A positive electrode lithium supplementing agent, a preparation method thereof, a positive electrode sheet, and a battery

Abstract

This invention discloses a core-shell structured positive electrode lithium replenisher. The lithium replenisher material has a core-shell structure composed of core particles and an outer shell. The core particles are composed of lithium-rich compounds, and the outer shell is a continuous or semi-continuous crystalline protective layer covering the core particles. The outer shell is composed of a lithium-ion conductor and an electronic conductor, with the electronic conductor selected from at least one of conductive carbon and conductive polymers. The outer shell achieves dual ion and electron transport through the synergistic cooperation of the lithium-ion conductor and the electronic conductor, and the ionic conductivity of the outer shell is ≥1×10⁻⁶. ‑4 S / cm, electronic conductivity ≥1×10 ‑2 S / cm. The core-shell structured positive electrode lithium replenisher of the present invention provides a sufficient active lithium source with a lithium-rich core to compensate for the irreversible capacity loss during the first charge and discharge of the battery, and the crystallized composite shell enables efficient dual transport of ions and electrons and protects the core, significantly improving the first charge and discharge efficiency and cycle stability of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a positive electrode lithium replenishing agent and its preparation method, a positive electrode sheet, and a battery. Background Technology

[0002] The core working principle of lithium-ion batteries is to store and release electrical energy by inserting and deintercalating lithium ions between the positive and negative electrodes. However, during the initial activation and formation process, a solid electrolyte interphase (SEI) film is formed on the surface of the negative electrode. This process consumes a large number of active lithium ions, resulting in low initial charge and discharge efficiency and a decrease in actual usable capacity. This irreversible capacity loss problem has become a key bottleneck restricting the performance improvement of lithium-ion batteries. To address this issue, the industry primarily employs two main technical solutions: negative electrode lithium replenishment and positive electrode lithium replenishment. However, both have significant drawbacks. Negative electrode lithium replenishment technology often uses lithium foil, lithium powder, and lithium silicide powder as replenishment materials, which are extremely sensitive to humidity and temperature in the production environment. This not only poses high operational risks but also results in poor compatibility with existing lithium-ion battery production lines. Furthermore, the high material costs make large-scale application difficult. Positive electrode lithium replenishment technology often uses lithium-rich materials such as Li2NiO2 and Li5FeO4 as replenishment agents. These lithium-rich materials have poor chemical stability and readily react with moisture and carbon dioxide in the air to form inert layers such as Li2CO3. This not only significantly reduces the activity of the replenishment agent but also increases the pH value of the positive electrode slurry, increasing processing difficulty. In addition, their high electrochemical decomposition potential and slow reaction kinetics lead to poor compatibility with the positive electrode active material, easily causing insufficient lithium replenishment and potentially even triggering electrolyte oxidation and decomposition, affecting battery safety and cycle stability. Summary of the Invention

[0003] The purpose of this invention is to provide a core-shell structured positive electrode lithium replenishing agent and its preparation method, positive electrode sheet and battery, to solve the problems of insufficient lithium replenishment and poor stability of existing lithium replenishment technologies, to achieve efficient lithium replenishment, improve battery charge and discharge efficiency and cycle stability, and at the same time have good process compatibility.

[0004] To achieve the above objectives, the technical solution provided by the present invention is as follows: The first aspect of this application provides a cathode lithium supplement agent with a core-shell structure: The lithium replenishing agent material has a core-shell structure consisting of core particles and an outer shell; wherein, the core particles are composed of lithium-rich compounds, and the outer shell is a continuous or semi-continuous crystallized protective layer covering the core particles. The outer shell is composed of a lithium-ion conductor and an electronic conductor, wherein the electronic conductor is selected from at least one of conductive carbon and conductive polymer. The outer shell achieves dual ion and electron transport through the synergistic cooperation of lithium-ion conductors and electronic conductors, and the ionic conductivity of the outer shell is ≥1×10⁻⁶. -4 S / cm, electronic conductivity ≥1×10 -2 S / cm.

[0005] To optimize the above technical solution, the specific limitations also include: The core particles have a particle size of 500 nm to 1.2 μm, and the outer shell has a thickness of 20 to 50 nm; the lithium-ion conductor is selected from Li3PO4, Li2SiO3, and Li 10 GeP2S 12 At least one of the following; the electronic conductor is selected from at least one of acetylene black, conductive graphite, and polythiophene.

[0006] Furthermore, the mass ratio of lithium-ion conductor to electronic conductor in the outer shell is 3:7 to 7:3; when the lithium-ion conductor is Li3PO4 and the electronic conductor is acetylene black, the mass ratio is 4:6 to 5:5.

