A method and system for researching a thermal decomposition mutation mechanism of a high-nickel positive electrode material precursor

Abstract

The application discloses a kind of high-nickel positive material precursor thermal decomposition mutation mechanism research method and system, by subdividing to high-nickel positive material microcosmic chemical reaction process;According to the reaction of the precursor element participating in the thermal decomposition reaction in the sintering process of high-nickel positive material according to the segmentation result is researched;According to the decomposition reaction kinetics formula and Arrhenius formula, the change relationship of particle number in the reaction process is established;According to the data and information of non-isothermal thermogravimetric experiment, differential scanning calorimetry thermal analysis experiment, X-ray diffraction experiment, the difference between the reaction process of element and mixed material is researched;Research is carried out for the difference part, combined with experimental data and chemical mechanism, the research method of corresponding difference part is proposed, and the change relationship of this part under different heating rates is obtained.The application not only studies the precursor element, but also effectively solves the problem of mixed material thermal decomposition dehydration mechanism mutation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of preparation of high-nickel positive electrode materials, and particularly discloses a method and system for researching a thermal decomposition mutation mechanism of a precursor in a high-nickel positive electrode material preparation process. BACKGROUND

[0002] China is developing new energy sources, and clean energy sources need to be matched with good energy storage devices to make the supply of new energy sources more stable and reliable. Therefore, it is very important to develop batteries with high energy density, long service life and environmental friendliness. Lithium ion batteries play an important role in solving environmental pollution and resource scarcity, have high capacity, are pollution-free, and are one of the most important energy storage devices in the future, thereby causing a research boom. In lithium ion batteries, the positive electrode material plays an important role and is the key to its development. Among the positive electrode materials, high-nickel positive electrode materials meet the above requirements and are one of the most promising materials for lithium ion battery positive electrode materials.

[0003] The yield of high-nickel positive electrode material sintering products and the energy consumption of the sintering process are the most concerned indicators in industrial production. Improving the consistency of the products and achieving energy saving and emission reduction are the ultimate goals of the project. In order to achieve this goal, a suitable sintering system needs to be developed. In the sintering process, the precursor and LiOH·H2O are mixed in a certain proportion, then dehydrated, combined and grain grown to obtain the final product. Researching from a macroscopic perspective cannot comprehensively analyze the sintering process of high-nickel positive electrode materials, and the microcosmic chemical reactions of the sintering process need to be studied. In order to clarify the mechanism of microcosmic reactions, the whole reaction process of sintering needs to be studied. However, in the sintering process, multiple chemical reactions are coupled together, the reactions between various substances influence and promote each other, the reaction mechanism is not clear, and the research is difficult.

[0004] The high-nickel positive electrode material precursor is one of the main substances participating in the sintering process reaction, and to a great extent determines the performance of the finished product. However, due to the complexity of the material structure and the variability of the chemical reaction after mixing with lithium source, the existing technology does not analyze the thermal decomposition reaction mechanism of the precursor in the sintering process of high-nickel positive electrode materials, and the reaction process mechanism and research method of the precursor after mixing with lithium source are not clear, which is a technical problem to be solved at present. SUMMARY

[0005] The present application provides a method and system for researching the thermal decomposition mutation mechanism of a high-nickel positive electrode material precursor, which aims to solve the technical problem that the existing technology does not analyze the thermal decomposition reaction mechanism of the precursor in the sintering process of high-nickel positive electrode materials, and the reaction process mechanism and research method of the precursor after mixing with lithium source are not clear.

[0006] One aspect of the present application relates to a method for studying the thermal decomposition mutation mechanism of high-nickel positive electrode material precursor, comprising the following steps:

[0007] Based on the chemical reaction mechanism and expert knowledge, the micro-chemical reaction process of the high-nickel positive electrode material is subdivided;

[0008] According to the segmentation results, the reaction of the precursor element participating in the thermal decomposition reaction in the sintering process of the high-nickel positive electrode material is studied;

[0009] According to the decomposition reaction kinetics formula and the Arrhenius formula, the relationship between the particle number change in the reaction process is established;

[0010] According to the data and information of non-isothermal thermogravimetric experiment, differential scanning calorimetry thermal analysis experiment and X-ray diffraction experiment, the difference between the reaction process of the element and the mixed material is studied;

[0011] For the difference part, the research method of the corresponding difference part is proposed by combining experimental data and chemical mechanism, and the change relationship of this part under different heating rates is obtained, and the parameters in the function relationship obtained by this part are solved by using the corresponding parameter identification method.

[0012] Further, in the step of subdividing the micro-chemical reaction process of the high-nickel positive electrode material based on the chemical reaction mechanism and expert knowledge, for the complex high-nickel positive electrode material sintering process, the thermogravimetric data obtained by non-isothermal thermogravimetric experiment and the unit heat flow rate data obtained by differential scanning calorimetry thermal analysis experiment under a certain heating rate are combined with chemical mechanism and expert knowledge, and the thermal decomposition reaction process of the high-nickel positive electrode material is segmented.

[0013] Further, in the step of studying the reaction of the precursor element participating in the thermal decomposition reaction in the sintering process of the high-nickel positive electrode material according to the segmentation results, according to the previous research, the chemical properties of the precursor element before and after adding lithium source are obtained by using the experimental data of the thermal decomposition reaction of the precursor element alone and the experimental data of the thermal decomposition reaction of the precursor after adding lithium source LiOH·H2O.

