Detection method and detection equipment for positive electrode active material

Abstract

The invention provides a detection method and detection equipment for a positive electrode active material, and the detection method comprises the following steps: carrying out the first charge-discharge cycle of an initial half-cell under a first non-concentration polarization current, and obtaining a charge-discharge initial standard potential curve of an initial positive electrode active material in the initial half-cell; performing a second charge-discharge cycle on the cycle half-cell under a second non-concentration polarization current to obtain a charge-discharge cycle standard potential curve of the to-be-detected positive active material in the cycle half-cell; and according to the charging and discharging initial standard potential curve and the charging and discharging cycle standard potential curve, judging the structural state of the to-be-detected positive electrode active material. The detection method can truly and objectively reflect the structure state of the to-be-detected positive electrode active material in the circulation process.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a detection method and detection equipment for positive electrode active materials. Background Art

[0002] As the core technology in the current energy storage field, the performance of secondary batteries is closely related to the stability of the crystal structure of the positive electrode active material. In practical applications, the positive electrode active material may be affected by a variety of external and internal factors, causing its crystal structure to change. For example, during the charge and discharge cycle of the battery, due to the repeated insertion and extraction of active ions, the positive electrode active material may undergo lattice expansion or contraction, or even induce phase change. In addition, high temperature environment will aggravate the thermodynamic instability inside the material, resulting in lattice distortion or irreversible structural collapse. External forces (such as mechanical extrusion or vibration) may also directly destroy the microstructure of the positive electrode active material, thereby affecting its electrochemical performance. These structural changes may manifest as changes in lattice parameters, the formation of new phases, or the destruction of the original crystal symmetry, thereby reducing the capacity of the battery, increasing internal resistance, and even causing safety problems.

[0003] Although existing electrochemical testing methods (such as cyclic voltammetry and electrochemical impedance spectroscopy) can indirectly reflect changes in battery performance, they cannot be directly linked to the specific structural changes of the positive electrode active materials. It is difficult to accurately distinguish whether the changes are caused by structural changes in the positive electrode active materials based solely on electrochemical data.

[0004] Therefore, during the battery cycle process, especially under complex working conditions (such as high temperature, external force or long cycle), technicians in this field are often unable to accurately determine whether the positive electrode active material has currently undergone a change in crystal structure. Summary of the Invention

[0005] The present application provides a method and apparatus for detecting positive electrode active materials. The method, under the premise of introducing a non-concentration polarization current, establishes standard potential curves of the positive electrode active materials before and after cycling, thereby being able to truly and objectively reflect the structural state of the positive electrode active materials to be tested during the cycling process.

[0006] The present application provides a method for detecting a positive electrode active material, comprising the following steps:

[0007] performing a first charge-discharge cycle on the initial half-cell at a first non-concentration polarization current to obtain an initial charge-discharge standard potential curve of the initial positive electrode active material in the initial half-cell;

[0008] performing a second charge-discharge cycle on the cycle half-cell under a second non-concentration polarization current to obtain a charge-discharge cycle standard potential curve of the positive electrode active material to be tested in the cycle half-cell;

[0009] The structural state of the positive electrode active material to be tested is judged according to the charge-discharge initial standard potential curve and the charge-discharge cycle standard potential curve.

[0010] The detection method as described above, wherein, before the first charge-discharge cycle and the second charge-discharge cycle, the method further comprises:

[0011] Perform current-potential detection on the negative metal symmetrical battery to obtain N sets of current-potential data;

[0012] Based on the N-group current-potential data and the Butler–Volmer reaction model, the relationship between the interfacial active ion concentration and the current / potential of the negative electrode metal is obtained;

[0013] According to the relationship between the interfacial active ion concentration and the current / potential, respectively obtaining a first non-concentration polarization current and a second non-concentration polarization current;

[0014] The negative electrode metal in the negative electrode metal symmetrical battery is the same as the negative electrode metal in the initial half-cell and the cycle half-cell, and N≥2.

[0015] The detection method as described above, wherein the first non-concentration polarization current and the second non-concentration polarization current are obtained respectively according to the relationship between the interfacial active ion concentration and the current / potential, comprising:

[0016] Obtaining a first non-concentration polarization current based on the relationship between the interfacial active ion concentration and the current / potential;

[0017] Obtaining a first non-concentration polarization reference current according to the first non-concentration polarization current, the negative electrode area of ​​the initial half-cell, and the initial positive electrode active material mass;

[0018] A second non-concentration polarization current is obtained according to the first non-concentration polarization reference current, the negative electrode area of ​​the cycle half-cell and the mass of the positive electrode active material to be measured.

[0019] The detection method as described above, wherein the first charge-discharge cycle is performed on the initial half-cell under the first non-concentration polarization current to obtain the initial charge-discharge standard potential curve of the initial cell, comprises:

[0020] Performing a first charge on the initial half-cell at a first non-concentration polarization current to obtain the charging initial potential curve and the initial half-cell to be discharged;

[0021] Obtaining an initial charging standard potential curve of the initial half-cell according to the initial charging potential curve and the first negative electrode potential correction coefficient;

[0022] performing a first discharge on the initial half-cell to be discharged under a first non-concentration polarization current to obtain an initial discharge potential curve of the initial half-cell;

[0023] Obtaining an initial discharge standard potential curve of the initial half-cell according to the initial discharge potential curve and the first negative electrode potential correction coefficient;

[0024] The first negative electrode potential correction coefficient is obtained according to the first non-concentration polarization current and the negative electrode metal coefficient.

[0025] The detection method as described above, wherein the second charge-discharge cycle is performed on the cycled half-cell under the second non-concentration polarization current to obtain the charge-discharge cycle standard potential curve of the cycled half-cell, comprises:

[0026] Performing a second charge on the cycle half-cell at a second non-concentration polarization current to obtain a charge cycle potential curve of the cycle half-cell and a cycle half-cell to be discharged;

[0027] Obtaining a charge cycle standard potential curve of the cycle half-cell according to the charge cycle potential curve and the second negative electrode potential correction coefficient;

[0028] performing a second discharge on the to-be-discharged cycle half-cell at a second non-concentration polarization current to obtain a discharge cycle potential curve of the cycle half-cell;

[0029] Obtaining a discharge cycle standard potential curve of the cycle half-cell according to the discharge cycle potential curve and the second negative electrode potential correction coefficient;

[0030] The second negative electrode potential correction coefficient is obtained according to the second non-concentration polarization current and the negative electrode metal coefficient.

[0031] The detection method as described above, wherein the step of judging the cyclic structural state of the positive electrode active material to be tested in the cycle half-cell according to the charge-discharge initial standard potential curve and the charge-discharge cycle standard potential curve comprises:

[0032] If the potential difference between the charging initial standard potential curve and the charging cycle standard potential curve at the first charging state of charge is greater than a first preset value, the cyclic structural state of the positive electrode active material to be tested at the first charging state of charge is a first changed state; and / or,

[0033] If the potential difference between the discharge initial standard potential curve and the discharge cycle standard potential curve in the second discharge charge state is greater than a second preset value, the cycle structure state of the positive electrode active material to be tested in the second discharge charge state is a second change state.