[0007] The second aspect of this application provides a method for preparing a positive electrode lithium supplement with a core-shell structure, comprising the following steps: S1: The core is prepared by spray pyrolysis, wherein the crystallinity and particle size uniformity of the core are controlled by setting the carrier gas flow rate, reaction temperature and residence time. S2: The shell is coated on the core using the sol-gel method. The stable interface between the shell and the core is achieved by controlling the sintering process: the interface bonding strength between the shell and the core is ≥15 MPa, and the shell forms a continuous or semi-continuous crystallized protective layer.

[0008] Further, step S1, which uses spray pyrolysis to prepare the core, is as follows: using lithium nitrate and nickel nitrate in a molar ratio of 2~2.1:1 as raw materials, a precursor solution with a total metal cation concentration of 0.4~0.6 mol / L is prepared. The precursor solution is then transported to an ultrasonic atomizer to form atomized droplets. The ultrasonic atomizer sends the atomized droplets into a tubular reactor using a carrier gas. The temperature of the tubular reactor is set to 730~770°C, and the residence time of the atomized droplets in the high-temperature zone is 15~20 seconds.

[0009] Furthermore, in the spray pyrolysis method of step S1, the carrier gas is nitrogen, the flow rate is controlled at 0.8~1.2L / min, and the crystallinity of the core particles is ≥95% and the particle size variation coefficient is ≤10%.

[0010] Step S2 involves coating the core with a shell using a sol-gel method, as follows: a lithium-ion conductor and an electronic conductor are mixed to form a sol, the core particles are dispersed in the sol, and after stirring and drying, the mixture is sintered at 300~600℃ under an inert atmosphere to form a crystallized protective layer outside the core particles.

[0011] Furthermore, in the sol-gel method of step S2, the sintering heating rate is 2~5℃ / min, and the interfacial bonding strength between the shell and the core is ≥15MPa.

[0012] A third aspect of this application provides a positive electrode sheet coated with a positive electrode active material, wherein the positive electrode active material contains the aforementioned core-shell structured positive electrode lithium supplementer.

[0013] A fourth aspect of this application provides a battery comprising the aforementioned positive electrode.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a sufficient active lithium source with a lithium-rich core as its core, effectively compensating for the irreversible capacity loss caused by the formation of the SEI film during the first charge and discharge of the battery, and solving the problem of insufficient lithium replenishment in existing lithium replenishment technologies. Through the crystallized shell composed of lithium-ion conductors and electronic conductors, the core is isolated from air to prevent it from becoming inactive, and efficient dual transport of ions and electrons is achieved, ensuring full utilization of the lithium source and significantly improving the battery's first charge and discharge efficiency.

[0015] The lithium replenishment agent core-shell structure of this invention achieves synergistic effects through functional adaptation between the core and shell. The core provides stable lithium source support, while the composite shell optimizes structural performance through a specific material combination, enabling efficient ion and electron transport. The synergistic effect of the two significantly improves the stability and reliability of the lithium replenishment effect. Simultaneously, the shell exhibits stability in transport and encapsulation, the core-shell structure possesses integrity and reliable interface bonding, and the shell and core are tightly bonded, preventing structural delamination during charging and discharging and maintaining the long-term effectiveness of the core-shell structure's synergistic effect.

[0016] This lithium replenishing agent, as a functional filler added to the positive electrode active material, can effectively compensate for the irreversible capacity loss of the positive electrode during the first charge and discharge process, improve the activity and charge and discharge efficiency of the positive electrode, improve ion transport at the positive electrode side interface, inhibit excessive interface growth, and improve the cycle stability of the positive electrode, thus providing a guarantee for the preparation of high-performance batteries. Detailed Implementation

[0017] The present invention will be further described in detail below through specific embodiments, but it should not be construed as limiting the scope of the subject matter of the present invention to the following embodiments. All technologies implemented based on the above content of the present invention fall within the scope of the present invention.

[0018] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the reagents, methods and equipment used are conventional reagents, methods and equipment in this technical field.

[0019] This invention provides a positive electrode lithium replenishing agent with a core-shell structure: The lithium replenishing agent material has a core-shell structure consisting of core particles and an outer shell; wherein, the core particles are composed of lithium-rich compounds, and the outer shell is a continuous or semi-continuous crystallized protective layer covering the core particles. The outer shell is composed of a composite of lithium-ion conductors and electronic conductors, wherein the electronic conductors are selected from at least one of conductive carbon and conductive polymers; The outer casing enables dual ion and electron transport through the synergistic cooperation of lithium-ion and electronic conductors, and the ionic conductivity of the casing is ≥1×10⁻⁶. -4 S / cm, electronic conductivity ≥1×10 -2 S / cm.