[0014] Further, in the step of establishing the relationship between the particle number change in the reaction process according to the decomposition reaction kinetics formula and the Arrhenius formula, according to the chemical properties of the precursor element participating in the thermal decomposition reaction studied, the change rule of the particle number of the corresponding substance is calculated by using the Arrhenius formula and the decomposition reaction kinetics formula, and the kinetic equation representing the reaction rate of the decomposition reaction is expressed as:

[0015]

[0016] Wherein, is the characterization reaction rate of the decomposition reaction, f(α) is the differential form of the kinetic mechanism function determined by the reaction mechanism; k is the rate constant in the kinetic equation, which has a very close relationship with temperature, and is usually described by the Arrhenius law:

[0017]

[0018] wherein k is the rate constant, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; T is the thermodynamic temperature, and the kinetic equation is applicable to all elementary reactions and part of the reactions with more complex mechanisms in most gas-solid phase reactions. The commonly used kinetic equation is:

[0019]

[0020] The reaction rate α of a certain reaction at t time is defined as: t

[0021]

[0022] wherein α t is the reaction rate of a certain reaction at t time, is the particle number of reactant a at t time, is the particle number of reactant a at initial time t0; at this time, the reaction kinetics discretization model of the decomposition reaction is:

[0023]

[0024] wherein α t is the reaction rate of a certain reaction at t time, α t+1 is the reaction rate of a certain reaction at t+1 time, Δt is the change amount of time, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; T is the thermodynamic temperature, and then the change amount Δα t of the reaction rate of substance a in a discrete time step is:

[0025]

[0026] wherein Δα t is the change amount of the reaction rate of substance a, α t is the reaction rate of a certain reaction at t time, α t+1 is the reaction rate of a certain reaction at t+1 time, Δt is the change amount of time, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; T is the thermodynamic temperature;

[0027] The change amount of the particle number of reactant a at t time is obtained as:

[0028]

[0029] ​wherein, is the change amount of the particle number of the reactant a at time t, is the particle number of the reactant a at initial time t0; alpha t is the reaction rate of a certain reaction at time t, Delta t is the change amount of time, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; T is the thermodynamic temperature.

[0030] Further, research is conducted on the difference part, a research method of the corresponding difference part is proposed by combining experimental data and chemical mechanism, the change relationship of the part under different heating rates is obtained, and in the step of solving the parameters in the function relationship obtained by the part, by comparing the thermogravimetric data related to the precursor element and the mixed material, the difference of the thermal decomposition reaction of the high-nickel positive electrode material precursor before and after the addition of lithium source is found, under the condition of conforming to the mechanism, the mass decline rate equation of the side reaction of the intermediate substance generated in the thermal decomposition reaction of the precursor element is:

[0031]

[0032]

[0033] wherein, are respectively the reaction rates of the mixed material precursor dehydration to generate Ni8O 10 and NiO x , are respectively the pre-exponential factors of the mixed material precursor dehydration to generate Ni8O 10 and NiO x , E NiOx are respectively the reaction activation energies of the mixed material precursor dehydration to generate Ni8O 10 and NiO x .

[0034] Another aspect of the present application relates to a high-nickel positive electrode material precursor thermal decomposition mutation mechanism research system, comprising:

[0035] The subdivision module is used for subdividing the micro-chemical reaction process of the high-nickel positive electrode material based on chemical reaction mechanism and expert knowledge;

[0036] The first research module is used for researching the reaction of the precursor element participating in the thermal decomposition reaction in the sintering process of the high-nickel positive electrode material according to the segmentation result;

[0037] The establishment module is used for establishing the particle number change relationship in the reaction process according to the decomposition reaction kinetics formula and the Arrhenius formula;

[0038] The second research module is used for researching the difference between the reaction processes of single substances and mixed materials according to data and information of non-isothermal thermogravimetric experiments, differential scanning calorimetry thermal analysis experiments and X-ray diffraction experiments.

[0039] The calculation module is used for researching the difference, combining experimental data and chemical mechanisms, proposing a research method of the corresponding difference, obtaining the change relationship of the difference under different heating rates, and solving the parameters in the function relationship obtained by the difference by using a corresponding parameter identification method.

[0040] Further, in the subdivision module, for the sintering process of high-nickel positive electrode materials with complex and variable conditions, the thermogravimetric data obtained by non-isothermal thermogravimetric experiments and the unit heat flow rate data obtained by differential scanning calorimetry thermal analysis experiments under a certain heating rate are combined with chemical mechanisms and expert knowledge to segment the thermal decomposition reaction process of high-nickel positive electrode materials.

[0041] Further, in the first research module, according to the previous research, the chemical properties of the precursor single substance before and after adding lithium source LiOH·H2O are obtained by using the experimental data of the thermal decomposition reaction of the precursor single substance alone and the experimental data of the thermal decomposition reaction of the precursor after adding lithium source.

[0042] Further, in the establishment module, according to the chemical properties of the precursor single substance participating in the thermal decomposition reaction, combining experimental data, using the Arrhenius formula and the decomposition reaction kinetics formula, the change rule of the number of particles of the corresponding substance is calculated, and the kinetic equation representing the reaction rate of the decomposition reaction is expressed as:

[0043]

[0044] wherein, is the reaction rate of the decomposition reaction, f(α) is the differential form of the kinetic mechanism function determined by the reaction mechanism; k is the rate constant in the kinetic equation, which has a very close relationship with temperature, and is commonly described by the Arrhenius law:

[0045]

[0046] wherein, k is the rate constant, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; T is the thermodynamic temperature, and the kinetic equation is applicable to all elementary reactions and some reactions with complex mechanisms in most gas-solid phase reactions. The commonly used kinetic equation is:

[0047]

[0048] The reaction rate α of a certain reaction at time t is defined as: t

[0049] ​

[0050] wherein, α t is the reaction rate of a certain reaction at time t, is the particle number of reactant a at time t, is the particle number of reactant a at initial time t0; at this time, the reaction kinetics discretization model of the decomposition reaction is:

[0051]

[0052] wherein, α t is the reaction rate of a certain reaction at time t, t+1 is the reaction rate of a certain reaction at time t+1, Δt is the change of time, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; T is the thermodynamic temperature; then the change Δα t of the reaction rate of substance a in a discrete time step is:

[0053]

[0054] wherein, Δα t is the change of the reaction rate of substance a, α t is the reaction rate of a certain reaction at time t, t+1 is the reaction rate of a certain reaction at time t+1, Δt is the change of time, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; T is the thermodynamic temperature;

[0055] The change of the particle number of reactant a at time t is obtained as:

[0056]

[0057] wherein, is the change of the particle number of reactant a at time t, is the particle number of reactant a at initial time t0; α t is the reaction rate of a certain reaction at time t, Δt is the change of time, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; T is the thermodynamic temperature.

