In-situ monitoring method for deintercalation of active ions in active material

Abstract

The invention provides an in-situ monitoring method for deintercalation of active ions in an active material. The method comprises the following steps: thinning a to-be-detected sample to be below 150nm by adopting an FIB technology to obtain a to-be-detected sheet; determining an included angle between a preferential orientation path of active ion embedding and an electron beam by adopting an EBSD technology, and selecting crystal grains with the included angle of 85-95 degrees as an in-situ monitoring object; transferring the active metal to the conductive microprobe, oxidizing a part of the active metal on the conductive microprobe to form an active metal oxide, and obtaining a negative electrode and an electrolyte attached to the conductive microprobe; the method comprises the following steps: fixing a to-be-tested sheet at a fixed end of a sample rod of an in-situ TEM tester, fixing a negative electrode and an electrolyte at a mobile end of the in-situ TEM tester, and constructing in a visual field of the tester to form a solid-state battery; and connecting the to-be-detected sheet with the negative electrode of the external power supply, connecting the negative electrode with the positive electrode of the external power supply, applying voltage to the solid-state battery, and collecting electron energy loss spectrums at different positions in the crystal grains of the to-be-detected active material.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to an in-situ monitoring method for the intercalation and deintercalation of active ions in active materials. Background Technology

[0002] As crucial energy storage and conversion devices, the energy density and cycle stability of batteries depend critically on the migration and reaction mechanisms of active ions in electrode active materials during charge and discharge. To optimize electrode material performance, in-situ monitoring of structural evolution and electrochemical behavior during ion insertion / extraction at the microscopic scale is essential. However, existing in-situ monitoring methods suffer from insufficient stability in constructing reliable battery circuits, making it difficult to continuously track material dynamics under real reaction conditions. Furthermore, the analysis of electrochemical reaction mechanisms is not in-depth, particularly regarding the ability to elucidate reaction pathways and interface mechanisms, thus hindering the development and application of high-performance electrode active materials in novel battery systems such as lithium-ion and sodium-ion batteries. Summary of the Invention

[0003] This application provides an in-situ monitoring method for the intercalation and deintercalation of active ions in active materials, which can construct highly stable in-situ electrochemical micro batteries and realize in-situ observation of the intercalation and deintercalation process of active materials.

[0004] The first aspect of this application provides an in-situ monitoring method for the intercalation and deintercalation of active ions in an active material, comprising: In the sample preparation process, focused ion beam technology is used to thin the sample to a thickness of less than 150 nm under conditions of voltage 2kV-30kV and / or current 0.01nA-0.35nA, resulting in a thin film containing the active material to be tested. For the selection of monitoring targets, backscattered electron diffraction technology was used to detect the crystal orientation of the grains in the active material to be tested, and the angle α between the preferred orientation path of active ion insertion and the electron beam was determined. Grains with 85°≤α≤95° were selected as in-situ monitoring targets. The preparation of the negative electrode and electrolyte involves transferring an active metal to a conductive microprobe, oxidizing some of the active metal on the conductive microprobe to form an active metal oxide, and obtaining a negative electrode and electrolyte attached to the conductive microprobe. Solid-state battery construction involves fixing the sheet to be tested to the fixed end of the sample rod of an in-situ TEM instrument, and fixing a conductive microprobe with an attached negative electrode and electrolyte to the moving end of the sample rod of the in-situ TEM instrument. A solid-state battery is then constructed using the sheet to be tested, electrolyte, and negative electrode within the field of view of the in-situ TEM instrument. In the in-situ monitoring process, the sheet to be tested is connected to the negative terminal of an external power supply, and the negative terminal is connected to the positive terminal of an external power supply. A voltage is applied to the solid-state battery and the electron energy loss spectrum at different positions in the grains of the active material to be tested is collected.