[0020] This invention achieves a core technological breakthrough in lithium replenishment agents through the core-shell structure and the dual ion and electron transport characteristics of the outer shell: the lithium-rich core can provide sufficient active lithium source, effectively compensating for the irreversible capacity loss caused by the formation of the SEI film during the first charge and discharge of the battery; the continuous or semi-continuous crystalline outer shell composed of lithium-ion conductors and electronic conductors can, on the one hand, isolate the core from contact with air, avoiding the formation of an inert layer in the core that leads to reduced activity, and on the other hand, enable efficient dual transport of ions and electrons, ensuring that the core lithium source is fully released and efficiently utilized, significantly improving the battery's first charge and discharge efficiency. At the same time, it avoids the drawbacks of existing lithium-rich replenishment agents, such as high electrochemical decomposition potential and slow kinetics, taking into account both the safety and efficiency of lithium replenishment, and solving the core problems of poor stability and insufficient lithium replenishment in existing lithium replenishment technologies.

[0021] In some embodiments, the core particles have a diameter of 500 nm to 1.2 μm, and the outer shell thickness is 20 to 50 nm; the lithium-ion conductor is selected from Li3PO4, Li2SiO3, and Li 10 GeP2S 12 At least one of the following; the electronic conductor is selected from at least one of acetylene black, conductive graphite, and polythiophene.

[0022] A reasonable core particle size ensures that it is uniformly dispersed in the positive electrode slurry, avoiding particle agglomeration that affects the lithium replenishment effect and battery performance; the appropriate shell thickness balances the protection effect and impedance, effectively isolating the core from air without hindering ion / electron transport due to excessive thickness.

[0023] In some implementations, the mass ratio of lithium-ion conductors to electronic conductors in the casing is 3:7 to 7:3. A reasonable mass ratio can achieve a precise balance between ion and electronic conductivity, avoiding transmission imbalance caused by an excessively high proportion of a single conductor.

[0024] In some implementations, when the lithium-ion conductor is Li3PO4 and the electronic conductor is acetylene black, the mass ratio of the two is 4:6 to 5:5. Setting the optimal ratio of specific material combinations can enable the shell to achieve the best transmission performance, ensure efficient release and rapid transmission of the core lithium source, further improve the lithium replenishment efficiency, and at the same time enhance the structural stability of the shell, avoid damage or detachment during charging and discharging, and ensure the long-term effectiveness of lithium replenishment.

[0025] This invention also provides a method for preparing a core-shell structured positive electrode lithium supplement, comprising the following steps: S1: The core is prepared by spray pyrolysis. The crystallinity and particle size uniformity of the core are controlled by setting the carrier gas flow rate, reaction temperature and residence time. S2: The shell is coated on the core using the sol-gel method. The stable interface between the shell and the core is achieved by controlling the sintering process: the interface bonding strength between the shell and the core is ≥15 MPa, and the shell forms a continuous or semi-continuous crystallized protective layer.

[0026] In some embodiments, step S1 uses a spray pyrolysis method to prepare the core as follows: using lithium nitrate and nickel nitrate in a molar ratio of 2~2.1:1 as raw materials, a precursor solution with a total metal cation concentration of 0.4~0.6 mol / L is prepared. The precursor solution is then transported to an ultrasonic atomizer to form atomized droplets. The ultrasonic atomizer sends the atomized droplets into a tubular reactor using a carrier gas. The temperature of the tubular reactor is set to 730~770°C, and the residence time of the atomized droplets in the high-temperature zone is 15~20 seconds.

[0027] A reasonable ratio of raw materials can compensate for the loss of lithium volatilization during high-temperature reactions, ensuring the lithium-rich core characteristics and guaranteeing lithium replenishment capacity; an appropriate precursor concentration can ensure the fluidity and uniformity of the solution, facilitating atomization to form uniform droplets; and appropriate reaction conditions can ensure a complete reaction, generating a lithium-rich core with complete crystals and high purity, avoiding insufficient core activity due to incomplete reaction.

[0028] In some embodiments, in the spray pyrolysis method of step S1, the carrier gas is nitrogen, the flow rate is controlled at 0.8~1.2L / min, the crystallinity of the core particles is ≥95%, and the particle size variation coefficient is ≤10%.

[0029] The appropriate carrier gas flow rate and reaction temperature ensure that the core crystallinity meets the standard, reduce structural defects, and improve the core chemical stability and lithium replenishment activity; the uniform core particle size can avoid particle agglomeration or excessive differences that lead to uneven dispersion of lithium replenishment agent, thereby avoiding affecting the battery charge-discharge and cycle performance.

[0030] In some embodiments, step S2 employs a sol-gel method to coat the core with a shell, specifically as follows: a lithium-ion conductor and an electronic conductor are mixed to form a sol, the core particles are dispersed in the sol, stirred and dried, and then sintered at 300~600℃ under an inert atmosphere to form a crystallized protective layer outside the core particles.