[0034] The detection method as described above, wherein the method further comprises:

[0035] In-situ structural monitoring is performed on the initial half-cell during the first charge and discharge cycle to obtain a full-cycle charge structural state and a full-cycle discharge structural state of the initial positive electrode active material.

[0036] The detection method as described above, wherein, if the positive electrode active material to be tested is in the first change state, further comprises:

[0037] performing a third charging on the cycling half-cell at the second non-concentration polarization current;

[0038] In the third charge, in-situ structural monitoring is performed on the cycled half-cell at the first charge state of charge to obtain a current charge structural state of the positive electrode active material to be tested at the first charge state of charge;

[0039] A first change state parameter of the positive electrode active material to be tested is obtained according to the current charging structure state and the full-cycle charging structure state.

[0040] The detection method as described above, wherein, if the positive electrode active material to be tested is in the second change state, further comprises:

[0041] performing a third discharge on the cycle half-cell at the second non-concentration polarization current;

[0042] In the third discharge, performing in-situ structural monitoring on the cycled half-cell in the second discharge state to obtain a current discharge structural state of the positive electrode active material to be tested in the second discharge state;

[0043] According to the current discharge structure state and the full-cycle discharge structure state, a second change state parameter of the positive electrode active material to be tested is obtained.

[0044] The present application also provides a positive electrode active material detection device, comprising: a memory, a processor;

[0045] The memory stores computer-executable instructions;

[0046] The processor executes the computer-executable instructions stored in the memory, so that the processor performs the above-mentioned method.

[0047] The method for detecting positive electrode active materials provided in this application, by introducing an innovative detection method of non-concentration polarization current, effectively eliminates the interference of negative electrode dendrite growth and negative electrode overpotential caused by concentration polarization in traditional testing, thereby achieving accurate characterization of the structural evolution of positive electrode active materials. Specifically, by establishing standard potential curves of positive electrode active materials before and after cycling, this method eliminates the influence of non-intrinsic factors such as electrolyte concentration gradient and interfacial impedance changes, so that the test results can truly and objectively reflect the intrinsic structural changes of positive electrode active materials during the charge and discharge process. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0049] Figure 1 The relationship between the interfacial active ion concentration and the current / potential of potassium metal in Example 1 of the present application is shown in FIG.

[0050] Figure 2 The charge initial potential curve and discharge initial potential curve of the initial half-cell of Example 1 of the present application;

[0051] Figure 3 The initial standard potential curve for charge and discharge of the initial half-cell of Example 1 of the present application;

[0052] Figure 4 The charge cycle potential curve and discharge cycle potential curve of the cycle half-cell of Example 1 of the present application;

[0053] Figure 5 The charge cycle standard potential curve and the discharge cycle standard potential curve of the cycle half-cell of Example 1 of the present application;

[0054] Figure 6 A comparison diagram of the initial charging standard potential curve and the charging cycle standard potential curve of Example 1 of the present application;

[0055] Figure 7 This is the initial in-situ XRD contour map of Example 1 of the present application;

[0056] Figure 8 for Figure 7 A partially enlarged schematic diagram of

[0057] Figure 9 The cyclic in-situ XRD contour map of Example 1 of the present application;

[0058] Figure 10 for Figure 9 A partially enlarged schematic diagram of . DETAILED DESCRIPTION

[0059] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below. The specific embodiments listed below are only for describing the principles and features of the present invention. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts are within the scope of protection of the present invention.

[0060] In this application, the terms "first" and "second" are used only for descriptive purposes to distinguish objects such as substances from each other, and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. For example, without departing from the scope of the embodiments of the present application, the first charge and discharge cycle may also be referred to as the second charge and discharge cycle, and similarly, the second charge and discharge cycle may also be referred to as the first charge and discharge cycle. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of such features.

[0061] Throughout this application, references to "one embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment, embodiment, or example is included in at least one embodiment of the present invention. Therefore, appearances of the phrases "one embodiment," "an embodiment," "an example," or "an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combinations and / or subcombinations in one or more embodiments or examples.

[0062] In order to more objectively reflect the real structural changes that occur in the positive electrode active material during the cycle, the inventors have conducted a detailed study of the electrochemical process. For example, during the charge and discharge process, due to the limited diffusion rate of active ions in the electrolyte, a significant concentration gradient will be formed at the electrode / electrolyte interface, which is the concentration polarization phenomenon. This polarization effect will not only eventually lead to the formation and growth of dendrites, but also affect the coulombic efficiency of the battery. The inventors found that, more importantly, the concentration polarization effect will trigger a series of complex interfacial reactions, such as the overpotential of the negative electrode. These interfering factors will seriously obscure the real structural evolution information of the positive electrode active material during the cycle, making it difficult to accurately obtain the intrinsic attenuation mechanism of the positive electrode active material.

[0063] In addition, due to this, eliminating concentration polarization interference is of vital importance for accurately characterizing the cycling structural stability of positive electrode active materials.

[0064] Based on this, the first aspect of the present application provides a method for detecting a positive electrode active material, comprising the following steps:

[0065] performing a first charge-discharge cycle on the initial half-cell at a first non-concentration polarization current to obtain an initial charge-discharge standard potential curve of the initial positive electrode active material in the initial half-cell;

[0066] performing a second charge-discharge cycle on the cycle half-cell under a second non-concentration polarization current to obtain a charge-discharge cycle standard potential curve of the positive electrode active material to be tested in the cycle half-cell;

[0067] The structural state of the positive electrode active material to be tested is judged according to the charge-discharge initial standard potential curve and the charge-discharge cycle standard potential curve.

[0068] This application is used to more objectively reflect whether the structure of the positive electrode active material has undergone an intrinsic attenuation change after it has undergone a certain complex working condition. This application does not limit the specific implementation conditions of the complex working condition, for example, it can be circulation, storage at any temperature (the specific number of cycles and storage time are also not specifically limited), or external force, etc. This application does not limit the chemical composition of the positive electrode active material, which can be a ternary material, Prussian blue material, cobalt salt material, phosphate material, etc. that are common in this field, and the active ions in the positive electrode active material can be lithium ions, sodium ions or potassium ions. In this application, the positive electrode active material before the implementation of the complex working condition is referred to as the initial positive electrode active material, and the initial positive electrode active material after experiencing the complex working condition is referred to as the positive electrode active material to be tested.

[0069] In the detection method of the present application, the positive electrode active material in the initial half-cell is the initial positive electrode active material, and the positive electrode active material in the cycle half-cell is the positive electrode active material to be tested; the first non-concentration polarization current and the second non-concentration current are respectively charge and discharge currents that will not cause the negative electrode metal to undergo concentration polarization at the negative electrode-electrolyte interface, thereby forming negative electrode metal dendrites. The first concentration polarization current and the second concentration polarization current in the present application may be the same or different. It will be understood that the selection of the negative electrode metal in the initial half-cell and the cycle half-cell is related to the active ions in the positive electrode active material. For example, when the active ions in the positive electrode active material are lithium ions, the negative electrode metals in both the initial half-cell and the cycle half-cell are lithium metal.