[0058] Further, in the calculation module (50), by comparing the thermogravimetric data related to the precursor element and the mixed material, the difference of the thermal decomposition reaction of the high-nickel positive electrode material precursor before and after the addition of lithium source is found, and under the condition of meeting the mechanism, the mass decline rate equation of the side reaction of the intermediate substance generated in the thermal decomposition reaction of the precursor element is:

[0059]

[0060]

[0061] wherein, respectively are the reaction rates of the mixed material precursor to generate Ni8O 10 , NiO x , respectively are the reaction pre-exponential factors of the mixed material precursor to generate Ni8O 10 , NiO x , E NiOx respectively are the reaction activation energies of the mixed material precursor to generate Ni8O 10 , NiO x .

[0062] The present application has the following beneficial effects:

[0063] The present application provides a high-nickel positive electrode material precursor thermal decomposition mutation mechanism research method and system, which subdivides the micro-chemical reaction process of the high-nickel positive electrode material based on chemical reaction mechanism and expert knowledge; studies the reaction of the precursor element participating in the thermal decomposition reaction in the sintering process of the high-nickel positive electrode material according to the segmentation result; establishes the particle number change relationship in the reaction process according to the decomposition reaction kinetics formula and the Arrhenius formula; studies the difference between the reaction processes of the elements and the mixed material according to the data and information of the non-isothermal thermogravimetric experiment, the differential scanning calorimetry thermal analysis experiment, and the X-ray diffraction experiment; studies the difference part, combines the experimental data and the chemical mechanism, proposes a research method for the corresponding difference part, obtains the change relationship of this part under different heating rates, and simultaneously uses the corresponding parameter identification method to solve the parameters in the function relationship obtained by this part. The high-nickel positive electrode material precursor thermal decomposition mutation mechanism research method and system provided by the present application creatively analyzes the high-nickel positive electrode material precursor thermal decomposition reaction part, not only studies the precursor element, but also effectively solves the problem of the thermal decomposition dehydration mechanism mutation of the mixed material; at the same time, the change law of the high-nickel positive electrode material precursor thermal decomposition process is obtained, which provides micro-guidance for subsequent research on the micro-chemical reaction process of the high-nickel positive electrode material and macro-research, and provides a basis for improving the electrochemical performance of the finished product. BRIEF DESCRIPTION OF DRAWINGS

[0064] Figure 1 FIG. 1 is a flowchart of an embodiment of the high-nickel positive electrode material precursor thermal decomposition mutation mechanism research method provided by the present application;

[0065] Figure 2 FIG. 2 is a functional block diagram of an embodiment of the high-nickel positive electrode material precursor thermal decomposition mutation mechanism research system provided by the present application;

[0066] Figure 3 FIG. 3 is a chemical reaction segmentation diagram of the high-nickel positive electrode material under a certain heating rate provided by the present application;

[0067] Figure 4 The thermal weight change of the precursor monomer thermal decomposition process provided by the present application and the thermal decomposition process schematic diagram of the mixture.

[0068] BRIEF DESCRIPTION OF DRAWINGS

[0069] 10, subdivision module; 20, first research module; 30, establishment module; 40, second research module; 50, calculation module. DETAILED DESCRIPTION

[0070] In order to better understand the above technical solutions, the above technical solutions will be described in detail in combination with the drawings of the specification and specific embodiments.

[0071] As Figure 1 shown, the first embodiment of the present application proposes a high-nickel positive electrode material precursor thermal decomposition mutation mechanism research method, including the following steps:

[0072] Step S100, based on chemical reaction mechanism and expert knowledge, the micro-chemical reaction process of high-nickel positive electrode material is subdivided.

[0073] The experimental samples used in this embodiment are all from 811 type high-nickel positive electrode material precursor and lithium source LiOH·H2O of a lithium ion battery ternary positive electrode material production enterprise, and the experimental data come from non-isothermal thermogravimetric experiment, differential scanning calorimetry thermal analysis experiment and X-ray diffraction experiment under different heating rates using the precursor and lithium source.

[0074] For the complex high-nickel positive electrode material sintering process, the thermogravimetric data obtained by non-isothermal thermogravimetric experiment under a certain heating rate and the unit heat flow rate data obtained by differential scanning calorimetry thermal analysis experiment are combined with chemical mechanism and expert knowledge, and the high-nickel positive electrode material thermal decomposition reaction process is segmented, as Figure 3 shown.

[0075] ① LiOH·H2O thermal decomposition process

[0076] In the kiln, LiOH·H2O occurs two-stage decomposition reaction, which is LiOH·H2O de-crystallization water to generate LiOH, which occurs at 40-60℃; LiOH decomposition to generate Li2O, which occurs at 460-470℃:

[0077] 2LiOH·H2O→2LiOH+2H2O(1)

[0078] 2LiOH (s) →Li2O (s) +H2O (g) (2)

[0079] ② Precursor thermal decomposition process

[0080] The precursor is a high-nickel material. By comparing the thermogravimetric curves of the precursor and Ni(OH)2, it can be seen that they have similar thermal kinetic properties. Therefore, the hydroxides of cobalt and manganese are used as auxiliary means for research, mainly focusing on the properties of Ni(OH)2. The thermal decomposition of Ni(OH)2 mainly occurs at about 210-800℃:

[0081] Ni(OH)2→ NiO + H2O (3)

[0082] Ni(OH)2+ OH - → NiOOH + H2O (4)

[0083] Step S200, research on the reaction of the precursor element involved in the thermal decomposition reaction in the sintering process of the high-nickel positive electrode material according to the segmentation result.

