Furnace temperature calibration method based on half-peak width of diffraction peak after precursor burning and application

Abstract

The invention discloses a furnace temperature calibration method based on the half-peak width of a diffraction peak after precursor burning and application, and belongs to the technical field of temperature calibration of lithium battery material production equipment. According to the method, accurate calibration of the actual temperature of the sintering furnace is achieved by establishing the function relation between the FWHM of an XRD diffraction peak after a nickel-based precursor is sintered at 250-600 DEG C and the temperature. The method specifically comprises the following five steps: establishing a standard curve; carrying out a sintering experiment on a to-be-measured furnace; measuring the half-peak width of a diffraction peak; calculating the temperature and adjusting the temperature of the to-be-measured furnace and then sintering. The method does not need to depend on a traditional temperature sensor, can effectively avoid measurement errors in a complex environment, is suitable for various types of sintering furnaces, and remarkably improves the accuracy and stability of furnace temperature control in lithium battery material production; the temperature measured by the method is closer to the real sintering temperature of the material, and the actual heating state of the material in the furnace can be accurately reflected, so that the precision and reliability of furnace temperature calibration and temperature control are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of temperature calibration technology for lithium battery material production equipment, specifically a furnace temperature calibration method and its application based on the half-peak width of the diffraction peaks after precursor combustion. Background Technology

[0002] In the production of lithium battery materials (such as ternary cathode materials NCM and NCA), sintering temperature is one of the key process parameters affecting the crystal structure and electrochemical performance of the product. Especially in the low-temperature stage of secondary or tertiary sintering (usually below 600℃), even small fluctuations in temperature can directly affect the crystallinity, particle size uniformity, and elemental distribution of the material, thus leading to unstable product performance.

[0003] Currently, the industry's commonly used methods for furnace temperature measurement and calibration primarily rely on temperature sensors such as thermocouples. Thermocouples obtain temperature data through direct contact or radiation measurement, but they are prone to aging or drift in high-temperature oxidizing, reducing, or corrosive environments, leading to inaccurate readings. Furthermore, the temperature field distribution varies significantly between different furnace types (such as box furnaces, rotary kilns, pusher kilns, and roller kilns), and differences in sensor installation location and service life often result in substantial deviations between the set temperature and the actual temperature. This deviation directly affects the consistency of the sintering process and the repeatability of product performance.

[0004] In the high-temperature range (>800℃), calibration can often be performed using a temperature sensing loop, standard thermocouple, or thermistor wire. However, in the low-temperature range (<600℃), existing temperature measurement methods generally suffer from the following problems: Thermocouple calibration method: can only measure a limited number of points in the furnace, and cannot reflect the overall temperature distribution and continuous changes in the furnace; Temperature wire recording method: It requires laying high-temperature resistant temperature wires in the furnace and connecting them to an external recorder. The operation is complicated, costly, and interferes with the atmosphere and temperature field in the furnace, resulting in low testing efficiency.

[0005] Therefore, there is a lack of a simple, repeatable, and sensor-independent method for calibrating the furnace temperature in the low-temperature range in the existing technology. In particular, it is difficult to accurately reflect the actual heating temperature of the material in the sintering process of lithium battery cathode material precursors using traditional methods.

[0006] Patent document CN107941370A discloses a method for detecting the high-temperature sintering temperature of cathode materials. This technology can better reflect the actual heating situation of the material than traditional thermocouple temperature measurement. However, it is mainly applicable to the sintering process of cathode materials in the high-temperature range (500-1200℃). It has obvious limitations for the sintering stage of nickel-based precursors in the low-temperature range (250-600℃): First, the crystallinity of the precursor is low in the low-temperature stage, making it difficult to directly use the linear fitting model of high-temperature materials; second, grain growth is slow in the low-temperature region, the change in the full width at half maximum (FWHM) is weak, and the sensitivity is insufficient; in addition, this method is only used for temperature estimation and does not form a closed-loop control mechanism for furnace temperature calibration; and it does not fully consider the influence of process parameters such as atmosphere and holding time on the crystallization behavior of the precursor.