[0005] In the aforementioned in-situ monitoring method, firstly, during sample preparation, focused ion beam technology is used to thin the sample layer by layer to a thickness of less than 150 nm under the aforementioned voltage and / or current. This ensures that the sample maintains good electron permeability while preserving the electrochemical activity of the active material itself, laying the foundation for obtaining high-resolution morphology and crystal structure of the active material. Subsequently, backscattered electron diffraction is used to analyze the crystal orientation of the grains in the active material and to screen out the target grains that preferentially undergo ion intercalation / deintercalation. This enables the monitoring of the pathways and crystal structures of active ions during different charge / discharge stages of the active material. Timely and accurate testing of bulk structural changes allows in-situ monitoring data to be more directly correlated with the key electrochemical behaviors of materials. Transferring active metals to conductive microprobes allows for the oxidation of some of the active metal on the microprobes to form active metal oxides, resulting in both the negative electrode and electrolyte. This integrated structure facilitates close contact between the negative electrode and electrolyte, reduces interfacial impedance, and promotes the formation of a stable electrochemical circuit. After the solid-state battery is constructed and a pathway is established, electron energy loss spectra at different locations on the target grains are collected, enabling dynamic tracking of the chemical environment, elemental valence states, and electronic structures along the active ion insertion / extraction pathways of the active material during the reaction. Through the close integration and synergistic effect of these steps, traditional local morphology observation is extended to the level of the chemical mechanism of active particles, providing direct data support for elucidating ion insertion / extraction pathways and interfacial reaction kinetics.

[0006] In any embodiment of the first aspect, the sample preparation process includes: The sample to be tested was thinned using focused ion beam technology under conditions of voltage of 10kV-30kV and / or current of 0.1nA-0.35nA to obtain a first thin film with a thickness of 800nm-1.5μm. A second thinning was performed on the first thin film using focused ion beam technology under conditions of voltage of 2kV-5kV and / or current of 0.01nA-0.3nA to obtain the thin film to be tested.

[0007] In any embodiment of the first aspect, the duration of each focused ion beam scan is less than 200 ns.

[0008] In any embodiment of the first aspect, a metal protective film is deposited on the surface of the sample to be tested before the sample is thinned using focused ion beam technology.

[0009] In any embodiment of the first aspect, the metal protective film is a platinum metal protective film.

[0010] In any embodiment of the first aspect, the thickness of the metal protective film is 2 μm - 4 μm.

[0011] In any embodiment of the first aspect, the conductive microprobe is a tungsten needle, a diamond probe, or a titanium alloy probe.

[0012] In any embodiment of the first aspect, the process of constructing a solid-state battery further includes confirming the presence of active metals and active metal oxides through electron diffraction results.

[0013] In any implementation of the first aspect, the in-situ monitoring process includes: The electron energy loss spectrum at different positions in the grains of the active material under test was acquired using an in-situ TEM instrument before the applied voltage was applied. A voltage was applied to a solid-state battery, and in-situ TEM was used to monitor the morphological changes of the grains of the active material under test. After the morphology of the active material to be tested is stabilized, the electron energy loss spectrum at different positions in the active material to be tested is collected using an in-situ TEM instrument. A reverse voltage was applied to a solid-state battery, and in-situ TEM was used to monitor the morphological changes of the grains of the active material under test. After the morphology of the active material to be tested is stabilized, an in-situ TEM instrument is used to collect the electron energy loss spectrum at different positions in the active material to be tested at this time.

[0014] In any embodiment of the first aspect, the active ions include lithium ions and sodium ions.

[0015] In any embodiment of the first aspect, the active material is a positive electrode active material or a negative electrode active material. The positive electrode active material includes one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, sodium vanadium fluorophosphate, and sulfur; and / or the negative electrode active material includes at least one of graphite, silicon, tin, lithium titanate, sulfides, nitrides, and phosphides. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0017] Figure 1 This is a transmission electron microscope image of the thin section to be tested in Example 1.

[0018] Figure 2 The electron diffraction results are those obtained in Example 1 after the tip of the tungsten needle is coated with lithium metal by lithium oxide electrolyte.

[0019] Figure 3a This is a transmission electron microscope image of the in-situ battery after the circuit was formed in Example 1.

[0020] Figure 3b This is a schematic diagram of the circuit formed by the in-situ battery in Example 1.

[0021] Figure 4a The image shows the real-space morphology of lithium titanate particles monitored in situ in Example 1.

[0022] Figure 4b for Figure 4a EELS spectral data of lithium titanate particles during charge and discharge in region a during in-situ monitoring.

[0023] Figure 4c for Figure 4a EELS spectral data of lithium titanate particles during charge and discharge process in region b during in-situ monitoring.

