A method and system for evaluating the effect of doping modification on layered oxide positive electrode materials

Abstract

The present invention relates to a method and system for evaluating the effect of doping and modifying layered oxide positive electrode materials, and belongs to the technical field of battery materials. The method of the present invention for evaluating the effect of doping and modifying layered oxide positive electrode materials establishes and optimizes a unit cell model and a surface model of the layered oxide positive electrode material, then dopes a target doping element into different sites, and determines the thermodynamically stable sites of the doping element after comparing the formation energies. This method can fully consider the doping effect corresponding to each site, avoid omissions, and improve the accuracy of the results. Finally, based on the unit cell parameter data and thermodynamic data of the stable unit cell model and the target structure model, the influence relationship of the target doping element on the electrochemical properties of the target layered oxide positive electrode material is determined. Then, based on the influence relationship and actual needs, the target doping element is evaluated, which can effectively improve the evaluation efficiency of the doping modification of the doping element and provide relatively accurate evaluation results.

Description

Technical Field

[0001] The invention relates to a method and system for evaluating the effect of doping and modification of layered oxide positive electrode materials, belonging to the technical field of battery materials. Background Art

[0002] Advanced battery technology will be a hot topic of cutting-edge competition worldwide over the next decade. Lithium- and sodium-ion batteries, with their advantages of high voltage, high specific capacity, long charge-discharge life, and wide operating temperature range, have become the preferred choice for many mobile electronics, electric vehicles, and wind and photovoltaic energy storage. Therefore, the rapid development of high-performance battery materials with high energy density, excellent safety, and fast charge and discharge speeds is essential.

[0003] As an important component of lithium / sodium ion batteries, cathode materials have a significant impact on the performance of lithium / sodium ion batteries. x MO2 (Y = Li and / or Na, M = Ni, Fe, Mn, Mg, Zn, B, Cr, Ti, Mo, V, Al, W, Ca, etc.) has attracted widespread attention due to its advantages of simple synthesis, diverse composition, high theoretical specific capacity, and reliable electrochemical performance. However, the trial-and-error method for selecting doping elements is expensive and time-consuming, resulting in high R&D costs and low R&D efficiency.

[0004] With the improvement of theoretical research and the improvement of computer performance, material screening technology with calculation as the core can be applied to the field of material research and development, providing reliable theoretical guidance for experiments, greatly shortening the research and development cycle, and reducing research and development costs. Among them, determining the structure and basic properties of known materials through first-principles calculations and achieving precise control at the atomic level is a powerful tool for solving experimental theoretical problems and predicting the structural properties of new materials at this stage, and can provide effective theoretical guidance for the preparation and modification of materials. For example, Chinese patent document CN106096279A discloses a method for predicting the performance of rare-earth-doped modified titanium-based tin dioxide electrodes. This method is based on the density functional theory of first principles and predicts the modified performance by calculating the changes in the crystal structure parameters of tin dioxide before and after rare-earth doping. Chinese patent document CN110046445A discloses a method for predicting the photoelectric properties of Sr-, Ba-, La-, and Er-doped c-ZrO2 under high pressure. First, a ZrO2 experimental sample is crushed into a powder of 1 to 10,000 nm, and then diffraction lines are obtained using X-ray powder diffraction. The diffraction lines are refined and analyzed to obtain the original data of the unit cell, and a rough model is established. Then, a stable crystal model is constructed through first-principles calculations, and its band structure, partial-wave density of states, and optical properties are calculated under different pressures. The structural stability, electronic excitation and transition characteristics, color rendering, and stimulated luminescence properties of the material under high pressure can be predicted from the obtained data or spectra.Chinese patent document CN107273559A discloses a method for designing and modifying electrode materials for battery devices, the method including a hybrid model combining an atomic-level model and a battery-level model, and including the following steps: 1) constructing an atomic-level model for the basic structure of the electrode material with respect to its composition and lattice structure based on first-principles density functional theory (DFT) or molecular dynamics; 2) calculating a series of parameters selected from the group consisting of the following parameters: at least one lattice constant, lithium layer thickness, system formation energy difference, lithium ion migration energy in the lattice, lithium ion diffusion path, lithium ion diffusivity in the lattice, lithium ion conductivity and specific heat capacity; 3) correlating the parameters calculated by the atomic-level model with battery performance including structural stability, voltage, capacity, rate performance and / or cycle performance; 4) for potential battery applications, based on the parameters calculated in step 2) and the results of the atomic-level model obtained in step 3), select an electrode material with a certain composition and structure; 5) for the battery cell of the selected electrode material, establish a battery-level model based on a quasi-2-dimensional (P2D) model or equivalent circuit model with a physical entity; 6) prioritize the importance of the physical parameters of the electrode material by simulating and comparing the cell charge and discharge behaviors calculated by the battery-level model; 7) optimize the important physical parameters of the electrode material in the battery-level model according to the battery application requirements; 8) based on the physical parameters of the electrode material selected in step 6), perform composition modification and structural modification in the atomic-level model; 9) optimize the modification in the atomic-level model with respect to the physical parameters of the electrode material and battery performance; and, 10) obtain the optimal electrode material design for synthesizing the electrode material optimized in steps 7) and 9). This method can improve the time and accuracy of battery material design and modification for specific application requirements for battery electrode materials and their derivatives with small composition or structural changes, while considering their atomic structure and the physical structure of the battery. However, when constructing the atomic-level model of the electrode material, this method does not consider the cross-validation between the atomic-level model and the real material, resulting in the computational model being unable to characterize the actual doping effect.

[0005] Therefore, there is an urgent need to develop a method to evaluate the effect of doping modification on layered oxide positive electrode materials. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for evaluating the effect of doping modification of layered oxide positive electrode materials, which can solve the problems of high cost and low efficiency in the current evaluation of doping modification of layered oxide positive electrode materials.

[0007] Another object of the present invention is to provide a system for evaluating the effect of doping modification on layered oxide positive electrode materials, which can solve the problem of low efficiency in evaluating doping elements using the current trial and error method.

