Composite negative electrode material doped with nitrogen / phosphorus / boron elements and preparation process of composite negative electrode material

Abstract

The invention relates to the technical field of lithium ion battery negative electrode material preparation, and discloses a nitrogen / phosphorus / boron element doped composite negative electrode material and a preparation process thereof, and the preparation process comprises the following steps: adding boric acid into a phytic acid aqueous solution, and controlling a reaction until the dynamic viscosity of a system rises to a specific interval to generate a boron-phosphate oligomer; thermally injecting the oligomer into a melamine thermal saturated solution in a high-shear state, adjusting the pH value, and inducing to generate nitrogen / phosphorus / boron supramolecular precursor gel adsorbed on the surface of a negative electrode active base material; according to the preparation method disclosed by the invention, the heat stability locking effect of a P-O-B bonding network in the boron-phosphate oligomer on boron atoms is utilized, so that the volatilization of boron at a high temperature is inhibited.

Description

Technical Field

[0001] This invention relates to a composite anode material doped with nitrogen / phosphorus / boron elements and its preparation process, belonging to the field of lithium-ion battery anode material preparation technology. Background Technology

[0002] The increasing demands for energy density and fast charging capabilities in electric vehicles and portable electronic devices have made anode materials with both high electronic conductivity and excellent ion transport dynamics a key research focus. In high-capacity silicon-carbon or hard carbon anode systems, heteroatom doping improves the intrinsic electronic structure and surface activity of the material, while multi-element co-doping of nitrogen, phosphorus, and boron synergistically optimizes the conductivity of the carbon matrix and ion adsorption sites. Existing technologies utilize chemical raw materials such as melamine, phytic acid, and boric acid to construct precursors through physical mixing or liquid-phase precipitation. High-temperature heat treatment is then used to introduce heteroatoms and rearrange the carbon structure. The high-temperature reaction characteristics of each component are utilized to simultaneously complete the heteroatom lattice substitution and graphitization transformation of the carbon material.

[0003] While existing technologies attempt to improve conductivity through multi-component composites and surface modification, they still have limitations in controlling the steady-state state of components during high-temperature heat treatment. Although simple physical mixing or surface coating can temporarily construct a conductive network, the lack of fine-grained control over precursor reaction kinetics makes it difficult to control the high-temperature evolution of the microstructure. For example, Chinese invention patent CN103474631B discloses a silicon suboxide composite anode material for lithium-ion batteries and its preparation method. The scheme constructs a nano-silicon layer and a carbon conductive layer sequentially from the inside to the outside on the surface of a silicon suboxide substrate through chemical vapor deposition and mechanical fusion. Although this process improves the electron transport capability of the particle surface, the binding between components still relies on van der Waals forces or mechanical interlocking, and a strong chemical bond network is not formed at the molecular level. When faced with the high-temperature thermal environment required for graphitization, the physical interface bonding strength is insufficient. This not only fails to suppress the pyrolysis escape of volatile dopants such as boron, but also makes it difficult to avoid the collapse of the coating structure caused by the mismatch of thermal expansion coefficients, resulting in a contradiction between the final graphitization degree and the heteroatom retention rate. In actual preparation, conventional co-doping processes are constrained by the mismatch between thermodynamics and kinetics. As a key flux for inducing low-temperature graphitization of amorphous carbon, the catalytic efficiency of boron atoms depends on the solid phase retention concentration during the high-temperature carbonization stage. The components of conventional mixed systems are maintained only by physical adsorption or hydrogen bonding, lacking strong chemical bonds that can withstand high-temperature thermal shear. Before the temperature rises to the graphitization initiation temperature, low-melting-boiling-point boric acid and dehydration products escape from the precursor in the form of gaseous oxides or volatile borates.

[0004] Therefore, the technical problem to be solved by this invention is how to construct a precursor component locking mechanism to suppress the high-temperature loss of key catalytic elements, solve the contradiction between high graphitization degree and high heteroatom retention rate, and achieve molecular-level uniform coupling between conductive network and active site to improve the high-rate performance and production consistency of materials. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A preparation process for a composite negative electrode material doped with nitrogen / phosphorus / boron elements, comprising the following steps: A 45wt%~55wt% phytic acid aqueous solution was selected as the base solution. Particulate boric acid with a purity of ≥99.5% was added to the base solution according to a boron to phosphorus molar ratio of 1.5:1~2.5:1. The mixture was heated to 80℃ to 95℃ and reacted at a stirring rate of ≥300r / min until the dynamic viscosity of the system increased from the initial state to the range of 25mPa·s to 45mPa·s, generating a branched boron-phosphate oligomer and obtaining an intermediate solution. Melamine was dispersed in deionized water and heated to 90°C to 95°C to prepare a melamine hot saturated solution. The temperature of the intermediate solution was kept above 60°C. The intermediate solution was injected into the melamine hot saturated solution under shear stirring at 2000 r / min to 4000 r / min using a peristaltic pump at a constant flow rate. After mixing, a regulator was added to adjust the pH of the system to 4.5 to 5.0, which induced the formation of nitrogen / phosphorus / boron supramolecular precursor gel adsorbed on the surface of the pre-dispersed negative electrode active substrate. The nitrogen / phosphorus / boron supramolecular precursor gel was subjected to solid-liquid separation and drying to remove the solvent and fix the precursor topology. It was then heat-treated in a non-oxidizing atmosphere at a temperature of 800℃ to 1000℃ to transform the nitrogen / phosphorus / boron supramolecular precursor gel into a nitrogen-phosphorus-boron co-doped graphitized carbon coating layer in situ.

[0006] Preferably, in the step of preparing the intermediate solution, the isothermal reaction time is controlled within the range of 2 to 4 hours; the increase in dynamic viscosity characterizes the degree of polymerization of free boric acid molecules and phytic acid molecules in the dehydration condensation reaction to form boron-phosphate oligomers; and the intermediate solution is a transparent homogeneous fluid without visible particles at the reaction endpoint.