[0084] According to the previous research, the chemical properties of the precursor element before and after adding lithium source LiOH·H2O are obtained based on the experimental data of the thermal decomposition reaction of the precursor element alone and the experimental data of the thermal decomposition reaction of the precursor after adding lithium source (hereinafter referred to as mixed material).

[0085] Among them, the precursor is a high-nickel material. By comparing the thermogravimetric curves of the precursor and Ni(OH)2, it can be seen that they have similar thermal kinetic properties. Therefore, the hydroxides of cobalt and manganese are used as auxiliary means for research, mainly focusing on the properties of Ni(OH)2. Taking the thermal decomposition at a certain heating rate as an example, the curve is divided into three sections according to the mechanism.

[0086] The precursor is a high-nickel material. By comparing the thermogravimetric curves of the precursor and Ni(OH)2, it can be seen that they have similar thermal kinetic properties. Therefore, the hydroxides of cobalt and manganese are used as auxiliary means for research, mainly focusing on the properties of Ni(OH)2. Regarding the research on Ni(OH)2, in the curve as shown in the figure, the curve is divided into three sections according to the mechanism.

[0087] The first stage (0-217.8℃) is a stage of slight mass decrease, mainly due to two reasons: one is the instrument data offset at room temperature, and the other is the desorption of free water on the surface. The mass decreases by 1.95%.

[0088] The second stage (217.8-261.8℃) is a stage of significant mass decrease because the nickel hydroxide dehydroxylates into nickel oxide as the temperature rises. The mass decreases by 15.77%.

[0089] Ni(OH) 2(s) = NiO (s) + H2O (g) (5)

[0090] The mechanism of the third stage (261.8-801.7℃) of slow mass decrease is not clear, and the same as the precursor, the mutation of topological chemical mechanism occurs, thus it can be seen that the mutation of precursor properties is caused by high nickel. By consulting the data, the reason of the mutation of chemical mechanism is the complete dehydrogenation reaction caused by steric hindrance, that is, the slow mass decrease rate caused by the fact that the spatial distance of hydroxyl groups is far away and the water molecules produced are difficult to diffuse out of the particle interior in the later stage of dehydration. At the same time, the byproduct NiOOH also has a certain influence on the mass change of the decomposition reaction, and the mass decreases by 4.11% in this stage.

[0091] Ni(OH) 2(s) +OH - =NiOOH (s) +H2O (g) (6)

[0092] In formula (6), after the precursor element adds lithium source, the dehydration rate and the mass decrease amplitude of the mixed material thermal decomposition process are changed due to the influence of lithium atoms.

[0093] Step S300, according to the decomposition reaction kinetics formula and the Arrhenius formula, the relationship between the particle number change in the reaction process is established.

[0094] The chemical properties of the precursor element participating in the thermal decomposition reaction are studied, combined with experimental data, the Arrhenius formula and the decomposition reaction kinetics formula are used to calculate the corresponding particle number change rule.

[0095] The kinetic equation for characterizing the reaction rate of the decomposition reaction can be expressed as:

[0096]

[0097] In formula (7), f(α) is the differential form of the kinetic mechanism function determined by the reaction mechanism; k is the rate constant in the kinetic equation, which has a very close relationship with temperature, and is usually described by the Arrhenius law:

[0098]

[0099] In formula (8), A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; T is the thermodynamic temperature. This kinetic equation is suitable for all elementary reactions and some reactions with more complex mechanisms in most gas-solid phase reactions, and the commonly used kinetic equation is:

[0100]

[0101] The reaction rate α of a certain reaction at a certain time t is defined as: t :

[0102]

[0103] In formula (10), is the particle number of the reactant a at the initial time t0; at this time, the reaction kinetics discretization model of the decomposition reaction is:

[0104]

[0105] Then, in a discrete time step, the change amount Δa of the reaction rate of the substance a t is:

[0106]

[0107] The change amount of the particle number of the reactant a at time t can be obtained as:

[0108]

[0109] Step S400, according to the data and information of the non-isothermal thermogravimetric experiment, the differential scanning calorimetry thermal analysis experiment, and the X-ray diffraction experiment, the difference between the reaction processes of the single element and the mixed material is studied.

[0110] The study of the chemical property change of the precursor single element before and after adding lithium source, due to the similarity between the reaction of the single element and the mixed material, the chemical property of the mixed material is studied according to the similarity.

[0111] Step S500, for the difference part, combining the experimental data and the chemical mechanism, the research method of the corresponding difference part is proposed, the change relationship of this part under different heating rates is obtained, and the corresponding parameter identification method is used to solve the parameters in the function relationship obtained by this part.

[0112] By comparing the thermogravimetric data of the precursor single element and the mixed material, the difference of the thermal decomposition reaction of the high-nickel positive electrode material precursor before and after adding lithium source is found.

