Lithium iron phosphate material composition for 300ah large capacity cells

Abstract

The application relates to the technical field of inorganic metal compounds, and discloses a lithium iron phosphate material composition for a 300Ah large-capacity battery cell, which comprises a lithium iron phosphate matrix, a niobium element and a titanium element, the molar ratio of the niobium element to the titanium element is 0.15 to 0.28, the niobium element has a nonlinear concentration gradient layer in a depth interval of 100nm to 300nm from the surface of the particle, and the particle is a kind of single-crystal dense entity with an internal microporosity of 0.5% to 1.2%. The niobium element and the titanium element jointly occupy transition metal sites to induce local lattice distortion, so that an inward compressive stress field is constructed on the surface layer of the particle. The application utilizes the energy dissipation effect of the inward compressive stress field when the particle is compressed to offset the external compaction load, maintain the integrity of the single-crystal structure, and inhibit the interface side reaction.

Description

Technical Field

[0001] This invention relates to the field of inorganic metal compound technology, and in particular to lithium iron phosphate material compositions for 300Ah high-capacity battery cells. Background Technology

[0002] Currently, the industry typically uses transition metal doping and surface carbon coating to improve the lattice stability of materials. For high-capacity cells of 300Ah and above, the compaction density of the positive electrode sheet needs to reach above 2.6g / cm³ to improve the volumetric energy density. During the manufacturing process, the electrode sheet needs to withstand heavy rolling loads. Existing lithium iron phosphate materials mostly adopt a cluster structure formed by secondary granulation. Due to the low intergranular binding energy and the presence of nano- and micro-sized pores inside the particles, the material exhibits structural fragility under strong mechanical fields. The mechanical stress generated by rolling is non-uniformly transmitted from the particle surface to the interior, and the stress concentrates at the pore edges or grain boundaries. When the external load exceeds the intrinsic cleavage energy of the crystal, the secondary particles undergo brittle fracture, exposing active fracture surfaces. The increase of such fracture surfaces will induce the oxidative decomposition of the electrolyte, causing the internal resistance of the cell to rise.

[0003] When overcoming the physical crushing challenge, research has relied too heavily on fine-tuning the precision of the rolling mill or simply increasing the coating thickness, neglecting the decisive role of the material synthesis logic in the mechanical response. This leads to a disconnect between the modification scheme and the complex rolling mill conditions. Even in the field of recycling, the mechanical resistance of the material has not been fundamentally strengthened. For example, Chinese invention patent CN117049499B discloses a method for preparing basic lithium iron phosphate and regenerating lithium iron phosphate from waste lithium iron phosphate cathode powder. It achieves high phase purity regeneration through fine control of hydrothermal parameters, reducing lithium source consumption. The technology focuses on the chemical composition. The method of restoring crystallinity and repairing crystallinity produces materials that are conventional growth products in thermodynamic equilibrium. The lattice lacks an active stress dissipation induction mechanism. Under high-density heavy loads, the particles exhibit isotropic mechanical fragility and are prone to pulverization due to stress concentration, which cannot meet the structural stability requirements of high-capacity battery cell manufacturing. The industry has tried to strengthen the particles by improving doping uniformity or increasing coating thickness, but homogeneous doping in thermodynamic equilibrium is difficult to build a stress buffer gradient inside the lattice, while thick coating layers will hinder charge transfer, resulting in a contradiction between structural strength and dynamic performance.

[0004] Therefore, the technical problem to be solved by this invention is how to construct a single-crystal-like configuration with specific element distribution characteristics and pre-set a stress compensation field inside the crystal lattice to offset external mechanical loads. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a lithium iron phosphate material composition for a 300Ah high-capacity battery cell, the lithium iron phosphate material composition comprising a lithium iron phosphate matrix, niobium, and titanium. The molar ratio of niobium to titanium is 0.15 to 0.28; niobium exhibits a nonlinear gradient distribution within the particles of the lithium iron phosphate material composition, and has a niobium concentration gradient layer within a depth range of 100 nm to 300 nm from the particle surface. The particles are dense solid particles with a near-single-crystal structure, and the internal microporosity of the particles is 0.5% to 1.2%. In the niobium concentration gradient layer, niobium and titanium elements jointly occupy the transition metal sites in the lithium iron phosphate matrix lattice to form local lattice distortion. The local lattice distortion generates an inward compressive stress field on the particle surface caused by lattice volume contraction. The lithium iron phosphate material composition has anti-rolling crushing performance. When a single particle is subjected to an external roller load of 250MPa, it maintains its near-single-crystal solid structure, and the breakage rate of the particles after being subjected to the external roller load is less than 3%. When the particles are subjected to external mechanical energy impact, the inward compressive stress field offsets the external stress through elastic deformation of local lattice distortion, thereby suppressing interfacial side reactions between the lithium iron phosphate matrix and external electrolyte components on the particle surface and maintaining the chemical stability of the particles under high compressive conditions.

[0006] Preferably, in the niobium concentration gradient layer, the atomic percentage concentration of niobium decreases exponentially from the particle surface towards the particle center; the total molar fraction of niobium and titanium in the lithium iron phosphate matrix is ​​0.02 to 0.05; the inward compressive stress field is caused by the difference in atomic radii between niobium and iron, and the shrinkage of the lattice constants a and c in the niobium concentration gradient layer satisfies the following relationship: Where Δa and Δc are the shrinkage of the lattice constant after doping, respectively. and , respectively, are the initial lattice constants of undoped lithium iron phosphate.

[0007] Preferably, the tap density of the lithium iron phosphate material composition is 1.55 g / cm³. 3 Up to 1.65 g / cm 3 The average particle size D50 ranges from 3.5 μm to 5.5 μm; the molar concentration of niobium in a single particle at 50% radius from the center. molar concentration of niobium on the particle surface Satisfy the proportional relationship: ,in, Analysis of elemental distribution within the particles.

[0008] Preferably, the surface of the particles is coated with a carbon coating layer, the thickness of which is 2 nm to 5 nm; the carbon coating layer includes amorphous carbon and graphitized carbon, wherein the amorphous carbon is generated by the thermal decomposition of niobium-based organic matter, and the graphitized carbon is generated by the thermal decomposition of a matrix organic carbon source; the specific surface area of ​​the lithium iron phosphate material composition is 10 m². 2 / g to 15m 2 / g.

[0009] Preferably, the titanium element is uniformly distributed inside the particles, and the titanium element occupies iron sites in the lithium iron phosphate matrix to form a solid solution structure, thereby improving the bonding energy between the primary grains of the lithium iron phosphate matrix; the doping amount of titanium element accounts for 0.5% to 1.5% of the mass percentage of iron element in the lithium iron phosphate matrix.

[0010] Preferably, the molar ratio of lithium to the total transition metal elements in the lithium iron phosphate material composition is 0.98 to 1.02; wherein the total transition metal elements are the sum of the molar amounts of iron, niobium and titanium.

[0011] Preferably, the main phase of the lithium iron phosphate material composition is olivine, and its X-ray diffraction pattern does not contain free niobium oxide and titanium oxide phases; the compaction density of the particles under 250 MPa pressure is not less than 2.65 g / cm³. 3 .

[0012] Preferably, in the niobium concentration gradient layer, the rate of change of niobium concentration in the depth direction decreases with increasing depth; the ratio of the average niobium concentration within 50 nm of the particle surface to the niobium concentration at the particle center is 5 to 10.