[0031] In some embodiments, in the sol-gel method of step S2, the sintering heating rate is 2~5℃ / min, and the interfacial bonding strength between the shell and the core is ≥15MPa.

[0032] Suitable sintering conditions allow a crystallized protective layer to form on the outer shell, improving structural and chemical stability while preventing side reactions between the core and the shell, thus ensuring the overall activity of the lithium supplement. The present invention also provides a positive electrode sheet coated with a positive electrode active material, wherein the positive electrode active material contains the above-mentioned positive electrode lithium supplement agent with a core-shell structure.

[0033] The present invention also provides a battery comprising the above-described positive electrode.

[0034] The lithium replenishing agent of the present invention is added to the positive electrode active material as a functional filler without changing the existing positive electrode preparation process, and has good process compatibility. The lithium replenishing agent can effectively compensate for the irreversible capacity loss of the positive electrode during the first charge and discharge process, improve the activity and charge and discharge efficiency of the positive electrode, improve the ion transport at the positive electrode side interface, inhibit excessive interface growth, and further improve the cycle stability of the positive electrode, thus providing a guarantee for the preparation of high-performance batteries.

[0035] The technical solution of the present invention will be further described in detail below with reference to specific embodiments: Example 1 S1: Core preparation by spray pyrolysis A precursor solution with a total metal cation concentration of 0.5 mol / L was prepared using analytical grade lithium nitrate and analytical grade nickel nitrate in a molar ratio of 2.05:1. The precursor solution was then fed into an ultrasonic nebulizer to form atomized droplets. Nitrogen was used as the carrier gas at a flow rate of 1.0 L / min. The atomized droplets were fed into a tubular reactor at a temperature of 750 °C, and the residence time of the atomized droplets in the high-temperature zone was 18 seconds. After the reaction, the powder was collected by a cyclone separator and annealed at 550 °C for 2 hours in an oxygen atmosphere to obtain core particles. The core crystallinity was found to be 96%, the coefficient of variation of particle size was 8%, and the core particle size was 0.8 μm. S2: Sol-gel coating of the outer shell A dispersion of lithium-ion conductor Li3PO4 and electronic conductor acetylene black was selected and mixed at a mass ratio of Li3PO4:acetylene black of 4.5:5.5 to form a sol. The core particles prepared in step S1 were dispersed in the sol, stirred, dried, and then sintered at 450℃ under an inert atmosphere at a heating rate of 3.5℃ / min for 4 hours to form a continuous crystalline protective layer. The outer shell thickness was measured to be 35nm, and the outer shell ionic conductivity was 1.5×10⁻⁶. -4 S / cm, electronic conductivity 1.5×10 -2 S / cm, the interfacial bonding strength between the shell and the core is 18MPa, and finally a core-shell structure positive electrode lithium replenisher is obtained; The core is Li2NiO2, which is generated by spray pyrolysis and annealing of lithium nitrate and nickel nitrate. S3: Battery Assembly Steps According to the positive electrode formulation NCM811:acetylene black:PVDF:lithium supplement = 96:2:2:3 by weight, each component was added to an appropriate amount of N-methylpyrrolidone solvent and stirred at high speed for 30 minutes to prepare a uniform positive electrode slurry. The positive electrode slurry was uniformly coated on an aluminum foil current collector and vacuum dried at 80°C for 12 hours. It was then cut into positive electrode sheets with a diameter of 12 mm. Using a lithium metal sheet as the counter electrode, Celgard2400 as the separator, and 1 mol / L LiPF6 / EC+DMC+EMC (volume ratio 1:1:1) as the electrolyte, a CR2032 type half cell was assembled in an argon-protected glove box. After standing for 24 hours, the electrochemical performance was tested. Example 2 Preparation steps: basically the same as in Example 1, except that the shell material ratio and sintering parameters in S2 were adjusted to make the shell ionic conductivity = 1×10 -4 S / cm, electronic conductivity = 1×10 -2 S / cm; specifically, the mass ratio of Li3PO4 to acetylene black is 5:5, the sintering heating rate is 2℃ / min, and the sintering temperature is 300℃; the battery assembly steps are completely consistent with those in Example 1. When the sintering temperature is reduced to 300℃, the degree of crystallization of the outer shell decreases slightly, but a continuous protective layer can still be formed. Example 3 Preparation steps: basically the same as in Example 1, except that the shell material ratio and sintering parameters in S2 were adjusted to make the shell ionic conductivity = 3 × 10⁻⁶. -4 S / cm, electronic conductivity = 3 × 10 -2 S / cm; specifically, the mass ratio of Li3PO4 to acetylene black is 4:6, the sintering heating rate is 5℃ / min, and the sintering temperature is 600℃; the battery assembly steps are completely consistent with those in Example 1. When the sintering temperature is increased to 600℃, the degree of crystallization of the outer shell is improved, and the transmission performance is optimized. Example 4 Preparation steps: basically the same as in Example 1, except that the parameters of the spray pyrolysis method in S1 are adjusted to make the core particle size 500nm; specifically, the carrier gas flow rate is 0.8L / min, the reaction temperature is 730℃, the residence time is 15 seconds, and the core particles with a particle size of 500nm are screened after annealing; the S2 step is completely the same as in Example 1; the battery assembly steps are completely the same as in Example 1. Example 5 Preparation steps: basically the same as in Example 1, except that the parameters of the spray pyrolysis method in S1 were adjusted to make the core particle size 1.2 μm; specifically, the carrier gas flow rate was 1.2 L / min, the reaction temperature was 770℃, the residence time was 20 seconds, and the core particles with a particle size of 1.2 μm were screened after annealing; the S2 step was completely the same as in Example 1; the battery assembly steps were completely the same as in Example 1. Example 6 Preparation steps: basically the same as in Example 1, except that the parameters of the sol-gel method in S2 are adjusted to make the shell thickness 20nm; specifically, the amount of lithium-ion conductor and electronic conductor is reduced, the stirring time is shortened to 4 hours, and the sintering time is shortened to 3 hours; the steps in S1 are completely the same as in Example 1; the battery assembly steps are completely the same as in Example 1. Example 7 Preparation steps: basically the same as in Example 1, except that the parameters of the sol-gel method in S2 are adjusted to make the shell thickness 50nm; specifically, the amount of lithium-ion conductor and electronic conductor is increased, the stirring time is extended to 8 hours, and the sintering time is extended to 7 hours; the steps in S1 are completely the same as in Example 1; the battery assembly steps are completely the same as in Example 1. Example 8 Preparation steps: basically the same as in Example 1, except that the precursor ratio in S1 is adjusted so that the molar ratio of lithium nitrate to nickel nitrate is 2:1; other parameters in S1 and steps in S2 are completely the same as in Example 1; battery assembly steps are completely the same as in Example 1. Example 9 Preparation steps: basically the same as in Example 1, except that the precursor ratio in S1 is adjusted so that the molar ratio of lithium nitrate to nickel nitrate is 2.1:1; other parameters in S1 and steps in S2 are completely the same as in Example 1; battery assembly steps are completely the same as in Example 1.