[0070] Furthermore, this application does not limit the composition of the electrolyte in the initial half-cell and the circulating half-cell; it can be any electrolyte commonly used in the art, including an organic solvent, an active ion salt, and an additive. However, it should be noted that the electrolyte composition in the initial half-cell and the circulating half-cell must be the same.

[0071] The initial charge-discharge standard potential curve of this application refers to the standard charge-discharge potential curve of the initial positive electrode active material after deducting the influence of the negative electrode in the initial half-cell. The charge-discharge cycle standard potential curve of this application refers to the standard charge-discharge potential curve of the positive electrode active material to be tested after deducting the influence of the negative electrode in the cycled half-cell. Specifically, the initial charge-discharge standard potential curve and the charge-discharge cycle standard potential curve are curves with the horizontal axis representing gram capacity and the vertical axis representing potential voltage.

[0072] When the detection method of the present application is specifically implemented, the initial half-cell is first charged and discharged under a first non-concentration polarization current to obtain an initial standard potential curve of charge and discharge of the initial positive electrode active material.

[0073] Subsequently, the same initial positive electrode active material, after undergoing complex operating conditions, is transformed into the positive electrode active material to be tested. This positive electrode active material to be tested is assembled into a half-cell, resulting in a cycled half-cell. A second charge-discharge cycle of the cycled half-cell is performed under a second non-concentration-polarized current to obtain a charge-discharge cycle standard potential curve for the positive electrode active material to be tested.

[0074] By comparing the initial charge-discharge standard potential curve with the charge-discharge cycle standard potential curve, it is determined whether the structure of the positive electrode active material under test has changed relative to the initial positive electrode active material after experiencing complex operating conditions. It can be understood that the greater the difference between the initial charge-discharge standard potential curve and the charge-discharge cycle standard potential curve, the greater the degree of structural change of the initial positive electrode active material after experiencing complex operating conditions.

[0075] In traditional testing methods, concentration polarization can cause uneven deposition at the negative electrode, forming dendrites that interfere with the test signal and obscure the structural evolution of the positive electrode active material. This method, however, suppresses concentration polarization by regulating the current excitation pattern, thereby avoiding dendrite interference with the test results. Furthermore, by comparing the standard potential curves before and after complex operating conditions, after subtracting the negative electrode's influence, it is possible to accurately identify whether the positive electrode active material undergoes key structural evolution under complex operating conditions, such as lattice distortion, phase transition, transition metal dissolution, or oxygen loss.

[0076] The advantage of the detection method of the present application is that it uses the electrochemical signal after the correction of concentration polarization to correlate the structural state of the material, providing a reliable basis for revealing the attenuation mechanism of the positive electrode active material. For example, if the peak position shifts or the intensity decays in the charge-discharge cycle standard potential curve, it can be inferred that the material has undergone an irreversible phase change or active material loss; if the shape of the charge-discharge cycle standard potential curve is distorted, it may correspond to a decrease in lattice stability or local structural disorder. Therefore, the detection method of the present application is not only suitable for the optimization of positive electrode active materials, but also can accelerate the development of new high-capacity, high-stability positive electrode active materials, and has important guiding significance for promoting the research and development of high-energy density, high-cycle batteries.

[0077] The present application does not limit the specific method for obtaining the first non-concentration polarization current and the second non-concentration polarization current. In a specific embodiment, before the first charge-discharge cycle and the second charge-discharge cycle, the method further includes:

[0078] Perform current-potential detection on the negative metal symmetrical battery to obtain N sets of current-potential data;

[0079] Based on the N-group current-potential data and the Butler–Volmer reaction model, the relationship between the interfacial active ion concentration and the current / potential of the negative electrode metal is obtained;

[0080] According to the relationship between the interfacial active ion concentration and the current / potential, respectively obtaining a first non-concentration polarization current and a second non-concentration polarization current;

[0081] The negative electrode metal in the negative electrode metal symmetrical battery is the same as the negative electrode metal in the initial half-cell and the cycle half-cell, and N≥2.

[0082] Specifically, a pair of negative metals is assembled into a cell. Note that the negative metal used is the same as that used in the cycled half-cell, and the electrolyte used in the pair is the same as that used in the cycled half-cell. N current-potential measurements are then performed on this negative metal symmetric cell. For example, the current is gradually increased according to an isogradient, and the negative metal symmetric cell has a corresponding potential at each current. By performing these N measurements at these N gradually increasing currents, N sets of current-potential data are obtained.

[0083] Substituting these N sets of current-potential data into the Butler–Volmer reaction model, we obtain the relationship between the interfacial active ion concentration of the negative electrode metal and the current / potential. The Butler–Volmer reaction model is shown below.

[0084]

[0085] Where i is the current value in the current-potential data, A / cm 2 η 界 is the potential value corresponding to i in the current-potential data, V; α is the energy barrier ratio from the reduction state to the transition state in the oxidation reaction, calculated as 0.5; β is the energy barrier ratio of the oxidation state in the corresponding reduction reaction, calculated as 0.5; n is the number of electrons in the negative electrode metal (for example, lithium, sodium, and potassium metals are all 1); F is the Farrand constant, 96485 C / mol; R is the ideal gas constant, 8.314 J / mol·K; T is the thermodynamic temperature, K; i dO is the active ion oxidation concentration difference, mol / L; i dRis the active ion reduction concentration, mol / L. Since the interface produces the limit of concentration polarization, the highest concentration of the interface will reach twice the electrolyte concentration C, so i dO with i dR The sum is 2C.

[0086] Specifically, according to the obtained N groups i dO -i dR The data is used to obtain the relationship between the interface active ion concentration of the negative electrode metal and the current / potential, which is a potential-current-interface active ion concentration curve. In this curve, the trend of the interface active ion concentration-current curve can be used to read the current range where concentration polarization does not occur. Any current value in this range can be regarded as the first non-concentration polarization current or the second non-concentration polarization current.

[0087] Furthermore, in order to improve the detection accuracy of the detection method of the present application, the first non-concentration polarization current and the second non-concentration polarization current are obtained respectively according to the relationship between the interfacial active ion concentration and the current / potential, including:

[0088] Obtaining a first non-concentration polarization current based on the relationship between the interfacial active ion concentration and the current / potential;

[0089] Obtaining a first non-concentration polarization reference current according to the first non-concentration polarization current, the negative electrode area of ​​the initial half-cell, and the initial positive electrode active material mass;

[0090] A second non-concentration polarization current is obtained according to the first non-concentration polarization reference current, the negative electrode area of ​​the cycle half-cell and the mass of the positive electrode active material to be measured.