[0013] Preferably, the average oxidation state of niobium in the particles is +5, and the average oxidation state of titanium is +4; niobium is coordinated through Nb-O bonds within the local lattice distortion region. The octahedron is distorted to lower the lithium-ion diffusion barrier inside the lithium iron phosphate matrix.

[0014] Preferably, the content of magnetic foreign matter in the lithium iron phosphate material composition is less than 20 ppb, and the content of ferric ions accounts for less than 0.5% of the total iron content by mass; after the particles are subjected to an external rolling load of 250 MPa, the increase in specific surface area of ​​the lithium iron phosphate material composition is less than 1.5 m². 2 / g.

[0015] The beneficial effects of this invention are: 1. In the lithium iron phosphate material of 300Ah high-capacity cells, the nonlinear gradient distribution of Nb elements in the main phase lattice in the region from 100nm to 300nm away from the particle surface induces local lattice distortion on the particle surface, thereby constructing an inward compressive stress compensation ring at the surface level. This pre-set stress field generates an active dissipation effect when the composition is subjected to external heavy rolling, offsetting the impact of external mechanical energy on the grain boundaries, maintaining the structural integrity of the near-single-crystal particles, avoiding abnormal increase in active surface area due to particle breakage, and inhibiting the oxidative decomposition of electrolyte on the fresh cross-section of the particles from a physical source.

[0016] 2. The synergistic occupancy of Nb and Ti in a molar ratio range of 0.15 to 0.28 guides the directional fusion of primary grains during the solid-state reaction, eliminating the internal micron-level pores present in traditional secondary granulation processes. This densified, near-single-crystal solid structure not only improves the intrinsic compaction density of the material, but also enhances the binding energy between grains, enabling individual particles to maintain geometric stability even under pressures exceeding 250 MPa, thus improving the material's suitability for high-compact manufacturing processes of 300 Ah high-capacity battery cell electrodes.

[0017] 3. The continuous concentration gradient formed by heterogeneous metal atoms on the particle surface changes the electron cloud distribution of the crystal domain, thereby reducing the interfacial diffusion barrier of lithium ions while maintaining an extremely thin coating layer. This asymmetric modulation of the interfacial energy level makes charge transfer no longer subject to the traditional interfacial impedance bottleneck. While ensuring the mechanical strength of the particles, it optimizes the charge transfer path and improves the DC internal resistance characteristics and dynamic response speed of the material under high-rate charge and discharge conditions. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the Nb / Ti synergistic induced inward compressive stress field modification mechanism of the present invention. Figure 2 This is a causal analysis diagram showing the relationship between the single-crystal dense structural elements of this invention and the material's compressive strength. Detailed Implementation

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0020] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0021] Secondly, an embodiment or embodiment referred to herein refers to a specific feature, structure or characteristic that may be included in at least one implementation of the present invention. An embodiment appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0022] This invention is described in detail with reference to the schematic diagrams. When describing the embodiments of this invention, for ease of explanation, the cross-sectional views of the device structure will be partially enlarged without adhering to the general scale. Moreover, the schematic diagrams are only examples and should not limit the scope of protection of this invention. In addition, in actual manufacturing, the three-dimensional spatial dimensions of length, width and depth should be included.

[0023] Furthermore, in the description of this invention, it should be noted that the terms such as "upper," "lower," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or component referred to has a specific orientation, or is constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention. In addition, the terms "first," "second," or "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0024] Unless otherwise explicitly specified and limited, the terms installation, connection, and linking in this invention should be interpreted broadly. For example, they can refer to fixed connection, detachable connection, or integrated connection; similarly, they can refer to mechanical connection, electrical connection, or direct connection, or indirect connection through an intermediate medium, or internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] This invention provides a lithium iron phosphate material composition for 300Ah high-capacity battery cells, comprising a lithium iron phosphate matrix, niobium, and titanium. The lithium iron phosphate material composition exhibits a near-single-crystal structure, with localized lattice distortion caused by niobium and titanium jointly occupying transition metal sites. This localized lattice distortion generates an inward compressive stress field on the particle surface, which dissipates energy under pressure to counteract external compaction loads. In the rolling process used for manufacturing 300Ah-specification positive electrode sheets, the positive electrode material must withstand extremely high mechanical loads. If the material has internal pores, load transmission can lead to particle breakage. The lithium iron phosphate material composition of this invention includes a main phase... Where 0.1≤x≤0.3, 0.001≤y≤0.01, M is selected from the combination of Nb and Ti, the molar ratio r of Nb to Ti is in the range of 0.15 to 0.28, the lithium iron phosphate material composition particles are dense solid particles with a near-single crystal structure, and its internal microporosity is 0.5% to 1.2%. The internal microporosity is measured by argon ion polishing cross section combined with scanning electron microscopy image recognition method. A sampling area of ​​500 square micrometers is selected at 5000x magnification, and the proportion of black pixel area to the total field of view is extracted by the binarization algorithm of image processing software. The process requires that the deviation of five consecutive independent sampling points be less than 0.1% to ensure the authenticity of the statistical characteristic values. Dense solid particles are generated through directional fusion during a high-temperature solid-state reaction. This low-porosity structure increases the intrinsic compaction density of the material and enhances the bonding energy between grains. A single dense solid particle maintains geometric stability under 250 MPa pressure. To eliminate the nano- and micro-sized micropores contained in traditional secondary granulation and to promote the directional aggregation of primary grains into single crystals in a defect-free state, this invention employs a two-stage thermodynamic crystallization control in the pre-high-temperature reaction. After spray drying, precursor particles with a median particle size of 0.35 micrometers were loaded into a high-temperature resistant graphite crucible and sent to a multi-zone temperature-controlled nitrogen-filled pusher furnace. In the first stage, the furnace temperature was increased to the primary sintering plateau of 650°C at a rate of 8°C / min and held at this temperature for 2 hours. During this stage, the atoms of each element inside the precursor powder undergo short-range regular diffusion driven by surface energy, forming an initial integrated sintering neck at the contact boundary of adjacent primary grains. In the second stage, the temperature was further increased to the final solid-state reaction plateau of 750°C and held continuously for 5 hours. The precursor was pre-treated with 1.0% by mass... The uniformly doped solid solution of titanium elements exerts a specific catalytic effect as a lattice crystallizer. After titanium ions enter the iron sites, they significantly lower the interfacial migration energy barrier between adjacent grains, causing primary grains with different crystal orientations to spontaneously rotate and recombine towards the crystal plane with lower thermodynamic energy. This leads to isotropic directional fusion in accordance with the same lattice orientation. This process continuously displaces and drives out the micron-sized residual pores that were originally trapped in the grain boundary gaps along the atomic flow direction until the outer surface of the single crystal collapses and disappears. Ultimately, the internal microporosity of the single-crystal particles is locked within the extremely dense range of 0.5% to 1.2%.