[0024] Figure 4d for Figure 4a EELS spectral data of lithium titanate particles during charge and discharge process in region c during in-situ monitoring. Detailed Implementation

[0025] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0026] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the in-situ monitoring method for the intercalation and deintercalation of active ions in the active material of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0027] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0028] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0029] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0030] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0031] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0032] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0033] [In-situ monitoring method for the intercalation and deintercalation of active ions in active materials] In existing technologies, to study active ions in active materials at the microscale, methods such as in-situ characterization of samples with different charge states or in-situ scanning electron microscopy / transmission electron microscopy to observe the charging and discharging process are commonly used. However, in-situ characterization is susceptible to the influence of water and oxygen environments and it is difficult to ensure sample consistency; while in in-situ characterization, scanning electron microscopy can only observe surface morphology changes, and although transmission electron microscopy can obtain structural information, its electrochemical circuit construction failure rate is high, and observations are mostly limited to apparent changes such as local morphology, expansion, and elemental distribution, without revealing the reaction pathways and interface evolution mechanisms in the ion intercalation and deintercalation process. Therefore, there is an urgent need for a method that can stably and reliably achieve in-situ monitoring of the active ion intercalation and deintercalation process.

[0034] Therefore, the first embodiment of this application provides an in-situ monitoring method for the intercalation and deintercalation of active ions in an active material, comprising: In the sample preparation process, focused ion beam technology is used to thin the sample to a thickness of less than 150 nm under conditions of voltage 2kV-30kV and / or current 0.01nA-0.35nA, resulting in a thin film containing the active material to be tested. For the selection of monitoring targets, backscattered electron diffraction technology was used to detect the crystal orientation of the grains in the active material to be tested, and the angle α between the preferred orientation path of active ion insertion and the electron beam was determined. Grains with 85°≤α≤95° were selected as in-situ monitoring targets. The preparation of the negative electrode and electrolyte involves transferring an active metal to a conductive microprobe, oxidizing some of the active metal on the conductive microprobe to form an active metal oxide, and obtaining a negative electrode and electrolyte attached to the conductive microprobe. Solid-state battery construction involves fixing the sheet to be tested to the fixed end of the sample rod of an in-situ TEM instrument, and fixing a conductive microprobe with an attached negative electrode and electrolyte to the moving end of the sample rod of the in-situ TEM instrument. A solid-state battery is then constructed using the sheet to be tested, electrolyte, and negative electrode within the field of view of the in-situ TEM instrument. In the in-situ monitoring process, the sheet to be tested is connected to the negative terminal of an external power supply, and the negative terminal is connected to the positive terminal of an external power supply. A voltage is applied to the solid-state battery and the electron energy loss spectrum at different positions in the grains of the active material to be tested is collected.

[0035] For example, the thickness of the sheet to be tested is less than 150nm, or less than 120nm, or less than 100nm, and can be 150nm, 140nm, 130nm, 120nm, 110nm, 100nm, 90nm, 80nm, 70nm, 60nm, 50nm, 40nm, 30nm, 20nm, 10nm, or within any two of the above values, or less than 10nm; α can be 85°, 86°, 87°, 88°, 89°, 90°, 91°, 92°, 93°, 94°, 95°, or within any two of the above values.

[0036] In the step of selecting monitoring targets, the grains with 85°≤α≤95° are those whose ion migration channels are approximately perpendicular to the electron beam, that is, the positions close to the positive band axis. These grains have the characteristics of rapid and direct insertion and extraction of corresponding active ions, and therefore can most sensitively and intuitively reflect the dynamic process of insertion / extraction of active ions when they reach the insertion / extraction potential.