[0091] As mentioned above, the first non-concentration polarization current and the second non-concentration polarization current in the active ion concentration-current / potential relationship are obtained by the negative electrode metal symmetric cell and its interface active ion concentration, where the current value in the range where no concentration polarization current occurs (unit: mA / cm 2 ) is calculated based on the area of ​​the electrode in the negative electrode pair battery. In order to improve the detection accuracy, enhance the adaptability of the positive electrode active material and the non-concentration polarization current, and avoid the structural state judgment deviation caused by the difference in the mass of the positive electrode active material in the initial half-cell and the cycle half-cell, the detection method of the present application takes the first non-concentration polarization current in this interval, and respectively uses the negative electrode area of ​​the initial half-cell and the initial positive electrode active material mass to convert to obtain the first non-concentration polarization reference current (unit is mA / g); the first non-concentration polarization reference current, the negative electrode area of ​​the cycle half-cell and the mass of the positive electrode active material to be measured are used to obtain the second non-concentration polarization current. By making the first charge and discharge cycle and the second charge and discharge cycle based on the current density per unit mass (mA / g), it is ensured that the initial half-cell and the cycle half-cell have similar reaction degrees,

[0092] Illustratively, the first non-concentration polarization current is multiplied by the negative electrode area in the initial half-cell and then divided by the mass of the initial positive electrode active material in the initial half-cell to obtain the first non-concentration polarization reference current of the present application; the first non-concentration polarization reference current is multiplied by the mass of the positive electrode active material to be tested in the cycle half-cell and then divided by the negative electrode area in the cycle half-cell to obtain the second non-concentration polarization current of the present application.

[0093] In a specific embodiment, the first charge-discharge cycle is performed on the initial half-cell under the first non-concentration polarization current to obtain the initial charge-discharge standard potential curve of the initial battery, including:

[0094] Performing a first charge on the initial half-cell at a first non-concentration polarization current to obtain the charging initial potential curve and the initial half-cell to be discharged;

[0095] Obtaining an initial charging standard potential curve of the initial half-cell according to the initial charging potential curve and the first negative electrode potential correction coefficient;

[0096] performing a first discharge on the initial half-cell to be discharged under a first non-concentration polarization current to obtain an initial discharge potential curve of the initial half-cell;

[0097] Obtaining an initial discharge standard potential curve of the initial half-cell according to the initial discharge potential curve and the first negative electrode potential correction coefficient;

[0098] The first negative electrode potential correction coefficient is obtained according to the first non-concentration polarization current and the negative electrode metal coefficient.

[0099] Specifically, the initial half-cell is first charged at a first non-concentration polarization current until the battery capacity reaches 100%, after which charging is stopped. The charge cutoff voltage is determined by the characteristics of the initial positive electrode active material. During the first charge, a potential curve is recorded, which is the initial charge potential curve. This initial charge potential curve is then corrected using the first negative electrode potential correction coefficient to obtain the initial charge standard potential curve.

[0100] After the first charge is completed, the initial half-cell has a 100% capacity, ready for discharge. Similarly, the initial half-cell undergoes a first discharge at the first non-concentration polarization current until the battery capacity reaches 0%, whereupon discharge is terminated. The discharge cutoff voltage depends on the characteristics of the initial positive electrode active material. During the first discharge, a potential curve is recorded, which is the initial discharge potential curve. The initial discharge potential curve is then corrected using the first negative electrode potential correction coefficient to obtain the initial discharge standard potential curve.

[0101] It should be noted that the first negative electrode potential correction factor in this application is derived based on the first non-concentration polarization current and the negative electrode metal coefficient. This correction factor is used to eliminate the effect of the negative electrode overpotential on the initial positive electrode active material standard potential curve during the first charge and first discharge processes. The negative electrode metal coefficient varies depending on the choice of negative electrode metal.

[0102] The present application does not limit the specific method for obtaining the first negative electrode potential correction coefficient.

[0103]

[0104] Where i1 is the first non-concentration polarization current, mAcm -2 f(i1) is the first negative electrode potential correction coefficient; a, b, c, and d are the negative electrode metal coefficients. When the negative electrode is potassium, a = -0.21, b = 0.20, c = -0.03, d = 0.37; when the negative electrode is sodium, a = -0.12, b = 0.12, c = 0.01, d = 0.35; when the negative electrode is lithium, a = -0.60, b = 0.06, c = 0.03, d = 0.50.

[0105] This application also does not limit the method for correcting the initial charge potential curve and the initial discharge potential curve using the first negative electrode potential correction coefficient. For example, the initial charge potential curve and the initial discharge potential curve can be corrected according to Formula 2 and Formula 3 to obtain the initial charge standard potential curve and the initial discharge standard potential curve.

[0106] E 1标准充 =E 1充 -0.8f(i1) Equation 2

[0107] E 1标准放 =E 1放 +0.2f(i1) Equation 3

[0108] Among them, E 1充 In the initial charge potential curve, E 1放 is the initial discharge potential curve, E 1标准充 is the initial standard potential curve of charging, E 1标准放 is the standard potential curve at the initial discharge.

[0109] The detection method of the present application accurately quantifies and deducts the parasitic influence of the negative electrode overpotential in the first charge and discharge cycle by correlating the negative electrode metal coefficient with the polarization current, thereby ensuring that the intrinsic standard potential curve of the initial positive electrode active material is not distorted by the negative electrode polarization effect, thereby improving the reliability of the detection of the structural state of the positive electrode active material.

[0110] In a specific embodiment, the second charge-discharge cycle is performed on the cycled half-cell under the second non-concentration polarization current to obtain a charge-discharge cycle standard potential curve of the cycled half-cell, including:

[0111] Performing a second charge on the cycle half-cell at a second non-concentration polarization current to obtain a charge cycle potential curve of the cycle half-cell and a cycle half-cell to be discharged;

[0112] Obtaining a charge cycle standard potential curve of the cycle half-cell according to the charge cycle potential curve and the second negative electrode potential correction coefficient;

[0113] performing a second discharge on the to-be-discharged cycle half-cell at a second non-concentration polarization current to obtain a discharge cycle potential curve of the cycle half-cell;

[0114] Obtaining a discharge cycle standard potential curve of the cycle half-cell according to the discharge cycle potential curve and the second negative electrode potential correction coefficient;

[0115] The second negative electrode potential correction coefficient is obtained according to the second non-concentration polarization current and the negative electrode metal coefficient.

[0116] Specifically, the cycled half-cell undergoes a second charge at a second, non-concentration-polarized current until the battery capacity reaches 100%, after which charging is stopped. The charge cutoff voltage depends on the characteristics of the initial positive electrode active material. During the second charge, a potential curve is recorded, which is the charge cycle potential curve. The charge cycle potential curve is then corrected using the second negative electrode potential correction factor to obtain a standard charge cycle potential curve.

[0117] After the second charge is complete, the circulating half-cell becomes a circulating half-cell ready for discharge with 100% capacity. Similarly, the circulating half-cell ready for discharge is discharged again at a second non-concentration polarization current until the battery capacity reaches 0%. The discharge cutoff voltage depends on the characteristics of the circulating positive electrode active material. During the second discharge, the potential curve is recorded, which is the discharge cycle potential curve. The discharge cycle potential curve is then corrected using the second negative electrode potential correction factor to obtain the discharge cycle standard potential curve.

[0118] It should be noted that the second negative electrode potential correction factor in this application is derived based on the second non-concentration polarization current and the negative electrode metal coefficient. This correction factor is used to eliminate the effect of the negative electrode overpotential on the standard potential curve of the cycled positive electrode active material during the second charge and second discharge processes. The negative electrode metal coefficient varies depending on the choice of negative electrode metal.

[0119] The present application does not limit the specific method for obtaining the second negative electrode potential correction coefficient.