[0007] Preferably, in the step of inducing the formation of nitrogen / phosphorus / boron supramolecular precursor gel, the regulator is ammonia or acetic acid; the pH value range of 4.5 to 5.0 corresponds to the zeta potential isoelectric point window of the melamine-phytic acid complex; the negative electrode active substrate is pre-dispersed in a melamine hot saturated solution, and the negative electrode active substrate includes at least one of natural graphite, artificial graphite, silicon-carbon composite particles or hard carbon particles.

[0008] Preferably, a constant flow rate is controlled by a peristaltic pump to ensure that the intermediate solution enters the high-shear region of the melamine hot saturated solution in the form of a thin stream; the shear stirring state is provided by a homogenizer, and this high shear action causes the boron-phosphate oligomer to undergo directional folding and encapsulation around the melamine molecules, thereby forming a micro-precipitate with a core-shell hierarchical structure.

[0009] Preferably, in the step of preparing the intermediate solution, the viscosity increase rate v of the reaction system is monitored in real time. η To determine the reaction endpoint, the viscosity increase rate v η The calculation follows the formula below: , where η t The reaction proceeds to time. The real-time dynamic viscosity at time η0 is the initial dynamic viscosity at the start of the reaction, and t is the reaction duration; when the monitored v η The value begins to show a downward trend and the real-time dynamic viscosity η t When the temperature falls within the range of 25 mPa·s to 45 mPa·s, heating should be stopped and the temperature should be reduced.

[0010] Preferably, the drying process employs a spray drying process, with the inlet air temperature set to 180°C to 220°C and the outlet air temperature set to 80°C to 100°C. This spray drying process removes the solvent while solidifying the nitrogen / phosphorus / boron supramolecular precursor gel into a continuous and dense film layer coating the surface of the negative electrode active substrate, and maintaining the component distribution state within the nitrogen / phosphorus / boron supramolecular precursor gel without segregation.

[0011] Preferably, the heat treatment step specifically includes: raising the temperature to 600°C at a heating rate of 3°C to 5°C per minute and holding it at that temperature for 1 hour to remove the organic functional groups in the precursor and initially form an amorphous carbon skeleton; raising the temperature to 800°C to 1000°C at a heating rate of 5°C to 8°C per minute and holding it at that temperature for 2 to 4 hours to use the anchored boron atoms as an in-situ flux to catalyze the transformation of the amorphous carbon skeleton into a graphitized structure.

[0012] Preferably, the thickness of the nitrogen-phosphorus-boron co-doped graphitized carbon coating layer is 5 nm to 50 nm; the interlayer spacing of the nitrogen-phosphorus-boron co-doped graphitized carbon coating layer is less than 0.340 nm, and the ratio of boron retention rate on the surface of the coating layer to the amount of feed is greater than 85%. The high retention rate is due to the thermal stability locking effect of the POB chemical bond in the boron-phosphate oligomer on boron atoms.

[0013] Preferably, after the heat treatment step, a post-treatment step of air jet milling and magnetic separation to remove iron from the obtained product is included; the pressure of air jet milling is controlled at 0.4 MPa to 0.6 MPa to disperse the soft agglomerates formed during the heat treatment process, while maintaining the integrity of the nitrogen-phosphorus-boron co-doped graphitized carbon coating layer. The amount of melamine used is such that the nitrogen atom content in the final nitrogen-phosphorus-boron co-doped graphitized carbon coating layer is 2 wt% to 8 wt%, the phosphorus atom content is 1 wt% to 5 wt%, and the boron atom content is 0.5 wt% to 3 wt%. The doping ratio of each atom is controlled by adjusting the concentration of the melamine hot saturated solution and the injection amount of the intermediate solution to adapt to lithium-ion battery anode systems with different energy density requirements.

[0014] A composite anode material doped with nitrogen, phosphorus, and boron elements, wherein the composite anode material doped with nitrogen, phosphorus, and boron elements is prepared by the aforementioned preparation process.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. In composite anode materials doped with nitrogen, phosphorus, and boron, a boron phosphate oligomer framework is pre-constructed in the liquid-phase precursor stage by utilizing the dehydration condensation reaction of boric acid and phytic acid under specific thermodynamic conditions. This transforms the volatile small-molecule boron source into a thermally stable boron-phosphorus covalently bonded state, locking the spatial positions of boron atoms at the chemical bonding level. The pre-designed molecular structure resists the thermal shearing effect in the early stage of high-temperature carbonization, inhibiting the escape of gaseous boron oxide species. This ensures that boron elements remain in a high concentration in the solid phase system even when the graphitization start-up temperature is reached. The high retention rate of boron atoms acts as an in-situ flux, reducing the activation energy for the transformation of amorphous carbon into graphitized carbon. This induces the formation of highly ordered graphite microcrystals with extremely low interlayer spacing at a lower heat treatment temperature in the anode material, reducing preparation energy consumption and solving the common industry problem of large-scale loss of nitrogen, phosphorus, and heteroatoms caused by traditional high-temperature graphitization processes.

[0016] 2. By controlling the self-assembly behavior of nitrogen-containing organic monomers and boron phosphate oligomers in a high-shear environment, a highly ordered precursor topology is shaped at the microscale. In the subsequent topological carbonization process, the hierarchical structure, with nitrogen-containing components as fillers and boron-phosphorus framework as support, evolves in situ into a graphitized microcrystalline conductive network and high-concentration nitrogen-phosphorus doped defect clusters distributed at grain boundaries. Atomic-level structural heterogeneity enables precise functional partitioning: the highly crystalline carbon framework provides low-impedance channels for rapid electron migration, while the abundant heteroatom defects at grain boundaries provide highly active reaction sites for metal ion adsorption, deintercalation, and exchange. The tight spatial coupling of the two eliminates the polarization bottleneck caused by the mismatch between electron conduction and ion diffusion rates under high-rate conditions, improving the capacity utilization and kinetic response performance of the battery under fast charging conditions.