[0037] The aforementioned in-situ monitoring method achieves stable monitoring of the microscopic mechanisms of ion intercalation and deintercalation in active materials. First, during sample preparation, focused ion beam technology is used to thin the sample layer by layer to a thickness below 150 nm under the aforementioned voltage and / or current. This ensures good electron permeability while maintaining the electrochemical activity of the active material, laying the foundation for obtaining high-resolution morphology and crystal structure. Subsequently, backscattered electron diffraction is used to analyze the crystal orientation of the grains in the active material and screen out target grains that preferentially undergo ion intercalation and deintercalation. This enables the monitoring of intercalation and deintercalation of the active material at different charge-discharge stages during the charge-discharge process. Timely and accurate testing of the pathways and crystal structure changes of active ions allows in-situ monitoring data to be more directly correlated with the key electrochemical behaviors of materials. Transferring active metals to conductive microprobes allows for the oxidation of some of the active metal on the probes to form active metal oxides, resulting in both the negative electrode and electrolyte. This integrated structure facilitates close contact between the negative electrode and electrolyte, reduces interfacial impedance, and promotes the formation of a stable electrochemical circuit. After the solid-state battery is constructed and the pathway is established, electron energy loss spectra at different locations on the target grains are collected, enabling dynamic tracking of the chemical environment, elemental valence states, and electronic structures along the active ion insertion / extraction pathways of the active material during the reaction. Through the close integration and synergistic effect of these steps, traditional local morphology observation is extended to the level of the chemical mechanism of active particles, providing direct data support for elucidating ion insertion / extraction pathways and interfacial reaction kinetics.

[0038] The above process includes: thinning the sample to be tested using focused ion beam technology at a voltage of 2kV-30kV and / or a current of 0.01nA-0.35nA. For example, the voltage of the focused ion beam technology can be 2kV, 3kV, 4kV, 5kV, 6kV, 7kV, 8kV, 9kV, 10kV, 11kV, 12kV, 13kV, 14kV, 15kV, 16kV, 17kV, 18kV, 19kV, 20kV, 21kV, 22kV, 23kV, 2... The voltage and current of the focused ion beam can be 4 kV, 25 kV, 26 kV, 27 kV, 28 kV, 29 kV, 30 kV, or any two of the above values, and / or the current of the focused ion beam technique can be 0.01 nA, 0.02 nA, 0.03 nA, 0.04 nA, 0.05 nA, 0.06 nA, 0.07 nA, 0.08 nA, 0.09 nA, 0.1 nA, 0.15 nA, 0.2 nA, 0.25 nA, 0.3 nA, 0.35 nA, or any two of the above values. Using ion beam voltage and current within the above ranges allows for a controllable and gentle thinning process of the sample, helping to reduce damage to the crystal structure of the sample from the high-energy ion beam, thereby better preserving the intrinsic structure of the active material and providing support for obtaining reliable in-situ observation results.

[0039] In some embodiments, the sample preparation process includes: A first thin film with a thickness of 800 nm to 1.5 μm was obtained by using focused ion beam technology under conditions of voltage of 10 kV-30 kV and / or current of 0.1 nA-0.35 nA to perform a first thin film on the sample to be tested. A second thinning was performed on the first thin film using focused ion beam technology under conditions of voltage of 2kV-5kV and / or current of 0.01nA-0.3nA to obtain the thin film to be tested.

[0040] For example, the voltage of the first thinning step can be 10kV, 11kV, 12kV, 13kV, 14kV, 15kV, 16kV, 17kV, 18kV, 19kV, 20kV, 21kV, 22kV, 23kV, 24kV, 25kV, 26kV, 27kV, 28kV, 29kV, 30kV or within any two of the above values, and / or the current of the first thinning step can be 0.1nA, 0.15nA, 0.2nA, 0.25nA, 0.3nA, 0.35nA or within any two of the above values, and the thickness of the first thin sheet can be 800nm, 900nm, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm or within any two of the above values. The voltage for the second thinning can be 2kV, 3kV, 4kV, 5kV, or any two of the above values, and / or the current for the second thinning can be 0.01nA, 0.02nA, 0.03nA, 0.04nA, 0.05nA, 0.06nA, 0.07nA, 0.08nA, 0.09nA, 0.1nA, 0.15nA, 0.2nA, 0.25nA, 0.3nA, or any two of the above values. Performing the first thinning with a higher voltage and current improves the efficiency of the initial thinning; subsequently, performing the second thinning refinement with a lower voltage and current helps reduce damage to the thin-film region by the ion beam at the end of the thinning process and improves the accuracy of the final thickness control. This step-by-step method improves sample preparation efficiency while also facilitating the acquisition of a more complete and uniformly thick thin film, thereby improving the quality of subsequent in-situ monitoring.