[0026] The molar ratio r of niobium to titanium was adjusted to fluctuate within the range of 0.15 to 0.28, and the DC internal resistance and particle breakage rate of the material were monitored. When the molar ratio r was below 0.15, the lattice shrinkage of the particle surface was observed. A value less than 0.015 is insufficient to offset the 250MPa external compaction load, resulting in microcracks in the particles after electrode rolling. When the molar ratio r is higher than 0.28, excess niobium forms segregation in the crystal lattice and occupies lithium-ion diffusion channels. Under 1C charge-discharge conditions, the DC internal resistance of the material increases from 1.22mΩ to over 1.85mΩ. Determining the working window allows the inward compressive stress field to counteract the external rolling load in situ, achieving an intrinsic fracture strength of 290MPa. The Nb element exhibits a nonlinear gradient distribution within the particles of the lithium iron phosphate material composition. The precursor particles exhibit a niobium concentration gradient layer within a depth range of 100 nm to 300 nm from the particle surface. The preparation procedure for the niobium concentration gradient layer is as follows: materials containing lithium, iron, manganese, phosphorus, and titanium sources are ground to a D50 of 0.3 μm to 0.5 μm and then spray-dried to obtain precursor particles; the precursor particles are heated to 740°C to 760°C under a nitrogen protective atmosphere and held at that temperature for 4 to 6 hours; during the isothermal stage, when the main phase lattice achieves 85% crystallinity, the crystallinity of the main phase lattice is simultaneously coupled using a differential scanning calorimeter. Offline calibration and verification were performed using in-situ high-temperature X-ray diffraction, or the instantaneous heat flux signal Q of the material during crystallization was collected by a platinum-rhodium thermocouple array installed on the inner wall of the constant-temperature section of the rotary kiln. When the filtered instantaneous heat flux signal showed a decreasing trend for 15 consecutive sampling points, and the decrease ratio compared with the reference heat flux peak reached 15% to 18%, it was determined that the current crystallinity of the main phase had entered the injection window period of 85% to 88%. Ethanol-niobium atomized liquid was then injected into the furnace using dry nitrogen gas at a pressure of 0.3 MPa to 0.5 MPa as a carrier. The ethanol-niobium atomized liquid was controlled... The amount added ensures that the molar ratio r of Nb to Ti in the final product satisfies 0.15 ≤ r ≤ 0.28. The thermal decomposition and non-equilibrium diffusion of niobium ethanol at high temperatures cause Nb ions to create non-uniform interstitial filling in the not-completely-sealed particle surface. In the niobium concentration gradient layer, Nb and Ti elements jointly occupy transition metal sites within the lithium iron phosphate matrix lattice, resulting in localized lattice distortion. This localized lattice distortion generates an inward compressive stress field on the particle surface caused by lattice volume contraction. The contraction of lattice constants a and c in the inward compressive stress field satisfies the following formula: Where Δa and Δc represent the shrinkage of the lattice constant after doping, and The initial lattice constants of undoped lithium iron phosphate are represented respectively. After the injection is completed, the temperature is maintained for 20 to 40 minutes and cold cycling is performed at a cooling rate of not less than 15℃ / min. This treatment method ensures that the particle integrity of the material remains unchanged and the D50 change rate is less than 2% when subjected to a 250MPa roller load.

[0027] The tap density of the lithium iron phosphate material composition ranges from 1.55 g / cm³ to 1.65 g / cm³. The dense solid particles with a near-single-crystal structure have a double-layer coating structure on their surface, consisting of an inner inorganic oxide layer and an outer carbon layer, with a total thickness of 2 nm to 5 nm. The inorganic oxide layer contains Nb and Ti elements, and the Nb element exhibits a continuous concentration gradient from the particle surface to the double-layer coating structure. The molar concentration of Nb element at 50% radius from the center of a single dense solid particle is... molar concentration of Nb on the particle surface The following proportional relationship must be satisfied: ,in, This represents the molar concentration of Nb at 50% of the particle's internal radius. The molar concentration of Nb on the particle surface is used to alter the electron cloud distribution of the crystal domains, reducing the interfacial diffusion barrier of lithium ions. This structure, while ensuring the mechanical strength of the particles, reduces the DC internal resistance of the material under high-rate charge-discharge conditions. Through the coupling of pre-set compressive stress on the surface and the non-porous single-crystal configuration, the lithium iron phosphate material composition inhibits the penetration path of the electrolyte into the particle interior and reduces the gas generation rate of interfacial side reactions. The morphology of the particles after rolling is observed using scanning electron microscopy, and the D50 change rate is monitored using a laser particle size analyzer. The dense solid with an internal microporosity of 0.5% to 1.2% is enhanced by... The intergranular binding energy ensures that the breakage rate of a single particle is less than 3% after being subjected to a load of 250MPa. When the change of raw material batch causes the median particle size D50 or particle size distribution coefficient Span of the slurry to shift, the grinding energy input of the sand mill is adjusted to stabilize the slurry D50 at 0.35μm and the Span at less than 0.85. This serves as a prerequisite for the precursor particles to form a dense entity in the solid-phase reaction. By generating a dense double-layer coating structure with a thickness of 2nm to 5nm on the particle surface, the microcrack propagation path driven by external load is blocked, enabling the 300Ah high-capacity battery cell to achieve a capacity retention rate of 86.5% after 3000 cycles.

[0028] Example 1: In the rolling process of the positive electrode sheet of a 300Ah high-capacity lithium iron phosphate energy storage cell, the electrode sheet design compaction density is set to 2.6 g / cm³, and the rolling load is set to 250 MPa. This example uses the lithium iron phosphate material composition for a 300Ah high-capacity cell as described in the aforementioned specific implementation method, wherein the main phase chemical formula is... The molar ratio r of niobium to titanium is 0.22. The lithium iron phosphate material composition exhibits a near-single-crystal structure with an internal microporosity of 0.8%. The niobium content within the near-single-crystal particles shows a nonlinear gradient distribution, and a concentration maxima exist within a depth range of 180 nm from the particle surface. This niobium concentration maxima causes local lattice distortion, and the measured lattice constant shrinkage satisfies the following formula: Where Δa and Δc are the shrinkage of the lattice constant after doping, respectively. and These represent the initial lattice constants of undoped lithium iron phosphate. To guide the precise synergistic occupation of transition metal sites by titanium and niobium and their in-situ transformation into a specific lattice distortion field, a two-stage solid solution control was employed in the solid-phase reaction stage. In the first stage, precursor particles containing uniformly doped titanium were heated to 750°C under a nitrogen atmosphere. Utilizing the similar ionic radii of titanium and iron, titanium was completely and uniformly dissolved in the iron sites within the unit cell when the main phase crystallinity reached 88%, thus initially constructing a high-binding-energy lattice framework core. The second stage was initiated by using high-pressure dry nitrogen to dissolve 0.15 mol / L ethylene oxide within a constant temperature window of 750°C. Niobium alkoxide atomized liquid was injected at a flow rate of 2.5 L / min, with the injection intensity strictly controlled at 0.8 L per square meter of material cross-section. Utilizing the pyrolysis driving force generated by the instantaneous high temperature, high-valence niobium ions were forced to embed into transition metal vacancies in the not-yet-completely-closed lattice boundaries of the particle surface under non-equilibrium diffusion conditions. By controlling the subsequent cooling rate to perform high-intensity thermal contraction locking at 18 °C / min, niobium and titanium elements were forced to jointly clamp the transition metal sites on the particle surface without destroying the main phase olivine structure. This successfully prevented macroscopic phase segregation of heteroatoms or the generation of downstream free oxide impurities, and achieved the transformation of chemical strain into a localized distortion field. The directional transformation; in the orthorhombic olivine cell structure, when calculating the total deformation of the lattice constant, the deformation along the second principal crystal axis is selectively ignored. The crystal dynamics are based on the extreme anisotropic rigidity difference of the main phase structure in different spatial orientations; the second principal crystal axis of the cell forms an open large channel for lithium ion transport in one-dimensional space. The channel walls are locked by a vertically arranged high-quality oxygen octahedral framework with shared edges, which has a great counterbalancing hardness in lattice mechanics, so that the filling or solid solution of any heterometallic atoms cannot cause spatial elastic slip in this axial dimension; within the doping range of this invention, the constant drift of the second principal crystal axis is always lower than At 0.002%, which is entirely within the negligible cutoff error in engineering, the linear summation of the relative changes in the other two symmetrical axes with high shear flexibility is sufficient to purely and sensitively characterize the level of elastic energy accumulation caused by surface volume shrinkage. Through extensive trial and error and engineering boundary limit determination, it has been confirmed that when the summation value of this biaxial deformation is below 0.015, the local distortion field is too weak to provide sufficient mechanical energy dissipation damping when the macroscopic electrode is subjected to 250MPa rolling pressure. Once this value exceeds the critical upper limit of 0.035, excessive lattice distortion will directly cause local amorphization collapse of the main phase framework, thus establishing this reverse safety boundary.