[0120]

[0121] Where i2 is the second non-concentration polarization current, mAcm -2 f(i2) is the second negative electrode potential correction coefficient; a, b, c, and d are the negative electrode metal coefficients. When the negative electrode is potassium, a = -0.21, b = 0.20, c = -0.03, d = 0.37; when the negative electrode is sodium, a = -0.12, b = 0.12, c = 0.01, d = 0.35; when the negative electrode is lithium, a = -0.60, b = 0.06, c = 0.03, d = 0.50.

[0122] This application also does not limit the method for correcting the charge cycle potential curve and the discharge cycle potential curve using the second negative electrode potential correction coefficient. For example, the charge cycle potential curve and the discharge cycle potential curve can be corrected according to Equations 5 and 6 to obtain the charge cycle standard potential curve and the discharge cycle standard potential curve.

[0123] E 2标准充 =E 2充 -0.8f(i2) Equation 5

[0124] E 2标准放 =E 2放 +0.2f(i2) Equation 6

[0125] Among them, E 2充 In the charge cycle potential curve, E 2放 is the discharge cycle potential curve, E 2标准充 is the standard potential curve of the charge cycle, E 2标准放 is the standard potential curve of the discharge cycle.

[0126] The detection method of the present application accurately quantifies and deducts the parasitic influence of the negative electrode overpotential in the second charge and discharge cycle by correlating the negative electrode metal coefficient with the polarization current, thereby ensuring that the intrinsic standard potential curve of the circulating positive electrode active material is not distorted by the negative electrode polarization effect, thereby improving the reliability of the detection of the structural state of the positive electrode active material.

[0127] Furthermore, judging the cyclic structural state of the positive electrode active material to be tested in the cycle half-cell according to the charge-discharge initial standard potential curve and the charge-discharge cycle standard potential curve includes:

[0128] If the potential difference between the charging initial standard potential curve and the charging cycle standard potential curve at the first charging state of charge is greater than a first preset value, the cyclic structural state of the positive electrode active material to be tested at the first charging state of charge is a first change state.

[0129] Specifically, by comparing the initial charge standard potential curve and the charge cycle standard potential curve, if the potential difference between the two at the same first state of charge is greater than a first preset value, it is determined that the initial positive electrode active material has undergone structural changes when charged to the first state of charge after experiencing complex operating conditions. The first state of charge can be the battery's gram capacity or the percentage of remaining capacity.

[0130] This application does not limit the specific selection of the first preset value. It is understood that the smaller the first preset value, the more sites where the initial positive electrode active material undergoes structural changes after experiencing complex operating conditions. For example, the first preset value can be 0.05V, 0.1V, 0.2V, 0.3V, 0.4V, 0.5V, etc. It should be emphasized that in this application, whether the positive electrode active material to be tested is in the first changed state is determined by comparing the absolute value of the potential difference with the first preset value.

[0131] In addition, if the potential difference between the discharge initial standard potential curve and the discharge cycle standard potential curve in the second discharge charge state is greater than a second preset value, the cycle structure state of the positive electrode active material to be tested in the second discharge charge state is the second change state.

[0132] Specifically, by comparing the initial discharge standard potential curve and the discharge cycle standard potential curve, if the potential difference between the two at the same second state of charge is greater than a second preset value, it is determined that the initial positive electrode active material has undergone structural changes when discharged to the second state of charge after experiencing complex operating conditions. The second state of charge can be the battery's gram capacity or the percentage of remaining capacity.

[0133] This application does not limit the specific selection of the second preset value. It can be understood that the smaller the second preset value, the more sites where the initial positive electrode active material undergoes structural changes after experiencing complex working conditions. For example, the second preset value can be 0.05V, 0.1V, 0.2V, 0.3V, 0.4V, 0.5V, etc. It should be emphasized that in this application, whether the positive electrode active material to be tested is in the second change state is determined by comparing the absolute value of the potential difference with the second preset value. In the detection method of this application, the first preset value and the second preset value can be the same or different.

[0134] This application effectively reveals the structural changes of positive electrode active materials under complex working conditions through a systematic comparative analysis of the initial standard potential curve of charge (discharge) and the standard potential curve of charge (discharge) cycle. Specifically, when the two curves show a potential difference exceeding the first (second) preset value at the same first (second) state of charge, this phenomenon essentially reflects the thermodynamic behavior change of the crystal structure of the positive electrode active material during the active ion deintercalation process. This confirms from an electrochemical perspective that the positive electrode active material has undergone irreversible structural reconstruction, providing a non-destructive, highly sensitive detection method for evaluating the structural stability of the positive electrode active material.

[0135] Furthermore, to improve the evaluation mechanism for structural changes in the positive electrode active material, the detection method of the present application also introduces in-situ structural monitoring. Specifically, the detection method of the present application also includes: performing in-situ structural monitoring on the initial half-cell during the first charge-discharge cycle to obtain the full-cycle charging and full-cycle discharge structural states of the initial positive electrode active material.

[0136] While traditional structural testing can provide structural and morphological information about the positive electrode active material, these tests typically only provide static information at a specific point in time and cannot continuously track the dynamic evolution of the positive electrode active material during battery cycling. The present detection method, however, employs in-situ structural monitoring, monitoring the structure of the initial positive electrode active material in real time during the initial battery's first charge-discharge cycle to obtain the full-cycle charge and discharge structural states of the initial positive electrode active material.

[0137] The present application does not limit the specific form of in-situ structural monitoring, for example, it can be in-situ X-ray diffraction detection, in-situ Raman spectroscopy detection, in-situ infrared spectroscopy detection, in-situ transmission electron microscopy detection, in-situ X-ray absorption spectroscopy detection, etc.

[0138] In a specific embodiment, if the positive electrode active material to be tested is in the first change state, the method further includes:

[0139] performing a third charging cycle on the cycling half-cell at the second non-concentration polarization current;

[0140] In the third discharge cycle, performing in-situ structural monitoring on the cycled half-cell at the first charge state of charge to obtain a current charge structural state of the positive electrode active material to be tested at the first charge state of charge;

[0141] A first change state parameter of the positive electrode active material to be tested is obtained according to the current charging structure state and the full-cycle charging structure state.

[0142] When the positive electrode active material to be tested is in the first change state, in order to provide an objective and quantifiable evaluation index, the present application also includes the step of performing a third charging cycle on the cycled half-cell. In the third charging cycle, the cycled half-cell is a half-cell whose SOC is 0% after completing the second discharge. When the cycled half-cell is charged to the first charging state of charge, the cycled half-cell is subjected to in-situ structural monitoring to obtain the current charging structure state of the positive electrode active material to be tested in the first charging state of charge. Subsequently, by comparing the current charging structure state with the full-cycle charging structure state, the first change state parameter of the positive electrode active material to be tested in the first charging state of charge can be quantified. It can be understood that when comparing, it is necessary to compare the portion of the full-cycle charging structure state that is in the first charging state of charge with the current charging structure state.

[0143] Taking in-situ structural monitoring as an example of in-situ X-ray diffraction detection, the above method can observe that relative to the initial positive electrode active material, the crystal structure evolution parameters of the positive electrode active material during the charging process after experiencing complex working conditions can be clearly located through information such as the position, peak intensity, and peak width of the diffraction peak. This has irreplaceable guiding value for battery failure, iteration of positive electrode active materials, and optimization of battery operating conditions.

