In-situ monitoring of active ion deintercalation in an active material

Abstract

The application provides a method for in-situ monitoring of active ion deintercalation in an active material. The method comprises: thinning a sample to be tested to below 150 nm by using a FIB technology to obtain a sample to be tested; determining an angle between a preferential orientation path of active ion intercalation and an electron beam by using an EBSD technology, and selecting a grain with an angle of 85°-95° as an in-situ monitoring object; transferring the active metal to a conductive microprobe, oxidizing 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; fixing the sample to be tested at a fixed end of a sample rod of an in-situ TEM tester, fixing the negative electrode and the electrolyte at a moving end thereof, and building a solid-state battery in a field of view of the tester; connecting the sample to be tested with a negative electrode of an external power supply, connecting the negative electrode with a positive electrode of the external power supply, applying a voltage to the solid-state battery, and collecting electron energy loss spectra at different positions in the grain of the active material to be tested.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of batteries, in particular to an in-situ monitoring method for active ion deintercalation in an active material. BACKGROUND

[0002] As an important energy storage and conversion device, the energy density and cycle stability of a battery depend on the migration and reaction mechanism of active ions of an electrode active material in the charging and discharging process. In order to optimize the performance of the electrode material, it is necessary to monitor the structural evolution and electrochemical behavior in the ion deintercalation process on a microscale. However, the existing in-situ monitoring means has the problem of insufficient stability in constructing a reliable battery circuit, and it is difficult to continuously track the dynamic changes of the material in a real reaction environment, and the electrochemical reaction mechanism analysis is not deep enough, especially the analysis ability of the reaction path and interface mechanism is limited, which restricts the development and application of high-performance electrode active materials in lithium ion, sodium ion and other new battery systems. SUMMARY

[0003] The application provides an in-situ monitoring method for active ion deintercalation in an active material, which can construct a high-stability in-situ electrochemical microbattery and realize in-situ observation of the ion deintercalation process of the active material.

[0004] The first aspect of the application provides an in-situ monitoring method for active ion deintercalation in an active material, comprising:

[0005] The sample preparation process adopts a focused ion beam technology to thin the sample to be tested to a thickness of less than 150 nm under the condition of a voltage of 2-30 kv and / or a current of 0.01-0.35 nA, to obtain a sample to be tested, and the sample to be tested includes an active material to be tested,

[0006] The monitoring object selection adopts a backscattered electron diffraction technology to detect the crystal face orientation of the crystal grains in the active material to be tested, determines the angle a between the preferential orientation path of active ion intercalation and the electron beam, and selects the crystal grains with 85°≤a≤95° as the in-situ monitoring object;

[0007] The preparation of the negative electrode and the electrolyte, the active metal is transferred to the conductive microprobe, and part of the active metal on the conductive microprobe is oxidized to form an active metal oxide, to obtain a negative electrode and an electrolyte attached to the conductive microprobe;

[0008] The solid-state battery is built, the sample to be tested is fixed at the fixed end of the sample rod of the in-situ TEM tester, the conductive microprobe with the attached negative electrode and electrolyte is fixed at the moving end of the sample rod of the in-situ TEM tester, and the solid-state battery is built in the field of view of the in-situ TEM tester by using the sample to be tested, the electrolyte and the negative electrode;

[0009] The in-situ monitoring process is performed by connecting the to-be-measured thin sheet to the negative electrode of an external power supply, connecting the negative electrode to the positive electrode of the external power supply, applying a voltage to the solid-state battery, and collecting electron energy loss spectra of different positions in the crystal grains of the to-be-measured active material.

[0010] In the above in-situ monitoring method, first, the to-be-measured sample is thinned to a thickness of less than 150 nm layer by layer under the above voltage and / or current by using a focused ion beam technique in the sample preparation process, so that the sample has good electron penetration under the premise of maintaining the electrochemical activity of the to-be-measured active material, thereby laying a foundation for obtaining high-resolution morphology and lattice structure of the to-be-measured active material; then, the crystal grains in the to-be-measured active material are analyzed by using a backscattered electron diffraction technique, and target crystal grains that preferentially undergo ion deintercalation are screened out, thereby realizing timely and accurate testing of the deintercalation path and crystal structure change of active ions of the active material corresponding to different charging and discharging stages in the charging and discharging process, so that the in-situ monitoring data can be more directly associated with the key electrochemical behavior of the material; after the active metal is transferred to the conductive microprobe, part of the active metal on the conductive microprobe is oxidized to form an active metal oxide to obtain a negative electrode and an electrolyte, and such an integrated structure helps to realize close contact between the negative electrode and the electrolyte, thereby reducing the interface impedance and being beneficial to the subsequent formation of a stable electrochemical loop; after the solid-state battery is built to form a path, electron energy loss spectra of different positions of the target crystal grains are collected, thereby realizing dynamic tracking of the chemical environment, element valence and electronic structure on the deintercalation path of active ions of the active material in the reaction process. Through the close connection and synergistic effect of the above steps, the traditional local morphology observation is extended to the chemical mechanism level of the active particles, thereby providing direct data support for analyzing the ion deintercalation path and interface reaction kinetics.