[0036] Example 10 Preparation steps: basically the same as in Example 1, except that the precursor concentration in S1 was adjusted to prepare a total metal cation concentration of 0.4 mol / L; other parameters of S1 and steps of S2 are completely the same as in Example 1; battery assembly steps are completely the same as in Example 1. Example 11 Preparation steps: basically the same as in Example 1, except that the precursor concentration in S1 was adjusted to prepare a total metal cation concentration of 0.6 mol / L; other parameters of S1 and steps of S2 are completely the same as in Example 1; battery assembly steps are completely the same as in Example 1. Example 12 Preparation steps: basically the same as in Example 1, except that the carrier gas flow rate in S1 is adjusted to 0.8 L / min; other parameters in S1 and steps in S2 are completely the same as in Example 1; battery assembly steps are completely the same as in Example 1. Example 13 Preparation steps: basically the same as in Example 1, except that the carrier gas flow rate in S1 is adjusted to 1.2 L / min; other parameters of S1 and steps of S2 are completely the same as in Example 1; battery assembly steps are completely the same as in Example 1. Example 14 Preparation steps: basically the same as in Example 1, except that the sintering temperature in S2 is adjusted to 300℃; other parameters in S2 and steps in S1 are completely the same as in Example 1; battery assembly steps are completely the same as in Example 1. Example 15 Preparation steps: basically the same as in Example 1, except that the sintering temperature in S2 is adjusted to 600℃; other parameters in S2 and steps in S1 are completely the same as in Example 1; battery assembly steps are completely the same as in Example 1. Example 16 Preparation steps: basically the same as in Example 1, except that the sintering heating rate in S2 is adjusted to 2℃ / min; other parameters in S2 and steps in S1 are completely the same as in Example 1; battery assembly steps are completely the same as in Example 1. Example 17 Preparation steps: basically the same as in Example 1, except that the sintering heating rate in S2 was adjusted to 5℃ / min; other parameters in S2 and steps in S1 were completely the same as in Example 1; battery assembly steps were completely the same as in Example 1. Comparative Example 1 Preparation steps: basically the same as in Example 1, except that the ratio of the shell material in S2 was adjusted to make the shell ionic conductivity 0.8 × 10⁻⁶. -4 S / cm, electronic conductivity 0.8×10 -3 S / cm; specifically, the mass ratio of Li3PO4 to acetylene black is 7:3, the sintering heating rate is 1℃ / min, and the sintering temperature is 280℃; the battery assembly steps are completely consistent with those in Example 1. Comparative Example 2 Preparation steps: Only step S1 of Example 1 is performed, without step S2 (shell coating), and the uncoated Li2NiO2 core is used directly as the lithium replenisher; the battery assembly steps are completely consistent with those of Example 1. Without an outer casing, the lithium core deteriorates upon contact with air and is easily corroded by the electrolyte, resulting in a significant decrease in lithium replenishment efficiency and cycle performance. Comparative Example 3 Preparation steps: basically the same as in Example 1, except that the parameters of the spray pyrolysis method in S1 are adjusted to make the core particle size 400nm; specifically, the carrier gas flow rate is 0.7L / min, the reaction temperature is 720℃, and the residence time is 14 seconds; the S2 step is completely the same as in Example 1; the battery assembly steps are completely the same as in Example 1. Comparative Example 4 Preparation steps: basically the same as in Example 1, except that the parameters of the sol-gel method in S2 were adjusted to make the shell thickness 60nm; specifically, the amount of lithium-ion conductor and electronic conductor was greatly increased, the stirring time was 10 hours, the sintering time was 9 hours, and the sintering temperature was appropriately increased to 500℃ (to ensure complete crystallization of the thick shell); the steps in S1 were completely the same as in Example 1; the battery assembly steps were completely the same as in Example 1. Comparative Example 5 Preparation steps: basically the same as in Example 1, except that the precursor ratio in S1 is adjusted so that the molar ratio of lithium nitrate to nickel nitrate is 1.9:1; other parameters in S1 and steps in S2 are completely the same as in Example 1; battery assembly steps are completely the same as in Example 1.