[0008] In order to achieve the above objectives, the technical solution adopted by the method for evaluating the effect of doping modification of layered oxide positive electrode materials of the present invention is:

[0009] A method for evaluating the effect of doping modification of a layered oxide positive electrode material comprises the following steps:

[0010] (1) establishing a supercell model of a target layered oxide cathode material, and then performing structural optimization, defining the optimized supercell model as a stable cell model; the target layered oxide cathode material is Y x MO2, wherein Y is Li and / or Na, and M is selected from one or any combination of Ni, Fe, and Mn;

[0011] (2) determining the most stable crystal face of the stable unit cell model by comparing surface energies according to the stable unit cell model, then establishing a surface model of the most stable crystal face, and then performing structural optimization, defining the optimized surface model as a stable surface model;

[0012] (3) adsorbing the target doping element at the optimal adsorption site in the stable surface model, and replacing each metal element in the stable surface model with the doping element in sequence, to obtain initial doping unit cell models corresponding to the doping elements at different positions; then structurally optimizing each initial doping unit cell model to obtain a stable structure of each initial doping unit cell model, and defining the stable structure of the initial doping unit cell model as an initial stable doping unit cell model;

[0013] (4) calculating the formation energy of the optimal adsorption site for adsorbing the target doping element in the stable surface model and the formation energy of replacing each metal element in the stable surface model with the doping element, and then determining the thermodynamically stable site of the target doping element;

[0014] (5) establishing a structural model of the target layered oxide positive electrode material at different Y removal amounts, and regulating the cationic redox couple to perform charge compensation to obtain a stable structure of each structural model, and defining the stable structure of each structural model as a stable structural model of the target layered oxide positive electrode material at different Y removal amounts; then doping the target doping element into the thermodynamically stable site of the stable structural model of the target layered oxide positive electrode material at different Y removal amounts to obtain a stable structural model of the target dopant at different Y removal amounts; the Y removal amount is a sodium removal amount and / or a lithium removal amount;

[0015] (6) Based on the stable structural model of the target layered oxide cathode material at different Y removal amounts and the unit cell parameter data and thermodynamic data of the stable structural model of the target dopant at different Y removal amounts, the influence of the target doping element on the electrochemical properties of the target layered oxide cathode material is determined, and the target doping element is evaluated.

[0016] The present invention provides a method for evaluating the effect of doping and modification of layered oxide positive electrode materials. The method establishes and optimizes a unit cell model and a surface model of the layered oxide positive electrode material, then dopes the target doping element into different sites, compares the formation energy, and determines the thermodynamically stable site of the doping element. This method can fully consider the doping effect corresponding to each site, make the simulation process close to the actual doping situation, and improve the accuracy of the results. The target doping element is then doped into the thermodynamically stable site to obtain a doping model, and then a structural model of the unit cell model at different sodium removal amounts and / or lithium removal amounts is established to obtain a target structural model. Finally, the influence relationship of the target doping element on the electrochemical properties of the target layered oxide positive electrode material is determined based on the unit cell parameter data and thermodynamic data of the stable unit cell model and the target structural model. The target doping element is then evaluated based on the influence relationship and actual needs. The method for evaluating the effect of doping and modification of layered oxide positive electrode materials does not require experimental trial and error, can effectively improve the evaluation efficiency of doping and modification of doping elements, and has relatively accurate evaluation results.

[0017] The schematic flow chart of the method for evaluating the effect of doping and modifying the layered oxide positive electrode material of the present invention is as follows: Figure 1 As shown, the specific calculation of performance parameters is mainly based on the first principles. The first principles is a set of theoretical methods about quantum mechanics / chemistry. The specific tools used for the first principles analysis and calculation can be set according to the actual situation. For example, Vasp can be used for analysis and calculation. After the calculation is completed, the modification effect of the doping element is mainly evaluated from aspects such as structural stability.

[0018] Preferably, the target doping element is selected from one or any combination of Mg, Zn, B, Cr, Ti, Mo, V, Al, W, and Ca.

[0019] Preferably, the optimal adsorption site of the stable surface model is determined by a method comprising the following steps: adding the target doping element above the stable surface model, comparing the adsorption energies corresponding to the adsorption of the target doping element at different positions of the stable surface model, and the position with the minimum adsorption energy is the optimal doping site of the target doping element.

[0020] Preferably, the thermodynamically stable site of the target doping element is determined by a method comprising the following steps: comparing the formation energy of the target doping element when doped at different doping sites, and when the formation energy of the target doping element when doped at a certain doping site is the smallest, the doping site is the thermodynamically stable site of the target doping element; the different doping sites include the metal element sites in the stable surface model and the optimal adsorption sites of the stable surface model.

[0021] Preferably, the electrochemical performance includes battery effective capacity, cycle stability and rate performance.

[0022] In the present invention, the effective capacity of a battery refers to the battery capacity when the charging voltage range of the battery is 2.0V to 4.0V.

[0023] Preferably, the method for determining the influence relationship of the target doping element on the battery capacity of the target layered oxide positive electrode material is as follows: the M is Ni, Fe and Mn; if the average voltage of the target dopant is greater than the average voltage of the target layered oxide positive electrode material, the target doping element can increase the battery capacity of the target layered oxide positive electrode material; the average voltage is the average voltage of the variable valence nickel complete valence stage before the iron valence changes.

[0024] Preferably, the method for determining the influence relationship of the target doping element on the cyclic stability performance of the target layered oxide positive electrode material is as follows: the M is Ni, Fe and Mn; if the unit cell volume change rate of the stable structural model corresponding to the target dopant when the Y removal amount is 0 and 1 is less than the unit cell volume change rate of the stable structural model corresponding to the target layered oxide positive electrode material when the Y removal amount is 0 and 1, or the sodium removal amount of the stable structural model corresponding to the interlayer spacing ratio of the target dopant is 1.62 is greater than the sodium removal amount of the stable structural model corresponding to the interlayer spacing ratio of the target layered oxide positive electrode material is 1.62, then the target doping element can improve the cyclic stability performance of the target layered oxide positive electrode material.

[0025] In the present invention, the interlayer spacing ratio is the ratio of the distance between the upper and lower layers of oxygen atoms connected to any Na atom in the model to the distance between the upper and lower layers of oxygen atoms connected to any atom in the same layer of Ni, Fe, and Mn.

[0026] Preferably, the method for determining the influence relationship of the target doping element on the rate performance of the target layered oxide positive electrode material is as follows: the M is Ni, Fe and Mn; if the Na layer interlayer spacing of the stable structural model corresponding to the target dopant when the Y removal amount is 0 is greater than the Na layer interlayer spacing of the stable structural model corresponding to the target layered oxide positive electrode material when the Y removal amount is 0, and the Na layer interlayer spacing of the stable structural model corresponding to the target dopant when the Y removal amount is 1 is greater than the Na layer interlayer spacing of the stable structural model corresponding to the target layered oxide positive electrode material when the Y removal amount is 1, then the target doping element can improve the rate performance of the target layered oxide positive electrode material.

[0027] The technical solution adopted by the system for evaluating the effect of doping and modifying layered oxide positive electrode materials of the present invention is:

[0028] The system for evaluating the effect of doping and modifying layered oxide cathode materials of the present invention includes a processor and a memory. The processor is used to execute instructions stored in the memory to implement the above-mentioned method for evaluating the effect of doping and modifying layered oxide cathode materials.