[0017] 3. By adopting a viscosity-based reaction endpoint control strategy, the problem of poor batch stability caused by uneven physical mixing in traditional multi-element co-doping processes is avoided. The dynamic viscosity jump of the reaction system is monitored and timely pH adjustment is implemented to induce the sol-gel phase transition of the system. The instantaneous spatial locking of each component is achieved by generating a cross-linked network before drying and desolvation. The phase freezing mechanism blocks the migration and segregation of components caused by differences in solute solubility or capillary forces during solvent evaporation. This ensures uniform and complete coverage of the active substrate surface of the nitrogen-phosphorus-boron ternary composite coating layer, eliminates local current density anomalies caused by coating layer thickness or component fluctuations, improves the consistency of electrochemical performance of negative electrode materials in industrial-scale production, and provides reliable process assurance for the mass production of high-performance fast-charging batteries. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the fabrication process for the dynamic locking and topology assembly of the present invention; Figure 2 This is a comparison curve of capacity retention rate of each test group under different charge / discharge rates according to the present invention; Figure 3 This is a diagram of the equipment architecture of the preparation system that integrates viscosity determination and temperature control logic according to the present invention.

[0019] Figure 4 Nitrogen adsorption curve of the composite negative electrode material doped with nitrogen / phosphorus / boron elements provided by the present invention.

[0020] Figure 5 The pore sizes of the nitrogen / phosphorus / boron-doped composite anode material provided by this invention are shown in the diagrams.

[0021] Figure 6 Scanning electron microscope (SEM) image of the nitrogen / phosphorus / boron-doped composite anode material provided by this invention.

[0022] Figure 7 The XRD pattern of the composite anode material doped with nitrogen / phosphorus / boron elements provided by the present invention. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] This invention provides a composite anode material doped with nitrogen, phosphorus, and boron, and its preparation process. It comprises four core engineering stages: boron-phosphorus pre-anchored framework construction, ternary supramolecular topological assembly, phase freezing, and in-situ topological carbonization. The top-level operational logic involves: using chemical bonding forces to lock volatile boron atoms in the liquid phase; uniformly coating the surface of the active substrate with this locked structure through rheological control and acid-base self-assembly; and finally, in-situ transcribing the precursor's chemical structure into a carbon coating layer with both high electronic conductivity and high ion adsorption activity during heat treatment. Addressing the engineering challenge in existing technologies where boron atoms readily volatilize and escape in oxide form before reaching the graphitization catalytic temperature, resulting in low graphitization and numerous surface defects in the final material, this invention introduces boron in the first step. - The phosphorus kinetic lockout procedure does not employ physical mixing but instead constructs a controlled dehydration condensation reaction environment. A phytic acid aqueous solution with a mass concentration of 45% to 55% is selected as the base solution. This concentration is set to balance the solubility of the reactants with the proton concentration required for dehydration condensation. Particulate boric acid with a purity of ≥99.5% is selected as the boron source and added to the base solution at a boron to phosphorus atom molar ratio of 1.5:1 to 2.5:1 (in one embodiment, the boron to phosphorus atom molar ratio is 2:1). In a reactor equipped with reflux condenser and mechanical stirring, the system is heated to 80°C to 95°C and maintained at a constant temperature. Under these thermodynamic conditions, the phosphate groups in the boric acid molecules undergo an esterification dehydration reaction with the phytic acid molecules.

[0025] To ensure that boron atoms are effectively locked and that excessive cross-linking does not lead to precipitation, this embodiment introduces a reaction endpoint determination mechanism based on viscosity characteristics. During the isothermal reaction, the dynamic viscosity of the system at 25°C is monitored in real time. In the initial stage of the reaction, the system is mainly composed of small molecules, and the viscosity is in the low range of 5 mPa·s to 10 mPa·s. As dehydration and condensation proceed, branched boron-phosphate oligomers are generated in the system. The increase in molecular weight leads to an increase in the internal friction of the fluid. When the dynamic viscosity is monitored to rise from the initial state to the range of 25 mPa·s to 45 mPa·s, heating is stopped and cooling is performed. The dynamic viscosity value of 25 mPa·s to 45 mPa·s refers to the absolute viscosity value measured at a standard temperature of 25°C after sampling of the reactants. The constant-temperature reaction process from 0℃ to 95℃ is controlled using an online viscometer in conjunction with a pre-established viscosity-temperature calibration curve for the boron-phytic acid system. Real-time high-temperature viscosity data is measured and converted to an equivalent viscosity value at 25℃ as the criterion for judgment. Alternatively, a rapid sampling procedure is adopted, where a sample is drawn from the reactor and cooled to 25℃±0.5℃ within 60 seconds using a water-cooling coil before offline measurement. A unified measurement standard eliminates interference from reaction temperature fluctuations on rheological property readings, ensuring industrial consistency in molecular weight distribution and branching degree across different batches of products. This viscosity window represents the experimentally calibrated optimal degree of polymerization range. A viscosity below 25 mPa·s indicates insufficient boric acid conversion, resulting in significant volatilization during subsequent carbonization; a viscosity above 45 mPa·s indicates excessive cross-linking of oligomers, preventing uniform spreading at the microscale. The viscosity increase rate v is then controlled. η During monitoring, a sliding window differential algorithm is used to process real-time data. The sampling interval is set to 30 to 60 seconds to filter out instantaneous fluid noise generated by stirring. The judgment logic is based on the value of v calculated by the monitoring system over three consecutive sampling cycles. η When the value exceeds the inflection point threshold of 1.5 mPa·s / min and the aforementioned converted dynamic viscosity at 25°C falls into the absolute range of 25 mPa·s to 45 mPa·s, the control system automatically triggers the reaction termination command. Based on this procedure, the intermediate solution is prepared and left to stand at room temperature under sealed conditions for 48 hours. If it remains homogeneous and transparent without any visible precipitates or stratification, it indicates that it has reached a kinetically stable oligomeric state. Through this step, a transparent and homogeneous boron-phosphate oligomer intermediate solution is obtained, in which volatile boron atoms are anchored to the thermally stable phosphate backbone in the form of POB covalent bonds.