[0011] In any embodiment of the first aspect, the sample preparation process comprises:

[0012] The first thin sheet is obtained by using a focused ion beam technique to perform first thinning on the to-be-measured sample under the condition that the voltage is 10 kv-30 kv and / or the current is 0.1 nA-0.35 nA, and the thickness of the first thin sheet is 800 nm-1.5 μm.

[0013] The to-be-measured thin sheet is obtained by using a focused ion beam technique to perform second thinning on the first thin sheet under the condition that the voltage is 2 kv-5 kv and / or the current is 0.01 nA-0.3 nA.

[0014] In any embodiment of the first aspect, the duration of each continuous scanning of the focused ion beam is less than 200 ns.

[0015] In any embodiment of the first aspect, before the to-be-measured sample is thinned by using a focused ion beam technique, a metal protective film is evaporated on the surface of the to-be-measured sample.

[0016] In any embodiment of the first aspect, the metal protective film is a platinum metal protective film.

[0017] In any embodiment of the first aspect, the metal protective film has a thickness of 2-4 μm.

[0018] In any embodiment of the first aspect, the conductive microprobe is a tungsten needle, a diamond probe or a titanium alloy probe.

[0019] In any embodiment of the first aspect, the process of building the solid-state battery further comprises confirming the presence of the active metal and the active metal oxide by electron diffraction results.

[0020] In any embodiment of the first aspect, the process of in-situ monitoring comprises:

[0021] collecting, by the in-situ TEM tester, electron energy loss spectra at different positions in the crystal grain of the active material to be tested before the voltage is applied;

[0022] applying a voltage to the solid-state battery, and monitoring, by the in-situ TEM, the morphology change of the crystal grain of the active material to be tested;

[0023] collecting, by the in-situ TEM tester, electron energy loss spectra at different positions in the crystal grain of the active material to be tested after the morphology of the crystal grain of the active material to be tested is stable;

[0024] applying a reverse voltage to the solid-state battery, and monitoring, by the in-situ TEM, the morphology change of the crystal grain of the active material to be tested;

[0025] collecting, by the in-situ TEM tester, electron energy loss spectra at different positions in the crystal grain of the active material to be tested after the morphology of the crystal grain of the active material to be tested is stable.

[0026] In any embodiment of the first aspect, the active ions include lithium ions, sodium ions.

[0027] 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 cobaltate, 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 phosphate, sodium vanadium fluoride phosphate, sulfur; and / or the negative electrode active material includes at least one of graphite, silicon, tin, lithium titanate, sulfide, nitride, phosphide. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of the drawings.

[0029] Figure 1 Transmission electron microscope image of the thin slice to be tested in Example 1.

[0030] Figure 2 Electron diffraction result after the tungsten needle tip end in Example 1 is wrapped by lithium oxide electrolyte.

[0031] Figure 3a Transmission electron microscope image of the in-situ battery in Example 1 after forming a channel.

[0032] Figure 3b Schematic diagram of the circuit formed by the in-situ battery in Example 1.

[0033] Figure 4a Real space morphology of the lithium titanate particles monitored in-situ in Example 1.

[0034] Figure 4b For Figure 4a EELS spectrum data of the lithium titanate particles monitored in-situ in Example 1 in the a region during the charging and discharging process.

[0035] Figure 4c For Figure 4a EELS spectrum data of the lithium titanate particles monitored in-situ in Example 1 in the b region during the charging and discharging process.

[0036] Figure 4d For Figure 4a EELS spectrum data of the lithium titanate particles monitored in-situ in Example 1 in the c region during the charging and discharging process. DETAILED DESCRIPTION

[0037] The embodiments of the present application will be further described in detail below in combination with the drawings and examples. The detailed description of the following examples and the drawings are used to exemplarily illustrate the principles of the present application, but cannot be used to limit the scope of the present application, i.e., the present application is not limited to the described examples.