[0041] When using focused ion beam (FIP) technology to thin a sample, the sample is thinned layer by layer. In some implementations, the duration of each FIP scan is less than 200 ns. For example, the duration of each FIP scan can be 199 ns, 195 ns, 190 ns, 185 ns, 180 ns, 175 ns, 170 ns, 165 ns, 160 ns, 155 ns, 150 ns, 140 ns, 130 ns, 120 ns, 110 ns, 100 ns, or within any two of the above values, or less than 100 ns. This short-pulse scanning method helps reduce the energy injection of the ion beam into the sample within a unit time, thereby mitigating the heat accumulation effect and material damage that may result from continuous scanning, and maintaining the integrity of the microstructure of the active material being tested.

[0042] In some implementations, a protective metal film is deposited on the surface of the sample before thinning using focused ion beam (FIP) technology. This operation provides a physical barrier to the sample surface during the subsequent FIP ​​thinning process, helping to reduce the etching damage and destruction of the sample surface crystal structure caused by direct ion beam bombardment, thereby better protecting the original surface morphology and structure of the active material being tested.

[0043] In some embodiments, the metal protective film is a platinum metal protective film. Platinum metal not only has high density and good chemical stability, but the protective film formed by it can more effectively block ion beams and withstand certain processing stresses. At the same time, its conductivity is also beneficial to improve the charge accumulation effect in subsequent electrical tests.

[0044] In some embodiments, the thickness of the metal protective film can be selected as 2μm-4μm. For example, the thickness of the metal protective film can be 2μm, 3μm, 4μm, or within any two of the above values. This thickness range helps to maintain the efficiency and controllability of the sample preparation process while ensuring the protective effect.

[0045] The following explanation uses the positive electrode as an example to illustrate the above sample preparation process: The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one side of the surface of the positive current collector, with the positive active material disposed in the positive electrode film layer. A positive electrode sheet with a thickness greater than 5 μm is selected, where the thickness direction is perpendicular to the stacking direction of the positive current collector and the positive electrode film layer. Then, a metal protective film is formed on the surface of the positive electrode sheet by vapor deposition. A focused ion beam is injected into the positive electrode sheet along the thickness direction to bombard it, causing the positive electrode film layer and the positive current collector to be thinned by the ion beam. During the process, the voltage and current of the focused ion beam scanning are controlled, and finally the positive electrode sheet is thinned to the target thickness. After purging, the sheet to be tested is obtained. The thickness of this sheet is less than 150 nm, and its height and width are basically not lost during the thinning process under the protection of the metal protective film, so it can be considered to have maintained the integrity of the positive electrode sheet structure.

[0046] During the preparation of the negative electrode and electrolyte, the active metal can be transferred to the conductive microprobe using methods commonly used in the field. For example, the active metal can be transferred to the conductive microprobe by scraping or electrochemical deposition.

[0047] In some embodiments, the conductive microprobe is a tungsten needle, a diamond probe, or a titanium alloy probe. These probes have comprehensive advantages such as high strength, high conductivity, and excellent chemical stability, which are beneficial for maintaining the long-term reliability of the micro-battery structure during in-situ monitoring.

[0048] In some implementations, the tip diameter of the conductive microprobe is less than 100 nm.

[0049] Furthermore, methods commonly used in the art can be employed to oxidize a portion of the active metal on the conductive microprobe, forming an active metal oxide. For example, the conductive microprobe with the active metal can be exposed to air to oxidize a portion of the active metal, forming an active metal oxide. In some embodiments, the exposure time to air is 5-15 seconds, for example, 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds, 10 seconds, 11 seconds, 12 seconds, 13 seconds, 14 seconds, 15 seconds, or any two of the above values. This time range helps to obtain an oxide solid electrolyte layer while retaining a portion of the active metal, thereby ensuring ion transport while reducing the risk of battery short circuits.

[0050] In some implementations, the solid-state battery construction process also includes confirming the presence of active metals and active metal oxides through electron diffraction results. This step provides experimental evidence of the successful formation of the active metal and its oxide, thereby increasing the reliability of subsequent in-situ monitoring of the initial state.

[0051] In some implementations, the in-situ monitoring process includes: The electron energy loss spectrum at different positions in the grains of the active material under test was acquired using an in-situ TEM instrument before the applied voltage was applied. A voltage was applied to a solid-state battery, and in-situ TEM was used to monitor the morphological changes of the grains of the active material under test. After the morphology of the active material to be tested is stabilized, the electron energy loss spectrum at different positions in the active material to be tested is collected using an in-situ TEM instrument. A reverse voltage was applied to a solid-state battery, and in-situ TEM was used to monitor the morphological changes of the grains of the active material under test. After the morphology of the active material to be tested is stabilized, an in-situ TEM instrument is used to collect the electron energy loss spectrum at different positions in the active material to be tested at this time.