[0113] For the thermal decomposition mutation mechanism of the precursor, the thermogravimetric change of the thermal decomposition process of the precursor single element is compared with the thermogravimetric change of the thermal decomposition process of the precursor in the mixed material, as shown in Figure 4 Through comparative study, it is found that in the comparison of the thermal decomposition of the precursor in the mixed material and the thermal decomposition of the precursor single element, the thermal decomposition mechanism of the precursor in the mixed material mutates, and there is a certain difference in the dehydration rate and the mass range. Through chemical mechanism and expert knowledge analysis, it is deduced that the existence of lithium source will affect the thermal decomposition of the precursor, resulting in the generation of intermediate products in the thermal decomposition process, which offsets the reduced mass, resulting in mass reduction. Combined with the X-ray diffraction spectrum analysis, it is judged that the thermal decomposition process of the mixed material precursor produces nickel oxide, and its reaction formula is shown in formula (17):

[0114]

[0115] In formula (14), the precursor thermal decomposition mutation mechanism under the influence of multiple reactions is proposed. According to the Arrhenius formula, the rate constant of the related reaction is calculated as shown in formula (18):

[0116]

[0117] In formula (15), k is the rate constant, R is the molar gas constant, T is the thermodynamic temperature, E is the reaction activation energy, and A is the pre-exponential factor.

[0118] Under the condition of conforming to the mechanism, the mass loss rate equation of the side reaction of the intermediate substance generated in the thermal decomposition reaction of the precursor single element is:

[0119]

[0120]

[0121] In formula (16) and (17), are the reaction rates of the mixed precursor dehydration to generate Ni8O 10 , NiO x , respectively, are the reaction pre-exponential factors of the mixed precursor dehydration to generate Ni8O 10 , NiO x , respectively, E NiOx are the reaction activation energies of the mixed precursor dehydration to generate Ni8O 10 , NiO x , respectively.

[0122] Based on the mass loss rate equations shown in formula (16) and (17), the particle number change rule in the side reaction process is obtained, and the side reaction particle number change rule is added to the precursor thermal decomposition main reaction model according to a certain proportion to solve the precursor thermal decomposition mechanism mutation problem in the mixed material. The particle number change relationship of the precursor thermal decomposition in the mixed material is shown in formula (18).

[0123]

[0124] In formula (18), is the particle number of the mixed precursor dehydration at time t+1, is the particle number of the mixed precursor dehydration product at time t, and p1, p2, p3 are the proportion of the mixed precursor dehydration product.

[0125] The least square estimation method is used to solve the parameters in the particle number change relation of the precursor thermal decomposition in the mixture shown in formula (18).

[0126] It is assumed that the change rule of the reaction occurrence proportions p1, p2 and p3 and the temperature rise rate is shown in formula (19):

[0127]

[0128] In formula (19), p1 is the proportion of the precursor dehydration of the mixture to generate Ni(OH)2, p2 is the proportion of the precursor dehydration of the mixture to generate NiOOH, p3 is the proportion of the precursor dehydration of the mixture to generate Ni8O 10 , θ1, θ2, θ3, is a parameter to be identified, and β is the temperature rise rate.

[0129] Let Then the above formula can be written as: P=Θ·β

[0130] According to the least square estimation, the matrix representation of the target loss function is shown in formula (20):

[0131]

[0132] In formula (20), J(Θ) is the matrix of the target loss function, P=Θ·β, is an estimated proportion matrix, T is the transpose of the matrix, p1 is the proportion of the precursor dehydration of the mixture to generate Ni(OH)2, p2 is the proportion of the precursor dehydration of the mixture to generate NiOOH, and p3 is the proportion of the precursor dehydration of the mixture to generate Ni8O 10 .

[0133] Formula (20) can be expanded to formula (21):

[0134] J(Θ)=Θ T β T β Θ-Θ T β T P-P T β Θ+P T P (21)

[0135] In formula (21), J(Θ) is the matrix of the target loss function, T is the transpose of the matrix, and P=Θ·β.

[0136] The partial derivative of the parameter Θ is taken and set to 0 to obtain formula (22):

[0137]

[0138] In formula (22), p1 is the proportion of the mixture precursor dehydrated to generate Ni(OH)2, p2 is the proportion of the mixture precursor dehydrated to generate NiOOH, and p3 is the proportion of the mixture precursor dehydrated to generate Ni8O7. is the partial derivative of the target loss function, T is the transpose of the matrix, and P = Θ·β.

[0139] Substituting the actual data into the closed-form solution of the parameter Θ above, the change law expression of the occurrence proportions p1, p2, and p3 and the heating rate can be obtained, as shown in formula (23):

[0140]

[0141] In formula (23), p1 is the proportion of the mixture precursor dehydrated to generate Ni(OH)2, p2 is the proportion of the mixture precursor dehydrated to generate NiOOH, and p3 is the proportion of the mixture precursor dehydrated to generate Ni8O7. 10 , and β is the heating rate.

[0142] The high-nickel positive electrode material precursor thermal decomposition mutation mechanism research method provided in the embodiment analyzes the high-nickel positive electrode material precursor thermal decomposition reaction part creatively, not only studies the precursor simple substance, but also effectively solves the problem of mixed material thermal decomposition dehydration mechanism mutation, and proposes a corresponding parameter identification method to identify the function relationship, which provides an effective reference for the complex and variable precursor thermal decomposition process research. The existing technology does not segmentally analyze the high-nickel positive electrode material precursor thermal decomposition reaction, and there is no clear explanation of the chemical mechanism of the precursor thermal decomposition process. The embodiment clearly segments the high-nickel positive electrode material thermal decomposition reaction, and conducts a detailed study on the mixed material precursor thermal decomposition process. Combined with the experimental data, the main and auxiliary reactions occurring in the thermal decomposition process are clearly understood, the corresponding thermal kinetics equation is established, and the different proportions of the main and auxiliary reactions under different heating rates are determined, which lays a foundation for subsequent establishment of the high-nickel positive electrode material precursor thermal decomposition model, analysis of the phase change of the material, and further analysis of the whole high-nickel positive electrode material micro-chemical reaction process.