[0029] The system for evaluating the effect of doping and modification of layered oxide cathode materials of the present invention can replace the current experimental method for evaluating the effect of doping and modification, effectively shorten the evaluation time, and provide more accurate evaluation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the process of evaluating the effect of doping and modifying a layered oxide positive electrode material according to the present invention;

[0031] Figure 2 Schematic diagram of the stable structure of the Na3NiFeMnO6 (NFM333) unit cell model established in Example 1 of the present invention;

[0032] Figure 3 Schematic diagram of the stable structure of the surface model with the surface NFM333-(001) established in Example 1 of the present invention;

[0033] Figure 4 Schematic diagram of the initial doping unit cell model after Mg is adsorbed at the optimal adsorption site in the stable structure of the surface model in Example 1 of the present invention;

[0034] Figure 5 Schematic diagram of the initial doping unit cell model after Mg replaces the Na element in the stable structure of the surface model in Example 1 of the present invention;

[0035] Figure 6 Schematic diagram of the initial doping unit cell model after Mg replaces Ni element in the stable structure of the surface model in Example 1 of the present invention;

[0036] Figure 7 Schematic diagram of the initial doping unit cell model after Mg replaces the Fe element in the stable structure of the surface model in Example 1 of the present invention;

[0037] Figure 8 Schematic diagram of the initial doping unit cell model after Mg replaces the Mn element in the stable structure of the surface model in Example 1 of the present invention;

[0038] Figure 9 Schematic diagram of a doping model obtained by doping Mg into the stable structure of the Na3NiFeMnO6 (NFM333) unit cell model in Example 1 of the present invention;

[0039] Figure 10Schematic diagram of the average voltage of Na3NiFeMnO6 (NFM333) during the Ni element valence change process in Example 1 of the present invention, and the average voltage of the materials corresponding to different doping elements at different sodium removal amounts;

[0040] Figure 11 Schematic diagram of the average voltage of Na3NiFeMnO6 (NFM333) during the Fe element valence change process in Example 1 of the present invention, and the average voltage of the materials corresponding to different doping elements at different sodium removal amounts;

[0041] Figure 12 Schematic diagram of the average length of the ab axis of the stable structure of the Na3NiFeMnO6 (NFM333) unit cell model and the average length of the ab axis of the doping model corresponding to the doping element in Example 1 of the present invention when the sodium removal amount is 0;

[0042] Figure 13 Schematic diagram of the unit cell volume of the stable structure of the Na3NiFeMnO6 (NFM333) unit cell model and the unit cell volume of the doping model corresponding to the doping element in Example 1 of the present invention when the sodium removal amount is 0;

[0043] Figure 14 Schematic diagram of the unit cell volume of the stable structure of the Na3NiFeMnO6 (NFM333) unit cell model and the unit cell volume of the doping model corresponding to the doping element when the sodium removal amount is 0 and the sodium removal amount is 1 in Example 1 of the present invention;

[0044] Figure 15 Schematic diagram of the volume change rate of the Na3NiFeMnO6 (NFM333) unit cell model and the volume change rate of the doping model corresponding to different doping elements in Example 1 of the present invention;

[0045] Figure 16 Schematic diagram of the Na layer spacing of the stable structure of the Na3NiFeMnO6 (NFM333) unit cell model and the Na layer spacing of the doping model corresponding to the doping element in Example 1 of the present invention when the sodium removal amount is 0;

[0046] Figure 17 Schematic diagram of the Na layer spacing of the stable structure of the Na3NiFeMnO6 (NFM333) unit cell model and the Na layer spacing of the doping model corresponding to the doping element when the sodium removal amount is 0.333 in Example 1 of the present invention;

[0047] Figure 18 This is a schematic diagram of the stable structure of the Na3NiFeMnO6 (NFM333) unit cell model and the sodium removal amount of the doping model corresponding to different doping elements when the interlayer spacing ratio (d_Na / d_TM) is 1.62 in Example 1 of the present invention. DETAILED DESCRIPTION

[0048] The technical solution of the present invention is further described below in conjunction with specific embodiment 1.

[0049] 1. Specific examples of the method for evaluating the effect of doping and modifying layered oxide positive electrode materials of the present invention are as follows:

[0050] Example 1

[0051] The method for evaluating the effect of doping and modifying the layered oxide positive electrode material in this embodiment, taking Na3NiFeMnO6 (NFM333) as an example, specifically includes the following steps:

[0052] (1) 5 g of Na3NiFeMnO6 (NFM333) powder sample was ground and pressed into a pellet (size not less than 5 mm × 5 mm) to obtain a test sample. The test sample was then subjected to an X-ray diffraction test. The anode target material of the X-ray diffraction instrument was Cu, the scanning step was 0.02°, and the 2θ range was set to 0-120°. After the test was completed, the X-ray diffraction data was obtained and output in the form of the NFM333.mdi file.

[0053] (2) Use Jade software to open the NFM333.mdi file obtained in step (1), click on the elements (elements include Na, Ni, Fe, Mn, O) to perform phase search, the X-ray diffraction spectrum of the Na3NiFeMnO6 (NFM333) sample matches the peak position and peak intensity ratio of the X-ray diffraction spectrum of NaFeO2, and NaFeO2 is used as the standard crystal form. The X-ray diffraction data obtained in step (1) are subjected to full spectrum fitting refinement (including crystal structure, atomic coordinates, microstructure and preferred orientation refinement). When the fitting factor R≤10%, the refinement is completed, and the full spectrum fitting is completed. The lattice parameters of the Na3NiFeMnO6 (NFM333) sample are obtained as follows: a, b, and c represent the a-axis lattice parameter, b-axis lattice parameter, and c-axis lattice parameter, respectively;

[0054] Based on the obtained lattice parameters of the Na3NiFeMnO6 (NFM333) sample, the original supercell model of the Na3NiFeMnO6 (NFM333) sample was established (the size of the model is 3×3×1, which means that the a-axis direction is expanded 3 times and the b-axis direction is expanded 3 times). Then, the lattice parameters of the original supercell model of NFM333 were structurally optimized using Vasp software according to the minimum energy principle, and the stable structure of the original supercell model of Na3NiFeMnO6 (NFM333) was obtained. The optimization parameters are as follows: ENCUT (plane wave cutoff energy) = 500 eV, ISPIN (spin) = 2, LVDW (van der Waals force) = .TRUE., LVDW_EWALD (van der Waals force correction) = .TRUE.; finite U value (Coulomb repulsion between localized electrons with opposite spins): Ni = 6.0, Fe = 4.0, Mn = 3.9; convergence conditions: EDIFF (electron step energy convergence, unit is eV) = 1e-05, EDIFFG (ion step force convergence, unit is )=-0.05; parameters of different systems can be adjusted according to actual conditions; among them, LVDW (van der Waals force)=.TRUE. means that van der Waals force is enabled during optimization, and LVDW_EWALD (van der Waals force correction)=.TRUE. means that van der Waals force correction is enabled during optimization;

[0055] After optimization, the lattice parameters of the stable structure (named as the stable unit cell model) of the original supercell model of Na3NiFeMnO6 (NFM333) are as follows: Where d_TM represents the distance between the upper and lower oxygen atoms connected to any metal atom in the same layer of Ni, Fe, and Mn, and d_Na represents the distance between the upper and lower oxygen atoms connected to any Na atom. The stable unit cell model of Na3NiFeMnO6 (NFM333) is as follows: Figure 2 As shown;

[0056] Comparing the lattice parameters of the stable unit cell model with those of the original supercell model shows that the deviation of the lattice parameters before and after optimization is less than 1.5%, and the deviation of the interlayer spacing is less than 0.05%, indicating that the optimization process and results are relatively reliable. Based on the stable unit cell model of Na3NiFeMnO6 (NFM333), the unit cell parameter data and thermodynamic data of the stable unit cell model are obtained.