[0037] Comparative Example 6 Preparation steps: basically the same as in Example 1, except that the precursor concentration in S1 was adjusted to prepare a total metal cation concentration of 0.3 mol / L; other parameters of S1 and steps of S2 are completely the same as in Example 1; battery assembly steps are completely the same as in Example 1. Comparative Example 7 Preparation steps: basically the same as in Example 1, except that the carrier gas flow rate in S1 is adjusted to 0.7 L / min; other parameters in S1 and steps in S2 are completely the same as in Example 1; battery assembly steps are completely the same as in Example 1. Comparative Example 8 Preparation steps: basically the same as in Example 1, except that the sintering temperature in S2 is adjusted to 280℃; other parameters in S2 and steps in S1 are completely the same as in Example 1; battery assembly steps are completely the same as in Example 1. Comparative Example 9 Preparation steps: basically the same as in Example 1, except that the sintering heating rate in S2 is adjusted to 1℃ / min; other parameters in S2 and steps in S1 are completely the same as in Example 1; battery assembly steps are completely the same as in Example 1.

[0038] Comparative Example 10 Preparation steps: basically the same as in Example 1, except that the ratio of shell materials and sintering parameters in S2 are adjusted to increase the ionic conductivity and electronic conductivity of the shell; specifically, the mass ratio of Li3PO4 to acetylene black is 3:7, the sintering heating rate is 6℃ / min, and the sintering temperature is 650℃; the battery assembly steps are completely the same as in Example 1.

[0039] Excessive sintering temperature, rapid heating rate, and high proportion of electronic conductors lead to excessive crystallization of the outer shell, increased internal stress, decreased interfacial bonding strength, and an imbalance in ion and electron transport.

[0040] Comparative Example 11 Preparation steps: basically the same as in Example 1, except that the sintering temperature in S2 is further increased to 700°C and the holding time is extended to cause the shell to over-crystallize and local microcracks to appear; the battery assembly steps are completely the same as in Example 1.

[0041] Excessive crystallization leads to increased shell brittleness and poorer interfacial bonding, making the structure prone to damage during charging and discharging, and significantly reducing the stability of lithium source release and transport.

[0042] Table 1

[0043] Conclusion Analysis: The various embodiments of the present invention achieve a balanced and excellent performance of the lithium replenishing agent, demonstrating the synergistic effect of the lithium-rich core and the composite crystallized shell of lithium-ion conductors and electronic conductors, which can effectively improve the lithium replenishment effect and battery electrochemical performance.

[0044] In Examples 2 and 3, different parameters of shell conductivity were used. The experimental results of both were superior to those of the comparative examples that did not meet the conductivity requirements, achieving efficient dual transport of ions and electrons and ensuring full utilization of the lithium source. In Comparative Example 1, the shell ion conductivity and electron conductivity did not meet the requirements of this invention, resulting in an imbalance between ion and electron transport and a significant decrease in lithium replenishment efficiency and cycle stability. In Comparative Example 10, the ratio of lithium-ion conductors to electronic conductors was unbalanced, and its cycle stability decreased accordingly. When the shell conductivity and the proportion of electronic conductors are too high, it will cause an imbalance between ion and electron transport, increase the internal stress of the shell, reduce the interfacial bonding strength, and ultimately affect the overall performance of the lithium replenishment agent.

