comparison of Gas Production from Chemical Regeneration B1 S1 (This invention) 0.08 BD2 D1 (Physical Mixing) 0.35 BD3 D2 (LiF-B) 0.52 As shown in Table 4, the battery B1 prepared in this embodiment of the invention has a formation gas production rate of only 0.08 mL / Ah, which is significantly lower than that of BD2 (0.35 mL / Ah) prepared by the physical mixing method of lithium replenishment agent and BD3 (0.52 mL / Ah) prepared by the LiF-B system lithium replenishment agent. This result indicates that the lithium replenishment agent prepared in this invention releases almost no gas during decomposition, or even if a small amount of CO2 is generated, this CO2 can be utilized in situ and participate in the formation process of the electrode / electrolyte interface (CEI film), rather than being simply released in gaseous form and causing the battery to swell.

[0101] Based on the test results of the above embodiments and comparative examples, the following conclusions can be drawn: 1. The in-situ reaction method achieved atomic / nanoscale dispersion of elemental B in Li2C2O4.

[0102] X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirm that the preparation method used in this invention enables elemental boron to be uniformly distributed within the Li₂C₂O₄ lattice in the form of 3-8 nm nanodomains, and that there is a strong interaction between elemental boron and the Li₂C₂O₄ lattice. This structural feature is completely impossible to achieve by the physical mixing method (corresponding to D₁).

[0103] 2. The unique microstructure endows the lithium replenisher with excellent electrochemical performance. Benefiting from the nanoscale dispersion characteristics of elemental boron, each boron atom can effectively catalyze the decomposition reaction of Li₂C₂O₄, significantly improving the utilization rate of the active material in the lithium replenisher. The lithium replenisher prepared in this invention achieves a maximum first-cycle charging capacity of 412 mAh / g for half-cells, far exceeding the 312 mAh / g of lithium replenishers prepared by the physical mixing method and the 189 mAh / g of the LiF-B system lithium replenisher. Simultaneously, its decomposition voltage can be reduced to 4.25 V, lower than the 4.45 V and above decomposition voltage levels of comparative lithium replenishers.

[0104] 3. The two-step process sequence plays a crucial role. Comparing Example 1 (using a two-step process) and Comparative Example 6 (using a one-step process), it is evident that even with the same in-situ reaction raw materials, the overall performance of the lithium supplement prepared by adding the conductive support and reaction raw materials simultaneously (i.e., the one-step process) is significantly inferior to that prepared by the two-step process. The core reason is that premature addition of the conductive support may interfere with the smooth progress of the in-situ reaction and is also detrimental to the formation and stability of B nanodomains. The step sequence of "first generating the complex through in-situ reaction, then adding the conductive support" adopted in this invention is the optimal process path selected through creative effort.

[0105] 4. The conductive carrier content needs to be controlled within a specific range of 5%-30%. Comparative results from Examples 1-3 and Comparative Examples 4-5 show that when the conductive carrier content is below 5%, the internal electron transport network of the lithium replenisher is incomplete, leading to a significant decrease in the utilization rate of the active material. When the conductive carrier content is above 30%, excessive conductive carrier will dilute the content of the active material in the lithium replenisher and may also damage the structural stability of the B nanodomains. This conductive carrier content range of 5%-30%, as an integral part of this invention, works synergistically with the specific microstructure and preparation process to jointly ensure the excellent electrochemical performance of the lithium replenisher and lithium-ion battery.

[0106] 5. The lithium replenishing agent prepared by this invention can effectively solve the inherent defects of Li2C2O4. When Li2C2O4 is used alone, it has technical problems such as low lithium replenishing capacity and significant hazards from decomposition residues. However, through the technical solution of this invention, not only is the lithium replenishing capacity greatly improved, reaching up to 412mAh / g, but its decomposition residue LiB(C2O4)2 itself is an excellent electrolyte additive, realizing the resource utilization of residues and achieving the technical effect of turning "waste" into "treasure". At the same time, it achieves the beneficial effect of no gas generation or controllable gas generation during the lithium replenishment process.