[0052] The above steps construct an in-situ observation process for a complete electrochemical cycle, including initial state, discharge ion extraction, and charging ion insertion. By comparing the morphology and chemical state (electron energy loss spectrum) data at different stages, the structural evolution and valence state changes of the active material grains during the reversible ion insertion / extraction process can be dynamically tracked. This provides more comprehensive and comparative data support for in-depth analysis of its reaction reversibility, phase transition path, and decay mechanism.

[0053] In some implementations, the active ions include lithium ions and sodium ions.

[0054] In some embodiments, the active material is a positive electrode active material or a negative electrode active material. In some embodiments, the positive electrode active material may be a positive electrode active material known in the art for use in batteries. As an example, when the active ion is lithium ion, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, lithium vanadium phosphate, lithium vanadium oxide phosphate, lithium vanadium phosphate and carbon composites, and lithium vanadium oxide phosphate and carbon composites.

[0055] When the active ion is sodium ion, as an example, the positive electrode active material of a sodium-ion secondary battery may include at least one of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0056] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0057] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The price state.

[0058] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0059] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0060] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni), and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0061] Prussian blue compounds can be compounds containing sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds include, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0062] In some embodiments, the active material is a positive electrode active material or a negative electrode active material. The positive electrode active material includes one or more of lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based oxide, lithium manganese oxide (LiMn2O4), lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, sodium vanadium fluorophosphate, and sulfur.

[0063] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0064] In some embodiments, the negative electrode active material includes at least one of graphite, silicon, tin, lithium titanate, sulfide, nitride, and phosphide.

[0065] During in-situ monitoring, a bias voltage is applied to drive the intercalation and deintercalation reaction of active ions. The bias voltage application strategy follows a dynamic observation and adjustment process: First, the characteristic voltage plateau value of the active material to be tested in the macroscopic battery or the conventional charge and discharge cutoff voltage (e.g., 4.25V) is preferentially used as the initial bias voltage; then, the occurrence of electrochemical reaction is confirmed by real-time monitoring of the morphological evolution of the grains in the TEM (e.g., volume expansion, surface deposition, etc.), and the bias voltage is dynamically adjusted accordingly. The specific adjustment principles are: (1) If a clear morphological change of the target grains is observed under the initial bias voltage, the bias voltage is maintained for continuous in-situ observation and data acquisition; (2) If no change is observed under the initial bias voltage, the bias voltage is gradually increased to a higher driving voltage (e.g., 10V) to enhance the driving force of ion migration until observable electrochemical deformation is induced.

[0066] [Example] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0067] Example 1 Preparation of the test sheet: Obtain a negative electrode sheet with a thickness of 5 μm. The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on one side surface of the negative current collector. The negative active material in the negative electrode film layer is lithium titanate coated with carbon material. The thickness direction here is perpendicular to the stacking direction of the negative current collector and the negative electrode film layer. Then, a 2.5 μm thick platinum metal protective film was deposited on the surface of the negative electrode. Subsequently, the negative electrode sample was machined using focused ion beam microscopy (FIB). The FIB machining process included: placing the negative electrode with the platinum protective film on an FIB grid; and bombarding the negative electrode with a focused ion beam along its thickness direction. First, the sample was bombarded at 30 kV and 0.26 nA to obtain a first thin film with a thickness of 800 μm; then, it was bombarded at 5 kV and 0.012 nA to obtain a final thin film with a thickness of 100 nm. The duration of each focused ion beam scan was less than 200 ns. The thin film was then placed on the FIB grid and imaged using a transmission electron microscope. Figure 1 As shown in the image, the surrounding black area is a platinum metal protective film, and the small gray particles in the middle are lithium titanate coated with carbon material.

[0068] Selection of monitoring targets: The backscattered electron diffraction detector of a scanning electron microscope is used to detect the crystal orientation of the grains in the active material to be tested, and the angle α between the preferred orientation path of lithium ion insertion into lithium titanate (i.e., the

[110] crystal plane) and the electron beam is determined. A grain with α of 90° is selected as the in-situ monitoring target.