[0143] As shown in formula (23), the proportions of the mixture precursor dehydrated to generate Ni(OH)2, NiOOH, and Ni8O7 are p1, p2, and p3, respectively, and the heating rate is β. Figure 2 Figure 2 ​A functional block diagram of one embodiment of the high-nickel positive electrode material precursor thermal decomposition mutation mechanism research system provided by the application, in this embodiment, the high-nickel positive electrode material precursor thermal decomposition mutation mechanism research system includes a subdivision module 10, a first research module 20, an establishment module 30, a second research module 40 and a calculation module 50, wherein the subdivision module 10 is used for subdividing the micro-chemical reaction process of the high-nickel positive electrode material based on the chemical reaction mechanism and expert knowledge; the first research module 20 is used for researching the reaction of the precursor element participating in the thermal decomposition reaction in the sintering process of the high-nickel positive electrode material according to the segmentation result; the establishment module 30 is used for establishing the particle number change relationship in the reaction process according to the decomposition reaction kinetics formula and the Arrhenius formula; the second research module 40 is used for researching the difference between the element and the mixed material reaction process according to the data and information of the non-isothermal thermogravimetric experiment, the differential scanning calorimetry thermal analysis experiment and the X-ray diffraction experiment; and the calculation module 50 is used for researching the difference part, combining the experimental data and the chemical mechanism, proposing a research method for the corresponding difference part, obtaining the change relationship of the part under different heating rates, and simultaneously using the corresponding parameter identification method to solve the parameters in the function relationship obtained by the part.

[0144] In the subdivision module 10, for the complex high-nickel positive electrode material sintering process, the thermogravimetric data obtained by the non-isothermal thermogravimetric experiment and the unit heat flow rate data obtained by the differential scanning calorimetry thermal analysis experiment under a certain heating rate are combined with the chemical mechanism and expert knowledge to segment the thermal decomposition reaction process of the high-nickel positive electrode material.

[0145] In the first research module 20, according to the previous research, the chemical properties of the precursor element before and after the addition of lithium source are obtained by using the experimental data of the thermal decomposition reaction of the precursor element alone and the experimental data of the thermal decomposition reaction of the precursor after the addition of lithium source LiOH·H2O.

[0146] In the establishment module 30, according to the chemical properties of the precursor element participating in the thermal decomposition reaction, the change rule of the particle number of the corresponding substance is calculated by using the Arrhenius formula and the decomposition reaction kinetics formula in combination with the experimental data, and the kinetic equation representing the reaction rate of the decomposition reaction is expressed as:

[0147]

[0148] In formula (24), is the decomposition reaction rate, f(α) is the differential form of the kinetic mechanism function determined by the reaction mechanism; k is the rate constant in the kinetic equation, which has a very close relationship with temperature, and is usually described by the Arrhenius law:

[0149]

[0150] In formula (25), k is the rate constant, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; and T is the thermodynamic temperature. The kinetic equation is applicable to all elementary reactions and some reactions with complex mechanisms in most gas-solid phase reactions. The commonly used kinetic equation is:

[0151]

[0152] The reaction rate a of a certain reaction at time t is defined as: t

[0153]

[0154] In formula (27), a is the reaction rate of a certain reaction at time t, t is the particle number of reactant a at time t, is the particle number of reactant a at initial time t0; and the reaction kinetics discretization model of the decomposition reaction at this time is:

[0155]

[0156] In formula (28), a is the reaction rate of a certain reaction at time t, t t+1 is the reaction rate of a certain reaction at time t+1, and At is the change in time. A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; and T is the thermodynamic temperature. Then, the change amount of the reaction rate of substance a in a discrete time step is: t

[0157]

[0158] In formula (29), a is the change amount of the reaction rate of substance a, t t t+1 is the reaction rate of a certain reaction at time t+1, and At is the change in time. A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; and T is the thermodynamic temperature.

[0159] The change amount of the particle number of reactant a at time t is obtained as:

[0160]

[0161] In formula (30), is the change amount of the particle number of reactant a at time t, t ​​​​​​​wherein k is the reaction rate of a certain reaction at time t, At is the change of time, A is the pre-exponential factor, E is the activation energy, R is the molar gas constant, and T is the thermodynamic temperature.

[0162] In the second research module 40, the research on the change of chemical properties of the precursor element before and after the addition of the lithium source, due to the similarity between the reaction of the element and the mixture, the chemical properties of the mixture are researched according to the similarity.

[0163] In the calculation module 50, by comparing the related thermogravimetric data of the precursor element and the mixture, the difference of the thermal decomposition reaction of the high-nickel positive electrode material precursor before and after the addition of the lithium source is found, and under the condition of conforming to the mechanism, the mass decline rate equation of the side reaction of the intermediate substance generated in the thermal decomposition reaction of the precursor element is:

[0164]

[0165]

[0166] In formulas (31) and (32), are the reaction rates of the dehydration reactions of the mixture precursor to generate Ni8O 10 and NiO x respectively, are the pre-exponential factors of the dehydration reactions of the mixture precursor to generate Ni8O 10 and NiO x respectively, E NiOx are the reaction activation energies of the dehydration reactions of the mixture precursor to generate Ni8O 10 and NiO x respectively.