[0026] To address the phase separation problem caused by solubility differences among multiple components during curing, this invention establishes a ternary supramolecular topological assembly procedure. This procedure utilizes a high shear field and pH-induced sol-gel transition to achieve molecular-level component locking. Melamine is dispersed in deionized water and heated to 90°C to 95°C to prepare a clear, heat-saturated melamine solution, which serves as an electron-rich acceptor and nitrogen source. The temperature of the previously prepared boron-phosphate oligomer intermediate solution is maintained above 60°C to prevent premature precipitation. A homogenizer is then activated to further saturate the melamine solution. Under high-shear stirring conditions of 2000 rpm to 4000 rpm, the intermediate solution is injected into this high-shear region at a constant flow rate using a peristaltic pump. During this process, the amino groups in the melamine molecules and the residual hydroxyl groups in the boron-phosphate oligomers rapidly combine through hydrogen bonds and Lewis acid-base interactions. The high-shear action causes the long-chain oligomers to undergo directional folding and encapsulation around the rigid melamine molecules, forming microscopic core-shell precursor units. After homogenization, ammonia or acetic acid is added to the system as a regulator to precisely adjust the pH to 4.5 to 5.0. The pH adjustment step employs a continuous feed method to control the rate of agent addition, ensuring the pH change rate does not exceed 0.1 pH / min. This avoids localized over-acidity or over-alkaliness leading to uneven precipitation. The control range of 4.5 to 5.0 is determined based on the Zeta potential-pH response curve at the melamine-phytic acid complex reaction concentration. Within this range, the absolute value of the Zeta potential is less than 10 mV. Stabilizing the pH within this low potential window eliminates the electrostatic repulsion barrier between precursor molecules. The synergistic effect of hydrogen bonds and van der Waals forces drives the sol-gel phase transition, forming a gel on the surface of the active substrate. A uniformly thick coating layer is formed. This pH range corresponds to the Zeta potential isoelectric point window of the melamine-phytic acid complex. At this point, the electrostatic repulsion in the system is minimal, inducing the formation of a dense nitrogen / phosphorus / boron supramolecular precursor gel. This gel network tightly encapsulates the negative electrode active substrate that is pre-dispersed in the system. The negative electrode active substrate can be natural graphite, artificial graphite, silicon-carbon composite particles, or hard carbon particles. This gel coating layer, formed through both rheological and chemical control, eliminates the random aggregation of components at the microscopic level and constructs a topological basis for the uniform atomic distribution of nitrogen, phosphorus, and boron.

[0027] To fix the topological structure of the aforementioned wet gel and remove the solvent, a phase freezing process was employed. The slurry was fed into a spray drying tower with an inlet air temperature set at 180°C to 220°C and an outlet air temperature set at 80°C to 100°C. This drying process not only rapidly removed moisture but also utilized the shrinkage force generated by the rapid evaporation of the solvent to further densify the gel layer, forming a continuous, crack-free solid precursor film. Finally, an in-situ topological carbonization process was performed to convert chemical energy into an electrochemically active structure, resulting in a dried gel. The powder is placed in a roller kiln or pusher kiln and heat-treated under nitrogen or argon protection. The temperature is increased to 600℃ at a rate of 3℃ / min to 5℃ / min and held for 1 hour. During this stage, the main process involves the thermal decomposition of organic functional groups, initially forming an amorphous carbon framework. The temperature is then further increased to 800℃ to 1000℃ at a rate of 5℃ / min to 8℃ / min and held for 2 to 4 hours. In this high-temperature range, the pre-anchored boron atoms play a crucial role. Due to the binding of the POB bonds, the boron atoms... The atoms cannot escape in gaseous form, but instead act as in-situ fluxes to reduce the activation energy of carbon atom rearrangement. The high retention rate of boron catalyzes the transformation of amorphous carbon into an ordered graphite structure at a lower temperature. At the same time, phosphorus and nitrogen atoms are dissolved in-situ at the grain boundaries of the carbon lattice or replace carbon atom sites. The composite anode material doped with nitrogen / phosphorus / boron elements obtained by this process has a surface coating thickness controlled between 5 nm and 50 nm. X-ray diffraction characterization shows that its graphite interlayer spacing is less than 0.340 nm, indicating extremely high graphitization degree and electronic conductivity. The boron retention rate on the coating surface is greater than 85% relative to the initial feed amount, the nitrogen content is 2 wt% to 8 wt%, the phosphorus content is 1 wt% to 5 wt%, and the boron content is 0.5 wt% to 3 wt%. This unique dual continuous structure of highly conductive carbon skeleton + high concentration of active sites reduces the polarization resistance of the electrode during charge and discharge, and significantly improves the cycle stability and capacity retention of lithium-ion batteries at rates above 4C.

[0028] Example 1: In the mass production scenario of anode materials for fast-charging power batteries of electric vehicles of 4C level and above, the core process challenge lies in how to solve the time window mismatch contradiction between the thermodynamics of heteroatom volatilization and the kinetics of carbon graphitization without using ultra-high temperature graphitization equipment with extremely high energy consumption, so as to simultaneously achieve the coexistence of high electronic conductivity and abundant ion transport sites in the carbon coating layer. For this case, this example implements a process procedure that combines boron-phosphorus kinetic locking and ternary supramolecular topological assembly. A 50% phytic acid aqueous solution is selected as the reaction base liquid. 99.5% pure particulate boric acid is added at a boron-phosphorus atomic molar ratio of 2:1, and the dehydration condensation reaction is initiated under constant temperature of 90°C. The rheological state of the system is monitored in real time using a rotational viscometer. When the dynamic viscosity jumps from the initial 8 mPa·s to 35 mPa·s, it is determined to be the reaction endpoint. At this time, the boron-phosphate oligomer generated in the system anchors the volatile boron atoms in the phosphate backbone through the POB covalent bond network.