[0057] (3) According to the lattice parameters of the stable unit cell model, by comparing the surface energy, it is determined that the most stable surface (crystal plane) in the stable structure (stable unit cell model) of the original supercell model of Na3NiFeMnO6 (NFM333) is NFM333-(001). Based on this, the thickness is increased along the

[001] crystal direction. The vacuum layer is used to construct a surface model with NFM333-(001) as the surface. Then, the three lowest layers of atoms in the surface model are fixed (in this embodiment, the number of relaxed atomic layers is 8 and the number of fixed atomic layers is 3). The surface model is structurally optimized. The parameters during optimization are as follows: ENCUT (plane wave cutoff energy) = 700 eV, ISPIN (spin) = 2, LVDW (van der Waals force) = .TRUE., LVDW_EWALD (van der Waals force correction) = .TRUE.; finite U value: Ni = 6.0, Fe = 4.0, Mn = 3.9; convergence condition: EDIFF = 1e-08, EDIFFG = -0.01; after optimization, a stable structure of the surface model is obtained; the stable structure of the obtained surface model (stable surface model) is as follows Figure 3 As shown;

[0058] (4) Based on the stable structure of the surface model obtained in step (3), the doping element is added above the stable structure of the surface model, and the adsorption energies corresponding to the adsorption of the doping element at different positions of the stable structure of the surface model are compared. The position with the minimum adsorption energy is the optimal adsorption site of the doping element; the adsorption positions of the doping element in the stable structure of the surface model include directly above the atom (top position), directly above the adjacent atomic bond (bridge position), and directly above the atomic gap (interstitial position);

[0059] Then, the doping element is adsorbed at the optimal adsorption site in the stable structure of the surface model, and the doping element replaces each metal element in the stable structure of the surface model in turn to obtain the initial doping unit cell model corresponding to the doping element at different positions (the doping positions of the doping element are the optimal adsorption site in the stable structure of the surface model and the positions corresponding to each metal element in the stable structure of the surface model); then, the structure of each initial doping unit cell model is optimized to obtain the stable structure of each initial doping unit cell model (named as the initial stable doping unit cell model); taking Mg as the doping element as an example, the initial doping unit cell model after Mg is adsorbed at the optimal adsorption site (void position) in the stable structure of the surface model is as follows Figure 4 As shown, the initial doping unit cell model after Mg replaces the Na element in the stable structure of the surface model is as follows Figure 5 As shown, the initial doping unit cell model after Mg replaces Ni element in the stable structure of the surface model is as follows Figure 6 As shown, the initial doping unit cell model after Mg replaces Fe in the stable structure of the surface model is as follows Figure 7 As shown, the initial doping unit cell model after Mg replaces the Mn element in the stable structure of the surface model is as follows Figure 8 As shown;

[0060] (5) Based on the stable structure of the surface model (stable surface model) in step (3) and the stable structure of each initial doping unit cell model (initial stable doping unit cell model) in step (4), the formation energy of the doping element at different positions is calculated, and the calculation formula is as follows:

[0061] When the doping element is adsorbed on the optimal adsorption site in the stable structure of the surface model, the formation energy = E TM-表面 =E total -E NFM(001) -E TM , where E total represents the system energy after the doping element is adsorbed on the optimal adsorption site in the stable structure of the surface model, E NFM(001) represents the (001) surface energy of the initial NFM system, E TM represents the single point energy of the doping element;

[0062] When the doping element replaces the metal element in the stable structure of the surface model, the formation energy = E = E total -E NFM-TM(001) -E Ni / Mn / Fe , where E total represents the system energy after the doping elements occupy different sites (Ni, Mn or Fe), E NFM-TM(001) represents the (001) surface energy of the system after the doping elements occupy different sites (Ni, Mn or Fe), E Ni / Mn / Fe represents the single point energy of Ni, Mn or Fe occupied by the doping element;

[0063] The formation energy of the doping element when it is adsorbed at the optimal adsorption site in the stable structure of the surface model is set to 0. The formation energy of the doping element at different positions is compared. When the formation energy of the doping element at a certain position is the smallest, the position is the thermodynamically stable site of the doping element.

[0064] The formation energies of different doping elements (Mg, Ti, Ca, B) when doped at different positions are shown in Table 1;

[0065] Table 1 Formation energy of different doping elements at different positions

[0066]

[0067] As can be seen from Table 1, the formation energy of a doping element at a certain position may be positive or negative. When the formation energy of a doping element at a certain position is positive, it means that the doping element is not easy to form a stable structure at this position; when the formation energy of a doping element at a certain position is negative, it means that the doping element is easy to form a stable structure at this position. The smaller the formation energy, the more stable the structure. According to Table 1, the thermodynamically stable site of Mg in NFM333 is the Ni site, the thermodynamically stable site of Ca in NFM333 is the Na site, the thermodynamically stable site of Ti in NFM333 is the Mn site, and the thermodynamically stable site of B in NFM333 is the optimal adsorption site in the stable structure of the surface model, that is, B can only be adsorbed on the surface of NFM333 when doped.

[0068] (6) According to the stable structure (stable unit cell model) of the original supercell model of Na3NiFeMnO6 (NFM333) in step (2) and the thermodynamically stable sites of the doping element, the doping element is doped into the thermodynamically stable sites in the stable unit cell model to obtain a stable unit cell model of the dopant obtained after the doping element is doped into NFM333; in this embodiment, the ratio of the sum of the number of Ni atoms, Fe atoms, and Mn atoms in the stable unit cell model to the number of doping atoms is controlled to be 8:1;

[0069] Taking Mg as an example, since the thermodynamically stable site of Mg is Ni, the Ni in the stable unit cell model of Na3NiFeMnO6 (NFM333) is replaced by Mg, and the stable unit cell model of the dopant obtained after Mg doping NFM333 is obtained, which is Na3Ni 2 / 3 FeMnMg 1 / 3 O6(NFM-Mg), the results are as follows Figure 9 As shown;

[0070] (7) Synchrotron radiation in situ XANES (X-ray absorption near-edge structure spectroscopy) and EXAFS (extended X-ray absorption spectroscopy fine structure) were used to analyze the bond length, analyze the X-ray absorption near-edge structure valence and chemical environment changes of Ni, Fe, and Mn elements in the voltage range of 2.0-4.0V, and determine the redox reaction contribution capacity of each metal element in Na3NiFeMnO6 (NFM333) during the charging process. When the charging voltage range is 2.0V~4.0V, the Ni in Na3NiFeMnO6 (NFM333) 2+ Transformed into Ni 4 + , the contribution capacity is provided by Ni element, the specific capacity contributed by Ni element is 160mAh / g, 2+ Transformed into Ni 4+The amount of sodium removal caused is 0.667, and the valence change (redox reaction) process of Ni element is: Ni 2+ →Ni 3+ →Ni 4+ , that is, the Ni element changes from divalent to trivalent, and then from trivalent to tetravalent; when the charging voltage is greater than 4.0V, the Fe in Na3NiFeMnO6 (NFM333) 3+ Converted to Fe 4+ , the contribution capacity is provided by the Fe element, and the valence change (redox reaction) process of the Fe element is: Fe 3+ →Fe 4+ ;