[0167] The high-nickel positive electrode material precursor thermal decomposition mutation mechanism research system provided in the embodiment creatively analyzes the thermal decomposition reaction of the high-nickel positive electrode material precursor, not only studies the precursor element, but also effectively solves the problem of the mutation of the dehydration mechanism of the mixture thermal decomposition, and proposes a corresponding parameter identification method to identify the parameters of the obtained function relationship, which provides an effective reference for the research on the complex and variable precursor thermal decomposition process. In the prior art, there is no segmented analysis of the thermal decomposition reaction of the high-nickel positive electrode material precursor, and there is no clear explanation of the chemical mechanism of the precursor thermal decomposition process. The embodiment clearly divides the thermal decomposition reaction of the high-nickel positive electrode material, and conducts a detailed research on the thermal decomposition process of the mixture precursor. Combined with the experimental data, the main and side reactions occurring in the thermal decomposition process are clearly understood, the corresponding thermokinetic equation is established, and the different proportions of the main and side reactions under different heating rates are determined, which lays a foundation for subsequent establishment of the thermal decomposition model of the high-nickel positive electrode material precursor, analysis of the phase change of the material, and further analysis of the whole high-nickel positive electrode material micro-chemical reaction process.

[0168] While preferred embodiments of the application have been described, those skilled in the art will appreciate that other modifications and variations to the preferred embodiments are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the application, modifications and variations of the preferred embodiments can be practiced by those of ordinary skill. Similarly, any one or more features of one embodiment can be combined with any one or more features of another embodiment, or with any one or more features of the application. Also, it should be understood that the term "application" as used herein covers all modifications and variations of the preferred embodiments and includes all the features and combinations thereof.