[0029] The hot intermediate solution was injected at a constant flow rate into a melamine hot-saturated solution under high shear at 3000 rpm. The high shear force caused the oligomers to fold directionally around the rigid melamine molecules. Ammonia was added to adjust the pH of the system to 4.8. This process induced the formation of a dense nitrogen / phosphorus / boron supramolecular precursor gel to encapsulate the pre-dispersed artificial graphite substrate. After spray drying and heat treatment at 900℃, thanks to the thermal stability locking effect of the POB bonds on boron atoms in the precursor stage, the boron atoms did not volatilize before reaching the graphitization initiation temperature. Instead, they catalyzed the conversion of amorphous carbon into interlayer spacing d at low temperatures with a high retention rate of over 85%. 002 It has a highly ordered graphite structure of 0.336 nm, while retaining 4.5% nitrogen atoms and 2.1% phosphorus atoms by mass as surface active sites.

[0030] Example 2: To verify the actual performance of the nitrogen / phosphorus / boron-doped composite anode material of the present invention in engineering applications, especially its conductivity retention and capacity utilization under high-rate charge-discharge conditions above 4C, this example constructs a complete verification process covering precursor synthesis, heat treatment, battery assembly, and electrochemical performance testing. A control group based on existing technology and key parameter boundaries is set up for comparative analysis. Verification platform construction and experimental process: This verification experiment is conducted in a standardized laboratory environment with constant temperature and humidity. The ambient temperature is controlled at 25±2℃, and the relative humidity is controlled below 45%. The precursor preparation stage uses a high-shear homogenizer (speed range 0-10000rpm) and precise temperature control (…). The synthesis system was carried out in a water bath reactor with an accuracy of ±0.5℃. The carbonization process used a programmed temperature rise tube furnace with 99.999% pure argon gas as a protective atmosphere. The electrochemical performance was tested using a CR2032 coin cell system with a lithium metal sheet as the counter electrode and a Celgard 2400 polypropylene microporous membrane as the separator. The electrolyte was 1.0M LiPF6 dissolved in a mixed solvent of EC / DEC / DMC (volume ratio 1:1:1). The battery charge-discharge test was performed on a LANDCT2001A battery test system with a test voltage range of 0.01V to 3.0V. The microstructure was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).

[0031] Experimental Groups and Key Parameter Settings: To systematically evaluate the synergistic effect of the technical solution of this invention and the influence of key process parameters, the following five experimental groups were set up: Invention Sample Group: Prepared strictly according to the process flow of Example 1. In the precursor synthesis stage, the molar ratio of boron atoms to phosphorus atoms was set to 2:1, and the dynamic viscosity at the reaction endpoint was controlled at 35 mPa·s. In the ternary assembly stage, the temperature of the melamine hot saturated solution was maintained at 90℃, and the pH was adjusted to 4.8 after injecting the boron-phosphate oligomer. The heat treatment temperature was set to 900℃. Control Group 1 (Physical Mixing): In this group, the prepolymerization reaction step of boric acid and phytic acid was omitted. Boric acid, phytic acid, and melamine were directly physically mixed in water at the same molar ratio. After adjusting the pH to 4.8 to form a precipitate, the mixture was spray-dried and heat-treated under the same conditions. The negative electrode materials were prepared by the following methods: Control group 2 (simple melamine-phytate): In this group, boric acid was not added, and only phytic acid and melamine were reacted to generate a supramolecular precursor, which was then used to prepare nitrogen-phosphorus co-doped carbon materials through the same subsequent process; Control group 3 (low viscosity endpoint): In this group, the prepolymerization reaction of boric acid and phytic acid was terminated when the dynamic viscosity reached 15 mPa·s (lower than the 25-45 mPa·s range specified in this invention), and the subsequent process was the same as that of the sample group of this invention; Control group 4 (high temperature heat treatment): This group used the same precursor as the sample group of this invention, but the heat treatment temperature was increased to 1200℃ to investigate the effect of high temperature on heteroatom retention and graphitization degree; The key performance data of the negative electrode materials prepared by each experimental group after standardized structural characterization and electrochemical testing are summarized in Table 1.

[0032] Table 1: Comparison of Key Structural Parameters and Electrochemical Performance of Anode Materials in Each Experimental Group

[0033] The following patterns and mechanisms can be clearly observed from the data in Table 1: Compared with the control group 1, the boron retention rate of the present invention sample is as high as 88.5%, which is better than the 32.1% of the physical mixing process. This confirms that the boron-phosphate prepolymerization kinetic locking mechanism successfully inhibits the volatilization of boron at high temperatures. In the control group 1, due to the lack of POB covalent bond binding, most of the boron escapes in gaseous form, resulting in the graphite interlayer spacing remaining at the amorphous carbon level of 0.358 nm, which cannot play a fluxing catalytic role, thus resulting in a capacity retention rate of only 45.3% at high rates; Compared with the control group 2, in the case of complete lack of boron source, the material's d 002Reaching 0.362 nm, it exhibits typical hard carbon characteristics, poor conductivity, and the lowest 5C rate performance. This proves that boron is not only a dopant in this system but also a key catalyst for inducing low-temperature graphitization. Data from control group 3 shows that when the prepolymerization reaction is insufficient (viscosity only 15 mPa·s), the formed POB bond network is not dense enough to effectively lock boron atoms, resulting in a final boron retention rate of only 54.3%, indicating insufficient graphitization (d). 002 The viscosity range of 25-45 mPa·s defined in this invention is a necessary condition to ensure the structural stability of the precursor. Comparing the sample group of this invention with control group 4, although high-temperature treatment at 1200℃ can also achieve a similar degree of graphitization (d... 002 The boron retention rate was 0.335 nm, but the high temperature exacerbated the pyrolysis escape of heteroatoms (the boron retention rate dropped to 65.8%), resulting in a reduction of active sites. The 0.1C capacity and 5C rate performance were actually lower than those of the sample group of this invention treated at 900 °C. This strongly proves that the process of this invention can break the traditional constraint that it is difficult to achieve both high graphitization and high heteroatom content at the same time with low energy consumption through the catalytic effect of high concentration of boron.