[0038] Hereinafter, embodiments of the method for in-situ monitoring of deintercalation of active ions in an active material according to the present application will be specifically described with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases of omitting detailed description of matters known well, and repeated description of substantially identical structures. This is to avoid the following description from becoming unnecessarily lengthy, and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0039] The ranges disclosed herein are defined by their lower and upper limits. Ranges can be inclusive or exclusive of their endpoints, and are arbitrarily combinable. For example, if a range is listed as 60-120 and 80-110, it is understood that 60-110 and 80-120 are also contemplated. Also, where a minimum range value of 1 and 2 is listed, and a maximum range value of 3, 4, and 5 is listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise indicated, a numerical range "a-b" is intended to mean any and all subcombinations of the values between a and b, inclusive of the values a and b. For example, the numerical range "0-5" is intended to mean that all real numbers between 0 and 5, inclusive of 0 and 5, have been listed herein. "0-5" is merely a shorthand for listing all of these numerical combinations. Also, when a parameter is stated to be an integer ≥ 2, it is equivalent to state that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0041] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0042] If not specifically stated, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0043] If not specifically stated, the present application refers to "including" and "comprising" as open-ended. For example, "including" and "comprising" can mean that other components not listed can also be included or contained.

[0044] If not specifically stated, in the present application, the term "or" is inclusive. 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 A and B are both true (or exist).

[0045] [In-situ monitoring method for active ion deintercalation in active material]

[0046] In the prior art, in order to study active ions in active materials at a microscale, methods such as ex-situ characterization of samples at different charge states or in-situ scanning electron microscope / transmission electron microscope observation of charging and discharging processes are often used. However, ex-situ characterization is easily affected by water and oxygen environment and it is difficult to ensure sample consistency; in in-situ characterization, scanning electron microscope can only observe surface morphology changes, and transmission electron microscope can obtain structural information, but its electrochemical loop construction failure rate is high, and observation is often limited to local area morphology, swelling and element distribution, etc. apparent changes, and does not reveal the reaction path and interface evolution mechanism in the ion deintercalation process. Therefore, there is an urgent need for a method that can stably and reliably realize in-situ monitoring of the active ion deintercalation process.

[0047] To this end, the first embodiment of the present application provides an in-situ monitoring method for active ion deintercalation in an active material, comprising:

[0048] The sample preparation process uses focused ion beam technology to thin the sample to be tested to a thickness of less than 150 nm under the condition of a voltage of 2-30 kv and / or a current of 0.01-0.35 nA, to obtain a sample to be tested, and the sample to be tested includes an active material to be tested,

[0049] The monitoring object is selected by using backscattered electron diffraction technology to detect the crystal face orientation of the crystal grains in the active material to be detected, to determine the angle a between the preferred orientation path of active ion insertion and the electron beam, and to select the crystal grains with 85°≤a≤95° as the in-situ monitoring object.

[0050] The negative electrode and the electrolyte are prepared by transferring the active metal to the conductive microprobe, oxidizing part of the active metal on the conductive microprobe to form an active metal oxide, and obtaining the negative electrode and the electrolyte attached to the conductive microprobe.

[0051] The solid-state battery is built by fixing the test sheet on the fixed end of the sample rod of the in-situ TEM tester, fixing the conductive microprobe with the attached negative electrode and electrolyte on the moving end of the sample rod of the in-situ TEM tester, and building the solid-state battery in the field of view of the in-situ TEM tester using the test sheet, the electrolyte, and the negative electrode.

[0052] The in-situ monitoring process is performed by connecting the test sheet to the negative electrode of the external power supply, connecting the negative electrode to the positive electrode of the external power supply, applying voltage to the solid-state battery, and collecting electron energy loss spectra at different positions in the crystal grains of the active material to be detected.

[0053] For example, the thickness of the test sheet can be less than 150 nm, or less than 120 nm, or less than 100 nm, and can be 150 nm, 140 nm, 130 nm, 120 nm, 110 nm, 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, 20 nm, 10 nm, or within a range between any two of the above values, or less than 10 nm; a can be 85°, 86°, 87°, 88°, 89°, 90°, 91°, 92°, 93°, 94°, 95°, or within a range between any two of the above values.

[0054] In the monitoring object selection step, the crystal grains with 85°≤a≤95°, i.e., the crystal grains with ion migration channels approximately perpendicular to the electron beam, i.e., the positions close to the positive axis, have the characteristics of rapid and most direct corresponding active ion deintercalation, and thus can most sensitively and most intuitively reflect the insertion / deintercalation dynamic process of active ions when reaching the insertion / deintercalation potential.