[0029] In this embodiment, The calculated value is 0.028. This inward compressive stress field generated by atomic radius mismatch is in situ opposed to the 250MPa external rolling load, dissipating mechanical field energy. The dense solid structure of the quasi-single-crystal particles reduces the stress concentration inside the particles, and the intrinsic fracture strength of a single particle reaches 290MPa. The cross-scale physical mechanism of the in-situ opposition between the inward compressive stress field and the external rolling load lies in the fact that the prestress layer constructed by lattice contraction on the particle surface significantly increases the cleavage fracture energy barrier of the surface crystal plane. When the 250MPa macroscopic external heavy rolling load is transferred to the surface of a single 3.5μm to 5.5μm lithium iron phosphate particle through the electrode system, this macroscopic load in the dense solid structure of the single-crystal particles reduces the stress concentration inside the particles, and the intrinsic fracture strength of a single particle reaches 290MPa. The dense, non-porous quasi-single crystal interior is uniformly distributed and transformed into local shear stress between the crystal lattice. At this time, the nanoscale inward compressive stress field in the 100nm to 300nm depth range of the surface layer is like the surface compressive stress reinforcement distribution of tempered glass. It can cancel the external tensile stress polarized in this microscopic crystal plane region and transfer it safely inward, thereby forcibly raising the microcrack initiation threshold of the overall quasi-single crystal particle to above the local stress extreme value corresponding to the macroscopic external load. The strain compensation mechanism of the inward compressive stress field constructed on the particle surface is the lattice mutual constraint effect caused by the uniformly dissolved titanium element and the gradient distribution of niobium element on the surface. In the core region inside the particle, iron is pre-uniformly occupied Due to their unique coordination electron cloud arrangement, titanium ions at the core site exert a weak outward expansion effect on the surrounding oxygen octahedrons, causing the core cell framework to be in a relatively expanded state and possessing extremely high rigidity modulus. When high-valence niobium ions subsequently undergo nonlinear gradient diffusion from the surface to the interior and reside within the 100nm to 300nm depth range, their strong covalent bonding tendency leads to local anisotropic contraction of the ferrite octahedrons in this region, resulting in a physical trend of volume reduction. Because the expanded and extremely rigid crystal core constitutes a strong constraint on volume deformation, the surface lattice cannot freely release its contraction deformation in three-dimensional space. This incomplete volume deformation, hindered by the core rigidity, is a consequence of this. The released contractile strain is transformed into mutual compression at the boundary tangential between the surface crystal planes, thereby constructing a self-sustaining inward compressive prestress field on the particle surface, which physically achieves a reasonable reversal and self-consistent closed loop of stress properties. After the rolling load is applied, the quasi-single-crystal particles in the positive electrode sheet maintain their morphological integrity. The measurement results show that the D50 change rate of the particles after rolling is 1.2%, and no fresh fracture surface caused by particle breakage was observed. This structure restricts the penetration path of electrolyte into the particle interior. The capacity retention rate of this 300Ah high-capacity cell after 3000 cycles under 1C / 1C charge and discharge conditions is 86.5%, and the gas generation rate of interfacial side reactions is reduced by 42% compared with conventional lithium iron phosphate materials.

[0030] Example 2: Addressing the issue of active particle breakage during high-pressure compaction of the positive electrode sheet in a 300Ah high-capacity battery cell, this experimental procedure simulates the mechanical load field of a real production environment to verify the mechanical resistance and chemical stability of the lithium iron phosphate material composition. The data used in this experiment comes from a physical experimental platform, where the electrode rolling equipment has a pressure adjustment range of 0 to 500 MPa and a pressure control accuracy of [missing information]. The material morphology was observed using a scanning electron microscope with a spatial resolution of 0.1 nm at 1 MPa, and the interfacial gas production was measured using a gas chromatograph with a sensitivity of 0.01 mL. In the experimental design, the setting of the roller pressure P depends on the balance between the target compaction density and the particle breakage threshold. In order to obtain the volumetric energy density at the target compaction density of 2.6 g / cm³, while avoiding triggering the material lattice collapse, the standard test pressure was set at 250 MPa based on the mapping relationship between particle breakage strength and stress dissipation capacity.

[0031] The experimental group prepared a lithium iron phosphate material composition for a 300Ah high-capacity battery cell using the aforementioned specific implementation method. The preparation procedure is as follows: Lithium, iron, manganese, phosphorus, and titanium source materials were ground to a D50 of 0.35 μm and then spray-dried to obtain precursor particles; the precursor particles were heated to 750℃ under a nitrogen protective atmosphere and held at that temperature for 5 hours; during the isothermal stage, when the main phase lattice achieved 88% crystallinity, niobium ethanol atomized liquid was sprayed into the furnace using dry nitrogen gas at a pressure of 0.4 MPa. The amount of niobium ethanol added was controlled so that the molar ratio r of Nb to Ti in the final product was 0.22. The thermal decomposition and non-equilibrium diffusion of niobium ethanol at high temperature were utilized to allow Nb to... Ions create non-uniform interstitial filling on the unsealed particle surface. After injection, the temperature is maintained for 30 minutes, followed by forced cooling cycling at a cooling rate of 18℃ / min. In the final lithium iron phosphate material composition, the maximum value of the Nb concentration gradient layer is located at a distance of 180nm from the surface, and the internal microporosity is 0.8%. To construct a multi-dimensional control system, control group 1 was set up, which used uniformly doped Nb and Ti elements; control group 2 was set up, with a molar ratio r of Nb to Ti of 0.12; control group 3 was set up, with a molar ratio r of Nb to Ti of 0.35; and control group 4 was set up, which used a traditional secondary granulation cluster structure material with an initial porosity of 15%.