[0069] Solid-state battery setup: The sheet to be tested was fixed to the fixed end of the sample rod of an in-situ TEM instrument. A nano-tungsten probe with a tip diameter of 50 nm was prepared electrochemically. The prepared tungsten probe was then rapidly traced across a pure lithium metal sheet and assembled onto the TEM rod, which was then inserted into the moving end of the sample rod inside the in-situ transmission electron microscope chamber. The tungsten probe was exposed to air for 5 seconds to form a lithium oxide electrolyte on its surface. Electron diffraction results confirmed the formation of lithium metal encapsulated by the lithium oxide electrolyte at the tip of the tungsten probe. Figure 2 As shown in the image. Subsequently, an in-situ half-cell cell was constructed using an in-situ TEM probe. The moving end of the sample probe was moved near the fixed end, allowing the tungsten probe tip to form a lithium metal encapsulated by lithium oxide electrolyte, which then approached and made contact with the sample sheet to form a pathway. The TEM image of this in-situ cell is shown in the image. Figure 3a As shown in the diagram, the upper right side shows the metallic lithium formed by the lithium oxide electrolyte at the tip of the tungsten probe. A schematic diagram of the circuit is shown below. Figure 3b As shown.

[0070] In-situ monitoring: An in-situ TEM instrument was used to collect electron energy loss spectra at different locations within the in-situ monitored object's grains before the applied voltage was applied. Subsequently, a voltage of 4.25V was applied to the solid-state battery, and the morphological changes of the in-situ monitored object's grains were monitored using in-situ TEM. After the morphology of the in-situ monitored object's grains stabilized, an in-situ TEM instrument was used to collect electron energy loss spectra at different locations within the in-situ monitored object's grains at this time. Finally, a reverse voltage of -4.25V was applied to the solid-state battery, and the morphological changes of the in-situ monitored object's grains were monitored using in-situ TEM. After the morphology of the in-situ monitored object's grains stabilized, an in-situ TEM instrument was used to collect electron energy loss spectra at different locations within the in-situ monitored object's grains at this time. Figure 4a The real-space morphology of the grains of the object being monitored in situ is shown. Figures 4b-4d The electron energy loss spectra (EELS spectra) at three different locations on the in-situ monitored grain are shown.

[0071] Figures 4b-4dEELS spectral data from different regions of lithium titanate particles during charge and discharge processes indicate that: 1) For region a on the surface, a distinct lithium characteristic peak was detected during charging, confirming that lithium ions were embedded in this region; however, this lithium peak disappeared during discharge, indicating that the embedded lithium ions reversibly extracted. 2) For region b, the binding energy of its titanium L-edge peak changed significantly during charge and discharge. Specifically, the binding energy changed from 466.13 eV in the original state to 466.42 eV after charging, and finally decreased to 465.78 eV after discharging. This final decrease in binding energy is consistent with the transformation of titanium ions from tetravalent (Ti) to tetravalent (Ti). 4+ ) was reduced to trivalent (Ti 3+ The valence state change characteristics of titanium. Although the transient increase in binding energy during charging can be attributed to experimental fluctuations, the binding energy failed to recover to its original value after discharge, constituting key evidence of irreversible reduction of titanium. This indicates that the lithium ions embedded in this region cannot be completely extracted during discharge, leading to irreversible lithium loss. 3) For region c, the EELS spectrum of this region did not change significantly compared to the original state throughout the process, proving that lithium ions did not diffuse into the particle core region and that this region did not participate in the electrochemical reaction.

[0072] In summary, the EELS spectral data analysis intuitively reveals the gradient-distributed embedding behavior of lithium ions within the particles: they can reversibly embed / extract from the surface region a, but irreversibly remain in part of the bulk phase region b, and fail to reach the more internal region c of the particles. This result provides direct spectroscopic evidence for defining the active reaction region and elucidating the capacity decay mechanism.

[0073] In addition, during the preparation of the thin film to be tested, the voltage and current of the focused ion beam were adjusted. Under the conditions of directly using a voltage of 30kV and a current of 0.3nA to directly thin the sample to be tested to 100nm, or under the conditions of Example 1 but with a focused ion beam scanning time of more than 200ns each time, or without setting a metal protective film, the resulting thin film to be tested caused certain damage to the grain structure, making it difficult to select the monitoring object.