[0071] According to the stable unit cell model of Na3NiFeMnO6 (NFM333) in step (2), the structural model corresponding to the stable unit cell model of Na3NiFeMnO6 (NFM333) at different sodium removal amounts (the sodium removal amount is equal to the ratio of the mass of the sodium element removed from the material during the charging process to the total mass of the sodium element in the material before charging) is determined, and the cationic redox couple is regulated (that is, the valence state of the Ni element or the Fe element in the structural model is adjusted according to the range or specific value of the sodium removal amount) to perform charge compensation, and the stable structure of each structural model (defined as the stable structural model) is obtained, that is, Na3NiFeMnO6 (NFM333) is obtained. 3) The stable structural model at different sodium removal amounts, and the cell parameter data and thermodynamic data of the stable structural model of Na3NiFeMnO6 (NFM333) at different sodium removal amounts are obtained at the same time; in the specific operation, the sodium removal amount can be gradually increased from 0, and then the structural model corresponding to the stable cell model of Na3NiFeMnO6 (NFM333) at different sodium removal amounts is obtained, and the cation redox couple is regulated for charge compensation to obtain the stable structural model of Na3NiFeMnO6 (NFM333) at different sodium removal amounts. In order to ensure the accuracy of the results, the amount is increased no more than 0.3 each time, and the stable structural model at different sodium removal amounts is expressed by Y 1- x MO2 represents, where x represents the amount of sodium removal, and the value of x ranges from 0 to 1;

[0072] Then, according to the thermodynamically stable site of the doping element determined in step (5), the doping element is doped into the thermodynamically stable site of the stable structural model of Na3NiFeMnO6 (NFM333) at different sodium removal amounts, and the stable structural model of the dopant obtained by doping the doping element into NFM333 at different sodium removal amounts is obtained, and at the same time, the unit cell parameter data and thermodynamic data of the stable structural model of the dopant at different sodium removal amounts are obtained;

[0073] (8) Based on the thermodynamic data of the stable structure models of Na3NiFeMnO6 (NFM333) at different sodiation levels and the thermodynamic data of the stable structure models of the dopants obtained after doping NFM333 with doping elements at different sodiation levels, calculate the voltage plateaus and average voltages of Na3NiFeMnO6 (NFM333) and the dopants obtained after doping NFM333 with doping elements at different sodiation levels respectively, and evaluate the influence of doping elements on the voltage window of Na3NiFeMnO6 (NFM333);

[0074] The method for calculating the voltage plateau is as follows: Where, represents the energy of the stable structure model at a sodiation level of x1, represents the energy of the stable structure model at a sodiation level of x2, where x1 < x2, E(Na) represents the energy of sodium element, and F is the Faraday constant;

[0075] The method for calculating the average voltage is as follows: represents the voltage plateau corresponding to the increase in sodiation level from x1 to x2, represents the voltage plateau corresponding to the increase in sodiation level from x3 to x4, where x1, x2, x3, and x4 represent different sodiation levels, x2 and x3 can be equal or x3 > x2, and both x2 - x1 and x4 - x3 are not greater than 0.3;

[0076] During the charging process, first, the Ni element provides the contribution capacity through redox reactions, and then the Fe element provides the contribution capacity through redox reactions. Due to different types of doping elements, when electrochemically active Ni, Fe, and Mn are doped and replaced by active or inactive elements, the redox capacity of the material increases or decreases. Therefore, the doping elements are classified. When the doping element is Cu 2+ , Mg 2+ , Zn 2+ [[ID=~]] 2+ These doping elements tend to occupy the Ni site, resulting in a decrease in the number of reversible Ni, and thus a reduction in the contribution capacity provided by Ni. The presence of these elements inhibits the JT distortion caused by the valence change of Ni, elevates the voltage plateau at this stage. At the same time, since the above doping elements do not undergo valence changes, the sodiation level corresponding to the complete valence change of the variable-valent Ni before the iron valence change is reduced to 0.445; according to the above formula for calculating the average voltage, based on the energies of the stable structure models of the dopant at sodiation levels of 0, 0.222, and 0.445, calculate the average voltage from sodiation level 0 to 0.445 (i.e., the average voltage during the stage of complete valence change of the variable-valent Ni before the iron valence change), as Figure 10 shown;

[0077] ​When the doping element is Ca 2+ When Ca 2+ The ionic radius is After doping, the influence of the Ni 2+ The electronic atmosphere of the ion can be observed through the DOS diagram, marked Ni 2+ The distance between the peak and Fermi level is greater than that of Fe 3+ The peak value of Ca 2+ After doping, it is close to Ni 2+ The redox reaction of Ni 2+ Better than Fe 3+ Oxidized, that is, 1 / 3 of Ni 2+ First by Ni 2+ →Ni 3+ , then Fe 3+ ByFe 3+ →Fe 4+ , the last 2 / 3 of Ni 2+ By Ni 2+ →Ni 3+ , causing the sodium removal amount corresponding to the complete sodium change of the variable valence nickel before the iron valence change to decrease to 0.222. According to the above-mentioned calculation formula for the average voltage, based on the energy of the stable structural model when the sodium removal amount of the dopant is 0, 0.111 and 0.222, the average voltage when the sodium removal amount is 0 to 0.222 (that is, the average voltage of the complete valence change stage of the variable valence nickel before the iron valence change) is calculated, as shown in the figure: Figure 10 As shown;

[0078] When the doping element is Al 3+ Cr 3+ 、B 3+ When Al 3+ and Cr 3+ Occupies the Fe position, while B 3+ It occupies the best adsorption site in the stable structure of the surface model, but only the bulk model can be used in the simulation. In order to compare with 3+ The thermodynamically stable site is adjusted to the Fe site (i.e., with Al 3+ Cr 3+ Same thermodynamically stable site), B 3+ The radius is Al 3+ The radius is Cr 3+ The radius is And Fe 3+ The radius is Therefore, the binding force between B, Al and Cr and O is stronger, and the doping will bind the adjacent O atoms and inhibit the adjacent atoms Ni from being converted from Ni to Ni. 3+ To you 4+Transformation, making 1 / 3 of Ni 3+ Cannot be oxidized to Ni 4+ , causing the sodium removal amount corresponding to the complete sodium change of the variable valence nickel before the iron valence change to decrease to 0.556. According to the above-mentioned calculation formula of the average voltage, based on the energy of the stable structure model when the sodium removal amount of the dopant is 0, 0.29 and 0.556, the average voltage when the sodium removal amount is 0 to 0.556 (that is, the average voltage of the complete valence change stage of the variable valence nickel before the iron valence change) is calculated, as shown in the figure: Figure 10 As shown;