[0055] The above in-situ monitoring method realizes stable monitoring of the micro-mechanism of active ion deintercalation: first, during sample preparation, the sample to be tested is thinned layer by layer to a thickness of less than 150 nm under the above voltage and / or current using focused ion beam technology, so that the sample has good electron penetration while maintaining the electrochemical activity of the active material to be tested, laying a foundation for obtaining high-resolution topography and lattice structure of the active material to be tested; then, the crystal grains in the active material to be tested are analyzed by backscattered electron diffraction technology, and the target grains preferentially deintercalated are selected according to the analysis, realizing timely and accurate testing of the deintercalation path of active ions and the change of crystal structure of the active material corresponding to different charging and discharging stages during charging and discharging, so that the in-situ monitoring data can be more directly related to the key electrochemical behavior of the material; after the active metal is transferred to the conductive microprobe, part of the active metal on the conductive microprobe is oxidized to form an active metal oxide to obtain a negative electrode and an electrolyte, and this integrated structure helps to realize the close contact between the negative electrode and the electrolyte, reduces the interface impedance, and is conducive to the subsequent formation of a stable electrochemical circuit; after the solid-state battery is formed, the electron energy loss spectrum of the target grain at different positions is collected, realizing dynamic tracking of the chemical environment, element valence and electronic structure of the active ion deintercalation path of the active material during the reaction. Through the close connection and synergistic effect of the above steps, the traditional local topography observation is extended to the chemical mechanism level of the active particles, providing direct data support for analyzing the ion deintercalation path and interface reaction kinetics.

[0056] The above process includes: using focused ion beam technology to thin the sample to be tested under 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, 24kv, 25kv, 26kv, 27kv, 28kv, 29kv, 30kv or within a range between any two of the above values, and / or the current of the focused ion beam technology 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, 0.35nA or within a range between any two of the above values. Through the ion beam voltage and current within the above range, a controllable and mild thinning process of the sample to be tested can be realized, which helps to reduce the damage of high-energy ion beam to the crystal structure of the sample, thereby better preserving the intrinsic structure of the active material to be tested, and providing support for obtaining true and reliable in-situ observation results subsequently.

[0057] In some embodiments, the sample preparation process comprises:

[0058] performing a first thinning on the sample to be measured using focused ion beam technology at a voltage of 10-30 kv and / or a current of 0.1-0.35 nA, to obtain a first thin slice with a thickness of 800 nm-1.5 μm,

[0059] performing a second thinning on the first thin slice using focused ion beam technology at a voltage of 2-5 kv and / or a current of 0.01-0.3 nA, to obtain the thin slice to be measured.

[0060] For example, the voltage for the first thinning can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 kv or within a range between any two of the above values, and / or the current for the first thinning can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 nA or within a range between any two of the above values, and / or the thickness of the first thin slice can be 800 nm, 900 nm, 1, 1.1, 1.2, 1.3, 1.4, 1.5 μm or within a range between any two of the above values. The voltage for the second thinning can be 2, 3, 4, 5 kv or within a range between any two of the above values, and / or the current for the second thinning can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3 nA or within a range between any two of the above values. The first thinning at a higher voltage and current can improve the efficiency of the initial thinning, and the second thinning at a lower voltage and current can help reduce damage to the thin slice at the end of the thinning and improve the control accuracy of the final thickness. This step-by-step method can improve the efficiency of sample preparation while helping to obtain a thin slice to be measured with better integrity and uniform thickness, thereby improving the quality of subsequent in-situ monitoring.

[0061] In some embodiments, the focused ion beam is configured to scan the sample for a duration of less than 200 ns at a time. For example, the focused ion beam can be configured to scan the sample for a duration of 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 a range between any two of the aforementioned values, or less than 100 ns. Such short duration of scanning can help to reduce the energy input to the sample by the ion beam per unit time, thereby mitigating the heat accumulation effect and material damage caused by continuous scanning, and maintaining the integrity of the microstructure of the active material under test.

[0062] In some embodiments, a metal protective film is deposited on the surface of the sample under test before the sample is thinned using the focused ion beam technique. This operation can provide a physical barrier on the surface of the sample during the subsequent focused ion beam thinning process, which can help to reduce the etching damage and destruction of the crystal structure of the surface layer of the sample caused by direct bombardment of the ion beam, thereby better protecting the original surface topography and structure of the active material under test.