[0034] Test example: Please see Figure 4-5 As shown, nitrogen adsorption tests were performed on the nitrogen / phosphorus / boron-doped composite anode material in Example 1. These tests were conducted at liquid nitrogen temperature (77 K) to determine the specific surface area and porosity of the material. The given BET specific surface area data is 2.5986 m². 2 The / g indicates that the composite anode material doped with nitrogen / phosphorus / boron has a low specific surface area. 2.6 m 2 The material with a surface area of ​​approximately 0.5 g is considered low, indicating that the anode material does not rely on a porous structure to provide active sites, but rather consists of a dense or layered structure. Furthermore, considering the pore size distribution diagram, the material may exhibit Type I or Type II isotherm characteristics. Type I indicates the presence of micropores (<2 nm); Type II indicates a predominantly macroporous or non-porous structure. The pore size distribution directly reflects the pore structure characteristics of the material. Low specific surface area typically corresponds to less contribution from micropores / mesopores. This low porosity structure is beneficial for improving the material's tap density (see Table 2 for reference) and volumetric energy density, and reducing side reactions caused by electrolyte wetting.

[0035] Please see Figure 6 As shown, Figure 6 Electron micrographs of composite anode materials doped with nitrogen, phosphorus, and boron were prepared.

[0036] Table 2. Test data of negative electrode tap density

[0037] Please see Figure 7 As shown, Figure 7 XRD patterns were prepared to obtain composite anode materials doped with nitrogen, phosphorus, and boron. The graphite material exhibits a strong and sharp (002) peak at 2θ≈26.5° with a spacing of 3.35 Å.

[0038] Example 3: This example combines Figures 1 to 3 This document describes a composite anode material doped with nitrogen, phosphorus, and boron elements and its preparation process. Figure 1 As shown, the process mainly consists of raw material premixing and heating, borophosphate oligomer construction, high-shear rheological assembly, pH-induced sol-gel transition, spray drying phase freezing, and in-situ topological carbonization. In the raw material premixing stage, a 45%-55% phytic acid aqueous solution is used as the base liquid, and granular boric acid is added. The boron-to-phosphorus molar ratio is controlled at 1.5:1-2.5:1, and the reaction is carried out at a constant temperature of 80℃-95℃. The process then proceeds to the critical viscosity endpoint determination mechanism, where the viscosity increase rate is monitored. The dynamic viscosity termination threshold was set at 25 mPa·s-45 mPa·s to prevent excessive crosslinking and lock the degree of polymerization, thereby generating an intermediate solution with a POB covalent bond network. This intermediate solution was assembled by constant-rate fine-flow injection into a melamine hot-saturated solution at 90℃-95℃ and under high-shear stirring at 2000rpm-4000rpm. Ammonia or acetic acid was added to adjust the pH to the Zeta potential isoelectric point of 4.5-5.0 to induce the formation of a nitrogen / phosphorus / boron supramolecular precursor gel encapsulating the substrate. Then, the solvent was removed and the precursor topology was fixed by spray drying at an inlet air temperature of 180℃-220℃ and an outlet air temperature of 80℃-100℃ to prevent component segregation. Finally, the graphite interlayer spacing d was obtained by heat treatment of first-stage functional group removal at 600℃ and second-stage boron-catalyzed graphitization at 800℃-1000℃, utilizing the POB bond to inhibit boron volatilization mechanism. 002 A composite anode material with a high-conductivity carbon framework and highly active doping sites, containing nitrogen, phosphorus, and boron elements, with a diameter of <0.340 nm and a boron retention rate of >85%.

[0039] like Figure 2 As shown, the horizontal axis of this coordinate graph represents the charge / discharge rate, ranging from 0.1C to 5C, and the vertical axis represents the capacity retention rate, expressed as a percentage. The graph contains four data curves. The solid line representing the sample group of this invention is located at the top of the graph, showing the highest capacity retention rate across the entire rate range. The dashed line representing control group 1 is located in the lower middle position. The dotted line representing control group 2 is located at the bottom, indicating that its performance is the lowest at all rates. The long dashed line representing control group 3 is located between the sample group of this invention and control group 1. Figure 3 As shown, the system is divided into three core operating areas: Area A is the liquid phase anchoring and assembly unit, which includes a constant temperature reactor, a precision peristaltic pump group, and a high shear homogenizer. This area is controlled by viscosity endpoint determination logic, which monitors the viscosity increase rate in real time and issues trigger cooling or stop commands. It is also regulated by rheological assembly control logic, which controls the high-speed shear flow field and constant flow rate injection and acid-base adjustment parameters. Area B is the phase freezing granulation unit, with the spray drying tower as the core equipment. It receives the product from Area A and is regulated by temperature control curve management logic, executing gas flow and drying power commands. Area C is the topology carbonization and finishing unit, which includes an atmosphere roller kiln and an airflow pulverizer and magnetic separation system. This area is also controlled by temperature control curve management logic, focusing on executing segmented heating rate and high-temperature constant temperature zone setting commands to complete the final heat treatment and post-treatment processes.

[0040] Example 4: To address the lag issue in precursor reaction endpoint control during actual industrial production, this example constructs a dynamic feedback control procedure based on viscosity growth rate for the critical process step of endpoint determination. In the development of highly consistent anode materials, a single dynamic viscosity threshold determination is often affected by temperature fluctuations, stirring efficiency, and differences in raw material purity, leading to actual polymerization degrees deviating from the optimal window. To solve this engineering challenge, this example introduces a viscosity growth rate v... η As a core performance indicator, a reaction control system incorporating real-time viscosity monitoring and data processing was established. This system continuously collects the real-time dynamic viscosity η of the reaction system with a sampling period of 1 minute. t .