[0079] When the doping element is V 3+ When V 3+ It can change valence (from trivalent to hexavalent), and V can be observed from the DOS diagram 3 + Better than Ni 2+ Oxidized to V 3+ →V 4+ →V 5+ , Ni 2+ →Ni 3+ →Ni 4+ The redox order of the above trivalent ions (Al 3+ Cr 3+ 、B 3+ ) for comparison, the average voltage in the range of 0 to 0.556 of sodium removal was selected for calculation, to replace the voltage when the doping element is V 3+ The average voltage during the entire period before the variable valence nickel completely changes valence before the iron changes valence at the time of the iron change. When specifically calculated, according to the above average voltage calculation formula, based on the energy of the stable structure model when the sodium removal amount of the dopant is 0, 0.29 and 0.556, the average voltage when the sodium removal amount is 0 to 0.556 is obtained. The results are as follows Figure 10 As shown;

[0080] When the doping element is Ti 4+ 、Sn 4+ 、Zr 4+ 、Ce 4+ 、Mo 6+ 、W 6+ When , these doping elements have no effect on the amount of reversible Ni and the valence change of Ni. Therefore, they will not affect the amount of sodium removal when the variable valence nickel is completely changed (0.667). According to the above-mentioned average voltage calculation formula, based on the energy of the stable structural model when the sodium removal amount of the dopant is 0, 0.250, 0.46 and 0.667, the average voltage when the sodium removal amount is 0 to 0.667 (that is, the average voltage of the variable valence nickel complete valence change stage before the iron valence change) is calculated, as shown in the figure: Figure 10 As shown;

[0081] Similarly, due to the different types of doping elements, Fe elements will be promoted or inhibited in the redox reaction. By simulating the effect of each doping element on the redox reaction of Fe elements, the corresponding sodium removal amount when the variable valence Fe is completely changed is obtained. The results show that when the doping element is Cu 2+ Mg 2+ 、Zn 2+ When the variable valence Fe in the dopant is completely changed, the corresponding sodium removal amount is 0.778; when the doping element is Ca 2+ When the variable valence Fe in the dopant is completely changed, the corresponding sodium removal amount is 0.778; when the doping element is Al 3+ Cr 3+ 、B 3+ When the dopant has no effect on the amount of variable valence Fe and the valence of Fe, the amount of sodium removal corresponding to the complete valence of variable valence Fe is 0.889 (due to 1 / 3 of Ni 3+ Cannot be oxidized to Ni 4+ ); When the doping element is V 3 + When the Fe element does not change valence, the variable valence elements are V and Ni, that is, the amount of variable valence iron is 0, and the amount of sodium removed when the variable valence Fe is completely changed is equal to the amount of sodium removed when the variable valence Ni is completely changed, that is, equal to 1; when the doping element is Ti 4+ 、Sn 4+ 、Zr 4+ 、Ce 4 + 、Mo 6+ When the variable valence Fe is fully changed, the amount of sodium removed when the variable valence Fe is fully changed is not affected. Therefore, the amount of sodium removed when the variable valence Fe is fully changed is 1. The average voltage of Na3NiFeMnO6 (NFM333) during the Fe element valence change process and the average voltage of the material corresponding to different doping elements at different sodium removal amounts are shown in the figure below. Figure 11 As shown;

[0082] Depend on Figures 10-11 It can be seen that when the doping element is Cu 2+ Mg 2+ 、Zn 2+ When the Mn is added, the average voltage of the variable valence nickel complete valence stage before the iron valence is increased, that is, the battery capacity is increased. When the high-valence element is doped, it will be accompanied by 3+ 、Mn 4+ The charge transfer causes the voltage to drop; therefore, from the perspective of improving battery capacity, the preferred doping element is Cu 2+ Mg 2+ 、Zn 2+ ;

[0083] (9) evaluating the effect of the doping elements on the lattice parameters of NFM333 based on the unit cell parameter data of the stable structural model of Na3NiFeMnO6 (NFM333) at different sodium removal amounts in step (7) and the unit cell parameter data of the stable structural model of the dopant obtained after doping NFM333 with the doping elements at different sodium removal amounts;

[0084] When the amount of sodium removal is 0, the average length of the ab axis of the stable unit cell model of Na3NiFeMnO6 (NFM333) and the average length of the ab axis of the stable structure model of the dopant obtained by doping NFM333 with doping elements are as follows: Figure 12 As shown; when the amount of sodium removal is 0, the unit cell volume of the stable unit cell model of Na3NiFeMnO6 (NFM333) and the unit cell volume of the stable structure model of the dopant obtained by doping NFM333 with doping elements are as follows: Figure 13 As shown; the cell volume of the stable unit cell model of Na3NiFeMnO6 (NFM333) and the cell volume of the stable structure model of the dopant obtained by doping NFM333 with the doping amount of 0 and the doping amount of 1 are plotted, and the results are shown in FIG. Figure 14 As shown. Then, the change rate of the unit cell volume of the stable unit cell model of Na3NiFeMnO6 (NFM333) when the sodium removal amount is 0 and 1 (that is, the unit cell volume change rate of the stable unit cell model of NFM333 before and after sodium removal) and the change rate of the unit cell volume of the stable structural model of the dopant obtained after doping NFM333 with doping elements when the sodium removal amount is 0 and 1 (that is, the unit cell volume change rate of the stable structural model of the dopant before and after sodium removal) are calculated respectively. The calculation formula is: change rate = |unit cell volume when sodium removal amount is 1 - unit cell volume when sodium removal amount is 0| / unit cell volume when sodium removal amount is 0. Then, the unit cell volume change rate of the stable unit cell model of NFM333 before and after sodium removal and the unit cell volume change rate of the stable structural model of the dopant before and after sodium removal are listed in Figure 15 middle;

[0085] Depend on Figure 12 and 13 It can be seen that compared with the stable unit cell model of Na3NiFeMnO6 (NFM333), as the valence state of the doping element increases and the radius of the doping element increases, the unit cell volume of the stable structure model of the dopant tends to increase; Figure 14 It can be seen that for different doping elements, the unit cell volume when the sodium removal amount is 0 is significantly smaller than the unit cell volume when the sodium removal amount is 1. Figure 15It can be seen that the introduction of doping elements generally increases the rate of change of the unit cell volume during charge and discharge; however, the unit cell volume change corresponding to different doping elements (the absolute value of the difference between the unit cell volume when the sodium removal amount is 0 and the unit cell volume when the sodium removal amount is 1) or the unit cell volume change rate is different. When a certain doping element is doped into NFM333, the rate of change of the unit cell volume of the stable structural model of the dopant when the sodium removal amount is 0 and 1 is less than the rate of change of the unit cell volume of the stable unit cell model of Na3NiFeMnO6 (NFM333) when the sodium removal amount is 0 and 1, the doping element can improve the cycle stability of Na3NiFeMnO6 (NFM333); Figure 15 It can be seen that for the doping element Cu that can increase the battery capacity 2+ Mg 2+ 、Zn 2+ Generally speaking, these doping elements are not conducive to improving the cycle stability of Na3NiFeMnO6 (NFM333);