[0107] 6. The technical solution of this invention differs fundamentally from the prior art. Comparative Example 2, simulating the technical solution of prior art document 1, uses a LiF-B system lithium replenishment agent with a lithium replenishment capacity of only 189 mAh / g and suffers from severe gas generation problems; Comparative Example 3, simulating the technical solution of prior art document 3, uses a MoS2 system lithium replenishment agent with a lithium replenishment capacity of only 245 mAh / g and a decomposition voltage as high as 4.52V. The technical solution of this invention significantly outperforms the prior art in key performance indicators such as lithium replenishment capacity, decomposition voltage, gas generation behavior, and cycle stability, achieving technical effects that are difficult for those skilled in the art to predict.

[0108] VII. Other Implementation Methods The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Those skilled in the art can make various improvements and modifications without departing from the spirit and principles of the invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

[0109] Specifically, in step S1, the inert gas, in addition to argon, can also be nitrogen, helium, etc.; the conductive carrier, in addition to carbon nanotubes and graphene, can also be acetylene black, Ketjen black, metal oxides (such as ZnO, TiO2), etc.; the mixing method in step S2, in addition to mechanical ball milling, can also be high-speed stirring, sand milling, etc.; the positive electrode active material, in addition to LiCoO2, can also be NCM ternary materials, lithium iron phosphate (LFP), lithium cobalt oxide (LCO), lithium manganese oxide (LMO), etc.; the negative electrode material, in addition to graphite, can also be silicon carbide, silicon oxide, lithium titanate, etc.

[0110] The scope of protection of this invention shall be determined by the claims. Any simple substitutions or equivalent transformations based on the technical concept of this invention shall fall within the scope of protection of this invention.

Claims

1. A composite lithium supplement, characterized in that, include: Lithium compound, wherein the lithium compound is Li2C2O4; The driving substance is element B; and Conductive carrier; The elemental B is dispersed in the Li2C2O4 lattice at the nanoscale.

2. The composite lithium supplement agent according to claim 1, characterized in that, The elemental B is uniformly distributed in the form of nanodomains with a diameter of 1nm-50nm within the lattice and at the grain boundaries of Li2C2O4.

3. The composite lithium supplement agent according to claim 1 or 2, characterized in that, The conductive carrier accounts for 5%-30% of the total mass of the composite lithium supplement; the particle size distribution of the composite lithium supplement is D90≤1μm.

4. The composite lithium supplement agent according to claim 3, characterized in that, The particle size distribution D90 of the composite lithium supplement is ≤0.5μm.

5. A method for preparing the composite lithium supplement agent according to any one of claims 1-4, characterized in that, Includes the following steps: Step S1: Mix lithium metal powder and LiB(C2O4)2 in a predetermined molar ratio and perform a first mechanical ball milling treatment under inert gas protection to allow lithium metal and LiB(C2O4)2 to undergo an in-situ chemical reaction to generate a nanocomposite of Li2C2O4 and elemental B. Step S2: The nanocomposite obtained in step S1 is mixed with a conductive carrier and subjected to a second mechanical ball milling process to form a nanoscale dispersed composite lithium supplement.

6. The preparation method according to claim 5, characterized in that, In step S1, the molar ratio of the lithium metal powder to LiB(C2O4)2 is (2.8-3.2):

1.

7. The preparation method according to claim 5 or 6, characterized in that, The ball milling speeds for the first and second mechanical ball milling processes are independently 400 rpm to 1200 rpm, the ball-to-material ratio is 10:1 to 50:1, and the ball milling time is 5 hours to 20 hours.

8. The preparation method according to claim 5 or 6, characterized in that, The inert gas is at least one of argon, nitrogen, and helium.

9. The preparation method according to claim 5 or 6, characterized in that, In step S2, the conductive carrier is selected from at least one of carbon nanotubes, graphene, acetylene black, Ketjen black, and metal oxides; the mixing is carried out by mechanical stirring or ball milling.

10. A positive electrode plate, characterized in that, It includes at least a current collector and a positive electrode material layer coated on at least one surface of the current collector, the positive electrode material layer including the composite lithium supplement agent according to any one of claims 1-4.

11. The positive electrode sheet according to claim 10, characterized in that, The positive electrode material layer comprises the following components in parts by weight: 70-90 parts of positive electrode active material, 2-15 parts of composite lithium supplement, 4-7.5 parts of conductive agent, and 4-7.5 parts of binder.

12. A lithium-ion battery, characterized in that, It includes at least the positive electrode sheet as described in claim 10 or 11.

13. A battery module, characterized in that, It includes at least the lithium-ion battery as described in claim 12.

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