[0032] Under a constant pressure of 250 MPa, the particle size distribution curves before and after roller pressing were analyzed to observe the mechanical response characteristics of different groups. Monitoring results showed that after experiencing a 250 MPa load, the particle D50 of the experimental group changed from the initial 2.15 μm to 2.12 μm, a change rate of 1.4%, and no surface cracks were observed under scanning electron microscopy. In control group one, the D50 change rate under the same pressure was 7.8%, and microcracks and spalling appeared at the particle edges, causing the compressive stress field generated by lattice distortion to fail to dissipate stress energy within the depth range of 100 nm to 300 nm. In control group four, the D50 change rate reached 19.5%, and the clustered particles underwent pulverization and disintegration. When the external load was increased stepwise from 150 MPa to an overload condition of 300 MPa, the D50 of the experimental group... The rate of change and pressure value showed a non-linear correlation. The data remained stable below 250 MPa. Local deformation of the particles only began to appear when the pressure exceeded 280 MPa. This verifies that the stress countermeasure mechanism constructed by Nb and Ti occupying transition metal sites has a clear protection threshold. The experiment further investigated the effect of the molar ratio r of Nb to Ti on electrical performance. In control group two, due to the low Nb content, the inward compressive stress field strength on the particle surface was insufficient. After rolling at 250 MPa, the fresh cross-section induced interfacial side reactions, and the gas production of its cell after 500 cycles was 0.32 mL / Ah. In control group three, due to the excessive Nb ions forming segregation in the lattice and occupying lithium ion diffusion channels, the DC internal resistance under 1C charge and discharge conditions was reduced from 1.22 m in the experimental group. Rise to 1.85m Within a working window of r = 0.22, the experimental group achieved an intrinsic fracture strength of 290 MPa and low impedance characteristics. This invention, through the coupling of a near-monocrystalline dense solid and a surface stress ring, blocks the propagation of load-driven microcracks, enabling the capacity retention rate of a 300 Ah high-capacity cell to reach 86.5% after 3000 cycles, and reducing the gas production rate by 42% compared to conventional materials.

[0033] Example 3: This example combines Figures 1 to 2 Description of lithium iron phosphate material compositions used in 300Ah high-capacity battery cells, such as... Figure 1As shown, the technical route begins with a material composition matrix containing lithium iron phosphate, niobium (Nb), and titanium (Ti). It integrates three key input elements: elemental ratio control of Nb to Ti molar ratio of 0.15 to 0.28, internal microporosity of 0.5% to 1.2% quasi-single-crystal dense solid structure, and nonlinear concentration gradient layer in the depth range of 100 nm to 300 nm. These elements together guide the synergistic occupation process of lattice sites where Nb and Ti jointly occupy transition metal sites. Subsequently, the elemental occupation induces local lattice distortion, constructing an inward compressive stress field on the particle surface. This causes the particles to generate energy dissipation effect when under pressure to offset the external compaction load, ultimately achieving the technical effect of suppressing interfacial side reactions and maintaining the integrity of the quasi-single-crystal structure.

[0034] like Figure 2 As shown, the multidimensional characteristics of the lithium iron phosphate material composition for the 300Ah high-capacity battery cell are further illustrated through a causal analysis diagram. The basic components include a lithium iron phosphate matrix, niobium (Nb) and titanium (Ti) elements, and an Nb / Ti molar ratio of 0.15-0.28. At the surface mechanism level, it involves the co-occupation of transition metal sites, induction of local lattice distortion, and the construction of an inward compressive stress field. At the structural feature level, it is manifested as a near-single-crystal dense entity with a microporosity of 0.5%-1.2% and a nonlinear Nb concentration gradient layer with a depth range of 100nm-300nm. The technical effectiveness generated by the combined effect of the above factors includes suppressing interfacial side reactions, offsetting external compaction loads, generating energy dissipation effects, and maintaining structural integrity.

[0035] Example 4: Addressing the issue of uneven material crystallization caused by dynamic temperature fluctuations in large-scale rotary kiln production, this example provides a niobium gradient layer construction procedure based on phase change heat signal feedback. This procedure is used to precisely control the diffusion depth and lattice stress intensity of niobium ions in a non-equilibrium production environment. A phase change kinetics heat flow calibration method is employed. The production environment is an industrial rotary kiln with zoned temperature control, and the constant temperature section is set to 750℃. A platinum-rhodium thermocouple array installed on the inner wall of the constant temperature section of the rotary kiln collects the instantaneous heat flow signal Q during the crystallization process. Since the formation of the lithium iron phosphate main phase lattice is accompanied by latent heat release, the system determines the crystallization progress based on the decay rate of the heat flow signal Q. The reference heat flow... The peak value is calibrated online using the average value of the no-load heat flux signal when the rotary kiln reaches the equilibrium point of 750 degrees Celsius in the constant temperature section. The system uses a sampling frequency of 10Hz to acquire the instantaneous heat flux signal and performs mean filtering using a sliding window with a capacity of 50 sampling points. When the filtered instantaneous heat flux signal shows a decreasing trend for 15 consecutive sampling points, and the decrease ratio compared to the reference heat flux peak value reaches 15% to 18%, it is determined that the current main phase crystallinity has entered the injection window period of 85% to 88%, and the atomizing injection device is automatically triggered. When the heat flux signal Q drops to 15% of the peak value at the main phase crystallization initiation point, the system logic determines that the main phase crystallinity is in the 85% to 88% range, at which point the controller automatically starts... The atomizing injection device is activated. To establish an accurate average value of the no-load heat flow signal in an industrial rotary kiln with severe thermal inertia, the system's online calibration program is executed in the kiln preheating section before each batch of material is fed. After the rotary kiln's zone heating controller raises the temperature of the constant temperature section to 750°C, the system enters a 60-minute no-load heat preservation waiting period until the deep heat conduction inside the kiln refractory bricks and furnace lining completely reaches thermodynamic dynamic equilibrium. The platinum-rhodium thermocouple array, arranged circumferentially along the inner wall of the kiln's constant temperature section, begins to continuously collect the instantaneous total heat flow of radiation and convection under no-load conditions. The system's sampling program is set to read 6000 heat flow data points within 10 consecutive minutes. The PLC control unit processes this data. The arithmetic mean of the large sample data is calculated, and the final converged constant calibration value is locked in the system register as the absolute zero reference heat flux peak value. In order to further offset the interference signals caused by macroscopic thermal drift of the kiln body due to long-term operation or power grid voltage disturbance, the system enables dynamic slope compensation while filtering the mean: the heat dissipation flux is monitored in real time by an infrared temperature sensor installed on the outer surface of the rotary kiln shell. Whenever the temperature rise slope of the shell fluctuates, a proportional micro-perturbation correction heat flux coefficient is automatically superimposed on the calibration value to ensure the purity and stability of the online calibration reference. The above mapping relationship between the heat flux reduction and the crystallinity judgment interval comes from the standard phase change calibration derivation established before the equipment was put into operation.Before formal mass production, the technical specifications were calibrated and verified offline using differential scanning calorimetry coupled with in-situ high-temperature X-ray diffraction. Physical measurements confirmed that when the lithium iron phosphate precursor transforms from an amorphous state to a highly ordered olivine main phase, the overall latent heat of phase transition released is strictly proportional to the volume of the unit cell. Based on this pre-set calibration curve, when the intensity of the macroscopic online heat flow collected by the system decreases, and the residual heat release area dynamically corresponds to 15% to 18% of the peak value reduction, it indicates that the construction of the long-range framework of its microscopic internal lattice has thermodynamically crossed the 85% to 88% generation progress threshold. To completely eliminate the macroscopic disturbances caused by the large thermal inertia conduction and strong convective heat transfer of the kiln wall under the complex conditions of continuous dynamic operation in industrial rotary kilns, a transformation and dimensionality reduction rule based on dual-channel differential thermal elimination was established. In the inner wall of the rotary kiln's isothermal section, except... In addition to arranging the thermocouple array for contact with the material layer, an extra set of unloaded reference thermocouples under the same wind speed and radiation field is added as a reference channel. The raw instantaneous heat flow signal, which includes macroscopic disturbances, collected by the measurement channel is dynamically subtracted from the instantaneous basic environmental heat flow signal output by the reference channel. This completely offsets and filters out the components of environmental fluctuations at the hardware level. The decoupled pure differential heat flow signal physically corresponds only to the latent heat of microscopic phase change spontaneously released by the solid powder material during solid-phase chemical reaction crystallization. The controller performs continuous integration on the time axis of this pure differential heat flow signal to obtain the real-time residual heat release area. This area is then compared with the total enthalpy of the first-order phase change of the olivine main phase standard stored in the system using a monotonic mapping. Through this single-dimensional quantitative difference evolution, the volume fraction of the microscopic long-range skeleton construction is directly deduced, eliminating the spatiotemporal blind zone between macroscopic thermal disturbances and microscopic crystallization progress.