[0041] The system performs differential calculations based on a sliding window and outputs the viscosity growth rate in real time. In the initial stage of the reaction, as dehydration condensation proceeds, the viscosity of the system slowly increases, v η Maintaining a low stability level, as the reaction progresses to a certain extent, a large number of branched oligomeric structures are formed, and the viscosity of the system exhibits an exponential growth trend. At this point, v η A surge signal will occur. This procedure sets the judgment logic as follows: when the real-time monitored v... η If the sampling rate exceeds a preset rate threshold (e.g., 2.0 mPa·s / min) for three consecutive sampling periods, and simultaneously satisfies the real-time dynamic viscosity η, tWhen the temperature falls within the absolute range of 25 mPa·s to 45 mPa·s, the system triggers a termination command. Once the termination command is triggered, the system automatically cuts off the heating source and starts a rapid cooling program to reduce the temperature of the reaction system to below 60°C within 5 minutes to freeze the current polymerization state. By introducing this dynamic rate determination mechanism, the static viscosity drift caused by equipment differences or raw material fluctuations is effectively shielded, ensuring that each batch of boron-phosphate oligomers has a highly consistent degree of branching and molecular weight distribution. Based on this dynamic control procedure, the precursor prepared, after subsequent standard process treatment, results in reduced batch-to-batch performance fluctuations in the final anode material. The graphite interlayer spacing of multiple batches of products is stably controlled within the range of 0.336 ± 0.001 nm, the average boron retention rate is stably above 88%, and the standard deviation is less than 1.5%.

[0042] Example 5: To verify the process adaptability and long-term operational stability of the nitrogen / phosphorus / boron-doped composite anode material of this invention in actual industrial production, this example establishes an adaptive pre-calibration procedure based on on-site environmental parameters for the core step of precursor assembly. This procedure aims to eliminate the instability of the gelation process caused by fluctuations in ambient temperature and humidity and differences in raw material batches, ensuring the consistency of supramolecular assembly. Before large-scale production or changing raw material batches, a standardized baseline calibration test is performed. A set of standard phytic acid and melamine raw materials are selected, and the gelation time and gel strength are measured at different pH values ​​under set standard experimental conditions, such as a constant temperature of 25°C, to construct a benchmark gelation curve. The real-time temperature T of the current production environment is introduced. env With relative humidity H env As a correction factor, the baseline curve is dynamically compensated. Through a pre-conducted gradient experiment, the influence coefficient α of the effect of a 1°C change in ambient temperature on gelation time and the influence coefficient β of a 10% change in relative humidity on gel strength are determined.

[0043] Based on the above calibration data, a fine-tuning strategy for on-site process parameters was formulated. When the production environment temperature T was monitored... env When the temperature deviates from the standard setpoint, the system uses a correction formula. Automatically calculate and adjust the reaction time t adj Alternatively, the dropping rate of the pH adjuster can be finely adjusted to compensate for the effect of temperature on reaction kinetics. For humidity fluctuations, the initial amount of solvent added or the air inlet parameters of the drying process can be adjusted to ensure that the solid content and microstructure of the final precursor gel are maintained within the preset quality control window.

[0044] Example 6: To address the difficulties in process parameter calibration and product performance consistency fluctuations caused by differences in the thermodynamic initial states of precursor reaction systems and variations in equipment geometry parameters across different application scenarios, this example constructs a standardized process scale-up and parameter calibration procedure based on dimensionless criterion number analysis. By establishing similarity criteria between laboratory-scale and industrial-scale reactors, it guides the precise setting of key process parameters, ensuring the equivalence of the boron-phosphorus kinetic locking process at different scales. Before process scale-up or equipment modification, a verification procedure for reactor geometrical similarity and kinetic similarity is executed. For stirred reactors, a dimensionless Reynolds number is defined. With power level As the core calibration basis, ρ is the fluid density, n is the stirring speed, d is the stirring blade diameter, μ is the fluid dynamic viscosity, and P is the stirring power.

[0045] The calibration procedure is as follows: First, the baseline parameters are determined. In a standard laboratory reactor, the Re value and N value of the system are measured under optimal reaction conditions, i.e., when the dynamic viscosity jumps to the target window. p The first step is to use the reference Re value as a baseline fingerprint parameter for process scale-up. The second step is to verify the geometric parameters by measuring the inner diameter, impeller type, and diameter of the target industrial reactor and calculating its geometric similarity ratio. If the geometric similarity ratio exceeds the preset linear scale-up range, such as 1:10, a correction factor needs to be introduced. The third step is to calibrate the kinetic parameters by using the reference Re value and the geometric parameters of the target reactor to deduce the required stirring speed n of the target reactor. target For boron-phosphate oligomer systems with non-Newtonian fluid properties, a shear rate correction factor is further introduced to ensure that the shear history experienced by the fluid micro-elements remains consistent during scale-up. The fourth step is heat transfer efficiency verification, calculating the heat transfer area to volume ratio of the target reactor. If this ratio is lower than that of the laboratory reactor, the medium temperature or flow rate of the heating jacket needs to be adjusted to compensate for the heat transfer lag caused by the reduced specific surface area, ensuring the uniformity of the system's temperature field. By executing the above calibration procedure, the reaction endpoint determination logic determined in the laboratory stage (based on the viscosity growth rate v) can be implemented. η Seamlessly migrated to industrial-grade production lines, actual test data shows that the boron-phosphate oligomers produced by the 1,000-liter reactor calibrated according to this procedure have a molecular weight distribution coefficient and branching degree index that deviate less than 3% from the laboratory small-scale sample.