[0074] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for in-situ monitoring of the intercalation and deintercalation of active ions in an active material, characterized in that, include: In the sample preparation process, focused ion beam technology is used to thin the sample to be tested to a thickness of less than 150 nm under conditions of voltage 2kV-30kV and / or current 0.01nA-0.35nA, thereby obtaining a thin film to be tested. The thin film to be tested includes the active material to be tested. For the selection of monitoring targets, backscattered electron diffraction technology is used to detect the crystal orientation of the grains in the active material to be tested, determine the angle α between the preferred orientation path of active ion insertion and the electron beam, and select grains with 85°≤α≤95° as in-situ monitoring targets. The preparation of the negative electrode and electrolyte involves transferring an active metal to a conductive microprobe, oxidizing a portion of the active metal on the conductive microprobe to form an active metal oxide, thereby obtaining a negative electrode and electrolyte attached to the conductive microprobe. Solid-state battery construction involves fixing the sheet to be tested to the fixed end of the sample rod of an in-situ TEM instrument, and fixing the conductive microprobe with the negative electrode and electrolyte attached to the moving end of the sample rod of the in-situ TEM instrument. A solid-state battery is then constructed using the sheet to be tested, the electrolyte, and the negative electrode within the field of view of the in-situ TEM instrument. In the in-situ monitoring process, the sheet to be tested is connected to the negative terminal of an external power supply, and the negative terminal is connected to the positive terminal of the external power supply. A voltage is applied to the solid-state battery, and the electron energy loss spectrum at different positions in the grains of the active material to be tested is collected.

2. The in-situ monitoring method according to claim 1, characterized in that, The sample preparation process includes: The sample to be tested was thinned using focused ion beam technology under conditions of voltage of 10kV-30kV and / or current of 0.1nA-0.35nA to obtain a first thin film with a thickness of 800nm-1.5μm. The first thin film is subjected to a second thinning using focused ion beam technology under conditions of 2kV-5kV voltage and / or 0.01nA-0.3nA current to obtain the thin film to be tested.

3. The in-situ monitoring method according to claim 1 or 2, characterized in that, The duration of each focused ion beam scan is less than 200 ns.

4. The in-situ monitoring method according to claim 1 or 2, characterized in that, Before thinning the sample under test using focused ion beam technology, a metal protective film is deposited on the surface of the sample under test.

5. The in-situ monitoring method according to claim 4, characterized in that, The metal protective film is a platinum metal protective film, and / or the thickness of the metal protective film is 2μm-4μm.

6. The in-situ monitoring method according to claim 1 or 2, characterized in that, The conductive microprobe is a tungsten needle, a diamond probe, or a titanium alloy probe.

7. The in-situ monitoring method according to claim 1 or 2, characterized in that, The process of building the solid-state battery also includes confirming the presence of the active metal and the active metal oxide through electron diffraction results.

8. The in-situ monitoring method according to claim 1 or 2, characterized in that, The in-situ monitoring process includes: The electron energy loss spectrum of the active material under test at different positions in the grains before the applied voltage was collected using an in-situ TEM instrument. A voltage is applied to the solid-state battery, and the morphological changes of the grains of the active material under test are monitored using in-situ TEM. After the morphology of the active material to be tested is stabilized, an in-situ TEM instrument is used to collect the electron energy loss spectrum at different positions in the active material to be tested at this time. A reverse voltage is applied to the solid-state battery, and the morphological changes of the grains of the active material under test are monitored using in-situ TEM. After the morphology of the active material to be tested is stabilized, an in-situ TEM instrument is used to collect the electron energy loss spectrum at different positions in the active material to be tested at this time.

9. The in-situ monitoring method according to claim 1 or 2, characterized in that, The active ions include lithium ions and sodium ions.

10. The in-situ monitoring method according to claim 1 or 2, characterized in that, The active material is a positive electrode active material or a negative electrode active material. The positive electrode active material includes one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, sodium vanadium fluorophosphate, and sulfur; and / or the negative electrode active material includes at least one of graphite, silicon, tin, lithium titanate, sulfides, nitrides, and phosphides.

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