[0045] Examples 4 and 5 used different core particle size values, and the test results were good. A reasonable core particle size can ensure that the lithium replenishing agent is uniformly dispersed in the positive electrode slurry, effectively avoid the problem of particle agglomeration, and thus ensure the stability of the lithium replenishment effect. In contrast, Comparative Example 3 had poor dispersion of the lithium replenishing agent due to its small core particle size, and its performance was significantly deteriorated. The small core particle size will affect the dispersion uniformity of the lithium replenishing agent, thereby reducing the lithium replenishment effect and battery performance.

[0046] Examples 6 and 7 conducted targeted tests on the shell thickness. The test results for both examples met the high-performance requirements, with Example 7 showing slightly better performance than Example 6. The appropriate shell thickness effectively balances protection and impedance, ensuring air isolation to protect the core without hindering ion and electron transport due to improper thickness. Comparative Example 4, due to excessive shell thickness, experienced increased shell impedance, hindering ion and electron transport and resulting in performance inferior to the examples with the required parameters. This demonstrates that thicker shells are not always better; exceeding a reasonable range can negatively impact the lithium replenishment's transport performance.

[0047] Examples 8 and 9 involved adjusting the molar ratio of lithium nitrate to nickel nitrate in the precursor. Both experiments showed good results, demonstrating that a reasonable raw material ratio can effectively compensate for lithium volatilization loss during the high-temperature reaction, ensuring the lithium-rich characteristics of the core and providing stable support for lithium replenishment capacity. Comparative Example 5, due to an excessively low precursor molar ratio, could not adequately compensate for lithium volatilization loss during the high-temperature reaction, resulting in insufficient lithium-rich characteristics in the core and a decreased lithium replenishment effect.

[0048] Examples 10 and 11 adjusted the total metal cation concentration of the precursor, and the experimental results all met the expected requirements. A suitable precursor concentration ensures the fluidity and uniformity of the solution, facilitating atomization to form uniform droplets, thereby ensuring complete core crystallization and high purity. When the concentration is at the upper limit of the reasonable range, it is more conducive to improving the quality of core preparation, thus optimizing the overall performance of the lithium supplement. Comparative Example 6, due to an excessively low total metal cation concentration in the precursor, resulted in poor solution fluidity and uniformity, leading to a decline in core preparation quality. Therefore, a suitable precursor concentration is crucial to ensuring complete core crystallization and sufficient activity.

[0049] Examples 12 and 13 employed different carrier gas flow rates in spray pyrolysis, and the experimental results were excellent. The appropriate carrier gas flow rate, in conjunction with the reaction temperature, ensured that the core crystallinity met the requirements, reduced structural defects, and improved the core's chemical stability and lithium replenishment activity. When the carrier gas flow rate was at the upper limit of the reasonable range, it was even more beneficial to improve the crystallinity of the core, thereby optimizing the performance of the lithium replenishing agent. Comparative Example 7, due to its excessively low carrier gas flow rate, suffered from insufficient core crystallinity, increased structural defects, and significantly inferior performance compared to the examples.

[0050] Examples 14 and 15 show variations in the sol-gel sintering temperature. Both experiments met the high-performance requirements. A suitable sintering temperature allows the shell to form a stable crystalline protective layer, effectively improving the shell's structural and chemical stability. When the sintering temperature is at the upper limit of the reasonable range, the shell exhibits higher crystallinity and better transport performance. It also enhances the interfacial bonding strength between the shell and the core, further improving the long-term performance of the lithium replenishing agent. Comparative Example 8, due to its excessively low sintering temperature, suffered from insufficient shell crystallinity, resulting in decreased transport performance and structural stability, performing worse than the corresponding example. Comparative Example 11, by further increasing the sintering temperature, caused excessive shell crystallinity and the appearance of localized microcracks. Its lithium replenishment performance and cycle stability significantly decreased. Excessive shell crystallinity increases brittleness, reduces interfacial bonding quality, and makes the structure prone to breakage during charging and discharging, thus reducing the stability of lithium source release and transport.

[0051] Examples 16 and 17 tested the sintering heating rate, and the results were good. A reasonable sintering heating rate can avoid side reactions between the shell and the core, ensuring the overall activity of the lithium supplement. When the heating rate is at the upper limit of the reasonable range, it is more conducive to the smooth crystallization process of the shell, improving the transport performance and structural stability of the shell. In Comparative Example 9, the sintering heating rate was too low, resulting in an incomplete crystallization process of the shell and a decrease in transport performance.

[0052] Comparative Example 2 lacks an outer shell structure and uses only the uncoated core as a lithium replenisher, making the core susceptible to electrolyte corrosion. This significantly reduces the lithium replenishment efficiency and cycle performance. This result highlights the protective role of the crystallized shell for the core and the importance of dual transport functions, and also verifies the core advantages of the core-shell structure design.