[0063] In some embodiments, the metal protective film is a platinum metal protective film. Platinum metal not only has a high density and good chemical stability, but the protective film formed by platinum metal can more effectively block the ion beam and withstand certain processing stress. In addition, the electrical conductivity of platinum metal is also conducive to improving the charge accumulation effect in subsequent electrical tests.

[0064] In some embodiments, the thickness of the metal protective film can be selected to be 2 μm - 4 μm. For example, the thickness of the metal protective film can be 2 μm, 3 μm, 4 μm, or a range between any two of the aforementioned values. Such thickness range can help to maintain the efficiency and controllability of the sample preparation process while ensuring the protection effect.

[0065] The following describes the above sample preparation process using a positive electrode sheet as an example of the sample under test:

[0066] The positive electrode tab includes a positive electrode current collector and a positive electrode film layer disposed on at least one side surface of the positive electrode current collector, and a positive electrode active material is disposed in the positive electrode film layer. A positive electrode tab with a thickness greater than 5 μm is taken, where the thickness direction is perpendicular to the stacking direction of the positive electrode current collector and the positive electrode film layer. Then a metal protective film is formed on the surface of the positive electrode tab by evaporation. A focused ion beam is injected into the positive electrode tab along the thickness direction to bombard the positive electrode tab, so that the positive electrode film layer and the positive electrode current collector are thinned by ion beam grinding. During the process, the voltage and current of the focused ion beam scanning are controlled, and finally the positive electrode tab is thinned to the target thickness. After purging, a test sheet is obtained, which has a thickness of less than 150 nm, and the height and width are basically not lost in the protection of the metal protective film during the thinning process, so the structure of the positive electrode tab is basically maintained.

[0067] During the preparation of the negative electrode and the electrolyte, the active metal can be transferred to the conductive microprobe by a method commonly used in the art, for example, the active metal can be transferred to the conductive microprobe by scraping or electrochemical deposition.

[0068] In some embodiments, the conductive microprobe is a tungsten needle, a diamond probe or a titanium alloy probe, which has comprehensive advantages such as high strength, high conductivity and excellent chemical stability, which is beneficial to maintain the long-term reliability of the micro-battery structure during in-situ monitoring.

[0069] In some embodiments, the diameter of the tip of the conductive microprobe is less than 100 nm.

[0070] In addition, the active metal on the conductive microprobe can be oxidized to form an active metal oxide by a method commonly used in the art, for example, the conductive microprobe with active metal can be exposed to air to oxidize part of the active metal to form an active metal oxide. In some embodiments, the exposure time in air is 5 s-15 s, for example, the exposure time in air can be 5 s, 6 s, 7 s, 8 s, 9 s, 10 s, 11 s, 12 s, 13 s, 14 s, 15 s or within a range of any two of the above values. The above time range helps to obtain an oxide solid electrolyte layer while retaining part of the active metal, thereby reducing the risk of short circuit while ensuring ion transmission.

[0071] In some embodiments, the process of building a solid-state battery further includes confirming the presence of the active metal and the active metal oxide by electron diffraction results. This step can provide experimental evidence for the successful formation of the active metal and its oxide, thereby improving the reliability of the initial state of the subsequent in-situ monitoring experiment.

[0072] In some embodiments, the in-situ monitoring process includes:

[0073] The in-situ TEM tester is used to collect the electron energy loss spectra of different positions in the crystal grains of the active material to be tested before the voltage is applied;

[0074] The voltage is applied to the solid-state battery, and the in-situ TEM is used to monitor the morphology change of the crystal grains of the active material to be tested;

[0075] After the morphology of the crystal grains of the active material to be tested is stable, the in-situ TEM tester is used to collect the electron energy loss spectra of different positions in the crystal grains of the active material to be tested at this time;

[0076] The reverse voltage is applied to the solid-state battery, and the in-situ TEM is used to monitor the morphology change of the crystal grains of the active material to be tested;

[0077] After the morphology of the crystal grains of the active material to be tested is stable, the in-situ TEM tester is used to collect the electron energy loss spectra of different positions in the crystal grains of the active material to be tested at this time.

[0078] Through the above steps, an in-situ observation process of a complete electrochemical cycle including the initial state, ion discharge during discharge, and ion insertion during charging is constructed. By comparing the morphology and chemical state (electron energy loss spectrum) data at different stages, the structural evolution and valence change of the crystal grains of the active material during the reversible ion deintercalation process can be dynamically tracked, which provides more comprehensive and comparative data support for in-depth analysis of the reaction reversibility, phase change path, and attenuation mechanism.