[0086] In addition, during the charging and sodium removal process, a transition from O3 phase to P3 phase will occur. The transition between O3 phase and P3 phase is mainly achieved through interlayer slip. The interlayer spacing ratio (d_Na / d_TM, that is, the ratio of the distance between the upper and lower layers of oxygen atoms connected to any layer of Na atoms and the distance between the upper and lower layers of oxygen atoms connected to any atom in the same layer of Ni, Fe, and Mn) can reflect the phase transition tendency; when the interlayer spacing ratio (d_Na / d_TM) is 1.62, the sodium removal amount of the stable unit cell model of Na3NiFeMnO6 (NFM333) and the stable structural model of the dopant obtained after doping NFM333 with doping elements are as follows: Figure 16 As shown in the figure; when the interlayer spacing ratio (d_Na / d_TM) is 1.62, if the sodium removal amount of the stable structural model of the dopant obtained after doping NFM333 with a certain doping element is greater than the sodium removal amount of the stable unit cell model of Na3NiFeMnO6 (NFM333), it is determined that the doping element can delay the phase transition (the transition between the O3 phase and the P3 phase), thereby improving the cyclic stability of the material; Figure 16 It can be seen that for the doping element Cu that can increase the battery capacity 2+ Mg 2+ 、Zn 2+ For example, when the interlayer spacing ratio (d_Na / d_TM) is 1.62, the sodium removal amount of the stable structural model of the dopant obtained after doping NFM333 with these doping elements is not greater than the sodium removal amount of the stable unit cell model of Na3NiFeMnO6 (NFM333). Therefore, these doping elements cannot delay the occurrence of phase transition (transition between O3 phase and P3 phase), which is not conducive to improving the cyclic stability performance of Na3NiFeMnO6 (NFM333);

[0087] When the amount of sodium removal is 0, the Na layer spacing of the stable unit cell model of Na3NiFeMnO6 (NFM333) and the Na layer spacing of the stable structure model of the dopant obtained by doping NFM333 with doping elements are as follows: Figure 17 As shown, when the amount of sodium removal is 0.333, the Na layer spacing of the stable unit cell model of Na3NiFeMnO6 (NFM333) and the Na layer spacing of the stable structure model of the dopant obtained by doping NFM333 with doping elements are as follows: Figure 18 shown by Figure 17 and 18 It can be seen that compared with the sodium layer spacing of the stable unit cell model of Na3NiFeMnO6 (NFM333) when the sodium removal amount is 0, the sodium layer spacing of the stable structure model of the dopant obtained after Cu and Mg elements are doped with NFM333 when the sodium removal amount is 0 is significantly increased, and compared with the sodium layer spacing of the stable unit cell model of Na3NiFeMnO6 (NFM333) when the sodium removal amount is 0.333, the sodium layer spacing of the stable structure model of the dopant obtained after Cu and Mg elements are doped with NFM333 when the sodium removal amount is 0.333 is significantly increased. Therefore, Cu and Mg elements can be beneficial to improving the Na + diffusion, improving rate performance.

[0088] 2. Specific embodiments of the system for evaluating the effect of doping and modifying layered oxide positive electrode materials of the present invention are as follows:

[0089] Example 2

[0090] The system for evaluating the effect of doping and modifying layered oxide positive electrode materials in this embodiment includes a processor and a memory. The processor is used to execute instructions stored in the memory to implement the method for evaluating the effect of doping and modifying layered oxide positive electrode materials in method embodiment 1 of the present invention.

[0091] Experimental example

[0092] (1) According to the conclusion obtained in step (5) of Example 1, the doping element Mg is selected 2+ The Na3NiFeMnO6 (NFM333) powder is doped as follows:

[0093] A mixed sulfate solution of Ni, Fe, and Mn (composed of nickel sulfate, iron sulfate, manganese sulfate, and water, with the Ni, Fe, and Mn elements satisfying a molar ratio of 2:3:3) was prepared, a 10% by mass ammonia solution was prepared as a complexing agent, and a 20% by mass sodium hydroxide solution was prepared as a precipitant;

[0094] The prepared mixed sulfate solution, complexing agent and precipitant were added to pure water by a peristaltic pump for coprecipitation reaction. After the coprecipitation reaction was completed, the obtained precipitate was washed with deionized water and dried to obtain Ni 2 / 8 Fe 3 / 8 Mn 3 / 8 (OH)2 precursor material.

[0095] Ni 2 / 8 Fe 3 / 8 Mn 3 / 8 The (OH)2 precursor material was uniformly mixed with Na2CO3 and MgO in a molar ratio of 16:10.395:2 and then placed in a muffle furnace for heat treatment to obtain a doped sodium ion layered oxide positive electrode material NaNi 2 / 9 Fe 1 / 3 Mn 1 / 3 Mg 1 / 9O2, after XRD test, the prepared positive electrode material NaNi 2 / 9 Fe 1 / 3 Mn 1 / 3 Mg 1 / 9 There is no impurity phase in the XRD spectrum of O2, and the prepared positive electrode material NaNi 2 / 9 Fe 1 / 3 Mn 1 / 3 Mg 1 / 9 O2 is spherical, with a minimum particle size of 1.5μm and a D50 particle size of 3μm.

[0096] Take 5g of NaNi 2 / 9 Fe 1 / 3 Mn 1 / 3 Mg 1 / 9 The O2 powder sample was subjected to X-ray diffraction and refined with Jade, and the average bond length of the ab axis of the Mg-doped material was obtained to be The average bond length along the c-axis is Then the prepared NaNi 2 / 9 Fe 1 / 3Mn 1 / 3 Mg 1 / 9 The O2 powder sample was subjected to a charge-discharge test. The electrolyte used in the test was a 1.0 mol / L NaPF6 solution. The solvent in the solution consisted of ethylene carbonate and propylene carbonate in a volume ratio of 1:1. The test results showed that the average voltage in the Ni valence range was 3.12 V, and the volume change rate was 3.2%, which was consistent with the simulation data.

[0097] (2) According to the conclusion obtained in step (5) of Example 1, the doping element Ca is selected. 2+ The Na3NiFeMnO6 (NFM333) powder is doped as follows:

[0098] A mixed sulfate solution of Ni, Fe, and Mn is prepared, wherein the molar ratio of Ni, Fe, and Mn elements is 3:3:3, a 10% by mass ammonia solution is prepared as a complexing agent, and a 20% by mass sodium hydroxide solution is prepared as a precipitant;

[0099] The prepared mixed sulfate solution, complexing agent and precipitant were added into pure water by peristaltic pump for coprecipitation reaction. The obtained precipitate was washed with deionized water and dried to obtain Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 precursor material.