[0053] In summary, this invention achieves synergistic effects by forming a core-shell structure composed of a lithium-rich core and a crystalline shell composed of lithium-ion conductors and electronic conductors. The lithium-rich core provides a sufficient active lithium source, effectively compensating for the irreversible capacity loss caused by the formation of the SEI film during the first charge and discharge of the battery. The composite crystalline shell can both isolate the core from air to prevent it from deactivating and enable efficient dual transport of ions and electrons, ensuring full utilization of the lithium source. This significantly improves the battery's first charge and discharge efficiency and cycle stability, while also possessing good process compatibility, providing a reliable guarantee for the preparation of high-performance batteries.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent substitutions, and improvements made by those skilled in the art to the above embodiments without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A positive electrode lithium replenishing agent with a core-shell structure, characterized in that: The lithium replenishing agent material has a core-shell structure consisting of core particles and an outer shell; wherein, the core particles are composed of lithium-rich compounds, and the outer shell is a continuous or semi-continuous crystallized protective layer covering the core particles. The outer shell is composed of a lithium-ion conductor and an electronic conductor, wherein the electronic conductor is selected from at least one of conductive carbon and conductive polymer. The outer shell achieves dual ion and electron transport through the synergistic cooperation of lithium-ion conductors and electronic conductors, and the ionic conductivity of the outer shell is ≥1×10⁻⁶. -4 S / cm, electronic conductivity ≥1×10 -2 S / cm.

2. The positive electrode lithium replenishing agent with a core-shell structure according to claim 1, characterized in that: The core particles have a particle size of 500 nm to 1.2 μm, and the outer shell has a thickness of 20 to 50 nm; the lithium-ion conductor is selected from Li3PO4, Li2SiO3, and Li 10 GeP2S 12 At least one of the following; the electronic conductor is selected from at least one of acetylene black, conductive graphite, and polythiophene.

3. The core-shell structured positive electrode lithium replenishing agent according to claim 2, characterized in that: The mass ratio of lithium-ion conductor to electronic conductor in the outer shell is 3:7 to 7:3; when the lithium-ion conductor is Li3PO4 and the electronic conductor is acetylene black, the mass ratio is 4:6 to 5:

5.

4. A method for preparing a core-shell structured positive electrode lithium supplement agent according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1: The core is prepared by spray pyrolysis, wherein the crystallinity and particle size uniformity of the core are controlled by setting the carrier gas flow rate, reaction temperature and residence time. S2: The shell is coated on the core using the sol-gel method. The stable interface between the shell and the core is achieved by controlling the sintering process: the interface bonding strength between the shell and the core is ≥15 MPa, and the shell forms a continuous or semi-continuous crystallized protective layer.

5. The method for preparing the core-shell structured positive electrode lithium replenishing agent according to claim 4, characterized in that: Step S1 uses a spray pyrolysis method to prepare the core as follows: using lithium nitrate and nickel nitrate in a molar ratio of 2~2.1:1 as raw materials, a precursor solution with a total metal cation concentration of 0.4~0.6mol / L is prepared. The precursor solution is then transported to an ultrasonic atomizer to form atomized droplets. The ultrasonic atomizer sends the atomized droplets into a tubular reactor with a carrier gas. The temperature of the tubular reactor is set to 730~770°C, and the residence time of the atomized droplets in the high-temperature zone is 15~20 seconds.

6. The method for preparing the core-shell structured positive electrode lithium supplement agent according to claim 5, characterized in that: In the spray pyrolysis method of step S1, the carrier gas is nitrogen, the flow rate is controlled at 0.8~1.2L / min, and the crystallinity of the core particles is ≥95% and the particle size variation coefficient is ≤10%.

7. The method for preparing the core-shell structured positive electrode lithium supplement agent according to claim 4, characterized in that: Step S2 involves coating the core with a shell using a sol-gel method, as follows: a lithium-ion conductor and an electronic conductor are mixed to form a sol, the core particles are dispersed in the sol, and after stirring and drying, the mixture is sintered at 300~600℃ under an inert atmosphere to form a crystallized protective layer outside the core particles.

8. The method for preparing the core-shell structured positive electrode lithium supplement agent according to claim 4, characterized in that: In step S2, the sol-gel method involves a sintering heating rate of 2-5°C / min, and the interfacial bonding strength between the outer shell and the core is ≥15MPa.

9. A positive electrode plate, characterized in that: It is coated with a positive electrode active material, wherein the positive electrode active material contains the positive electrode lithium supplement with a core-shell structure as described in any one of claims 1 to 3.

10. A battery, characterized in that: It includes the positive electrode sheet as described in claim 9.

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