[0079] In some embodiments, the active ions include lithium ions, sodium ions.

[0080] 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 can be a positive electrode active material for a battery known in the art. As an example, when the active ions are lithium ions, the positive electrode active material can include at least one of the following materials: lithium phosphate containing lithium of an olivine structure, lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries can also be used. These positive electrode active materials can be used alone or in combination with two or more. Examples of lithium transition metal oxides can include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3O2 (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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] The polyanionic compound can also be a compound having sodium ions, tetrahedral (YO4) n- anion units and halogen 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 the valence of (YO4) n- ; the halogen can be at least one of F, Cl, and Br.

[0085] The polyanionic compound can also be a compound having sodium ions, tetrahedral (YO4) n- anion units, polyhedral units (ZO y ) m+ , and optional halogen anions. Y can be at least one of P, S, and Si, and n represents the valence of (YO4) n- ; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents the valence of (ZO y ) m+ ; the halogen can be at least one of F, Cl, and Br.

[0086] The polyanionic compound can be at least one of NaFePO4, Na3V2(PO4)3(Na3V2P3), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' being one or more of V, Fe, Mn, and Ni), and Na3(VO y )2(PO4)2F 3-2y (0≤y≤1).

[0087] The Prussian blue compound can be a compound having sodium ions, transition metal ions, and cyanide ions (CN - ). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The Prussian blue compound can be, for example, Na a Me b Me' c (CN)6, where Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0

[0088] In some embodiments, the active material is a positive active material or a negative active material, and the positive 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.

[0089] In some embodiments, the negative active material can employ a negative active material for a battery cell known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery cell can also be used. These negative active materials can be used alone or in combination of two or more.

[0090] In some embodiments, the negative active material includes at least one of graphite, silicon, tin, lithium titanate, sulfide, nitride, and phosphide.

[0091] In the in-situ monitoring process, the bias voltage is applied to drive the deintercalation reaction of active ions, and the application strategy of the bias voltage follows a dynamic observation and adjustment process: first, the characteristic voltage platform value of the active material to be tested in the macroscopic battery or the conventional charge and discharge cutoff voltage (for example, 4.25 V) is applied as the initial bias voltage; then, whether the electrochemical reaction occurs is confirmed by real-time monitoring of the morphology evolution (such as volume expansion, surface deposit generation, etc.) of the crystal grains in the TEM, and the bias voltage is dynamically adjusted accordingly. The specific adjustment principle is: (1) if the target crystal grain is observed to have a clear change in morphology at the initial bias voltage, the bias voltage is maintained for continuous in-situ observation and data acquisition; (2) if no change is observed at the initial bias voltage, the bias voltage is gradually increased to a higher driving voltage (for example, 10 V) to enhance the driving force of ion migration until an observable electrochemical deformation is induced.

[0092] [Examples]

[0093] Hereinafter, examples of the present application will be described. The examples described below are illustrative and are presented for the purpose of explanation only, and are not to be construed as limiting the present application. In the examples, specific techniques or conditions not otherwise described are performed according to techniques or conditions described in the literature in the field or according to product instructions. Reagents or instruments not otherwise described are all conventional products that can be obtained commercially.

[0094] Example 1

[0095] Preparation of the test slice: a negative electrode slice with a thickness of 5 μm was obtained, the negative electrode slice comprising a negative electrode current collector and a negative electrode film layer provided on one side surface of the negative electrode current collector, the negative electrode active material in the negative electrode film layer being a carbon material-coated lithium titanate, and the thickness direction being perpendicular to the stacking direction of the negative electrode current collector and the negative electrode film layer. Then, 2.5 μm thick platinum metal was evaporated on the surface of the negative electrode slice as a protective film, and then the negative electrode slice sample was machined by a focused ion beam electron microscope (FIB), the FIB machining comprising: placing the negative electrode slice provided with the platinum metal protective film on the FIB net, and firing a focused ion beam at the negative electrode slice in the thickness direction to bombard the negative electrode slice, first bombarding the test sample at a voltage of 30 kv and a current of 0.26 nA to obtain a first slice with a thickness of 800 μm; and then bombarding the test sample at a voltage of 5 kv and a current of 0.012 nA to obtain a test slice with a final thickness of 100 nm, wherein the continuous scanning time of each focused ion beam is less than 200 ns. The test slice was placed on the FIB net, and a transmission electron microscope was used to take a picture of the test slice, as shown in FIG. 1, wherein the surrounding black part in the picture is the platinum metal protective film, and the small gray particles in the middle are the carbon material-coated lithium titanate. Figure 1

[0096] Selection of monitoring object: a scanning electron microscope backscattered electron diffraction detector was used to detect the crystal face orientation of the crystal grains in the test active material, to determine the angle a between the preferred orientation path of lithium ion insertion into lithium titanate (i.e. the

[110] crystal face) and the electron beam, and to select a crystal grain with an angle a of 90° as the in-situ monitoring object.