[0100] Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The (OH)2 precursor material was uniformly mixed with Na2CO3 and CaO in a molar ratio of 16:8.395:1 and then placed in a muffle furnace for heat treatment to obtain a doped sodium ion layered oxide positive electrode material Na 8 / 9 Ca 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3Mg 1 / 9 O2, after XRD test, the prepared positive electrode material Na 8 / 9 Ca 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 Mg 1 / 9 There is no impurity phase in the XRD spectrum of O2, and the prepared positive electrode material Na 8 / 9 Ca 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 Mg 1 / 9 O2 is spherical, with a minimum particle size of 1.43 μm and a D50 particle size of 3.4 μm.

[0101] Take 5g of Na 8 / 9 Ca 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 Mg 1 / 9 The O2 powder sample was subjected to X-ray diffraction and refined with Jade, and the average bond length of the ab axis of the Ca-doped material was obtained to be The average bond length along the c-axis is Then the prepared Na 8 / 9Ca 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 Mg 1 / 9The O2 powder sample was subjected to a charge-discharge test. The electrolyte used in the test was a 1.0 mol / L NaPF6 solution. The solvent in the solution consisted of ethylene carbonate and propylene carbonate in a volume ratio of 1:1. The test results showed that the average voltage in the Ni valence change range was 2.95 V, and the volume change rate was 5.1%, which was consistent with the simulation data.

[0102] (3) According to the conclusion obtained in step (5) of Example 1, the doping element Ti is selected. 4+ The Na3NiFeMnO6 (NFM333) powder is doped as follows:

[0103] A mixed sulfate solution of Ni, Fe, and Mn is prepared, wherein the molar ratio of Ni, Fe, and Mn elements is 3:3:2, a 10% by mass ammonia solution is prepared as a complexing agent, and a 20% by mass sodium hydroxide solution is prepared as a precipitant;

[0104] The prepared mixed sulfate solution, complexing agent and precipitant were added into pure water by peristaltic pump for coprecipitation reaction. The obtained precipitate was washed with deionized water and dried to obtain Ni 3 / 8 Fe 3 / 8 Mn 2 / 8 (OH)2 precursor material.

[0105] Ni 3 / 8 Fe 3 / 8 Mn 2 / 8 The (OH)2 precursor material was uniformly mixed with Na2CO3 and TiO2 in a molar ratio of 16:10.395:2 and then placed in a muffle furnace for heat treatment to obtain the doped sodium ion layered oxide positive electrode material NaNi 1 / 3 Fe 1 / 3 Mn 2 / 9 Ti 1 / 9O2, after XRD test, the prepared positive electrode material NaNi 1 / 3 Fe 1 / 3 Mn 2 / 9 Ti 1 / 9 There is no impurity phase in the XRD spectrum of O2, and the prepared positive electrode material NaNi 1 / 3 Fe 1 / 3 Mn 2 / 9 Ti 1 / 9 O2 is a flake structure with an average length of 2.3 μm, an average width of 1.6 μm, and an average thickness of 0.34 μm.

[0106] Take 5g of NaNi 1 / 3 Fe 1 / 3 Mn 2 / 9 Ti 1 / 9The O2 powder sample was subjected to X-ray diffraction and refined with Jade, and the average bond length of the ab axis of the Ti-doped material was obtained to be The average bond length along the c-axis is Then the prepared NaNi 1 / 3 Fe 1 / 3Mn 2 / 9 Ti 1 / 9 The O2 powder sample was subjected to a charge-discharge test. The electrolyte used in the test was a 1.0 mol / L NaPF6 solution. The solvent in the solution consisted of ethylene carbonate and propylene carbonate in a volume ratio of 1:1. The test results showed that the average voltage in the Ni valence change range was 2.75 V, and the volume change rate was 3.71%, which was consistent with the simulation data.

Claims

1. A method for evaluating the effect of doping modification on layered oxide positive electrode materials, characterized in that: The following steps are involved: (1) establishing a supercell model of a target layered oxide cathode material, and then performing structural optimization, defining the optimized supercell model as a stable cell model; the target layered oxide cathode material is Y x MO2, wherein Y is Li and / or Na, and M is selected from one or any combination of Ni, Fe, and Mn; (2) determining the most stable crystal face of the stable unit cell model by comparing surface energies according to the stable unit cell model, then establishing a surface model of the most stable crystal face, and then performing structural optimization, defining the optimized surface model as a stable surface model; (3) adsorbing the target doping element at the optimal adsorption site in the stable surface model, and replacing each metal element in the stable surface model with the doping element in sequence, to obtain initial doping unit cell models corresponding to the doping elements at different positions; then structurally optimizing each initial doping unit cell model to obtain a stable structure of each initial doping unit cell model, and defining the stable structure of the initial doping unit cell model as an initial stable doping unit cell model; (4) calculating the formation energy of the optimal adsorption site for adsorbing the target doping element in the stable surface model and the formation energy of replacing each metal element in the stable surface model with the doping element, and then determining the thermodynamically stable site of the target doping element; (5) establishing a structural model of the target layered oxide positive electrode material at different Y removal amounts, and regulating the cationic redox couple to perform charge compensation to obtain a stable structure of each structural model, and defining the stable structure of each structural model as a stable structural model of the target layered oxide positive electrode material at different Y removal amounts; then doping the target doping element into the thermodynamically stable site of the stable structural model of the target layered oxide positive electrode material at different Y removal amounts to obtain a stable structural model of the target dopant at different Y removal amounts; the Y removal amount is a sodium removal amount and / or a lithium removal amount; (6) Based on the stable structural model of the target layered oxide cathode material at different Y removal amounts and the unit cell parameter data and thermodynamic data of the stable structural model of the target dopant at different Y removal amounts, the influence of the target doping element on the electrochemical properties of the target layered oxide cathode material is determined, and the target doping element is evaluated.

2. The method for evaluating the effect of doping modification of a layered oxide positive electrode material according to claim 1, wherein: The optimal adsorption site of the stable surface model is determined by a method comprising the following steps: adding a target doping element above the stable surface model, comparing the adsorption energies corresponding to the adsorption of the target doping element at different positions on the stable surface model, and the position with the minimum adsorption energy is the optimal doping site of the target doping element.

3. The method for evaluating the effect of doping modification of a layered oxide positive electrode material according to claim 1, wherein: The thermodynamically stable site of the target doping element is determined by a method comprising the following steps: comparing the formation energies of the target doping element when doped at different doping sites, and determining that a doping site where the formation energy of the target doping element is the smallest is the thermodynamically stable site of the target doping element; The different doping sites include metal element sites in the stable surface model and optimal adsorption sites in the stable surface model.

4. The method for evaluating the effect of doping modification of a layered oxide positive electrode material according to any one of claims 1 to 3, wherein: The target doping element is selected from one or any combination of Mg, Zn, B, Cr, Ti, Mo, V, Al, W, and Ca.

5. A system for evaluating the effect of doping and modification of layered oxide cathode materials, characterized in that: The invention comprises a processor and a memory, wherein the processor is used to execute instructions stored in the memory to implement the method for evaluating the effect of doping and modifying a layered oxide positive electrode material according to any one of claims 1 to 4.

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