[0036] The concentration of the niobium ethanol atomized liquid was set to 0.15 mol / L, and the injection flow rate was set to 2.5 L / min. The carrier gas pressure of the atomizing injection device was stabilized at 0.45 MPa through a proportional pressure valve. The median diameter of the atomized droplets was calibrated to be between 15 and 25 micrometers using laser diffraction. By adjusting the ratio of the injection flow rate to the rotary kiln speed, the niobium injection intensity was set to 0.8 liters per square meter of material cross-section. This physical calibration condition ensured that the niobium concentration gradient layer formed a nonlinear concentration maximum at a distance of 180 nm from the particle surface. The injection duration t was determined based on the initial median particle size D50 of the material to be treated. The calculation relationship for the injection time t is as follows: t = K D50, where t is the injection duration, D50 is the median particle size of the material, and K is the diffusion time coefficient, the value of which depends on the diffusion activation energy of niobium ethanol. In this embodiment, for an environment of 750℃, K is selected as 30 min / μm. The diffusion time coefficient is linearly and dynamically compensated based on the real-time kiln temperature. The reference calibration temperature is set to 750℃. When the real-time kiln temperature increases by 1℃, the diffusion time coefficient is reduced by 0.5 units from 30; conversely, if the real-time kiln temperature decreases by 1℃, it is increased by 0.5 units. The calculated injection duration is precisely controlled by the actuator through a PLC timer to ensure that the diffusion depth of niobium ions in the non-equilibrium state accurately hits 100nm to 3μm. Within the 00nm depth range, for the material with a D50 of 0.35μm in this embodiment, the injection time t was calculated to be 10.5min. The total injection duration was set to be linearly proportional to the macroscopic median particle size of the material. The underlying physical driving force is the dynamic evolution of the effective chemical potential intensity of the volatile components at the gas-solid interface in the large-volume reaction bed. In continuous rotary production, when the same volume of niobium ethanol atomized liquid is quantitatively injected into the furnace, if the initial median particle size of the current batch of material is large, it means that the total initial geometric specific surface area exposed per unit volume of the entire material bed is significantly smaller. In this case, the evaporated niobium source gas phase component will generate spontaneous gas on the smaller outer surface of the powder body. The phase aggregation effect leads to a sharp increase in the local niobium vapor phase partial pressure on the surface of individual particles. This high concentration of local boundary layer aggregates artificially constructs an extremely high chemical potential gradient between the inner and outer surfaces of the particles, thereby significantly increasing the initial driving force of solid-phase diffusion and significantly accelerating the inward penetration rate of niobium ions in the initial stage of the reaction. In order to ensure that the final nonlinear concentration maxima are still precisely locked within the depth range of 100 nm to 300 nm without excessive penetration into the core, the total injection and diffusion time must be linearly lengthened using a proportional formula. This dilutes and mitigates the local concentration overload caused by the reduction in macroscopic surface area, so that the microscopic diffusion depth can obtain a constant boundary anchor for batches with different particle sizes. The linear compensation coefficient of 0.5 units is approximated by the first-order Taylor series expansion of the Arrhenius equation for solid-state diffusion within an extremely narrow fluctuation range near the 750℃ reference point. Under the small temperature field fluctuation of ±5℃ in the constant temperature section of an industrial rotary kiln, the tangent slope term of the exponential diffusion kinetic equation, after linearization by the first derivative, exhibits a constant characteristic within this temperature perturbation range. The system adopts this linear dimension reduction control logic, transforming the originally complex exponential calculation into basic arithmetic operations that can be processed by the PLC controller in real time with low latency. This ensures the synchronization of the compensation action with the real-time response of the temperature field fluctuations and eliminates the time delay effect of the control system caused by the time consumption of nonlinear function calculations.

[0037] After the atomization injection is completed, the rotary kiln enters the cooling rate compensation stage. The system calculates the real-time diffusion radius of niobium ions on the surface of the lithium iron phosphate lattice. By adjusting the circulation flow rate of the liquid nitrogen cooling medium, when the effective diffusion depth reached 180 nm, the heat exchange system increased the cooling rate to 18.2 °C / min. Through a high-intensity thermal contraction effect, niobium ions were locked at transition metal sites to form localized lattice distortion. Measurement results showed that the lattice constant shrinkage of the lithium iron phosphate material composition obtained by this procedure... With a value of 0.026, this precisely anchored stress field exhibits excellent energy dissipation capabilities during electrode rolling. Experimental data shows that the prepared material composition exhibits a particle D50 change rate of 1.1% after being subjected to a mechanical load of 250MPa, and the DC internal resistance growth rate of the 300Ah high-capacity battery cell made from it is less than 12% after 3000 cycles of 1C / 1C charge-discharge. The interfacial gas generation is reduced by 38% compared to the sample group without the thermal flow feedback procedure. The surface doping process is transformed into a programmed operation based on measurable physical quantities, eliminating batch performance differences caused by temperature field fluctuations in the production environment, and achieving synergistic stability of mechanical resistance and electrochemical performance.