[0097] Construction of solid-state battery: the test slice was fixed on the fixed end of the sample rod of the in-situ TEM tester. A nanometer tungsten probe was prepared by an electrochemical method, the diameter of the tip of the tungsten probe was 50 nm, and then the prepared tungsten probe was quickly drawn across a pure metal lithium sheet and assembled on the moving end of the TEM rod, and then loaded into the cavity of the in-situ transmission electron microscope, the tungsten probe was exposed to the air for 5 s to form a lithium oxide electrolyte on the surface, and the formation of the metal lithium wrapped by the lithium oxide electrolyte on the tip of the tungsten probe was confirmed by electron diffraction results, as shown in FIG. 2. Then, a half-cell in-situ cell was constructed by the in-situ TEM probe rod, the moving end of the sample rod was moved to the vicinity of the fixed end, so that the metal lithium wrapped by the lithium oxide electrolyte formed by the tip of the tungsten probe was close to the test slice and contacted to form a channel, and the TEM image of the in-situ cell is shown in FIG. 3, wherein the metal lithium wrapped by the lithium oxide electrolyte formed by the tip of the tungsten probe is on the upper right side of the figure. Figure 2 Figure 3a Figure 3b

[0098] ​​​​In-situ monitoring: The electron energy loss spectra of different positions in the in-situ monitoring object grain before applying voltage were collected by the in-situ TEM tester, then the voltage of 4.25 V was applied to the solid-state battery, the morphology change of the in-situ monitoring object grain was monitored by the in-situ TEM; after the morphology of the in-situ monitoring object grain was stable, the electron energy loss spectra of different positions in the in-situ monitoring object grain at this time were collected by the in-situ TEM tester; finally, the reverse voltage of-4.25 V was applied to the solid-state battery, the morphology change of the in-situ monitoring object grain was monitored by the in-situ TEM; after the morphology of the in-situ monitoring object grain was stable, the electron energy loss spectra of different positions in the in-situ monitoring object grain at this time were collected by the in-situ TEM tester. Figure 4a The real space morphology of the in-situ monitoring object grain is shown, Figures 4b-4d The electron energy loss spectra (EELS spectra) of three different positions on the in-situ monitoring object grain are shown.

[0099] Figures 4b-4d The EELS spectrum data of different regions of the lithium titanate particle during the charging and discharging process show that: 1) for the a region on the surface, a clear lithium element characteristic peak is detected during the charging process, confirming that lithium ions have been embedded in this region; and during the discharging process, the lithium peak disappears, indicating that the lithium ions embedded in the surface phase are reversibly removed. 2) For the b region, the binding energy of its titanium L-edge spectrum peak changes significantly during the charging and discharging process, specifically, the binding energy changes from 466.13 eV in the original state, to 466.42 eV after charging, and finally to 465.78 eV after discharging. The final decrease in the binding energy is consistent with the valence change characteristics of titanium ions being reduced from tetravalent (Ti 4+ ) to trivalent (Ti 3+ ). Although the temporary increase in the binding energy during the charging process can be attributed to experimental fluctuations, the failure of the binding energy to return to the original value after discharging constitutes key evidence of irreversible reduction of titanium, indicating that the lithium ions embedded in this region cannot be completely removed during the discharging process, resulting in irreversible lithium loss. 3) For the c region, the EELS spectrum of this region does not change significantly compared to the original state during the entire process, proving that lithium ions have not diffused to the core region of the particle, and this region has not participated in the electrochemical reaction.

[0100] In summary, the EELS spectrum data analysis directly reveals the gradient distribution of lithium ions embedded in the particle: it is reversibly embedded / removed from the surface a region, but irreversibly remains in part of the b region, and fails to reach the more internal c region of the particle, which provides direct spectroscopic evidence for defining the active reaction region and explaining the capacity attenuation mechanism.

[0101] In addition, in the process of preparing the test wafer, the voltage and current of the focused ion beam were adjusted, and under the condition of directly using a voltage of 30 kV and a current of 0.3 nA to directly thin the test sample to 100 nm, or under the condition of using the condition of Example 1 but with a focused ion beam scanning time of more than 200 ns each time, or under the condition of not setting a metal protective film, certain damage to the grain structure was caused when obtaining the test wafer, which resulted in difficulty in selecting the monitoring object.