[0007] In summary, existing furnace temperature measurement and calibration methods suffer from problems such as large measurement errors, incomplete distribution information, and complex operation during the low-temperature sintering stage, making it difficult to meet the requirements of precise furnace temperature control in modern lithium battery material production. Therefore, there is an urgent need for a furnace temperature calibration method that does not rely on thermocouples or external sensors and can indirectly reflect the actual temperature through the material's own physical properties, in order to achieve accurate calibration and long-term stable control of sintering furnace temperature and improve the consistency and reliability of material production. Summary of the Invention

[0008] The technical problem to be solved by this invention is to overcome the shortcomings of existing methods and provide a furnace temperature calibration method and application based on the half-width at half-maximum (WHM) of the diffraction peaks after precursor sintering. By inferring the temperature from the material's crystal structure characteristics (WHM of the diffraction peaks), the measurement error caused by environmental interference of traditional sensors is avoided, and the method is closer to the actual heating state of the material. It is applicable to various furnace types such as box furnaces, rotary kilns, pusher kilns, and roller kilns. It can be placed in the same position during material sintering and is not significantly affected by the atmosphere (air, oxygen, nitrogen) and holding time (1-10h). It is flexible in operation and can effectively solve the problems in the background technology.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a furnace temperature calibration method and application based on the full width at half maximum (FWHM) of diffraction peaks after precursor combustion, comprising: 1. Establish a standard curve: (a) Select a nickel-based precursor (one of pure nickel hydroxide (Ni(OH)2), nickel-cobalt-manganese (NCM) precursor, or nickel-cobalt-aluminum (NCA) precursor); (b) Place the precursor in a standard furnace and sinter at at least three temperature points (e.g., 300°C, 400°C, 500°C, 600°C) within the range of 250°C to 600°C. The holding time is 1-10 hours (e.g., 1 hour, 3 hours, or 5 hours). The sintering atmosphere is any one of air, oxygen, or nitrogen. (c) Perform XRD analysis on the sintered samples at each temperature point and derive the full width at half maximum (FWHM) of the 111 peak, 200 peak or 220 peak (preferably 200 peak). (d) Using temperature as the ordinate and half-peak width as the abscissa, fit the relationship function between temperature and half-peak width (preferably a linear equation).

[0010] 2. Sintering experiment of the furnace to be tested: The nickel-based precursors from the same batch as in step 1 were placed in the target area of ​​the furnace to be tested, and sintered using the same precursor weight, holding time, and atmosphere as in step 1.

[0011] 3. Measurement of half-width at half-maximum (FWHM) of diffraction peaks: XRD analysis was performed on the sintered sample in step 2 to obtain the full width at half maximum (FWHM) values ​​of the same diffraction peaks (e.g., peak 200) as in step 1.

[0012] 4. Calculation of actual temperature in the target area: Substitute the half-peak width value measured in step 3 into the relational function T=k×FWHM+b established in step 1 to output the actual temperature of the target area of ​​the furnace under test.

[0013] 5. Compare the actual temperature with the set temperature. If the difference is ≤5℃, the temperatures are considered consistent; if the difference is >5℃, they are considered inconsistent, and the temperature should be readjusted for calibration. The nickel-based precursor used in this invention has a sintering temperature range of 250–600°C. Below 250°C, the precursor does not exhibit obvious crystallinity after sintering and cannot be used to determine the temperature. Above 600°C, the crystallinity changes little, and the half-peak width is not linear with the temperature curve, making it difficult to determine the temperature.

[0014] The relationship function is T = k × FWHM + b, where k is the linear slope, representing the sensitivity of FWHM change to temperature change; b is the intercept, representing the theoretical temperature of the material in the ideal crystallization state; when the fitting correlation coefficient R² ≥ 0.99, the relationship has high linear repeatability and can be used to accurately invert furnace temperature.

[0015] Within the temperature range of 250–600℃, the half-width at half-maximum (FWHM) of the 200 diffraction peak after sintering of the nickel-based precursor shows a linear relationship with the sintering temperature, with a linear fitting coefficient of determination R² ≥ 0.99. This indicates that the function has excellent correlation and repeatability and can be used for precise calibration of furnace temperature.

[0016] Furthermore, the furnace to be tested can be any one of a box furnace, rotary kiln, pusher kiln, or roller kiln.

[0017] Furthermore, the nickel hydroxide precursor is at least one of the α-type or β-type crystal forms, and the full width at half maximum (FWHM) of the 001 peak of the nickel cobalt manganese hydroxide and nickel cobalt aluminum hydroxide precursors ranges from 0.2 to 1.0°.

[0018] Furthermore, the standard furnace temperature used to establish the standard curve was calibrated by a thermocouple that was certified by the National Metrology Institute.