Claims

1.A method for studying thermal decomposition mutation mechanism of a high-nickel positive electrode material precursor, characterized in that, The method comprises the following steps: The micro-chemical reaction process of the high-nickel positive electrode material is subdivided based on chemical reaction mechanism and expert knowledge; The reaction of the precursor element participating in the thermal decomposition reaction in the sintering process of the high-nickel positive electrode material is researched according to the subdivision result; The particle number change relationship in the reaction process is established according to the decomposition reaction kinetics formula and the Arrhenius formula; The difference between the reaction process of the element and the mixed material is researched according to the data and information of the non-isothermal thermogravimetric experiment, the differential scanning calorimetry thermal analysis experiment and the X-ray diffraction experiment; The research method of the corresponding difference part is proposed by combining the experimental data and the chemical mechanism, the change relationship of the part under different heating rates is obtained, and the parameters in the function relationship obtained by the part are solved by using the corresponding parameter identification method. 2.The method for studying thermal decomposition mutation mechanism of high-nickel cathode material precursor according to claim 1, wherein, In the step of subdividing the micro-chemical reaction process of the high-nickel positive electrode material based on chemical reaction mechanism and expert knowledge, the thermal gravimetric data obtained by the non-isothermal thermogravimetric experiment and the unit heat flow rate data obtained by the differential scanning calorimetry thermal analysis experiment under a certain heating rate are used, and the chemical mechanism and expert knowledge are combined to subdivide the thermal decomposition reaction process of the high-nickel positive electrode material. 3.The method of claim 1, wherein the high-nickel positive electrode material precursor thermal decomposition mutation mechanism research method is characterized by, In the step of researching the reaction of the precursor element participating in the thermal decomposition reaction in the sintering process of the high-nickel positive electrode material according to the subdivision result, the chemical properties of the precursor element before and after adding the lithium source are obtained according to the experimental data of the thermal decomposition reaction of the precursor element alone and the experimental data of the thermal decomposition reaction of the precursor after adding the lithium source LiOH·H2O. 4.The method for studying thermal decomposition mutation mechanism of high-nickel cathode material precursor according to claim 3, wherein, In the step of establishing the particle number change relationship in the reaction process according to the decomposition reaction kinetics formula and the Arrhenius formula, the particle number change rule of the corresponding substance is calculated by using the Arrhenius formula and the decomposition reaction kinetics formula according to the chemical properties of the precursor element participating in the thermal decomposition reaction and combining the experimental data, and the kinetic equation representing the reaction rate of the decomposition reaction is expressed as: wherein is the characteristic reaction rate of the decomposition reaction, f(a) is the differential form of the kinetic mechanism function determined by the reaction mechanism; k is the rate constant in the kinetic equation, which has a very close relationship with temperature, which is usually described by the Arrhenius law: Wherein, k is the rate constant, A is the pre-exponential factor, E is the activation energy, R is the molar gas constant, and T is the thermodynamic temperature; The kinetic equation is applicable to all elementary reactions and part of reactions with complex mechanism in most gas-solid phase reactions, and the commonly used kinetic equation is: wherein is the rate of the decomposition reaction, f(a) is the differential form of the kinetic mechanism function determined by the reaction mechanism; A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; and T is the thermodynamic temperature; The reaction rate α of a certain reaction at time t is defined as: t is: wherein α t is the reaction rate of a certain reaction at time t, is the particle number of reactant a at time t, is the particle number of reactant a at initial time t0; at this time, the reaction kinetics discretization model of the decomposition reaction is: wherein, α t is the reaction rate of a certain reaction at time t, α t+1 is the reaction rate of a certain reaction at time t+1, Δt is the change in time, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; and T is the thermodynamic temperature; Then the change in the reaction rate of species a, Δa, over a discrete time step, Δt, is given by: t Δa = -k a a2+ k b a b2- k c a b2 where Δα t is the change in the reaction rate of the substance a, α t is the reaction rate of a certain reaction at time t, α t+1 is the reaction rate of a certain reaction at time t+1, Δt is the change in time, A is the pre-exponential factor, E is the activation energy, R is the molar gas constant, and T is the thermodynamic temperature. The change amount of the particle number of the reactant a at time t is obtained as: wherein, is the amount of change in the number of particles of the reactant a at time t, is the number of particles of the reactant a at the initial time t0; α t is the reaction rate of a certain reaction at time t, Δt is the amount of change in time, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; and T is the thermodynamic temperature. 5.The method for studying thermal decomposition mutation mechanism of high-nickel cathode material precursor according to claim 1, wherein, In the step of researching the difference part, combining the experimental data and the chemical mechanism, proposing the research method of the corresponding difference part, obtaining the change relationship of the part under different heating rates, and solving the parameters in the function relationship obtained by the part by using the corresponding parameter identification method, the difference between the thermal decomposition reaction of the precursor of the high-nickel positive electrode material before and after adding the lithium source is found by comparing the related thermal gravimetric data of the precursor element and the mixed material, and under the condition of conforming to the mechanism, the mass decrease rate equation of the side reaction of the intermediate substance generated in the thermal decomposition reaction of the precursor element is: wherein, respectively, are the reaction rates of the mixed precursor to produce Ni8O 10 , NiO x , respectively, are the reaction rates of the mixed precursor to produce Ni8O 10 , NiO x , E NiOx respectively, are the reaction activation energies of the mixed precursor to produce Ni8O 10 , NiO x . 6.A system for researching thermal decomposition mutation mechanism of a high-nickel positive electrode material precursor, characterized in that, The method comprises the following steps: A subdivision module (10) is configured to subdivide the micro-chemical reaction process of the high-nickel positive electrode material based on chemical reaction mechanism and expert knowledge; The first research module (20) is used for researching the reaction of the precursor element participating in the thermal decomposition reaction in the sintering process of the high-nickel positive electrode material according to the segmentation result; The establishing module (30) is used for establishing the particle number change relationship in the reaction process according to the decomposition reaction kinetics formula and the Arrhenius formula; The second research module (40) is used for researching the difference between the element and the mixed material reaction process according to the data and information of the non-isothermal thermogravimetric experiment, the differential scanning calorimetry thermal analysis experiment and the X-ray diffraction experiment; The calculating module (50) is used for researching the difference part, combining the experimental data and the chemical mechanism, proposing the research method of the corresponding difference part, obtaining the change relationship of the part under different heating rates, and simultaneously using the corresponding parameter identification method to solve the parameters in the function relationship obtained by the part. 7.The system for researching thermal decomposition mutation mechanism of high-nickel cathode material precursor according to claim 6, wherein, In the subdivision module (10), for the sintering process of the high-nickel positive electrode material with complex and changeable conditions, the thermogravimetric data obtained by the non-isothermal thermogravimetric experiment and the unit heat flow rate data obtained by the differential scanning calorimetry thermal analysis experiment under a certain heating rate are combined with the chemical mechanism and expert knowledge to segment the thermal decomposition reaction process of the high-nickel positive electrode material. 8.The system for researching thermal decomposition mutation mechanism of high-nickel cathode material precursor according to claim 6, wherein, In the first research module (20), according to the previous research, the chemical properties of the precursor element before and after adding lithium source are obtained by using the experimental data of the thermal decomposition reaction of the precursor element alone and the experimental data of the thermal decomposition reaction of the precursor after adding lithium source LiOH·H2O. 9.The system for researching thermal decomposition mutation mechanism of high-nickel cathode material precursor according to claim 8, wherein, In the establishing module (30), according to the chemical properties of the precursor element participating in the thermal decomposition reaction, the change rule of the particle number of the corresponding substance is calculated by using the Arrhenius formula and the decomposition reaction kinetics formula combined with the experimental data, and the kinetic equation representing the reaction rate of the decomposition reaction is expressed as: wherein is the characteristic reaction rate of the decomposition reaction, f(a) is the differential form of the kinetic mechanism function determined by the reaction mechanism; k is the rate constant in the kinetic equation, which has a very close relationship with temperature, which is usually described by the Arrhenius law: Wherein, k is the rate constant, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; T is the thermodynamic temperature; The kinetic equation is suitable for all elementary reactions in most gas-solid phase reactions and part of reactions with complex mechanism, and the commonly used kinetic equation is: wherein is the rate of the decomposition reaction, f(a) is the differential form of the kinetic mechanism function determined by the reaction mechanism; A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; and T is the thermodynamic temperature; The reaction rate α of a certain reaction at time t is defined as: t is: wherein α t is the reaction rate of a certain reaction at time t, is the particle number of reactant a at time t, is the particle number of reactant a at initial time t0; at this time, the reaction kinetics discretization model of the decomposition reaction is: wherein α t is the reaction rate of a certain reaction at time t, α t+1 is the reaction rate of a certain reaction at time t+1, Δt is the change in time, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; and T is the thermodynamic temperature; Then the change in the reaction rate of species a, Δa, over a discrete time step, Δt, is: t Δa = -kabΔt where Δα t is the change in the reaction rate of substance a, α t is the reaction rate of a certain reaction at time t, α t+1 is the reaction rate of a certain reaction at time t+1, Δt is the change in time, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; and T is the thermodynamic temperature. The change amount of the particle number of the reactant a at time t is obtained as: wherein, is the amount of change in the number of particles of the reactant a at time t, is the number of particles of the reactant a at the initial time t0; α t is the reaction rate of a certain reaction at time t, Δt is the amount of change in time, A is the pre-exponential factor; E is the activation energy; R is the molar gas constant; and T is the thermodynamic temperature. 10.The system for researching thermal decomposition mutation mechanism of high-nickel cathode material precursor according to claim 6, wherein, In the calculating module (50), by comparing the thermogravimetric data of the precursor element and the mixed material, the difference of the thermal decomposition reaction of the high-nickel positive electrode material precursor before and after adding lithium source is found, and under the condition of conforming to the mechanism, the mass decline rate equation of the side reaction of the intermediate substance generated in the thermal decomposition reaction of the precursor element is wherein, are the reaction rates of the dehydration of the mixture precursor to form Ni8O 10 , NiO x , respectively, are the reaction pre-exponential factors of the dehydration of the mixture precursor to form Ni8O 10 , NiO x , respectively, E NiOx are the reaction activation energies of the dehydration of the mixture precursor to form Ni8O 10 , NiO x , respectively.

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