[0102] Although the present application has been described with reference to the preferred embodiments, various modifications can be made to it without departing from the scope of the application, and equivalent parts can be substituted for the parts thereof. In particular, the technical features mentioned in each of the embodiments can be combined in any manner as long as there is no structural conflict. The present 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 deintercalation of active ions from an active material, characterized in that, The method comprises the following steps: a sample preparation process, in which a sample to be tested, which is a positive electrode sheet or a negative electrode sheet, is thinned to a thickness of less than 150 nm by using a focused ion beam technique under the conditions of a voltage of 2 kV-30 kV and / or a current of 0.01 nA-0.35 nA, to obtain a test sheet, wherein the test sheet comprises a test active material, a monitoring object selection process, in which the crystal face orientation of crystal grains in the test active material is detected by using a backscattered electron diffraction technique, the angle α between the preferential orientation path of active ion intercalation and the electron beam is determined, and the crystal grains with 85°≤α≤95° are selected as in-situ monitoring objects, a negative electrode and electrolyte preparation process, in which active metal is transferred to a conductive microprobe, and part of the active metal on the conductive microprobe is oxidized to form an active metal oxide, to obtain a negative electrode and electrolyte attached to the conductive microprobe, a solid-state battery building process, in which the test sheet is fixed to the fixed end of a sample rod of an in-situ TEM tester, the conductive microprobe with the negative electrode and electrolyte attached thereto is fixed to the movable end of the sample rod of the in-situ TEM tester, and a solid-state battery is built in the field of view of the in-situ TEM tester by using the test sheet, the electrolyte and the negative electrode, an in-situ monitoring process, in which the test sheet is connected to the negative electrode of an external power supply, the negative electrode is connected to the positive electrode of the external power supply, a voltage is applied to the solid-state battery, and electron energy loss spectra of different positions in the crystal grains of the test active material are collected.

2. The in-situ monitoring method of claim 1, wherein, The sample preparation process comprises: a first thinning process, in which the sample to be tested is thinned by using a focused ion beam technique under the conditions of a voltage of 10 kV-30 kV and / or a current of 0.1 nA-0.35 nA, to obtain a first sheet with a thickness of 800 nm-1.5 μm; a second thinning process, in which the first sheet is thinned by using a focused ion beam technique under the conditions of a voltage of 2 kV-5 kV and / or a current of 0.01 nA-0.3 nA, to obtain the test sheet.

3. The in-situ monitoring method of claim 1 or 2, wherein, The continuous scanning time of the focused ion beam is less than 200 ns each time.

4. The in-situ monitoring method of claim 1 or 2, wherein, Before the sample to be tested is thinned by using a focused ion beam technique, a metal protective film is evaporated on the surface of the sample to be tested.

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

6. The in-situ monitoring method of claim 1 or 2, wherein, The conductive microprobe is a tungsten needle, a diamond probe or a titanium alloy probe.

7. The in-situ monitoring method of claim 1 or 2, wherein, The solid-state battery building process further comprises confirming the presence of the active metal and the active metal oxide by electron diffraction results.

8. The in-situ monitoring method of claim 1 or 2, wherein, The in-situ monitoring process comprises: collecting, by using an in-situ TEM tester, electron energy loss spectra of different positions in the crystal grains of the test active material before a voltage is applied; applying a voltage to the solid-state battery, and monitoring the morphology change of the crystal grains of the test active material by using the in-situ TEM tester; after the morphology of the crystal grains of the test active material is stable, collecting, by using the in-situ TEM tester, electron energy loss spectra of different positions in the crystal grains of the test active material at this time; applying a reverse voltage to the solid-state battery, and monitoring the morphology change of the crystal grains of the test active material by using the in-situ TEM tester; After the morphology of the crystal grains of the active material to be tested is stabilized, an in-situ TEM tester is used to collect electron energy loss spectra of different positions in the crystal grains of the active material to be tested at this time.

9. The in-situ monitoring method of claim 1 or 2, wherein, The active ions include lithium ions and sodium ions.

10. The in-situ monitoring method of claim 1 or 2, wherein, 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 cobaltate, 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 phosphate, sodium vanadium fluorophosphate, sulfur; and / or the negative electrode active material includes at least one of graphite, silicon, tin, lithium titanate, sulfide, nitride, and phosphide.

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