[0019] Furthermore, the method is applied to the temperature calibration and monitoring of sintering furnaces. By monitoring the FWHM changes of nickel-based precursors after sintering, the temperature distribution in different regions of the furnace can be plotted and the long-term temperature drift can be evaluated in real time.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention utilizes the measurable characteristics of the material's own crystal structure to deduce the actual heating temperature, fundamentally avoiding the systematic errors caused by environmental factors such as oxidation, radiation, and atmospheric changes in traditional thermocouples and temperature measuring wires. The temperature measured by this method is closer to the material's true sintering temperature and can accurately reflect the actual heating state of the material in the furnace, thereby effectively improving the accuracy and reliability of furnace temperature calibration and temperature control.

[0021] 2. This method can be applied to various types of sintering equipment, including industrial furnaces with different structures such as box furnaces, rotary kilns, pusher kilns, and roller kilns. It can be directly placed at the same position of the material sintering for measurement. It can maintain a stable linear response relationship under different atmospheres (such as air, oxygen, and nitrogen) and different holding times (1 to 10 hours), and is not affected by changes in furnace structure and atmosphere. It has good versatility and flexibility and can be widely applied to the sintering process of lithium battery cathode materials and their precursors.

[0022] 3. This method does not require the purchase of additional high-precision temperature sensors, temperature measuring loops, or recorders. It can achieve indirect calibration of furnace temperature using only a conventional X-ray diffractometer (XRD) in a laboratory. The detection process is simple and highly repeatable. It significantly reduces hardware investment, maintenance costs, and testing cycles, making it easy to promote and apply in laboratory research and large-scale production lines.

[0023] 4. This invention can also draw a temperature distribution map inside the furnace by arranging samples at multiple points and using the differences in FWHM values ​​at each point, thereby realizing the spatial uniformity analysis of the furnace temperature field; at the same time, by monitoring the FWHM change trend of samples at the same location during the production process, the furnace temperature fluctuation can be reflected, thereby enabling real-time evaluation and long-term monitoring of process stability.

[0024] 5. This invention is the first to apply the XRD diffraction peak half-width-temperature relationship to the low-temperature sintering stage (250–600℃) of nickel-based precursors, establishing a function model T = k×FWHM +b that can be accurately linearly fitted in the low-temperature range. This model exhibits excellent linear correlation and sensitivity under the condition of R²≥0.99, filling the technical gap in existing high-temperature detection methods that cannot be accurately calibrated in the low-temperature range. Attached Figure Description

[0025] Figure 1 This is a schematic diagram showing the relationship between the full width at half maximum (FWHM) of the 200 diffraction peak and the sintering temperature after sintering of the nickel hydroxide precursor of the present invention. Detailed Implementation

[0026] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Example

[0027] like Figure 1 As shown, the temperature calibration of the box furnace is based on the nickel hydroxide precursor; The implementation steps are as follows: 1. Establish a standard curve: (1) Select nickel hydroxide precursor, take 100g and place it in a crucible; (2) Place the sagger into the material sintering position in the standard box furnace and sinter at 290℃, 300℃, 310℃, 400℃, 500℃ and 600℃ respectively, with a holding time of 6 hours and an oxygen atmosphere; (3) After sintering, the sample was cooled to room temperature and then detected by an X-ray diffractometer (Cu target, λ=1.5406Å). The scanning range was 2θ=15°~70°. The full width at half maximum (FWHM) of the 200 peak was derived. The results are as follows: FWHM=1.436° for 290℃, FWHM=1.385° for 300℃, FWHM=1.311° for 310℃, FWHM=0.967° for 400℃, FWHM=0.561° for 500℃, and FWHM=0.147° for 600℃. (4) The fitted linear relationship function is: T = -0.0041 × FWHM + 2.6085 (R 2 =0.9992); In the range of 250 to 600℃, the half width at half maximum (FWHM) of the 200 diffraction peak after sintering of the nickel-based precursor is linearly related to the sintering temperature, and its linear fitting determination coefficient R²≥0.99 indicates that the function has excellent correlation and repeatability and can be used for accurate calibration of furnace temperature.

[0028] 2. Sintering experiment of the box furnace to be tested: Take 100g of nickel hydroxide precursor from the same batch as in step 1, place it in the sintering area of ​​the box furnace to be tested, set the temperature to 450℃, hold for 6 hours, and use oxygen atmosphere.

[0029] 3. Half-peak width measurement: XRD analysis of the sintered sample revealed a half-peak width of 0.811° for peak 200.