[0144] In the detection method of the present application, the third charging cycle is only initiated when the positive electrode active material to be tested is in the first change state. It can be understood that if in-situ structural monitoring of the cycle half-cell is initiated during the second charging, once the initial positive electrode active material does not undergo structural changes after experiencing complex working conditions, it will cause unnecessary activation of the monitoring equipment, reducing the service life of the monitoring equipment. In addition, in the third charging, when the positive electrode active material to be tested enters the first charging state of charge, the in-situ structural monitoring is initiated. The timing of this detection is highly consistent with the timing of the structural change of the positive electrode active material to be tested, avoiding the generation of a large amount of redundant data, significantly reducing the data collection burden, reducing the detection cost of the detection method of the present application, and improving the detection efficiency of the detection method of the present application.

[0145] Similarly, if the positive electrode active material to be tested is in the second change state, the method further includes:

[0146] performing a third discharge on the cycle half-cell at the second non-concentration polarization current;

[0147] In the third discharge, performing in-situ structural monitoring on the cycled half-cell in the second discharge state to obtain a current discharge structural state of the positive electrode active material to be tested in the second discharge state;

[0148] According to the current discharge structure state and the full-cycle discharge structure state, a second change state parameter of the positive electrode active material to be tested is obtained.

[0149] The cycle half-cell that performs the third discharge is the cycle half-cell that is thirdly charged to a SOC of 100%.

[0150] It can be understood that the execution of the above-mentioned third discharge and in-situ structure monitoring has the same significance as the above-mentioned second discharge and in-situ structure monitoring, and can guide the acquisition of the crystal structure evolution parameters of the positive electrode active material to be tested during the discharge process after experiencing complex working conditions. It will not be repeated here.

[0151] A second aspect of the present application further provides a detection device for a positive electrode active material, comprising:

[0152] a first acquisition module, configured to perform a first charge-discharge cycle on the initial half-cell under a first non-concentration polarization current to obtain an initial charge-discharge standard potential curve of the initial positive electrode active material in the initial half-cell;

[0153] a second acquisition module, performing a second charge-discharge cycle on the cycle half-cell under a second non-concentration polarization current to obtain a charge-discharge cycle standard potential curve of the positive electrode active material to be tested in the cycle half-cell;

[0154] The processing module is used to judge the structural state of the positive electrode active material to be tested according to the charge-discharge initial standard potential curve and the charge-discharge cycle standard potential curve.

[0155] The processing module is further used to perform current-potential detection on the negative electrode metal symmetrical battery before the first charge and discharge cycle and the second charge and discharge cycle to obtain N groups of current-potential data; obtain the relationship between the interface active ion concentration-current / potential of the negative electrode metal based on the N groups of current-potential data and the Butler–Volmer reaction model; obtain the first non-concentration polarization current and the second non-concentration polarization current respectively based on the interface active ion concentration-current / potential relationship; wherein the negative electrode metal in the negative electrode metal symmetrical battery is the same as the negative electrode metal in the initial half-cell and the cycle half-cell, and N≥2.

[0156] The processing module is specifically used to obtain a first non-concentration polarization current based on the relationship between the interfacial active ion concentration and the current / potential; obtain a first non-concentration polarization reference current based on the first non-concentration polarization current, the negative electrode area of ​​the initial half-cell, and the initial positive electrode active material mass; and obtain a second non-concentration polarization current based on the first non-concentration polarization reference current, the negative electrode area of ​​the cycle half-cell, and the positive electrode active material mass to be measured.

[0157] The processing module is further configured to perform a first charge on the initial half-cell under a first non-concentration polarization current to obtain the initial charge potential curve and the initial half-cell to be discharged; obtain an initial charge standard potential curve of the initial half-cell based on the initial charge potential curve and the first negative electrode potential correction coefficient; perform a first discharge on the initial half-cell to be discharged under the first non-concentration polarization current to obtain an initial discharge potential curve of the initial half-cell; and obtain an initial discharge standard potential curve of the initial half-cell based on the initial discharge potential curve and the first negative electrode potential correction coefficient; wherein the first negative electrode potential correction coefficient is obtained based on the first non-concentration polarization current and the negative electrode metal coefficient.

[0158] The processing module is further specifically configured to perform a second charge on the circulating half-cell under a second non-concentration polarization current to obtain a charge cycle potential curve of the circulating half-cell and a circulating half-cell to be discharged; obtain a charge cycle standard potential curve of the circulating half-cell based on the charge cycle potential curve and the second negative electrode potential correction coefficient; perform a second discharge on the circulating half-cell to be discharged under the second non-concentration polarization current to obtain a discharge cycle potential curve of the circulating half-cell; and obtain a discharge cycle standard potential curve of the circulating half-cell based on the discharge cycle potential curve and the second negative electrode potential correction coefficient; wherein the second negative electrode potential correction coefficient is obtained based on the second non-concentration polarization current and the negative electrode metal coefficient.

[0159] The processing module is also used to determine that if the potential difference between the charging initial standard potential curve and the charging cycle standard potential curve at the first charging state of charge is greater than a first preset value, the cyclic structural state of the positive electrode active material to be tested at the first charging state of charge is a first changed state.

[0160] The processing module is further configured to determine that the cyclic structural state of the positive electrode active material to be tested in the second discharge charge state is a second changed state if the potential difference between the discharge initial standard potential curve and the discharge cycle standard potential curve in the second discharge charge state is greater than a second preset value.

[0161] The processing module is further configured to perform in-situ structural monitoring on the initial half-cell during the first charge-discharge cycle to obtain a full-cycle charge structural state and a full-cycle discharge structural state of the initial positive electrode active material.

[0162] If the positive electrode active material to be tested is in the first change state, the processing module is further used to execute a third charge of the circulating half-cell under the second non-concentration polarization current; in the third charge, in-situ structural monitoring of the circulating half-cell at the first charging state of charge is performed to obtain the current charging structural state of the positive electrode active material to be tested at the first charging state of charge; and according to the current charging structural state and the full-cycle charging structural state, obtain the first change state parameter of the positive electrode active material to be tested.

[0163] If the positive electrode active material to be tested is in the second change state, the processing module is further configured to perform a third discharge on the cycled half-cell under the second non-concentration polarization current; during the third discharge, perform in-situ structural monitoring on the cycled half-cell when it is in the second discharge charge state to obtain a current discharge structural state of the positive electrode active material to be tested in the second discharge charge state; and obtain a second change state parameter of the positive electrode active material to be tested based on the current discharge structural state and the full-cycle discharge structural state.

[0164] The detection device for positive electrode active materials provided in the present application can execute the method provided in the first aspect above, and its implementation principle and technical effects are similar, so they will not be described in detail in this embodiment.

[0165] A third aspect of the present application provides a device for detecting positive electrode active materials. The device includes at least one processor and a memory. Optionally, the device also includes a communication component. The processor, memory, and communication component are connected via a bus.