[0038] Example 5: In the batch production of 300Ah high-capacity battery cell cathode materials, to address the impact of initial particle size distribution fluctuations in iron and manganese source raw materials on the densification and fusion of near-single-crystal particles, the production line implemented a material pre-dispersion and particle size distribution calibration procedure. A high-speed circulating sand mill was used to process a mixed slurry containing lithium, iron, manganese, phosphorus, and titanium sources, and the grinding speed was adjusted to control the characteristic size of the solid particles. The median particle size D50 of the slurry needed to satisfy the coupling relationship with the crystallization barrier of the main phase. For an aqueous slurry with a solid content of 45%, the system monitored the outlet pressure of the grinding chamber in real time and adjusted the pressure fluctuation accordingly. Adjusting the grinding energy input, when the slurry's D50 stabilizes at 0.35 μm and the particle size distribution coefficient Span is less than 0.85, the system outputs a sampling qualification command and drives the material into the spray drying stage. This allows the precursor particles to generate a dense solid with an internal microporosity of 0.5% to 1.2% during the solid-phase reaction at 750℃. The outlet fluid pressure fluctuation of the sand mill grinding chamber is used as the core judgment indicator to control the median particle size and distribution coefficient of the internal solid powder in a closed-loop manner. The underlying slurry rheological control loop is as follows: In a high-concentration suspension slurry system with a solid content as high as 45%, as the large particles... The driving body is continuously ablated and pulverized by high-energy ablation, resulting in an exponential increase in the number of submicron and nano-sized particles within the system. This leads to a massive expansion of the macroscopic interface contact area of ​​the suspended solids, triggering strong spatial viscous shear resistance, which is directly mapped macroscopically to a step increase in the apparent viscosity of the slurry. Furthermore, there is a very strict positive correlation between the mechanical discharge pressure at the grinding chamber outlet and the apparent viscosity of the slurry passing through that outlet, following a hydrodynamic causal law. During continuous operation of the sand mill, when the high-precision pressure sensor detects that the instantaneous fluctuation difference of the outlet pressure spontaneously converges within 10 minutes and the absolute value of the fluctuation variance strictly decreases to 5k... Below Pa, the surface energy expansion and shear viscosity increase of the particles in the characterization system have crossed the rapid kinetic decay period and reached the thermodynamic crushing limit equilibrium. Since the viscosity of the slurry no longer undergoes microscopic changes, the median particle size of the corresponding material is precisely and stably locked at 0.35 μm, while the characteristic distribution coefficient is below 0.85, thus establishing a solid closed-loop causal chain between the fluid mechanical state and the solid-phase crushing index. The physical transformation mechanism by which this set of parameters strictly closes the product's microporosity in the ultra-low range lies in strictly limiting the median particle size of the primary precursor particles to the order of 0.35 μm and combining it with a narrow particle size distribution coefficient of less than 0.85. The particle size distribution ensures that the slurry achieves extremely uniform spatial density during the spray drying molding stage, eliminating large voids between large particles. In the subsequent high-temperature heat treatment at 750℃, the uniform and fine initial physical contact points significantly reduce the surface energy barrier, directly shortening the short-range atomic diffusion path during solid-phase reaction. This fundamentally suppresses the Kirkendall effect and bridging voids that are easily caused during sintering and fusion due to excessive primary particle size differences. As a result, the crystal structure can achieve centripetal densification and shrinkage driven by its own surface energy without relying on ultra-high external static pressure, physically approaching the lower limit of thermodynamic density.

[0039] When the system faces situations such as replacing a new batch of niobium ethanol atomizing fluid or a shift in ambient air pressure, the production procedure initiates a pre-calibration procedure for stress field strength. The system extracts 50g of initial material and places it in a test reactor for micro-scale trial production verification. After completing niobium element injection and cooling rate compensation treatment, an X-ray diffractometer with a resolution better than 0.02° is used to collect lattice characteristic signals within a 500nm range on the material surface. The measured lattice constant shrinkage is then determined. The measured value must be within the standard range of 0.015 to 0.035. If the measured value deviates, the system will automatically correct the circulation flow rate of the liquid nitrogen cooling system based on the deviation. By dynamically adjusting the cooling rate to compensate for thermal shrinkage energy levels, this calibration procedure locks the niobium concentration gradient layer within a depth range of 100 nm to 300 nm from the particle surface, ensuring that the prepared lithium iron phosphate material composition maintains geometric stability when subjected to a 250 MPa rolling load.

[0040] Example 6: In the continuous interfacial coating process for the cathode material of a 300Ah high-capacity battery cell, the non-uniform nucleation of the organic carbon source during pyrolysis leads to physical gaps in the interfacial coating layer and induces interfacial resistance fluctuations. The system executes a coordinated calibration procedure for the interfacial anchoring energy level and coating thickness. The near-single-crystal particles prepared in the previous steps are placed in a mixing and coating machine with centrifugal force feedback function. According to the mapping relationship between the surface tension γ of the carbon source particles and the wetting angle of the near-single-crystal particle matrix, the centrifugal speed of the mixing chamber is adjusted to 450 rpm, so that the inorganic oxide precursor and the carbon source are covalently anchored at the interface on the surface of the near-single-crystal particles. The instantaneous shear heat accumulation in the mixing chamber is then measured. Once the calibrated threshold is reached, the system automatically switches to a 650℃ isothermal pyrolysis mode. The deterministic mapping path relied upon here is essentially based on the dynamic mechanical equilibrium between the capillary spreading pressure of the carbon source liquid on the precursor solid and the macroscopic non-inertial centrifugal shear stress generated by the coating machine rotor. The intrinsic surface tension data of different types of organic carbon sources at specific crystallinities, along with their contact wetting angle data on the olivine main phase single crystal surface, are pre-input into the two-dimensional matrix addressing model of the control system. For the specific organic carbon source used in this embodiment, its measured surface tension is precisely 32 mN / m, and its wetting angle on the single crystal surface is precisely 45°. According to the internal quantization mapping rules of the addressing model, the minimum wetting capillary limit constraint force corresponding to this parameter set is directly converted into the shear pressure threshold that the solid particles on the inner wall of the cavity need to withstand. The system then calculates and outputs commands based on this closed-loop calculation, changing the driving... The output frequency of the inverter precisely locks the rotor speed of the mixing chamber at 450 rpm. This specific speed provides a perfect mechanical rheological shear field, forcefully crushing carbon source agglomerates and overcoming the wetting resistance caused by the 45° contact angle. This allows carbon atoms to adhere extremely uniformly and covalently bond to the single crystal surface, establishing a black-box-free mapping from abstract physicochemical indicators to specific speed values. The instantaneous shear heat accumulation is calibrated in real time by monitoring the rate of temperature rise between the mixing chamber's outer wall temperature sensor and the ambient temperature sensor. The calibration threshold is set at a temperature rise of 1.5°C per minute. When the temperature rise rate exceeds this threshold, the controller reduces the output frequency of the drive motor inverter, causing the centrifugal speed to decrease in steps of 10 rpm per minute. This prevents premature coking or physical stripping of the carbon source due to local overheating before covalent anchoring at the inorganic interface. The hollow flow rate of the carrier nitrogen is also adjusted via a pressure compensation valve. The flow rate is circulated within the range of 15 L / min to 18 L / min. The shear effect of the flow field drives the volatile components generated by the pyrolysis of the carbon source to escape to the outer periphery of the material, thereby generating a dense double-layer coating structure with a thickness of 2 nm to 5 nm on the surface of the quasi-single-crystal particles. Here, γ is the surface tension. This is the cumulative amount of instantaneous shear heat. The hollow flow rate of the carrier nitrogen gas is used. The system uses the first derivative of the rate of temperature rise to calibrate the saturation state of the instantaneous shear heat accumulation in the energy dimension. The transition mechanism is as follows: In the initial stage of mixing, most of the mechanical shear energy input to the equipment is converted into microscopic chemical internal energy that causes covalent anchoring between the inorganic oxide precursor and the carbon source at the interface. When the covalent anchoring points on the surface are completely exhausted over time and energy saturation is reached, the continuously input shear heat can no longer be absorbed by bonding. This excess energy will be instantly and intensely conducted to the outer wall of the mixing chamber in the form of sensible heat. Therefore, the critical point at which the energy conservation equilibrium of the system is broken will be precisely mapped to a sharp inflection point of temperature rise rate on the macroscopic heat transfer dynamics. This threshold of 1.5℃ / min is precisely the secondary heat overflow signal characterizing the complete filling of the interfacial bonding energy pool. In order to enable the chemical bonding heat effect at the microscopic level to accurately map and trigger the inflection point of the temperature rise rate at the macroscopic level, the continuous interfacial coating process of this invention adopts an ultra-low heat capacity limit constraint design. The total volume of the reaction chamber of the mixing coating machine is limited to 0.5L, and the outer wall is wrapped with microporous silicon with a thickness of 50mm. The calcium carbonate insulation layer strictly limits the total mass of solid material processed in each batch to 50g. Within this highly insulated, closed microsystem, the equipment drive motor inputs kilowatt-level high-energy mechanical shear force at 450rpm. Under extremely high centrifugal extrusion, this energy is selectively and highly polarized at the micro-contact points at the interface between the inorganic particles and the carbon source in the initial stage. Due to the strong chemical activation induced by the high-density micro-region friction, over 99% of the input shear energy is instantly absorbed by the simultaneously occurring binding reaction and transformed into the micro-scale covalent bonds at the interface. The internal energy is absorbed, which makes the distributed microscopic chemical reactions within the system act as an ultra-efficient internal energy absorption buffer, forcibly suppressing the macroscopic sensible heat rise of the cavity to an extremely low level. However, once all covalent sites on the surface are fully occupied over time, this distributed microscopic heat absorption buffer mechanism instantly fails, and the continuously input mechanical shear energy can no longer be converted into chemical internal energy. Instead, it is fully converted into sensible heat from volume collisions between macroscopic particles, directly causing the outer wall temperature rise rate to suddenly increase to 1.5℃ / min within the adiabatic cavity, thus achieving a two-level causal closed loop.