[0030] 4. Actual temperature calculation: Substituting into the function, the actual temperature T = -0.0041 × FWHM + 2.6085 is obtained, which is 438.4℃. This indicates that when the furnace is set to 450℃, the actual temperature of the sintering zone is 438.4℃. The furnace temperature control system needs to be calibrated or the furnace temperature needs to be adjusted for sintering.

[0031] The furnace temperature deviation was adjusted to ±12℃, and 100g of nickel hydroxide precursor was sintered again. After sintering, the XRD measurement of the 200 peak half-peak width was 0.763°, and the calculated temperature was 450.1℃. It was considered that the furnace temperature under test had been adjusted to be consistent with the target temperature.

[0032] like Figure 1 As shown, FWHM decreases significantly with increasing sintering temperature, exhibiting a good linear negative correlation.

[0033] XRD analysis of the nickel hydroxide precursor at different temperatures (290℃, 300℃, 310℃, 400℃, 500℃, 600℃) yielded the full width at half maximum (FWHM) of the 200 diffraction peak, and a linear function between temperature and FWHM was established based on this. Figure 1 It can be seen that when the temperature is in the range of 250 to 600℃, the two show a linear relationship, and the correlation coefficient R² of the linear equation is as high as 0.9992, indicating that the method has excellent stability and repeatability. This linear function can be used to back-calculate the actual furnace temperature at any sintering temperature, thereby achieving accurate calibration.

[0034] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Various changes and modifications can be made to the present invention without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A method for calibrating the furnace temperature based on the half-peak width of the diffraction peak after precursor firing, characterized in that, The method comprises the following steps: (a) establishing a standard curve: sintering the nickel-based precursor at at least three temperature points in the range of 250-600℃, measuring the X-ray diffraction (XRD) pattern of each sintered sample, and deriving the half-peak width (FWHM) of the diffraction peak, fitting the temperature T and the FWHHM relationship function to obtain a linear equation: T=kxFWHM+b, wherein k is the slope, b is the intercept, and the linear fitting determination coefficient R²≥0.99; (b) sintering in a to-be-tested furnace: placing the same batch of nickel-based precursor sample as used in step (a) in the target area of the to-be-tested furnace, and sintering under the same atmosphere, holding time and process conditions; (c) half-peak width measurement: conducting XRD detection on the sintered sample and deriving the FWHM value of the diffraction peak; (d) temperature calculation: substituting the FWHM value measured in step (c) into the relationship function in step (a) to calculate the actual sintering temperature T of the region; (e) temperature calibration: if the deviation between the actual temperature and the set temperature of the to-be-tested furnace is ≤5℃, it is considered that the furnace temperature is consistent and no adjustment is needed; if the deviation is >5℃, repeat steps (b)-(d) after adjusting the furnace temperature parameters until the output actual temperature is consistent with the set temperature of the to-be-tested furnace.

2. The method for calibrating the furnace temperature based on the half-peak width of the post-sintering diffraction peak of the precursor according to claim 1, characterized in that: The nickel-based precursor is one of nickel hydroxide, nickel-cobalt-manganese hydroxide precursor or nickel-cobalt-aluminum hydroxide precursor.

3. The method according to claim 1 or 2, characterized in that: During the establishment of the standard curve, the sintering holding time is 1-10 hours, and the atmosphere is any one of air, oxygen or nitrogen.

4. The method of claim 1, wherein the method is characterized by: Any one of the 111, 200 or 220 diffraction peaks in the XRD pattern is selected as the analysis object, and the 200 peak is preferably selected.

5. The method of claim 1, wherein the method is characterized by: The to-be-tested furnace is any one of a box furnace, a rotary kiln, a push plate kiln or a roller kiln.

6. The method for calibrating the furnace temperature based on the half-peak width of the post-sintering diffraction peak of the precursor according to any one of claims 1-5, characterized in that: The nickel hydroxide precursor is at least one of α or β crystal form, and the FWHM of the 001 peak of the nickel-cobalt-manganese hydroxide and nickel-cobalt-aluminum hydroxide precursor ranges from 0.2 to 1.0°.

7. The method of claim 1, wherein the method is characterized by: The standard furnace temperature used for establishing the standard curve is calibrated by a thermocouple certified by the national metrology.

8. Use of the method according to any one of claims 1 to 6 for temperature calibration and monitoring of a sintering furnace, characterized in that By monitoring the FWHM change of the nickel-based precursor after sintering, the temperature distribution in different regions of the furnace is drawn and the real-time evaluation of long-term temperature drift is realized.

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