[0166] In a specific implementation process, at least one processor executes computer-executable instructions stored in a memory, so that the at least one processor performs the above method.

[0167] The specific implementation process of the processor can refer to the above method. Its implementation principle and technical effects are similar and will not be repeated here in this embodiment.

[0168] In the above embodiments, it should be understood that the processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASICs), etc. A general-purpose processor may be a microprocessor or any conventional processor. The steps of the method disclosed in the present invention may be directly executed by a hardware processor or by a combination of hardware and software modules in the processor.

[0169] The memory may include a high-speed memory (Random Access Memory, RAM), and may also include a non-volatile memory (NVM), such as at least one disk memory.

[0170] The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus. Buses can be classified into address buses, data buses, and control buses. For ease of illustration, the buses in the drawings of this application are not limited to just one bus or just one type of bus.

[0171] The fourth aspect of the present application further provides a computer program product, comprising a computer program, which implements the above method when executed by a processor.

[0172] The fifth aspect of the present application further provides a computer-readable storage medium, in which computer-executable instructions are stored. When a processor executes the computer-executable instructions, the above method is implemented.

[0173] The above-mentioned readable storage medium can be implemented by any type of volatile or non-volatile memory device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic memory, flash memory, magnetic disk or optical disk. The readable storage medium can be any available medium that can be accessed by a general-purpose or special-purpose computer.

[0174] An exemplary readable storage medium is coupled to a processor so that the processor can read information from the readable storage medium and write information to the readable storage medium. Of course, the readable storage medium can also be an integral part of the processor. The processor and the readable storage medium can be located in an application specific integrated circuit (ASIC). Of course, the processor and the readable storage medium can also exist in the device as discrete components.

[0175] The division of units is merely a logical functional division; actual implementations may employ alternative divisions, such as combining or integrating multiple units or components into another system, or omitting or disabling certain features. Furthermore, any direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between devices or units, either through an interface, electrical, mechanical, or other means.

[0176] Units described as separate components may or may not be physically separate, and components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0177] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0178] If the function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the various embodiments of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, and other media that can store program code.

[0179] Those skilled in the art will appreciate that all or part of the steps in the above-described method embodiments can be implemented using hardware associated with program instructions. The aforementioned program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above-described method embodiments. The aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[0180] Example

[0181] The positive electrode active material detection method of this embodiment includes the following steps:

[0182] 1) A potassium metal pair battery was assembled using potassium metal and an electrolyte. The electrolyte consisted of 0.8 mol / L KPF6 salt dissolved in EC@DEC solvent with a solvent volume ratio of 1:1. The negative electrode area was 1.77 cm 2 ; The quality and thickness of potassium metal do not affect the results.

[0183] The current-potential test of the potassium metal symmetric battery was carried out to obtain the current-potential data shown in Table 1. Substituting the data in Table 1 into the Butler–Volmer reaction model, we obtain Figure 1 The curve shown. Figure 1 The relationship between the interfacial active ion concentration and the current / potential of potassium metal in Example 1 of the present application is shown in FIG. Figure 1 As shown, curve 1 is the anode interface active ion concentration-current curve, curve 2 is the current-potential curve, and curve 3 is the cathode interface active ion concentration-current curve. The range shown in the dotted box is the current range where concentration polarization does not occur, which is 0-0.106 mA / cm 2 .

[0184] Table 1

[0185] Current (mA) Potential (V) 0.354 0.109813 0.708 0.155274 0.885 0.162566 1.77 0.188861 3.54 0.229439 5.31 0.312438 7.08 0.498829

[0186] 2) K 1.8 Zn 0.2 Ni 0.2 Co 0.2 Al 0.2 Mn 0.2 Fe(CN)6 powder, conductive carbon black, and PVDF were mixed in a mass ratio of 8:1:1, stirred for 4 hours, and then coated on a current collector. The mixture was then dried overnight in a vacuum drying oven at 60 degrees Celsius to obtain the positive electrode sheet of the initial half-cell. The positive electrode sheet, potassium metal negative electrode sheet, and electrolyte were assembled into an initial half-cell. The electrolyte composition was the same as that of the potassium metal symmetric cell.

[0187] The negative electrode area used in this embodiment is 1.77 cm 2 , select 0.032mA / cm in this range 2 As the first non-concentration polarization current, it is counted as i1; the positive electrode active material K in the initial half-cell 1.8 Zn 0.2 Ni 0.2 Co 0.2 Al 0.2 Mn 0.2 The mass of Fe(CN)6 powder is 0.72 mg. The first non-concentration polarization current is multiplied by the area of ​​the potassium metal negative electrode and then divided by K 1.8 Zn 0.2 Ni 0.2 Co 0.2 Al0.2 Mn 0.2 The mass of Fe(CN)6 powder is converted to 0.0787 mA / g as the unit mass current density of the positive electrode material (i.e., the first non-concentration polarization reference current);

[0188] 3)K 1.8 Zn 0.2 Ni 0.2 Co 0.2 Al 0.2 Mn 0.2 A full battery was assembled using Fe(CN)6 powder as the positive electrode and matching graphite as the negative electrode. It was cycled for 2000 cycles at 200 mA / g (calculated based on the mass of the positive electrode active material) and then disassembled.

[0189] 4) disassembling the positive electrode sheet of the full battery in step 3), scraping off the positive electrode active layer to prepare a positive electrode sheet for a cycled half-battery; and assembling the positive electrode sheet into a cycled half-battery according to the steps of step 2);

[0190] Cathode active material K in cycled half-cell 1.8 Zn 0.2 Ni 0.2 Co 0.2 Al 0.2 Mn 0.2 The mass of Fe(CN)6 powder is 0.7 mg, and the unit mass current density of the positive electrode material is 0.0787 mA / g. The negative electrode area is 1.77 cm 2 , after conversion 0.0311mA / cm 2 As the second non-concentration polarization current, it is recorded as i2;

[0191] 5) Performing a first charge-discharge cycle on the initial half-cell using the first non-concentration polarization current i1, while simultaneously starting in-situ XRD monitoring to obtain a charge initial potential curve, a discharge initial potential curve, and an initial in-situ XRD pattern. Figure 2 The charge initial potential curve and discharge initial potential curve of the initial half-cell of Example 1 of the present application;

[0192] According to Formula 1, Formula 2 and Formula 3, the initial standard potential curve of charge and the initial standard potential curve of discharge are obtained. Figure 3 The initial standard potential curve for charge and discharge of the initial half-cell of Example 1 of the present application;

[0193] 6) Performing a second charge-discharge cycle on the cycle half-cell using the second non-concentration polarization current i2 to obtain a charge cycle potential curve and a discharge cycle potential curve. Figure 4 The charge cycle potential curve and discharge cycle potential curve of the cycle half-cell of Example 1 of the present application;

[0194] According to equations 4, 5, and 6, the charge cycle standard potential curve and the discharge cycle standard potential curve are obtained. Figure 5 The charge cycle standard potential curve and the discharge cycle standard potential curve of the cycle half-cell of Example 1 of the present application;