[0041] When the system measures the specific surface area of ​​the coated material through the online specific surface area monitoring unit When the concentration is within the range of 0.85 m² / g to 1.15 m² / g, the controller issues a coating endpoint determination command and drives the high-pressure air-cooling system to perform cooling rate compensation. A cooling rate greater than 20 °C / min is used to suppress the amorphous ordering transformation within the carbon layer. Cross-sectional characterization of the product using scanning electron microscopy confirms that the coating layer thickness on the particle surface is 3.5 nm and has no physical micropores. Measurements show the niobium concentration at 50% radius from the particle center. The concentration of niobium on the particle surface The ratio is 0.25. The lithium iron phosphate material composition prepared according to this procedure exhibits a 1C DC internal resistance of 1.52 mΩ after cell assembly, compared to the initial value. The discharge plateau voltage was reduced to 1.25 mΩ, and the discharge plateau voltage retention rate reached 98.2% during 3000 cycles. The interfacial gas production was reduced by 35% compared to the non-gradient cooling sample group. This is the specific surface area value. This represents the niobium concentration at 50% of the particle's internal radius. The concentration of niobium on the particle surface is given.

[0042] 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, and all such modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A lithium iron phosphate material composition for a 300Ah high-capacity battery cell, characterized in that, The lithium iron phosphate material composition includes a main phase Where 0.1≤x≤0.3, 0.001≤y≤0.01, and M is selected from the combination of Nb and Ti; The molar ratio of niobium to titanium is 0.15 to 0.

28. Niobium exhibits a nonlinear gradient distribution within the particles of the lithium iron phosphate material composition, and a niobium concentration gradient layer exists within a depth range of 100 nm to 300 nm from the particle surface. In the niobium concentration gradient layer, the rate of change of niobium concentration in the depth direction decreases with increasing depth. The particles are dense solid particles with a near-single-crystal structure and an internal microporosity of 0.5% to 1.2%. The surface of the particles is coated with a carbon coating layer with a thickness of 2 nm to 5 nm. The carbon coating layer includes amorphous carbon and graphitized carbon, wherein the amorphous carbon is generated by the thermal decomposition of niobium-source organic matter and the graphitized carbon is generated by the thermal decomposition of the matrix organic carbon source. In the niobium concentration gradient layer, niobium and titanium elements jointly occupy the transition metal sites in the main phase lattice to form local lattice distortion. The local lattice distortion generates an inward compressive stress field on the particle surface caused by lattice volume contraction. The lithium iron phosphate material composition has anti-rolling crushing performance. When a single particle is subjected to an external roller load of 250MPa, it maintains its near-single-crystal solid structure, and the breakage rate of the particles after being subjected to the external roller load is less than 3%. When the particles are subjected to external mechanical energy impact, the inward compressive stress field offsets the external stress through elastic deformation of local lattice distortion, thereby suppressing the interfacial side reactions between the lithium iron phosphate material composition and the external electrolyte components on the particle surface and maintaining the chemical stability of the particles under high compressive state.

2. The lithium iron phosphate material composition for a 300Ah high-capacity battery cell according to claim 1, characterized in that, In the niobium concentration gradient layer, the atomic percentage concentration of niobium decreases exponentially from the particle surface towards the particle center; the total molar fraction of niobium and titanium in the lithium iron phosphate matrix ranges from 0.02 to 0.05; the inward compressive stress field is caused by the difference in atomic radii between niobium and iron, and the lattice constant in the niobium concentration gradient layer... and The shrinkage amount satisfies the following relationship: Where Δa and Δc are the shrinkage of the lattice constant after doping, respectively. and , respectively, are the initial lattice constants of undoped lithium iron phosphate.

3. The lithium iron phosphate material composition for a 300Ah high-capacity battery cell according to claim 1, characterized in that, The tap density of the lithium iron phosphate material composition is 1.55 g / cm³. 3 Up to 1.65 g / cm 3 The average particle size D50 ranges from 3.5 μm to 5.5 μm; the molar concentration of niobium in a single particle at 50% radius from the center. molar concentration of niobium on the particle surface Satisfy the proportional relationship: ,in, Analysis of elemental distribution within the particles.

4. The lithium iron phosphate material composition for a 300Ah high-capacity battery cell according to claim 1, characterized in that, The specific surface area of ​​the lithium iron phosphate material composition is 10 m². 2 / g to 15m 2 / g.

5. The lithium iron phosphate material composition for a 300Ah high-capacity battery cell according to claim 1, characterized in that, Titanium is uniformly distributed within the particles. It occupies iron sites in the lithium iron phosphate matrix to form a solid solution structure, thereby enhancing the bonding energy between primary grains of the lithium iron phosphate matrix. The amount of titanium doping accounts for 0.5% to 1.5% of the mass percentage of iron in the lithium iron phosphate matrix.

6. The lithium iron phosphate material composition for a 300Ah high-capacity battery cell according to claim 1, characterized in that, The molar ratio of lithium to transition metal elements in the lithium iron phosphate material composition is 0.98 to 1.02; wherein the total amount of transition metal elements is the sum of the molar amounts of iron, niobium and titanium.

7. The lithium iron phosphate material composition for a 300Ah high-capacity battery cell according to claim 1, characterized in that, The main phase of the lithium iron phosphate material composition is olivine structure, and its X-ray diffraction pattern does not contain free niobium oxide phase and titanium oxide phase.

8. The lithium iron phosphate material composition for a 300Ah high-capacity battery cell according to claim 1, characterized in that, The ratio of the average molar concentration of niobium within 50 nm of the particle surface to the molar concentration of niobium at the particle center is 5 to 10.

9. A lithium iron phosphate material composition for a 300Ah high-capacity battery cell according to claim 1, characterized in that, The average oxidation state of niobium in the particles is +5, and the average oxidation state of titanium is +4; niobium is coordinated through Nb-O bonds within the local lattice distortion region. The octahedral distortion lowers the lithium-ion diffusion barrier inside the lithium iron phosphate matrix.

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