[0046] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation process for a composite anode material doped with nitrogen / phosphorus / boron elements, characterized in that, Includes the following steps: A 45wt%~55wt% phytic acid aqueous solution was selected as the base solution. Particulate boric acid with a purity of ≥99.5% was added to the base solution according to a boron to phosphorus molar ratio of 1.5:1~2.5:

1. The mixture was heated to 80℃ to 95℃ and reacted at a stirring rate of ≥300r / min for 2 to 4 hours until the dynamic viscosity of the system increased from the initial state to the range of 25mPa·s to 45mPa·s, generating a branched boron-phosphate oligomer and obtaining an intermediate solution. Melamine was dispersed in deionized water and heated to 90°C to 95°C to prepare a melamine thermal saturated solution. The temperature of the intermediate solution was kept above 60°C. The intermediate solution was injected into the melamine thermal saturated solution under shear stirring at 2000 r / min to 4000 r / min using a peristaltic pump at a constant flow rate. After mixing, a regulator was added to adjust the pH of the system to 4.5 to 5.0, which induced the formation of nitrogen / phosphorus / boron supramolecular precursor gel adsorbed on the surface of a pre-dispersed negative electrode active substrate. The negative electrode active substrate was pre-dispersed in the melamine thermal saturated solution. The nitrogen / phosphorus / boron supramolecular precursor gel was subjected to solid-liquid separation and drying to remove the solvent and fix the precursor topology. It was then heat-treated in a non-oxidizing atmosphere at a temperature of 800℃ to 1000℃ to transform the nitrogen / phosphorus / boron supramolecular precursor gel into a nitrogen-phosphorus-boron co-doped graphitized carbon coating layer in situ.

2. The preparation process of a composite anode material doped with nitrogen / phosphorus / boron elements according to claim 1, characterized in that, In the step of inducing the formation of nitrogen / phosphorus / boron supramolecular precursor gel, the regulator is selected from ammonia or acetic acid; the pH range of 4.5 to 5.0 corresponds to the isoelectric point window of the melamine-phytic acid complex; the negative electrode active substrate includes at least one of natural graphite, artificial graphite, silicon-carbon composite particles or hard carbon particles.

3. The preparation process of a composite negative electrode material doped with nitrogen / phosphorus / boron elements according to claim 1, characterized in that, A constant flow rate is controlled by a peristaltic pump to ensure that the intermediate solution enters the high-shear region of the melamine hot saturated solution in the form of a thin stream; the shear stirring state is provided by a homogenizer, and this high shear force causes the boron-phosphate oligomer to undergo directional folding and encapsulation around the melamine molecules, thereby forming a micro-precipitate with a core-shell hierarchical structure.

4. The preparation process of the composite anode material doped with nitrogen / phosphorus / boron elements according to claim 1, characterized in that, In the step of preparing the intermediate solution, the viscosity increase rate v of the reaction system is monitored in real time. η To determine the reaction endpoint, the viscosity increase rate v η The calculation follows the formula below: , where η t The dynamic viscosity is η0 at time t, where η0 is the initial dynamic viscosity at the start of the reaction, and t is the reaction duration; when the monitored v0 η The value begins to show a downward trend and the real-time dynamic viscosity η t When the temperature falls within the range of 25 mPa·s to 45 mPa·s, heating should be stopped and the temperature should be reduced.

5. The preparation process of a composite negative electrode material doped with nitrogen / phosphorus / boron elements according to claim 1, characterized in that, The drying process employs a spray drying technique, with the inlet air temperature set at 180°C to 220°C and the outlet air temperature set at 80°C to 100°C. This spray drying process removes the solvent while solidifying the nitrogen / phosphorus / boron supramolecular precursor gel into a continuous and dense film layer coating the surface of the negative electrode active substrate, and maintaining the component distribution within the nitrogen / phosphorus / boron supramolecular precursor gel without segregation.

6. The preparation process of a composite negative electrode material doped with nitrogen / phosphorus / boron elements according to claim 1, characterized in that, The heat treatment steps specifically include: raising the temperature to 600°C at a heating rate of 3°C to 5°C per minute and holding it for 1 hour to remove the organic functional groups in the precursor and initially form an amorphous carbon skeleton; raising the temperature to 800°C to 1000°C at a heating rate of 5°C to 8°C per minute and holding it for 2 to 4 hours to use the anchored boron atoms as an in-situ flux to catalyze the transformation of the amorphous carbon skeleton into a graphitized structure.

7. The preparation process of a composite negative electrode material doped with nitrogen / phosphorus / boron elements according to claim 1, characterized in that, The thickness of the nitrogen-phosphorus-boron co-doped graphitized carbon coating layer is 5 nm to 50 nm; the interlayer spacing of the graphite layer in the nitrogen-phosphorus-boron co-doped graphitized carbon coating layer is less than 0.340 nm, and the ratio of boron retention rate on the surface of the coating layer to the amount of feed is greater than 85%. The high retention rate is due to the thermal stability locking effect of the POB chemical bond in the boron-phosphate oligomer on boron atoms.

8. The preparation process of a composite negative electrode material doped with nitrogen / phosphorus / boron elements according to claim 1, characterized in that, Following the heat treatment step, the product undergoes post-processing steps including air jet milling and magnetic separation to remove iron. The pressure of the air jet milling is controlled between 0.4 MPa and 0.6 MPa to break up the soft agglomerates formed during the heat treatment process, while maintaining the integrity of the nitrogen-phosphorus-boron co-doped graphitized carbon coating. The amount of melamine used ensures that the nitrogen atom content in the final nitrogen-phosphorus-boron co-doped graphitized carbon coating is 2 wt% to 8 wt%, the phosphorus atom content is 1 wt% to 5 wt%, and the boron atom content is 0.5 wt% to 3 wt%. The doping ratio of each atom is controlled by adjusting the concentration of the melamine hot saturated solution and the amount of intermediate solution injected to adapt to lithium-ion battery anode systems with different energy density requirements.

9. A composite anode material doped with nitrogen / phosphorus / boron elements, characterized in that, The composite anode material doped with nitrogen / phosphorus / boron elements is prepared by the preparation process described in claim 1.

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