[0195] 7) Take 0.4V as the first preset value Figure 3 and Figure 5 For comparison, Figure 6 This is a comparison diagram of the initial charging standard potential curve and the charging cycle standard potential curve of Example 1 of this application. Figure 6 As shown, at least when the gram capacity is 10-30 mAh / g (the part in the circle), the potential difference between curve 4 (charging cycle standard potential curve) and curve 5 (charging initial standard potential curve) is greater than the first preset value, indicating that K 1.8 Zn 0.2 Ni 0.2 Co 0.2 Al 0.2 Mn 0.2 After the Fe(CN)6 powder has undergone the complex working conditions of step 3), when it is charged to the gram capacity, its crystal structure changes;

[0196] 8) charging the cycle half-cell that has completed the second charge and discharge in step 6) again with the second non-concentration polarized current i2, and starting in-situ XRD monitoring when the gram capacity is 10-30 mAh / g to obtain a cyclic in-situ XRD pattern;

[0197] Figure 7 This is the initial in-situ XRD contour map of Example 1 of the present application, Figure 8 for Figure 7 Partially enlarged schematic diagram, specifically, Figure 8 The XRD patterns of the initial half-cells were charged to 10-30 mAh / g. Figure 9 This is the cyclic in-situ XRD contour map of Example 1 of the present application, Figure 10 for Figure 9 Partially enlarged schematic diagram, specifically, Figure 10 The XRD patterns of the half-cells were shown when charged to 10-30 mAh / g. Comparison of the two revealed a peak shift, indicating that the lattice has changed when the voltage platform changes significantly.

[0198] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting a positive electrode active material, characterized in that: The following steps are involved: performing a first charge-discharge cycle on the initial half-cell at a first non-concentration polarization current to obtain an initial charge-discharge standard potential curve of the initial positive electrode active material in the initial half-cell; performing a second charge-discharge cycle on the cycle half-cell under a second non-concentration polarization current to obtain a charge-discharge cycle standard potential curve of the positive electrode active material to be tested in the cycle half-cell; The structural state of the positive electrode active material to be tested is judged according to the charge-discharge initial standard potential curve and the charge-discharge cycle standard potential curve.

2. The detection method according to claim 1, wherein Before the first charge-discharge cycle and the second charge-discharge cycle, the method further includes: Perform current-potential detection on the negative metal symmetrical battery to obtain N sets of current-potential data; Based on the N-group current-potential data and the Butler–Volmer reaction model, the relationship between the interfacial active ion concentration and the current / potential of the negative electrode metal is obtained; According to the relationship between the interfacial active ion concentration and the current / potential, respectively obtaining a first non-concentration polarization current and a second non-concentration polarization current; The negative electrode metal in the negative electrode metal symmetrical battery is the same as the negative electrode metal in the initial half-cell and the cycle half-cell, and N≥2.

3. The detection method according to claim 2, characterized in that The obtaining of the first non-concentration polarization current and the second non-concentration polarization current according to the relationship between the interfacial active ion concentration and the current / potential includes: Obtaining a first non-concentration polarization current based on the relationship between the interfacial active ion concentration and the current / potential; Obtaining a first non-concentration polarization reference current according to the first non-concentration polarization current, the negative electrode area of ​​the initial half-cell, and the initial positive electrode active material mass; A second non-concentration polarization current is obtained according to the first non-concentration polarization reference current, the negative electrode area of ​​the cycle half-cell and the mass of the positive electrode active material to be measured.

4. The detection method according to any one of claims 1 to 3, characterized in that The first charge-discharge cycle is performed on the initial half-cell under the first non-concentration polarization current to obtain the initial charge-discharge standard potential curve of the initial battery, including: Performing a first charge on the initial half-cell at a first non-concentration polarization current to obtain the charging initial potential curve and the initial half-cell to be discharged; Obtaining an initial charging standard potential curve of the initial half-cell according to the initial charging potential curve and the first negative electrode potential correction coefficient; performing a first discharge on the initial half-cell to be discharged under a first non-concentration polarization current to obtain an initial discharge potential curve of the initial half-cell; Obtaining an initial discharge standard potential curve of the initial half-cell according to the initial discharge potential curve and the first negative electrode potential correction coefficient; The first negative electrode potential correction coefficient is obtained according to the first non-concentration polarization current and the negative electrode metal coefficient.

5. The detection method according to claim 4, characterized in that The step of performing a second charge-discharge cycle on the cycle half-cell under the second non-concentration polarization current to obtain a charge-discharge cycle standard potential curve of the cycle half-cell comprises: Performing a second charge on the cycle half-cell at a second non-concentration polarization current to obtain a charge cycle potential curve of the cycle half-cell and a cycle half-cell to be discharged; Obtaining a charge cycle standard potential curve of the cycle half-cell according to the charge cycle potential curve and the second negative electrode potential correction coefficient; performing a second discharge on the to-be-discharged cycle half-cell at a second non-concentration polarization current to obtain a discharge cycle potential curve of the cycle half-cell; Obtaining a discharge cycle standard potential curve of the cycle half-cell according to the discharge cycle potential curve and the second negative electrode potential correction coefficient; The second negative electrode potential correction coefficient is obtained according to the second non-concentration polarization current and the negative electrode metal coefficient.

6. The detection method according to claim 5, characterized in that The step of judging the cycle structure state of the positive electrode active material to be tested in the cycle half-cell according to the charge-discharge initial standard potential curve and the charge-discharge cycle standard potential curve comprises: If the potential difference between the charging initial standard potential curve and the charging cycle standard potential curve at the first charging state of charge is greater than a first preset value, the cyclic structural state of the positive electrode active material to be tested at the first charging state of charge is a first changed state; and / or, If the potential difference between the discharge initial standard potential curve and the discharge cycle standard potential curve in the second discharge charge state is greater than a second preset value, the cycle structure state of the positive electrode active material to be tested in the second discharge charge state is a second change state.

7. The detection method according to claim 6, characterized in that Also includes: In-situ structural monitoring is performed on the initial half-cell during the first charge and discharge cycle to obtain a full-cycle charge structural state and a full-cycle discharge structural state of the initial positive electrode active material.

8. The detection method according to claim 7, characterized in that If the positive electrode active material to be tested is in the first change state, the method further includes: performing a third charging on the cycling half-cell at the second non-concentration polarization current; In the third charge, in-situ structural monitoring is performed on the cycled half-cell at the first charge state of charge to obtain a current charge structural state of the positive electrode active material to be tested at the first charge state of charge; A first change state parameter of the positive electrode active material to be tested is obtained according to the current charging structure state and the full-cycle charging structure state.

9. The detection method according to claim 7, characterized in that If the positive electrode active material to be tested is in the second change state, the method further includes: performing a third discharge on the cycle half-cell at the second non-concentration polarization current; In the third discharge, performing in-situ structural monitoring on the cycled half-cell in the second discharge state to obtain a current discharge structural state of the positive electrode active material to be tested in the second discharge state; According to the current discharge structure state and the full-cycle discharge structure state, a second change state parameter of the positive electrode active material to be tested is obtained.

10. A detection device for positive electrode active materials, characterized in that: include: Memory, processor; The memory stores computer-executable instructions; The processor executes the computer-executable instructions stored in the memory, so that the processor performs the method according to any one of claims 1 to 9.

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